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LTC4365 UV, OV and Reverse Supply Protection Controller FEATURES
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DESCRIPTION
The LTC(R)4365 protects applications where power supply input voltages may be too high, too low or even negative. It does this by controlling the gate voltages of a pair of external N-channel MOSFETs to ensure that the output stays within a safe operating range. The LTC4365 can withstand voltages between -40V and 60V and has an operating range of 2.5V to 34V, while consuming only 125A in normal operation. Two comparator inputs allow configuration of the overvoltage (OV) and undervoltage (UV) set points using an external resistive divider. A shutdown pin provides external control for enabling and disabling the MOSFETs as well as placing the device in a low current shutdown state. A fault output provides status of the gate pin pulling low. A fault is indicated when the part is in shutdown or the input voltage is outside the UV and OV set points.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and ThinSOT, No RSENSE and Hot Swap are trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.
Wide Operating Voltage Range: 2.5V to 34V Overvoltage Protection to 60V Reverse Supply Protection to -40V Blocks 50Hz and 60Hz AC Power No Input Capacitor or TVS Required for Most Applications Adjustable Undervoltage and Overvoltage Protection Range Charge Pump Enhances External N-Channel MOSFET Low Operating Current: 125A Low Shutdown Current: 10A Fault Status Output Compact 8-Lead, 3mm x 2mm DFN and TSOT-23 (ThinSOTTM) Packages
APPLICATIONS
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Portable Instrumentation Industrial Automation Laptops Automotive
TYPICAL APPLICATION
12V Automotive Application
VIN 12V Si4946 VOUT 3A 30V VALID WINDOW GND VOUT UV = 3.5V OV = 18V VIN
Load Protected from Reverse and Overvoltage at VIN
VIN 510k 1820k UV 243k OV 59k
GATE LTC4365
VOUT
VOUT
SHDN 10V/DIV FAULT -30V VIN
1s/DIV GND
4365 TA01a
4365 TA01b
OV = 18V UV = 3.5V
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LTC4365 ABSOLUTE MAXIMUM RATINGS
Supply Voltage (Note 1) VIN .......................................................... -40V to 60V Input Voltages (Note 3) UV, SHDN .............................................. -0.3V to 60V OV ............................................................ -0.3V to 6V VOUT....................................................... -0.3V to 40V Output Voltages (Note 4) FAULT..................................................... -0.3V to 60V GATE ....................................................... -40V to 45V Operating Ambient Temperature Range LTC4365C ................................................ 0C to 70C LTC4365I .............................................-40C to 85C LTC4365H .......................................... -40C to 125C Storage Temperature Range .................. -65C to 150C Lead Temperature (Soldering, 10 sec) for TSOT Only ................................................... 300C
PIN CONFIGURATION
TOP VIEW GND 1 OV 2 UV 3 VIN 4 9 GND 8 7 6 5 SHDN FAULT VOUT GATE TOP VIEW VIN UV OV GND 1 2 3 4 8 7 6 5 GATE VOUT FAULT SHDN
DDB PACKAGE 8-LEAD (3mm x 2mm) PLASTIC DFN TJMAX = 150C, JA = 76C/W EXPOSED PAD (PIN 9) PCB GROUND CONNECTION OPTIONAL
TS8 PACKAGE 8-LEAD PLASTIC TSOT-23 TJMAX = 150C, JA = 195C/W
ORDER INFORMATION
Lead Free Finish
TAPE AND REEL (MINI) LTC4365CDDB#TRMPBF LTC4365IDDB#TRMPBF LTC4365HDDB#TRMPBF LTC4365CTS8#TRMPBF LTC4365ITS8#TRMPBF LTC4365HTS8#TRMPBF TAPE AND REEL LTC4365CDDB#TRPBF LTC4365IDDB#TRPBF LTC4365HDDB#TRPBF LTC4365CTS8#TRPBF LTC4365ITS8#TRPBF LTC4365HTS8#TRPBF PART MARKING* LFKS LFKS LFKS LTFKT LTFKT LTFKT PACKAGE DESCRIPTION 8-Lead (3mm x 2mm) Plastic DFN 8-Lead (3mm x 2mm) Plastic DFN 8-Lead (3mm x 2mm) Plastic DFN 8-Lead Plastic TSOT-23 8-Lead Plastic TSOT-23 8-Lead Plastic TSOT-23 TEMPERATURE RANGE 0C to 70C -40C to 85C -40C to 125C 0C to 70C -40C to 85C -40C to 125C
