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CS8121
CS8121
5V, 1A Linear Regulator with RESET and ENABLE
Description
The CS8121 is a 5V, 1A precision linear regulator with two microprocessor compatible control functions and protection circuitry included on chip. The composite NPN-PNP output pass transistor assures a lower dropout voltage (1.2V @ 1A) without requiring excessive supply current (4mA). The CS8121Os two logic control functions make this regulator well suited to applications requiring microprocessorbased control at the board or module level. ENABLE controls the output stage. A high voltage (>2.9V) on the ENABLE lead turns off the regulatorOs pass transistor and sends the IC into Sleep mode where it draws only 250A. RESET sends a RESET signal when the IC is powering up or whenever the output voltage falls out of regulation. The RESET signal is valid down to VOUT = 1V. The CS8121 design optimizes supply rejection by switching the internal bandgap reference from the supply input to the regulator output as soon as the nominal output voltage is achieved. Additional on chip filtering enhances rejection of high frequency transients on all external leads. The CS8121 is fault protected against short circuit, over voltage and thermal runaway conditions.
Features
s 5V 4% Output Voltage s Low Dropout Voltage (1.2V @ 1A) s Low Quiescent Current (4mA @ IOUT = 1A) s P Compatible Control Functions
RESET ENABLE
s Low Current Sleep Mode IQ = 250A s Fault Protection Thermal Shutdown Short Circuit 60V Peak Transient Voltage
Block Diagram
Package Options
5 Lead TO-220 5 Lead TO-220 Overmolded
V OUT V IN Over Voltage Shutdown ENABLE Comparator Bandgap Supply + Error Amplifier 5 Lead TO-220 Output Current Limit
1 VIN
V OUT(SENSE)
VREF
RESET
Rev. 5/4/99
+ TO VOUT
-
ENABLE
2 ENABLE 3 Gnd
1
Thermal Shutdown Bandgap Reference RESET Comparator + Gnd
4 RESET 5 VOUT 1 NC 2 VIN
1
7 Lead D2PAK
3 ENABLE 4 Gnd 5 RESET 6 VOUT 7 VOUT(SENSE)
1
Cherry Semiconductor Corporation 2000 South County Trail, East Greenwich, RI 02818 Tel: (401)885-3600 Fax: (401)885-5786 Email: info@cherry-semi.com Web Site: www.cherry-semi.com
1
A
Company
CS8121
Absolute Maximum Ratings DC Input Voltage ...........................................................................................................................................................-0.7 to 26V Peak Transient Voltage (46V Load Dump).............................................................................................................................60V Output Current .................................................................................................................................................Internally Limited Electrostatic Discharge (Human Body Model) ......................................................................................................................2kV Operating, Temperature ..........................................................................................................................................-40C to 125C Junction Temperature...............................................................................................................................................-40C to 150C Storage Temperatures.............................................................................................................................................-55C to 150C Lead Temperature Soldering Wave Solder (through hole styles only) .....................................................................................10 sec. max, 260C peak Reflow (SMD styles only) ......................................................................................60 sec. max above 183C, 230C peak Electrical Characteristics: IOUT = 5mA, -40uC TJ 150uC , 7V VIN 26V, -40C TA 125C unless otherwise specified
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
