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19-2664; Rev 1; 4/03
50mA/100mA Current-Limit Switches
General Description
The MAX4785-MAX4788 family of switches feature internal current limiting to prevent host devices from being damaged due to faulty load conditions. These analog switches have a low 0.7 on-resistance and operate from a 2.3V to 5.5V input voltage range. They are available with guaranteed 50mA and 100mA current limits, making them ideal for load-switching applications. When the switch is on and a load is connected to the port, a guaranteed blanking time of 14ms ensures that the transient voltages settle down. If after this blanking time the load current is greater than the current limit, the MAX4785 and MAX4787 enter a latch-off state where the switch is turned off and FLAG is issued to the microprocessor. The switch can be turned on again by cycling the power or the ON pin. The MAX4786 and MAX4788 have an autoretry feature where the switch turns off after the blanking time and then continuously checks to see if the overload condition is present. The switch remains on after the overload condition disappears. The MAX4785 and MAX4787 are available in a tiny space-saving 4-pin or 5-pin SC70 package. The MAX4786 and MAX4788 are available only in the 4-pin SC70 package. For higher current current-limiting switches, refer to the MAX4789-MAX4794 and MAX1693 data sheets. o Thermal-Shutdown Protection o Reverse-Current Protection o 0.7 On-Resistance o 14ms Guaranteed Blanking Time o FLAG Function (MAX4785/MAX4787) o 65A Supply Current o 8A Latch-Off Current (MAX4785/MAX4787) o 0.01A Shutdown Current o 2.3V to 5.5V Supply Range o Undervoltage Lockout o Fast Current-Limit Response Time o Tiny SC70 Package
Features
o Guaranteed Current Limit: 50mA, 100mA
MAX4785-MAX4788
Ordering Information
PART MAX4785EXS-T MAX4785EXK-T MAX4786EXS-T MAX4787EXS-T TEMP RANGE -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C PINPACKAGE 4 SC70-4 5 SC70-5 4 SC70-4 4 SC70-4 5 SC70-5 4 SC70-4 TOP MARK AGE ADL AGF AGG AND AGH
Applications
PDAs and Palmtop Devices Cell Phones GPS Systems Hand-Held Devices
MAX4787EXK-T MAX4788EXS-T
Selector Guide appears at end of data sheet.
Typical Operating Circuit
2.3V TO 5.5V
Pin Configurations
TOP VIEW
ON OUT 1 GND 2 FLAG 3 5 IN OUT 1 4 IN IN P
MAX4785 MAX4787
4 ON GND 2
MAX4785- MAX4788
3 ON
MAX4785 MAX4787
FLAG
TO EXTERNAL PORT OUT GND
SC70
SC70 1
________________________________________________________________ Maxim Integrated Products
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50mA/100mA Current-Limit Switches MAX4785-MAX4788
ABSOLUTE MAXIMUM RATINGS
IN, ON, FLAG, OUT to GND .....................................-0.3V to +6V OUT Short Circuit to GND .................................Internally Limited Continuous Power Dissipation (TA = +70C) 4-Pin SC70 (derate 3.1mW/C above +70C) ..............245mW 5-Pin SC70 (derate 3.1mW/C above +70C) ..............247mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VIN = 2.3V to 5.5V, TA = -40C to +85C, unless otherwise noted. Typical values are at VIN = 3.3V, TA = +25C.) (Note 1)