TRM = 500 pieces. *Temperature grades are identified by a label on the shipping container. Consult LTC Marketing for parts specified with wider operating temperature ranges. Consult LTC Marketing for information on lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
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LTC4365 ELECTRICAL CHARACTERISTICS
SYMBOL VIN, VOUT VIN IVIN Input Voltage Range Input Supply Current Operating Range Protection Range SHDN = 0V, VIN = VOUT, -40C to 85C SHDN = 0V, VIN = VOUT, -40C to 125C SHDN = 2.5V VIN = -40V, VOUT = 0V VIN Rising SHDN = 0V, VIN = VOUT SHDN = 2.5V, VIN = VOUT VIN = -40V, VOUT = 0V VIN = VOUT = 5.0V, IGATE = -1A VIN = VOUT = 12V to 34V, IGATE = -1A GATE = VIN = VOUT = 12V Fast Shutdown, GATE = 20V, VIN = VOUT = 12V Gentle Shutdown, GATE = 20V, VIN = VOUT = 12V CGATE = 2.2nF, UV or OV Fault CGATE = 2.2nF, SHDN Falling, VIN = VOUT = 12V VIN = 12V, Power Good to VGATE > 0V UV Falling VGATE = 0V OV Rising VGATE = 0V
l l l l l l l l l l l l l l l l l l l l l l l l
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 2.5V to 34V, unless otherwise noted. (Note 2)
PARAMETER CONDITIONS MIN 2.5 -40 10 10 25 -1.2 1.8 2.2 6 100 20 3 7.4 -12 31 50 150 26 492.5 492.5 20 20 3.6 8.4 -20 50 90 2 250 36 500 500 25 25 1 TYP MAX 34 60 50 100 150 -1.8 2.4 30 250 50 4.2 9.8 -30 72 150 4 350 49 507.5 507.5 32 32 10 2 UNITS V V A A A mA V A A A V V A mA A s s ms mV mV mV mV nA s
IVIN(R) VIN(UVLO) IVOUT
Reverse Input Supply Current Input Supply Undervoltage Lockout VOUT Input Current
GATE VGATE IGATE(UP) N-Channel Gate Drive (GATE-VOUT ) N-Channel Gate Pull Up Current
IGATE(FAST) N-Channel Gate Fast Pull Down Current IGATE(SLOW) N-Channel Gate Gentle Pull Down Current tGATE(FAST) N-Channel Gate Fast Turn Off Delay tGATE(SLOW) N-Channel Gentle Turn Off Delay tRECOVERY UV, OV VUV VOV VUVHYST VOVHYST ILEAK tFAULT SHDN VSHDN ISHDN tSTART tSHDN(F) tLOWPWR FAULT VOL IFAULT FAULT Output Voltage Low FAULT Leakage Current SHDN Input Threshold SHDN Input Current Delay Coming Out of Shutdown Mode SHDN to FAULT Asserted Delay from Turn Off to Low Power Operation UV Input Threshold Voltage OV Input Threshold Voltage UV Input Hysteresis OV Input Hysteresis UV, OV Leakage Current UV, OV Fault Propagation Delay GATE Recovery Delay Time
V = 0.5V, VIN = 34V Overdrive = 50mV VIN = VOUT = 12V SHDN Falling to VGATE = 0V SHDN = 0.75V, VIN = 34V SHDN Rising to VGATE > 0V, VIN = VOUT = 12V VIN = VOUT = 12V VIN = VOUT = 12V IFAULT = 500A FAULT = 5V, VIN = 34V
l l l l l l l
0.4 400 26
0.75 800 1.5 36 0.15 20
1.2 10 1200 3 55 0.4
V nA s s ms V nA
Note 1. Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2. All currents into pins are positive; all voltages are referenced to GND unless otherwise noted.
Note 3. These pins can be tied to voltages below -0.3V through a resistor that limits the current below 1mA. Note 4. The GATE pin is referenced to VOUT and does not exceed 44V for the entire operating range.
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LTC4365 TYPICAL PERFORMANCE CHARACTERISTICS
VIN Operating Current vs Temperature
100 SHDN = 2.5V VOUT = VIN 80 VIN = 34V 20 IVIN (A) IVIN (A) 70C 15 25C 10 20 VIN = 2.5V 0 -50 -25 75 25 0 50 TEMPERATURE (C) 100 125 -45C 5 0 0 5 10 20 15 VIN (V) -1200 25C IVIN (A) 60 VIN = 12V -400 -45C 30 VIN = VOUT SHDN = 0V 25 125C 0
VIN Shutdown Current vs VIN
400
VIN Current vs VIN (-40 to 60V)
SHDN = UV = 0V 25C
40
-800
125C
25
30
35
-1600 -50
-25
0 VIN (V)
25
50
75
4365 G03
4365 G01
4365 G02
VOUT Operating Current vs Temperature
200 SHDN = 2.5V VIN = VOUT 160 VOUT = 34V IVOUT (A) IVOUT (A) 120 VOUT = 12V 80 15 20
VOUT Shutdown Current vs Temperature
25 SHDN = 0V VIN = VOUT 20
VOUT Current vs Reverse VIN
VOUT = 0V
-45C IVOUT (A) VOUT = 34V 15 25C 10 125C 5 VOUT = 2.5V
10 VOUT = 12V 5
40
VOUT = 2.5V 0 -50
0 -50
-25
0 75 25 50 TEMPERATURE (C)
100
125
-25
0 25 75 50 TEMPERATURE (C)
100
125
0 0 -10 -30 -20 VIN (V) -40
-50
4365 G06
4365 G04
4365 G05
12 10 8 VGATE (V) 6 4 2 0
GATE Drive vs VIN
10 VOUT = 0V 8 VOUT = VIN VGATE (V) 6
GATE Drive vs Temperature
25 VIN = VOUT = 34V IGATE = -1A VIN = VOUT = 12V IGATE(UP) (A) 20
GATE Current vs GATE Drive
VIN = VOUT = 12V 125C
15
25C
4
10 -45C 5