s Output Stage Output Voltage, VOUT Line Regulation Load Regulation Supply Voltage Rejection Dropout Voltage Quiescent Current 7V VIN 26V, 1mA IOUT 1A 7V VIN 26V, IOUT = 5mA 5mA IOUT 1A VIN = 14VDC + 1VRMS @120Hz, ILOAD = 501/2 IOUT = 1A ENABLE = High, VIN = 12V ENABLE = Low, IOUT = 1A 54 4.8 5.0 0 10 70 1.2 0.25 4 1.8 0.65 20 5.2 50 70 V mV mV dB V mA mA
s Protection Circuits Short Circuit Current Thermal Shutdown Overvoltage Shutdown s RESET RESET Saturation Voltage RESET Output Leakage Current Power ON/OFF RESET Peak Output Voltage RESET Threshold ON (VOUT Increasing) RESET Threshold OFF (VOUT Decreasing) RESET Threshold Hysteresis s ENABLE Input High Voltage Input Low Voltage Input Hysteresis Input Current 7V < VIN < 26V 7V < VIN < 26V 7V < VIN < 26V Gnd < VIN(HI) < VOUT 1.1 0.4 2.9 2.1 0.8 0 2.8 10 3.9 V V V A 4.75 10 1V < VOUT < VRT(OFF), 3.1k1/2 pull-up to VOUT ENABLE = Low VOUT > VRT(ON), V RESET = VOUT 3.1k1/2 pull-up to VOUT 0.1 0 0.7 VOUT - 0.10 VOUT - 0.14 40 0.4 25 1.0 VOUT - 0.04 V A V V V mV 150 26 1.5 190 40 A uC V
2
CS8121
Package Lead Description
PACKAGE LEAD # LEAD SYMBOL FUNCTION
7 Lead D2PAK 1 2 3 4 5
5 Lead TO-220 & Overmolded TO-220 NC 1 2 3 4 VIN ENABLE Gnd RESET No Connection. Supply voltage to IC, usually direct from the battery. CMOS compatible logical. VOUT is disabled i.e. placed in a high impedance state when ENABLE is high. Ground connection. CMOS compatible output lead. RESET goes low whenever VOUT falls out of regulation. The RESET delay is externally programmed.
6 7
5
VOUT VOUT(SENSE)
Regulated output voltage, 5V (typ). Remote sensing of output voltage.
Typical Performance Characteristics
Output Voltage vs. Temperature
5.02
Load Regulation vs. Output Current Over Temperature
0
IOUT = 100mA
5.01
-5 -10 -15 Load Reg. (mV) -20 -25 -30 -35 -40 -45 VIN =14V 125C
40C
5.00V @ 25uC
VOUT (V)
5 4.99 4.98 4.97 4.96 4.95 -40
25C
-20
0
20
40
60
80
100
120 140 150
-50 0 200 400 IOUT (A) 600 800 1A
Junction Temperature (uC)
Line Regulation vs. Output Current Over Temperature
Dropout Voltage vs. Output Current Over Temperature
1.5
50 VIN = 7 to 26V 40 Line Reg. (mV)
Dropout Voltage (V)
1.4 1.3 1.2
30 20 125uC 10 -40uC 0 -10 0 0.2 0.4 0.6 0.8 1A
1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 0 0.1 0.2 0.3 0.4 0.5 0.6 IOUT (A) 0.7 0.8 0.9 1.0 -40C 25C 125C
25uC
IOUT(A)
3
CS8121
Typical Performance Characteristics: continued
Quiescent Current vs. Output Current Over Temperature Output Voltage and Supply Current vs. Input Voltage
3.5
3.0
Quiescent Current (mA)
-40C 2.5 25C 2.0 125C 1.5
VOUT
16.0
4.0
3.0 2.0 1.0
IQ
12.0 8.0 4.0 0.0 10.0
1.0
0.5 VIN = 14V 0.0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
0.0 0.0
IOUT
2.0
4.0
6.0
8.0
Supply Voltage
RESET Output Voltage vs. Output Current
2000 1800 Reset Output Voltage (mV) 1600 1400 1200 1000 800 600 400 200 0 1 5 10 15 20 25 30 35 40 Reset Output Current (mA) VIN = 5V
Circuit Description Voltage Reference and Output Circuitry Precision Voltage Reference The regulated output voltage depends on the precision band gap voltage reference in the IC. By adding an error amplifier into the feedback loop, the output voltage is maintained within 4% over temperature and supply variation. Output Stage The composite PNPNPN output structure (Figure 1) provides 1A (typ) of output current while maintaining a low drop out voltage (1.2V) and drawing little quiescent current (4mA).
VOUT
The NPN pass device prevents deep saturation of the output stage which in turn improves the ICOs efficiency by preventing excess current from being used and dissipated by the IC. Output Stage Protection The output stage is protected against overvoltage, short circuit and thermal runaway conditions (Figure 2).
> 30V VIN
VIN
VOUT
IOUT
Load Dump
Short Circuit
Thermal Shutdown
Figure 1. Composite Output Stage of the CS8121
Figure 2. Typical Circuit Waveforms for Output Stage Protection.