PARAMETER Operating Voltage Quiescent Current Latch-Off Current (Note 2) Shutdown Current Forward Current Limit Reverse Current Limit ON Input Leakage Off Switch Leakage Undervoltage Lockout Undervoltage Lockout Hysteresis On-Resistance ON Input Logic High Voltage ON Input Logic Low Voltage FLAG Output Logic Low Voltage FLAG Output High Leakage Current Thermal Shutdown Thermal-Shutdown Hysteresis DYNAMIC Turn-On Time (Note 3) Turn-Off Time (Note 3) ON from low to high; IOUT = 10mA, CL = 0.1F ON from high to low; IOUT = 10mA, CL = 0.1F 50 30 s ns RON VIH VIL ISINK = 1mA (MAX4785/MAX4787) VIN = V F LAG = 5.5V (MAX4785/MAX4787) 150 15 TA = +25C, IOUT = 20mA TA = -40C to +85C, IOUT = 20mA 2.0 0.8 0.4 1 UVLO SYMBOL VIN IQ ILATCH ISHDN IFWD IREV VON = VIN, IOUT = 0, VIN = 2.3V to 5.0V switch on VIN = 5.0V to 5.5V VON = VIN, after an overcurrent fault (MAX4785/MAX4787) VON = 0V MAX4785/MAX4786 MAX4787/MAX4788 MAX4785/MAX4786 MAX4787/MAX4788 VON = VIN or GND VON = 0V, VOUT = 0V Rising edge 1.8 100 0.7 1 1.3 -1 0.01 50 100 CONDITIONS MIN 2.3 65 TYP MAX 5.5 100 120 8 0.01 15 1 120 240 120 240 +1 1 2.2 UNITS V A A A mA mA A A V mV V V V A C C
2
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50mA/100mA Current-Limit Switches
ELECTRICAL CHARACTERISTICS (continued)
(VIN = 2.3V to 5.5V, TA = -40C to +85C, unless otherwise noted. Typical values are at VIN = 3.3V, TA = +25C.) (Note 1)
PARAMETER Blanking Time Short-Circuit Current-Limit Response Time Retry Time (Note 4) tRETRY SYMBOL tBLANK CONDITIONS Overcurrent fault, Figures 2, 3 VON = VIN = 3.3V, short circuit applied to OUT MAX4786/MAX4788: overcurrent fault, Figure 2 98 MIN 14 5 420 TYP MAX 60 UNITS ms s ms
MAX4785-MAX4788
Note 1: All parts are 100% tested at +25C. Limits across the full temperature range are guaranteed by design and correlation. Note 2: Latch-off current does not include the current flowing into FLAG. Note 3: The on-time is defined as the time taken for the current through the switch to go from 0mA to full load. The off-time is defined as the time taken for the current through the switch to go from full load to 0mA. Note 4: Retry time is typically 7x the blanking time.
Typical Operating Characteristics
(VIN = 3.3V, TA = +25C, unless otherwise noted.)
QUIESCENT SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX4785-01
SUPPLY CURRENT vs. TEMPERATURE
MAX4785-02
LATCH-OFF CURRENT vs. TEMPERATURE
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 -40 VON = VIN
MAX4785 toc03
90 80 SUPPLY CURRENT (A) 70 60 50 40 30 20 10 0 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 VON = VIN
90 80 SUPPLY CURRENT (A) 70 VIN = 3.3V VON = VIN VIN = 5V
50 40 30 20 10 0
LATCH-OFF (A)
60
VIN = 5V
VIN = 3.3V
6.0
-40
-15
10
35
60
85
-15
10
35
60
85
SUPPLY VOLTAGE (V)
TEMPERATURE (C)
TEMPERATURE (C)
SHUTDOWN SUPPLY CURRENT vs. TEMPERATURE
MAX4785-04
SHUTDOWN LEAKAGE CURRENT vs. TEMPERATURE
MAX4785-05
LATCH-OFF LEAKAGE CURRENT vs. TEMPERATURE
LATCH-OFF LEAKAGE CURRENT (nA)
MAX4785 toc06
10 SHUTDOWN SUPPLY CURRENT (nA)
10 SHUTDOWN LEAKAGE CURRENT (nA)
100 10 1 0.1 0.01 0.001 VIN = 5V VIN = 3.3V
1
1
VIN = 5V
0.1
0.1
0.01
VIN = 3.3V
0.01
0.001
0.001 -40 -15 10 35 60 85 TEMPERATURE (C)
0.0001 -40
0.0001 -15 10 35 60 85 -40 -15 10 35 60 85 TEMPERATURE (C) TEMPERATURE (C)
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50mA/100mA Current-Limit Switches MAX4785-MAX4788
Typical Operating Characteristics (continued)
(VIN = 3.3V, TA = +25C, unless otherwise noted.)