2 T = 25C IGATE = -1A 0 5 10 15 20 VIN (V) 25 30 35
VIN = VOUT = 2.5V
0 -50
-25
75 25 0 50 TEMPERATURE (C)
100
0 125 0 2 4 6 VGATE (V)
8
10
4365 G09
4365 G07
4365 G08
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LTC4365 TYPICAL PERFORMANCE CHARACTERISTICS
UV Threshold vs Temperature
507.5 VIN = VOUT = 12V 505.0 502.5 VUV (mV) 500.0 497.5 495.0 492.5 -50 VOV (mV) 505.0 0.75 502.5 500.0 497.5 0.25 495.0 492.5 -50 0 -75 UV OV -25 75 0 50 25 TEMPERATURE (C) 100 125 -25 75 0 50 25 TEMPERATURE (C) 100 125 -25 75 25 125 TEMPERATURE (C) 175
4365 G12
OV Threshold vs Temperature
507.5 VIN = VOUT = 12V 1.00
UV/OV Leakage vs Temperature
VUV/OV = 0.5V VIN = 12V
ILEAK (nA)
4365 G11
0.50
4365 G10
UV/OV Propagation Delay vs Overdrive
20 VIN = VOUT = 12V T = 25C 50
Recovery Delay Time vs Temperature
50
Recovery Delay Time vs VIN
-45C 125C 25C 30
16 tRECOVERY (ms)
40
VIN = 34V tRECOVERY (ms) 100 125 VIN = 12V
40
tFAULT (s)
12
30
8
20 VIN = 2.5V
20
4
10
10
0 1 10 100 OVERDRIVE (mV)
1000
4365 G13
0 -50
-25
75 25 0 50 TEMPERATURE (C)
0 0 5 10 20 15 VIN (V)
25
30
35
4365 G15
4365 G14
AC Blocking
1V/DIV VOUT GND 5V/DIV
Turn-On Timing
100F 12 LOAD ON VOUT , 60V SI9945 DUAL NCH MOSFET VIN = 12V VOUT GND 10F 1k LOAD ON VOUT , 60V DUAL NCH MOSFET 2.5ms/DIV
4365 G16
Turn-Off Timing
GATE 5V/DIV VOUT GND 3V/DIV SHDN 250s/DIV
4365 G18
GATE
100F 12 LOAD ON VOUT , 60V SI9945 DUAL NCH MOSFET
VIN 20V/DIV GND
GATE
3V/DIV
SHDN
4365 G17
GND 250s/DIV
GND
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LTC4365 PIN FUNCTIONS
Exposed Pad: Connect to device ground. FAULT: Fault Indication Output. This high voltage open drain output is pulled low if UV is below its monitor threshold, if OV is above its monitor threshold, if SHDN is low, or if VIN has not risen above VIN(UVLO). GATE: Gate Drive Output for External N-channel MOSFETs. An internal charge pump provides 20A of pull-up current and up to 9.8V of enhancement to the gate of an external N-channel MOSFET. When turned off, GATE is pulled just below the lower of VIN or VOUT. When VIN goes negative, GATE is automatically connected to VIN. GND: Device Ground. OV: Overvoltage Comparator Input. Connect this pin to an external resistive divider to set the desired VIN overvoltage fault threshold. Input to an accurate, fast (1s) comparator with a 0.5V rising threshold and 25mV of hysteresis. When OV rises above its threshold, a 50mA current sink pulls down on the GATE output. When OV falls back below 0.475V, and after a 36ms recovery delay waiting period, the GATE charge pump is enabled. The low leakage current of the OV input allows the use of large valued resistors for the external resistive divider. Connect to GND if unused. SHDN: Shutdown Control Input. SHDN high enables the GATE charge pump which in turn enhances the gate of an external N-channel MOSFET. A low on SHDN generates a pull down on the GATE output with a 90A current sink and places the LTC4365 in low current mode (10A). If unused, connect to VIN. If VIN goes below ground, or if VIN rings to 60V, use a current limiting resistor of at least 100k. UV: Undervoltage Comparator Input. Connect this pin to an external resistive divider to set the desired VIN undervoltage fault threshold. Input to an accurate, fast (1s) comparator with a 0.5V falling threshold and 25mV of hysteresis. When UV falls below its threshold, a 50mA current sink pulls down on the GATE output. When UV rises back above 0.525V, and after a 36ms recovery delay waiting period, the GATE charge pump is enabled. The low leakage current of the UV input allows the use of large valued resistors for the external resistive divider. If unused, connect to VIN. While connected to VIN, if VIN goes below ground, or if VIN rings to 60V, use a current limiting resistor of at least 100k. VIN: Power Supply Input. Maximum protection range: -40V to 60V. Operating range: 2.5V to 34V. VOUT: Output Voltage Sense Input. This pin senses the voltage at the output side of the external N-channel MOSFET. The GATE charge pump voltage is referenced to VOUT. It is used as the charge pump input when VOUT is greater than approximately 6.5V.