4
Supply Current (mA)
5.5 5.0
22.0 20.0
VOUT(V)
CS8121
Circuit Description: continued If the input voltage rises above 30V (e.g. load dump), the output shuts down. This response protects the internal circuitry and enables the IC to survive unexpected voltage transients. Using an emitter sense scheme, the amount of current through the NPN pass transistor is monitored. Feedback circuitry insures that the output current never exceeds a preset limit. Should the junction temperature of the power device exceed 180uC (typ) the power transistor is turned off. Thermal shutdown is an effective means to prevent die overheating since the power transistor is the principle heat source in the IC. Regulator Control Functions The CS8121 contains two microprocessor compatible control functions: ENABLE and RESET (Figure 3).
FOR 7V < VIN < 26V
RESET Function A RESET signal (low voltage) is generated as the IC powers up (VOUT > VOUT - 100mV) or when VOUT drops out of regulation (VOUT < VOUT - 140mV, typ). 40mV of hysteresis is included in the function to minimize oscillations. The RESET output is an open collector NPN transistor, controlled by a low voltage detection circuit. The circuit is functionally independent of the rest of the IC, thereby guaranteeing that the RESET signal is valid for VOUT as low as 1V. An external RC network on the RESET lead (Figure 4) provides a sufficiently long delay for most microprocessor based applications. RC values can be chosen using the following formula: tDelay RTOT CRST
[
ln
(
VT VOUT VRST VOUT
)]
VIN
ENABLE
HI VIN(HI) LO VRT(ON) VRT(OFF)
where: RTOT RIN CRST tDelay
= RRST in parallel with RIN, = P port impedance, = RESET delay capacitor, = desired delay time, = VSAT of RESET lead (0.7V @ turn - on), and
VRST VT = P logic threshold voltage.
VOUT
(1) VR
PEAK
VOUT
(2) VR
PEAK SAT
RESET
VR
(1) = NO RESET DELAY CAPACITOR (2) = WITH RESET DELAY CAPACITOR
CS8121
RESET
RRST
10mF tantalum
5V to mP and System Power
Figure 3. Circuit Waveforms for the CS8121
to mP RESET Port CRST
ENABLE Function The ENABLE function switches the output transistor. When the voltage on the ENABLE lead exceeds 2.9V typ, the output pass transistor turns off, leaving a high impedance facing the load. The IC will remain in Sleep mode, drawing only 250A, until the voltage on the lead drops below 2.1V typ. Hysteresis (800mV) is built into the ENABLE function to provide good noise immunity.
Figure 4. RC Network for RESET Delay
5
CS8121
Applications Notes
VBAT C1 0.1mF
VIN
VOUT C2 10mF
VCC
500kW
CS-8121
ENABLE RESET
RRST
mP
SWITCH
Gnd
RESET CRST I/O Port
Q1 100kW 100kW 500kW
Figure 5. Microprocessor control of CS8121 using external switching transistor Q1.