NORMALIZED ON-RESISTANCE vs. TEMPERATURE
MAX4785-07
OUTPUT CURRENT vs. OUTPUT VOLTAGE
MAX4785 toc08
1.4 1.2 NORMALIZED RON 1.0 0.8 0.6 0.4 0.2 0 -40 -15 10 35 60 VCC = 3.3V
300 250 OUTPUT CURRENT (mA) 200 150 100 50 0 MAX4785/MAX4786 MAX4787/MAX4788
85
0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 3.0 3.3 VIN - VOUT (V)
TEMPERATURE (C)
SWITCH TURN-ON/OFF TIMES vs. TEMPERATURE
MAX4785 toc09
FLAG-BLANKING TIMEOUT vs. TEMPERATURE
MAX4785 toc10
100 ON TURN-ON/OFF TIMES (s) 10 ILOAD = 10mA VCC = 3.3V VCC = 5V
50 45 FLAG-BLANKING TIME (ms) 40 35 30 25
1
0.1 OFF
0.01
0.001 -40 -15 10 35 60 85 TEMPERATURE (C)
20 -40 -15 10 35 60 85 TEMPERATURE (C)
CURRENT-LIMIT RESPONSE
MAX4785 toc11
CURRENT-LIMIT RESPONSE
MAX4785 toc12
COUT = 1F
VIN = 3.3V CIN = 1F
VIN 2V/div VON 2V/div VIN = VON 1V/div
IOUT 100mA/div
VIN = VON CIN = 1F COUT = 1F 20s/div
IOUT 100mA/div
40s/div
4
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50mA/100mA Current-Limit Switches
Typical Operating Characteristics (continued)
(VIN = 3.3V, TA = +25C, unless otherwise noted.)
CURRENT-LIMIT RESPONSE (OUT SHORTED TO GND)
MAX4785 toc13
MAX4785-MAX4788
SWITCH TURN-ON TIME RESPONSE
MAX4785 toc14
CIN = 1F COUT = 1F
VIN = 3.3V VIN 2V/div VON
VOUT 2V/div IOUT 10mA/div
IOUT 2A/div 40s/div 100s/div
SWITCH TURN-OFF TIME RESPONSE
MAX4785 toc15
FLAG-BLANKING RESPONSE
MAX4785 toc16
VIN = 3.3V VON 2V/div
VIN 2V/div VON 2V/div
IOUT 10mA/div
FLAG 2V/div IOUT 100mA/div
100ns/div
4ms/div
Pin Description
PIN SC70 1 2 -- 3 4 SC70 1 2 3 4 5 NAME OUT GND FLAG ON IN FUNCTION Switch Output. Bypass with a 0.1F capacitor to ground. Ground Fault Output. This open-drain output goes low when the device stays in forward or reverse current limit for more than the blanking time period. FLAG is high impedance when a fault is not present or when ON is low. Active-High Switch-On Input. A logic high turns the switch on. Input. Bypass with a 0.1F ceramic capacitor to ground.
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5
50mA/100mA Current-Limit Switches MAX4785-MAX4788
REVERSE-CURRENT DETECTOR
MAX4785/MAX4787 ONLY FLAG BLANKING TIME CIRCUITRY N
FORWARD CURRENT DETECTOR IN
N
OUT
ON
UNDERVOLTAGE LOCKOUT
+2.0V
LOGIC GND AUTORETRY
MAX4785-MAX4788
Figure 1. MAX4785-MAX4788 Functional Diagram
Detailed Description
The MAX4785-MAX4788 are forward/reverse currentlimited switches that operate from a 2.3V to 5.5V input voltage range and guarantee a 50mA and 100mA minimum current-limit threshold for different options. The voltage drop across an internal sense resistor is compared to two reference voltages to indicate a forward or reverse current-limit fault. When the load current exceeds the preset current limit for greater than the fault-blanking time, the switch opens. The MAX4786 and MAX4788 have an autoretry function that turns on the switch again after an internal retry time expires. If the faulty load condition is still present after the blanking time, the switch turns off again and the cycle is repeated. If the faulty load condition is not present, the switch remains on. The MAX4785 and MAX4787 do not have the autoretry option and the switch remains in latch-off mode until the ON pin or the input power is cycled from high to low and then high again. The undervoltage lockout (UVLO) circuit prevents erroneous switch operation when the input voltage goes too low during startup conditions.