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LTC4365 BLOCK DIAGRAM
VIN -40V TO 60V REVERSE PROTECTION - 5V INTERNAL SUPPLY LDO 6.5V INTERNAL SUPPLY GATE CHARGE PUMP f = 400kHz IGATE VOUT ENABLE 2.2V UVLO UV SHDN DELAY TIMERS LOGIC + - 50mA 25mV HYSTERESIS 90A FAULT OV + - 0.5V GND
4365 BD
GATE
+
CLOSES SWITCH WHEN VIN IS NEGATIVE
FAULT OFF
TURN OFF
SHDN
GATE PULLDOWN
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LTC4365 OPERATION
Many of today's electronic systems get their power from external sources such as a wall wart adapter, batteries and custom power supplies. These power sources are often unreliable, wired incorrectly, out of spec, or just plain wrong. This can lead to supply voltages that are too high, too low, or even negative. If these power sources are applied directly to the electronic systems, the systems could be subject to damage. The LTC4365 is an input voltage fault protection N-channel MOSFET controller. The part isolates an input supply from its load to protect the load from unexpected supply voltage conditions, while providing a low loss path for qualified power. To protect electronic systems from improperly connected power supplies, system designers will often add discrete diodes, transistors and high voltage comparators. The high voltage comparators enable system power only if the input supply falls within a desired voltage window. A Schottky diode or P-channel MOSFET typically added in series with the supply protects against reverse supply connections. The LTC4365 provides accurate overvoltage and undervoltage comparators to ensure that power is applied to the system only if the input supply meets the user selectable voltage window. Reverse supply protection circuits automatically isolate the load from negative input voltages. During normal operation, a high voltage charge pump enhances the gate of external N-channel power MOSFETs. Power consumption is 10A during shutdown and 125A while operating. The LTC4365 integrates all these functions in tiny TSOT-23 and 3mm x 2mm DFN packages.
APPLICATIONS INFORMATION
The LTC4365 is an N-channel MOSFET controller that protects a load from faulty supply connections. A basic application circuit using the LTC4365 is shown in Figure 1. The circuit provides a low loss connection from VIN to VOUT as long as the voltage at VIN is between 3.5V and
VIN 12V NOMINAL M1 SI4946 60V DUAL M2 VOUT 3.5V TO 18V
18V. Voltages at VIN outside of the 3.5V to 18V range are prevented from getting to the load and can be as high as 60V and as low as -40V. The circuit of Figure 1 protects against negative voltages at VIN as shown. No other external components are needed. During normal operation, the LTC4365 provides up to 9.8V of gate enhancement to the external back-to-back N-channel MOSFETs. This turns on the MOSFET, thus connecting the load at VOUT to the supply at VIN. GATE Drive
+
COUT 100F
VIN R5 100k R3 1820k R2 243k OV R1 59k
GATE LTC4365
VOUT
SHDN UV FAULT
The LTC4365 turns on the external N-channel MOSFETs by driving the GATE pin above VOUT. The voltage difference between the GATE and VOUT pins (gate drive) is a function of VIN and VOUT.
OV = 18V UV = 3.5V
GND
4365 F01
Figure 1. LTC4365 Protects Load from -40V to 60V VIN Faults
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LTC4365 APPLICATIONS INFORMATION
Figure 2 highlights the dependence of the gate drive on VIN and VOUT. When system power is first turned on (SHDN low to high, VOUT = 0V), gate drive is at a maximum for all values of VIN. This helps prevent start-up problems into heavy loads by ensuring that there is enough gate drive to support the load. As VOUT ramps up from 0V, the absolute value of the GATE voltage remains fixed until VOUT is greater than the lower of (VIN -1V) or 6V. Once VOUT crosses this threshold, gate drive begins to increase up to a maximum of 9.8V (for VIN 12V). The curves of Figure 2 were taken with a GATE load of -1A. If there were no load on GATE, the gate drive for each VIN would be slightly higher. Note that when VIN is at the lower end of the operating range, the external N-channel MOSFET must be selected with a corresponding lower threshold voltage.
12 10 8 VGATE (V) 6 4 2 0 0 VIN = 12V VIN = 5V VIN = 3.3V VIN = 2.5V 3 6 9 VOUT (V) 12 15
4365 F02 4365 F03
Overvoltage and Undervoltage Protection The LTC4365 provides two accurate comparators to monitor for overvoltage (OV) and undervoltage (UV) conditions at VIN. If the input supply rises above the user adjustable OV threshold, the gate of the external MOSFET is quickly turned off, thus disconnecting the load from the input. Similarly, if the input supply falls below the user adjustable UV threshold, the gate of the external MOSFET also is quickly turned off. Figure 3 shows a UV/OV application for an input supply of 12V.