The circuit depicted in Figure 5 lets the microprocessor control its power source, the CS8121 regulator. An I/O port on the P and the SWITCH port are used to drive the base of Q1. When Q1 is driven into saturation, the voltage on the ENABLE lead falls below its lower threshold and the regulatorOs output is switched on. When the drive current is removed, the voltage on the ENABLE lead rises, the output is switched off and the IC moves into Sleep mode where it typically draws 250A. By coupling these two controls with ENABLE , the system has added flexibility. Once the system is running, the state of the SWITCH is irrelevant as long as the I/O port continues to drive Q1. The P can turn off its own power by withdrawing drive current, once the SWITCH is open. This software control at the I/O port allows the P to finish key housekeeping functions before power is removed. The logic options are summarized in Table 1 below Table 1: Logic Control of CS8121 Output P I/O drive SWITCH ENABLE Output ON Closed LOW ON Open LOW ON OFF Closed LOW ON Open HIGH OFF The I/O port of the P typically provides 50 A to Q1. In automotive applications the SWITCH is connected to the ignition switch. Stability Considerations The output or compensation capacitor C2 helps determine three main characteristics of a linear regulator: start-up delay, load transient response and loop stability. The capacitor value and type should be based on cost, availability, size and temperature constraints. A tantalum or aluminum electrolytic capacitor is best, since a film or ceramic capacitor with almost zero ESR can cause instability. The aluminum electrolytic capacitor is the least 6
expensive solution, but, if the circuit operates at low temperatures (-25C to -40C), both the value and ESR of the capacitor will vary considerably. The capacitor manufacturers data sheet usually provides this information. The value for the output capacitor C2 shown in the test and applications circuit should work for most applications, however it is not necessarily the optimized solution. To determine an acceptable value for C2 for a particular application, start with a tantalum capacitor of the recommended value and work towards a less expensive alternative part. Step 1: Place the completed circuit with a tantalum capacitor of the recommended value in an environmental chamber at the lowest specified operating temperature and monitor the outputs with an oscilloscope. A decade box connected in series with the capacitor will simulate the higher ESR of an aluminum capacitor. Leave the decade box outside the chamber, the small resistance added by the longer leads is negligible. Step 2: With the input voltage at its maximum value, increase the load current slowly from zero to full load while observing the output for any oscillations. If no oscillations are observed, the capacitor is large enough to ensure a stable design under steady state conditions. Step 3: Increase the ESR of the capacitor from zero using the decade box and vary the load current until oscillations appear. Record the values of load current and ESR that cause the greatest oscillation. This represents the worst case load conditions for the regulator at low temperature. Step 4: Maintain the worst case load conditions set in step 3 and vary the input voltage until the oscillations increase. This point represents the worst case input voltage conditions. Step 5: If the capacitor is adequate, repeat steps 3 and 4 with the next smaller valued capacitor. A smaller capacitor will usually cost less and occupy less board space. If the output oscillates within the range of expected operating conditions, repeat steps 3 and 4 with the next larger standard capacitor value.
CS8121
Application Notes: continued
5V to mP and System Power RRST RESET ENABLE to mP RESET Port CRST C2** 10mF
VIN C 1* 0.1mF
VOUT
CS-8121
C1*required if regulator is located far from the power supply filter. C2** required for stability.
Figure 6: Test and application circuit showing output compensation.
Step 6: Test the load transient response by switching in various loads at several frequencies to simulate its real working environment. Vary the ESR to reduce ringing. Step 7: Remove the unit from the environmental chamber and heat the IC with a heat gun. Vary the load current as instructed in step 5 to test for any oscillations. Once the minimum capacitor value with the maximum ESR is found, a safety factor should be added to allow for the tolerance of the capacitor and any variations in regulator performance. Most good quality aluminum electrolytic capacitors have a tolerance of +/- 20% so the minimum value found should be increased by at least 50% to allow for this tolerance plus the variation which will occur at low temperatures. The ESR of the capacitor should be less than 50% of the maximum allowable ESR found in step 3 above. Calculating Power Dissipation in a Single Output Linear Regulator The maximum power dissipation for a single output regulator (Figure 7) is: PD(max) = {VIN(max) - VOUT(min)}IOUT(max) + VIN(max)IQ (1)
where: VIN(max) is the maximum input voltage, VOUT(min) is the minimum output voltage, IOUT(max) is the maximum output current for the application, and IQ is the quiescent current the regulator consumes at IOUT(max). Once the value of PD(max) is known, the maximum permissible value of RQJA can be calculated: RQJA = 150C - TA PD (2)
The value of RQJA can then be compared with those in the package section of the data sheet. Those packages with RQJA's less than the calculated value in equation 2 will keep the die temperature below 150C. In some cases, none of the packages will be sufficient to dissipate the heat generated by the IC, and an external heatsink will be required. Heat Sinks A heat sink effectively increases the surface area of the package to improve the flow of heat away from the IC and into the surrounding air.
IIN VIN
Smart Regulator
IOUT VOUT
Each material in the heat flow path between the IC and the outside environment will have a thermal resistance. Like series electrical resistances, these resistances are summed to determine the value of RQJA: RQJA = RQJC + RQCS + RQSA (3) where: RQJC = the junctiontocase thermal resistance, RQCS = the casetoheatsink thermal resistance, and RQSA = the heatsinktoambient thermal resistance. RQJC appears in the package section of the data sheet. Like RQJA, it too is a function of package type. RQCS and RQSA are functions of the package type, heatsink and the interface between them. These values appear in heat sink data sheets of heat sink manufacturers.