6
Reverse-Current Protection
The MAX4785-MAX4788 limit the reverse current (VOUT to VIN) from exceeding the maximum IREV value. The switch is shut off and FLAG is asserted (MAX4785/ MAX4787) if the reverse current-limit condition persists for more than the blanking time. This feature prevents excessive reverse currents from flowing through the device.
Switch-On/Off Control
Toggle ON high to enable the current-limited switches. The switches are continuously on, only if VIN exceeds the UVLO threshold (typically 2V) and there is no fault. When a forward/reverse current fault is preset or the die exceeds the thermal-shutdown temperature of +150C, OUT is internally disconnected from IN and the supply current decreases to 8A (latch off). The switch is now operating in one of its off states. The switch off-state also occurs when driving ON low, thus reducing the supply current (shutdown) to 0.01A. Table 1 illustrates the ON/OFF state of the MAX4785-MAX4788 currentlimit switches.
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50mA/100mA Current-Limit Switches MAX4785-MAX4788
Table 1. MAX4785-MAX4788 Switch Truth Table
ON Low High High High FAULT X Undervoltage lockout Thermal Current limit OFF OFF OFF immediately (tBLANK period does not apply) OFF after tBLANK period has elapsed ON during tBLANK period, OFF during tRETRY period for the MAX4786 and MAX4788; cycle repeats until fault is removed SWITCH ON/OFF SUPPLY CURRENT MODE Shutdown Shutdown Latch off Latch off See the Autoretry section
FLAG Indicator
The MAX4785 and MAX4787 feature a latched fault output, FLAG. Whenever a fault is activated, it latches FLAG output low and also turns the switch off. FLAG is an open-drain output transistor and requires an external pullup resistor from FLAG to IN. During shutdown (ON is low), the pulldown on FLAG output is released in order to limit power dissipation. FLAG goes low when any of the following conditions occur: * The die temperature exceeds the thermal-shutdown temperature limit of +150C. * The device is in current limit for more than the faultblanking period. * VIN is below UVLO threshold.
tBLANK tRETRY tBLANK tBLANK CURRENT LIMIT LOAD CURRENT SHORT CONDITION REMOVED
ON SWITCH STATUS OFF
Figure 2. MAX4786/MAX4788 Autoretry Fault Blanking Diagram
Autoretry (MAX4786/MAX4788)
When the forward or reverse current-limit threshold is exceeded, tBLANK timer begins counting (Figure 2). The timer resets if the overcurrent condition disappears before tBLANK has elapsed. A retry time delay, tRETRY, is started immediately after tBLANK has elapsed and during that time, the switch is latched off. At the end of tRETRY, the switch is turned on again. If the fault still exists, the cycle is repeated. If the fault has been removed, the switch stays on. The autoretry feature saves system power in the case of an overcurrent or short-circuit condition. During tBLANK, when the switch is on, the supply current is at the current limit. During tRETRY, when the switch is off, the current through the switch is zero. Instead of observing the full load current, the switch sees the equivalent load current times duty cycle or ISUPPLY = I LOAD t BLANK /(t BLANK + t RETRY ). With a typical tBLANK = 37ms and typical tRETRY = 259ms, the duty cycle is 12%, which results in an 88% power savings over the switch being on the entire time. The duty cycle is consistent across the process and devices.
resets if the overcurrent condition disappears before tBLANK has elapsed. The switch is shut off if the overcurrent condition continues up to the end of the blanking time. Reset the switch by either toggling ON (Figure 3a) or cycling the input voltage below UVLO, typically 2V (Figure 3b).