LTC4365 UV COMPARATOR
12V R3 1820k UVTH = 3.5V
VIN
R2 243k T = 25C IGATE = -1A VIN = 30V OVTH = 18V R1 59k
0.5V
OV
0.5V
-
Figure 3. UV, OV Comparators Monitor 12V Supply
Figure 2. Gate Drive (GATE - VOUT) vs VOUT
Table 1 lists some external MOSFETs compatible with different VIN supply voltages.
Table 1. Dual MOSFETs for Various Supply Ranges
VIN 2.5V 3.3V 5V 30V 60V MOSFET SiB914 Si5920 Si7940 Si4230 Si9945 V TH(MAX) 0.8V 1.0V 1.5V 3.0V 3.0V VGS(MAX) 5V 5V 8V 20V 20V VDS(MAX) 8V 8V 12V 30V 60V
The external resistive divider allows the user to select an input supply range that is compatible with the load at VOUT. Furthermore, the UV and OV inputs have very low leakage currents (typically < 1nA at 100C), allowing for large values in the external resistive divider. In the application of Figure 3, the load is connected to the supply only if VIN lies between 3.5V and 18V. In the event that VIN goes above 18V or below 3.5V, the gate of the external N-channel MOSFET is immediately discharged with a 50mA current sink, thus isolating the load from the supply.
+
OV COMPARATOR
-
25mV DISCHARGE GATE WITH 50mA SINK
UV
+
25mV
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LTC4365 APPLICATIONS INFORMATION
Figure 4 shows the timing associated with the UV pin. Once a UV fault propagates through the UV comparator (tFAULT), the FAULT output is asserted low and a 50mA current sink discharges the GATE pin. As VOUT falls, the GATE pin tracks VOUT.
UV VUV VUV + VUVHYST
Procedure for Selecting UV/OV External Resistor Values The following 3-step procedure helps select the resistor values for the resistive divider of Figure 3. This procedure minimizes UV and OV offset errors caused by leakage currents at the respective pins. 1. Choose maximum tolerable offset at the UV pin, VOS(UV). Divide by the worst case leakage current at the UV pin, IUV (10nA). Set the sum of R1 + R2 equal to VOS(UV) divided by 10nA. Note that due to the presence of R3, the actual offset at UV will be slightly lower:
tFAULT FAULT tGATE(FAST) GATE
tFAULT
tRECOVERY EXTERNAL N-CHANNEL MOSFET TURNS OFF
4365 F04
R1+R2 =
VOS(UV) I UV
Figure 4. UV Timing (OV < (VOV - VOVHYST), SHDN > 1.2V)
2. Select the desired VIN UV trip threshold, UV TH. Find the value of R3: R3 = 2 * VOS(UV) I UV * UV TH - 0.5V
Figure 5 shows the timing associated with the OV pin. Once an OV fault propagates through the OV comparator (tFAULT), the FAULT output is asserted low and a 50mA current sink discharges the GATE pin. As VOUT falls, the GATE pin tracks VOUT.
OV VOV VOV - VOVHYST
(
)
3. Select the desired VIN OV trip threshold, OV TH. Find the values of R1 and R2: VOS(UV) R1= I UV +R3
tFAULT FAULT tGATE(FAST) GATE
tFAULT
2 * OV TH VOS(UV) I UV - R1
tRECOVERY EXTERNAL N-CHANNEL MOSFET TURNS OFF
4365 F05
R2 =
Figure 5. OV Timing (UV > (VUV + VUVHYST), SHDN > 1.2V)
When both the UV and OV faults are removed, the external MOSFET is not immediately turned on. The input supply must remain within the user selected power good window for at least 36ms (tRECOVERY ) before the load is again connected to the supply. This recovery timeout period filters noise (including line noise) at the input supply and prevents chattering of power at the load.
The example of Figure 3 uses standard 1% resistor values. The following parameters were selected: VOS(UV) = 3mV IUV = 10nA UV TH = 3.5V OV TH = 18V
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LTC4365 APPLICATIONS INFORMATION
The resistor values can then be solved: 1. R1+ R2 = 3mV = 300k 10nA detected, an internal switch connects the gates of the external back-to-back N-channel MOSFETs to the negative input supply. As shown in Figure 6, external back-to-back N-channel MOSFETs are required for reverse supply protection. When VIN goes negative, the reverse VIN comparator closes the internal switch, which in turn connects the gates of the external MOSFETs to the negative VIN voltage. The body diode (D1) of M1 turns on, but the body diode (D2) of M2 remains in reverse blocking mode. This means that the common source connection of M1 and M2 remains about a diode drop higher than VIN. Since the gate voltage of M2 is shorted to VIN, M2 will be turned off and no current can flow from VIN to the load at VOUT. Note that the voltage rating of M2 must withstand the reverse voltage excursion at VIN. Figure 7 illustrates the waveforms that result when VIN is hot plugged to -20V. VIN, GATE and VOUT start out at ground just before the connection is made. Due to the parasitic inductance of the VIN and GATE connections, the voltage at the VIN and GATE pins ring significantly below -20V. Therefore, a 40V N-channel MOSFET was selected to survive the overshoot. The speed of the LTC4365 reverse protection circuits is evident by how closely the GATE pin follows VIN during the negative transients. The two waveforms are almost indistinguishable on the scale shown.
VOUT
2. R3 = 2 *
3mV * (3.5V - 0.5V) =1.8M 10nA
The closest 1% value: R3 = 1.82M: 3. R1 = 300k +1.82M = 58.9k 2 * 18V
The closest 1% value: R1 = 59k: R2 = 300k - 59k = 241k The closest 1% value: R2 = 243k Therefore: OV = 17.93V, UV = 3.51V. Reverse VIN Protection The LTC4365's rugged and hot-swappable VIN input helps protect the more sensitive circuits at the output load. If the input supply is plugged in backwards, or a negative supply is inadvertently connected, the LTC4365 prevents this negative voltage from passing to the output load. The LTC4365 employs a novel, high speed reverse supply voltage monitor. When the negative VIN voltage is
D1 D2
GND VIN = -40V M1 M2
+
TO LOAD COUT 5V/DIV
VIN
GATE
VOUT LTC4365
-20V GATE
VIN
REVERSE VIN COMPARATOR + GND - CLOSES SWITCH WHEN VIN IS NEGATIVE
4365 F06
500ns/DIV
4365 F07
Figure 7. Hot Swapping VIN to -20V
Figure 6. Reverse VIN Protection Circuits
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LTC4365 APPLICATIONS INFORMATION
The trace at VOUT, on the other hand, does not respond to the negative voltage at VIN, demonstrating the desired reverse supply protection. The waveforms of Figure 7 were captured using a 40V dual N-channel MOSFET, a 10F ceramic output capacitor and no load current on VOUT. Recovery Timer The LTC4365 has a recovery delay timer that filters noise at VIN and helps prevent chatter at VOUT. After either an OV or UV fault has occurred, the input supply must return to the desired operating voltage window for at least 36ms in order to turn the external MOSFET back on as illustrated in Figures 4 and 5. Going out of and then back into fault in less than 36ms will keep the MOSFET off continuously. Similarly, coming out of shutdown (SHDN low to high) triggers an 800s start-up delay timer (see Figure 10). The recovery timer is also active while the LTC4365 is powering up. The 36ms timer starts once VIN rises above VIN(UVLO) and VIN lies within the user selectable UV/OV power good window. See Figure 8.
VIN VIN(UVLO)
to track VOUT, thus keeping the external MOSFETs off as VOUT decays. Note that when VOUT < 4.5V, the GATE pin is pulled to within 400mV of ground. Gentle gate turn off reduces load current slew rates and mitigates voltage spikes due to parasitic inductances. To further decrease GATE pin slew rate, place a capacitor across the gate and source terminals of the external MOSFETs. The waveforms of Figure 9 were captured using the Si4230 dual N-channel MOSFETs, and a 2A load with 100F output capacitor.
VIN = 12V T = 25C GATE VOUT 5V/DIV SHDN GND
100s/DIV
4365 F9
Figure 9. Gentle Shutdown: GATE Tracks VOUT as VOUT Decays
FAULT Status
tRECOVERY
GATE
MOSFET OFF
MOSFET ON
4365 F08
The FAULT high voltage open drain output is driven low if SHDN is asserted low, if VIN is outside the desired UV/OV voltage window, or if VIN has not risen above VIN(UVLO). Figures 4, 5 and 10 show the FAULT output timing.
SHDN
Figure 8. Recovery Timing During Power-On (OV = GND, UV = SHDN = VIN)
tGATE(SLOW) GATE VGATE GATE = VOUT VOUT tSHDN(F) FAULT
tSTART
Gentle Shutdown The SHDN input turns off the external MOSFETs in a gentle, controlled manner. When SHDN is asserted low, a 90A current sink slowly begins to turn off the external MOSFETs. Once the voltage at the GATE pin falls below the voltage at the VOUT pin, the current sink is throttled back and a feedback loop takes over. This loop forces the GATE voltage
4365 F10
Figure 10. Gentle Shutdown Timing
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LTC4365 APPLICATIONS INFORMATION
Select Between Two Input Supplies With the part in shutdown, the VIN and VOUT pins can be driven by separate power supplies. The LTC4365 then automatically drives the GATE pin just below the lower of the two supplies, thus turning off the external back-to-back MOSFETs. The application of Figure 11 uses two LTC4365s to select between two power supplies. Care should be taken to ensure that only one of the two LTC4365s is enabled at any given time.