Fault Blanking
The MAX4785-MAX4788 feature 14ms (min) fault blanking. Fault blanking allows current-limit faults, including momentary short-circuit faults that occur when hot swapping a capacitive load, and also ensures that no fault is issued during power-up. When a load transient causes the device to enter current limit, an internal counter starts. If the load-transient fault persists beyond the fault-blanking timeout, the MAX4785 and MAX4787s' FLAG asserts low. Load-transient faults less than tBLANK do not cause a FLAG output assertion. Only current-limit faults are blanked. A thermal fault and input voltage drops below the UVLO threshold cause FLAG to assert immediately and do not wait for the blanking time.
Thermal Shutdown
The MAX4785-MAX4788 have a thermal shutdown feature to protect the devices from overheating. The switch turns off and FLAG goes low immediately (no fault blanking) when the junction temperature exceeds +150C.
7
Latch Off (MAX4785/MAX4787)
When the forward or reverse current-limit threshold is exceeded, tBLANK timer begins counting. The timer
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50mA/100mA Current-Limit Switches MAX4785-MAX4788
the MAX4785-MAX4788 from tripping erroneously. If the load capacitance is too large, then current may not have enough time to charge the capacitance and the device assumes that there is a faulty load condition. The maximum capacitive load value that can be driven from OUT is obtained by the following formula: CMAX <
OFF ON PIN VOLTAGE
tBLANK
tBLANK
LOAD CURRENT ON SWITCH STATUS
IFWD _ MIN x tBLANK _ MIN VIN
Layout and Thermal Dissipation
To optimize the switch response time to output shortcircuit conditions, it is very important to keep all traces as short as possible to reduce the effect of undesirable parasitic inductance. Place input and output capacitors as close as possible to the device (no more than 5mm). IN and OUT pins must be connected with short traces to the power bus. During normal operation, the power dissipation is small and the package temperature change is minimal. If the output is continuously shorted to ground at the maximum supply voltage, the operation of the switches with the autoretry option does not cause problems because the total power dissipated during the short is scaled by the duty cycle: PMAX = VIN _ MAX x IOUT _ MAX x tBLANK = 161mW tRETRY + tBLANK
FLAG PIN STATUS (a) tBLANK tBLANK
LOAD CURRENT ON SWITCH STATUS
OFF UVLO
IN PIN VOLTAGE FLAG PIN STATUS
(b)
where VIN = 5.5V, IOUT = 240mA, tBLANK = 14ms, and tRETRY = 98ms. Attention must be given to the MAX4785 and MAX4787 where the latch-off condition must be manually reset by toggling ON from high to low. If the latch-off time duration is not sufficiently high, it is possible for the device to reach the thermal-shutdown threshold and never be able to turn the device on until it cools down.
Figure 3. MAX4785/MAX4787 Latch Off Fault Blanking
The switches with autoretry feature turn back on when the device temperature drops approximately 15C. The switches with latchoff feature require ON cycling.
Applications Information
Input Capacitor
To limit the input voltage drop during momentary output short-circuit conditions, connect a capacitor from IN to GND. A 0.1F ceramic capacitor is adequate for most applications; however, higher capacitor values further reduce the voltage drop at the input and are recommended for lower voltage applications.
PART MAX4785EXS MAX4785EXK MAX4786EXS MAX4787EXS MAX4787EXK MAX4788EXS CURRENT LIMIT (mA) 50 50 50 100 100 100
Selector Guide
FLAG FUNCTION No Yes No No Yes No AUTORETRY No No Yes No No Yes
Output Capacitance
Connect a 0.1F capacitor from OUT to GND. This capacitor helps prevent inductive parasitics from pulling OUT negative during turn-off, thus preventing
8
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50mA/100mA Current-Limit Switches
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)
SC70, 4L.EPS
MAX4785-MAX4788
Chip Information
TRANSISTOR COUNT: 1659 PROCESS: BiCMOS
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9
50mA/100mA Current-Limit Switches MAX4785-MAX4788
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)
SC70, 5L.EPS
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
10 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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