V1 M1 M2
Limiting Inrush Current During Turn-On The LTC4365 turns on the external N-channel MOSFET with a 20A current source. The maximum slew rate at the GATE pin can be reduced by adding a capacitor on the GATE pin: Slew Rate = 20A CGATE
Since the MOSFET acts like a source follower, the slew rate at VOUT equals the slew rate at GATE. Therefore, inrush current is given by: COUT * 20A CGATE
VIN SHDN
GATE LTC4365
VOUT OUT
IINRUSH =
SEL OUT 0 V1 1 V2 V2 M1 M2
For example, a 1A inrush current to a 330F output capacitance requires a GATE capacitance of: CGATE = 20A * COUT IINRUSH 20A * 330F = 6.6nF 1A
VIN SEL SHDN
GATE LTC4365
VOUT
4365 F11
Figure 11. Selecting One of Two Supplies
CGATE =
Single MOSFET Application When reverse VIN protection is not needed, only a single external N-channel MOSFET is necessary. The application circuit of Figure 12 connects the load to VIN when VIN is less than 30V, and uses the minimal set of external components.
VIN 24V SI7120DN 60V VOUT
The 6.8nF CGATE capacitor in the application circuit of Figure 13 limits the inrush current to approximately 1A. RGATE makes sure that CGATE does not affect the fast GATE turn off characteristics during UV/OV faults, or during reverse VIN connection. R4A and R4B help prevent high frequency oscillations with the external N-channel MOSFET and related board parasitics.
VIN M1 R4A 10 R4B 10 M2
+
VIN GATE LTC4365 SHDN UV R2 2370k OV R1 40.2k OV = 30V GND
4365 F12
COUT 100F
+
VOUT COUT 330F
VOUT
FAULT
VIN
GATE LTC4365
VOUT
RGATE 5.1k CGATE 6.8nF
4365 F13
Figure 13. Limiting Inrush Current with CGATE Figure 12. Small Footprint Single MOSFET Application Protects Against 60V
4365f
13
LTC4365 APPLICATIONS INFORMATION
Transients During OV Fault The circuit of Figure 14 was used to display transients during an overvoltage condition. The nominal input supply is 24V and it has an overvoltage threshold of 30V. The parasitic inductance is that of a 1 foot wire (roughly 300nH). Figure 15 shows the waveforms during an overvoltage condition at VIN. These transients depend on the parasitic inductance and resistance of the wire along with the capacitance at the VIN node. D1 is an optional power clamp (TVS, Tranzorb) recommended for applications where the DC input voltage can exceed 24V and with large VIN parasitic inductance. No clamp was used to capture the waveforms of Figure 15. In order to maintain reverse supply protection, D1 must be a bi-directional clamp rated for at least 225W peak pulse power dissipation.
12 INCH WIRE LENGTH SI9945 60V
MOSFET Selection To protect against a negative voltage at VIN, the external N-channel MOSFETs must be configured in a back-toback arrangement. Dual N-channel packages are thus the best choice. The MOSFET is selected based on its power handling capability, drain and gate breakdown voltages, and threshold voltage. The drain to source breakdown voltage must be higher than the maximum voltage expected between VIN and VOUT. Note that if an application generates high energy transients during normal operation or during Hot SwapTM, the external MOSFET must be able to withstand this transient voltage. Due to the high impedance nature of the charge pump that drives the GATE pin, the total leakage on the GATE pin must be kept low. The gate drive curves of Figure 2 were measured with a 1A load on the GATE pin. Therefore, the leakage on the GATE pin must be no greater than 1A in order to match the curves of Figure 2. Higher leakage currents will result in lower gate drive. The dual N-channel MOSFETs shown in Table 1 all have a maximum GATE leakage current of 100nA. Additionally, Table 1 lists representative MOSFETs that would work at different values of VIN. Layout Considerations
VIN 24V
VOUT
+
CIN 1000F
M1 GATE LTC4365 SHDN UV R2 2370k OV R1 40.2k
M2
+
COUT 100F
9
VIN R3 100k D1 OPTIONAL
VOUT
FAULT
OV = 30V GND
4365 F14
Figure 14. OV Fault with Large VIN Inductance
GATE VOUT 20V/DIV VOUT GATE GND
The trace length between the VIN pin and the drain of the external MOSFET should be minimized, as well as the trace length between the GATE pin of the LTC4365 and the gates of the external MOSFETs. Place the bypass capacitors at VOUT as close as possible to the external MOSFET. Use high frequency ceramic capacitors in addition to bulk capacitors to mitigate Hot Swap ringing. Place the high frequency capacitors closest to the MOSFET. Note that bulk capacitors mitigate ringing by virtue of their ESR. Ceramic capacitors have low ESR and can thus ring near their resonant frequency.
VIN 20V/DIV GND IIN 2A/DIV 250ns/DIV
4365 F15
0A
Figure 15. Transients During OV Fault When No Tranzorb (TVS) Is Used
4365f
14
LTC4365 PACKAGE DESCRIPTION
TS8 Package 8-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1637)
0.52 MAX 0.65 REF 2.90 BSC (NOTE 4)
1.22 REF
3.85 MAX 2.62 REF
1.4 MIN
2.80 BSC
1.50 - 1.75 (NOTE 4) PIN ONE ID
RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR
0.65 BSC
0.22 - 0.36 8 PLCS (NOTE 3)
0.80 - 0.90 0.20 BSC 1.00 MAX DATUM `A' 0.01 - 0.10
0.30 - 0.50 REF 0.09 - 0.20 (NOTE 3) NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DRAWING NOT TO SCALE 3. DIMENSIONS ARE INCLUSIVE OF PLATING 4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR 5. MOLD FLASH SHALL NOT EXCEED 0.254mm 6. JEDEC PACKAGE REFERENCE IS MO-193
1.95 BSC
TS8 TSOT-23 0802
DDB Package 8-Lead Plastic DFN (3mm x 2mm)
(Reference LTC DWG # 05-08-1702 Rev B)
0.61 0.05 (2 SIDES) 0.70 0.05 2.55 0.05 1.15 0.05 PACKAGE OUTLINE 0.25 0.05 0.50 BSC 2.20 0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS NOTE: 1. DRAWING CONFORMS TO VERSION (WECD-1) IN JEDEC PACKAGE OUTLINE M0-229 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE
4365f
3.00 0.10 (2 SIDES)
R = 0.05 TYP
R = 0.115 TYP 5
0.40 0.10 8
PIN 1 BAR TOP MARK (SEE NOTE 6)
2.00 0.10 (2 SIDES) 0.56 0.05 (2 SIDES) 0.75 0.05
0.200 REF
4 0.25 0.05 2.15 0.05 (2 SIDES)
1 0.50 BSC
PIN 1 R = 0.20 OR 0.25 x 45 CHAMFER
(DDB8) DFN 0905 REV B
0 - 0.05
BOTTOM VIEW--EXPOSED PAD
Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
15
LTC4365 TYPICAL APPLICATION
LTC4365 Protects Step Down Regulator from -30V to 30V VIN Faults
CMDSH-3
VIN 12V NOMINAL VOUT PROTECTED FROM -30V TO 30V
SI4230 30V DUAL N-CHANNEL
VOUT
3.5V TO 18V INPUT RANGE VIN 4.7F CERAMIC SHDN SYNC
0.18F BOOST LT1765-3.3 FB GND VC 2.2nF UPS120 4.7F CERAMIC 1.5H VSW OUTPUT 3.3V 2.5A
VIN 510k 1820k UV 243k OV 59k
GATE LTC4365
VOUT
SHDN FAULT
GND
4365 TA02
OV = 18V UV = 3.5V
RELATED PARTS
PART NUMBER LTC4356 LTC1696 LTC1735 LTC1778 LTC2909 LTC2912/LTC2913 LTC2914 DESCRIPTION Surge Stopper Overvoltage/Overcurrent Protection Regulator Overvoltage Protection Controller High Efficiency Synchronous Step-Down Switching Regulator No RSENSE TM Wide Input Range Synchronous Step-Down Controller Triple/Dual Inputs UV/OV Negative Monitor Single/Dual UV/OV Voltage Monitor Quad UV/OV Monitor COMMENTS Wide Operating Range: 4V to 80V, Reverse Protection to -60V, Adjustable Output Clamp Voltage ThinSOT Package, 2.7V to 28V Output Fault Protection, 16-Pin SSOP Up to 97% Efficiency, 4V VIN 36V, 0.8V VOUT (0.9)(VIN), IOUT Up to 20A Pin Selectable Input Polarity Allows Negative and OV Monitoring Ads UV and OV Trip Values, 1.5% Threshold Accuracy For Positive and Negative Supplies 4V VIN 36V, 0.8V VOUT 14V 4V VIN 36V, 0.8V VOUT 10V, 80A Quiescent Current Single Channel LTC3827/LTC3827-1 4V VIN 60V, 1.23V VOUT 36V, 120A Quiescent Current
LTC3727/LTC3727-1 2-Phase, Dual, Synchronous Controller LTC3827/LTC3827-1 Low IQ, Dual, Synchronous Controller LTC3835/LTC3835-1 Low IQ, Synchronous Step-Down Controller LT3845 LT3850 LT4256 LTC4260 LTC4352 LTC4354 LTC4355 Low IQ, Synchronous Step-Down Controller
Dual, 550kHz, 2-Phase Synchronous Step-Down Dual 180 Phased Controllers, VIN 4V to 24V, 97% Duty Cycle, 4mm x 4mm QFN-28, SSOP-28 Packages Controller Positive 48V Hot Swap Controller with Open-Circuit Detect Positive High Voltage Hot Swap Controller with ADC and I2C Ideal MOSFET ORing Diode Negative Voltage Diode-OR Controller Positive Voltage Diode-OR Controller Foldback Current Limiting, Open-Circuit and Overcurrent Fault Output, Up to 80V Supply Wide Operating Range 8.5V to 80V External N-Channel MOSFETs Replace ORing Diodes, 0V to 18V Controls Two N-Channel MOSFETs, 1s Turn-Off, 80V Operation Controls Two N-Channel MOSFETs, 0.5s Turn-Off, 80V Operation
4365f
16 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
LT 0910 * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORA TION 2010

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