}
Control Features
IQ
Figure 7: Single output regulator with key performance parameters labeled.
7
CS8121
Package Specification
PACKAGE DIMENSIONS IN mm (INCHES) 5 Lead TO-220 (T) Straight PACKAGE THERMAL DATA
Thermal Data
10.54 (.415) 9.78 (.385) 2.87 (.113) 6.55 (.258) 2.62 (.103) 5.94 (.234)
4.83 (.190) 4.06 (.160) 3.96 (.156) 3.71 (.146)
1.40 (.055) 1.14 (.045)
RQJC RQJA
typ typ
5 Lead 5 Lead TO-220 TO-220 (Overmold) 4.0 2.5 50 50
7 Lead D2PAK 2.5 10-50* uC/W uC/W
*Depending on thermal properties of substrate, RQJA = RQJC + RQCA.
5 Lead TO-220 (TVA) Vertical
14.99 (.590) 14.22 (.560)
10.54 (.415) 9.78 (.385) 3.96 (.156) 3.71 (.146)
4.83 (.190) 4.06 (.160)
1.40 (.055) 1.14 (.045)
14.22 (.560) 13.72 (.540)
6.55 (.258) 5.94 (.234) 2.87 (.113) 2.62 (.103) 14.99 (.590) 14.22 (.560)
1.02 (.040) 0.76 (.030)
1.78 (.070) 2.92 (.115) 2.29 (.090) 8.64 (.340) 7.87 (.310)
1.02(.040) 0.63(.025) 6.93(.273) 6.68(.263)
1.83(.072) 1.57(.062)
0.56 (.022) 0.36 (.014) 2.92 (.115) 2.29 (.090)
1.70 (.067) 6.80 (.268) 1.68 (.066) typ 0.56 (.022) 0.36 (.014)
4.34 (.171) 7.51 (.296)
5 Lead Overmolded TO-220 (TFVA) Vertical
10.3 (.405) 10.0 (.395) .761 (.030) .508 (.020) 3.30 (.130) 2.89 (.114) 15.6 (.614) 15.3 (.604) 3.17 (.125) 2.92 (.115) 7.18 (.283) 6.94 (.273) 2.79 (.110) 2.54 (.100)
.94 (.037) .69 (.027)
7 Lead D2PAK (DPS)* Short-Leaded
3.30 (.130) DIA 3.05 (.120) 4.70 (.185) 4.44 (.175)
1.68 (.066) 1.40 (.055)
10.31 (.406) 10.05 (.396)
1.40 (.055) 1.14 (.045)
3.10 (.122) 10.4 (.409) Note: Leads maintain a right angle with respect to the package body to within .015. 5.89 (.232) 4.01 (.158) 8.05 (.317)
3.18 (.125) 2.92 (.115)
8.53 (.336) 8.28 (.326)
14.71 (.579) 13.69 (.539)
2.79 (.110) 2.54 (.100)
.94 (.037) .69 (.027) 1.70 (.067) 6.80 (.268) 1.68 (.066) TYP
.56 (.022) .36 (.014)
1.98 (.078) 1.47 (.058)
0.91 (.036) 0.66 (.026) TERMINAL 8 6.50 (.256) REF
1.27 (.050) REF
.254 (.010) REF
Ordering Information
7.75 (.305) REF
4.57 (.180) 4.31 (.170)
Part Number CS8121YT5 CS8121YTVA5 CS8121YTHA5 CS8121YTFVA5 CS8121YDPS7 CS8121YDPSR7
Description 5 Lead TO-220 Straight 5 Lead TO-220 Vertical 5 Lead TO-220 Horizontal 5 Lead Overmolded TO-220 Vertical 7 Lead D2PAK Short-Leaded 7 Lead D2PAK Short-Leaded (tape & reel) 8
0.10 (.004) 0.00 (.000)
*CHERRY SEMICONDUCTOR SHORT-LEADED FOOTPRINT
Cherry Semiconductor Corporation reserves the right to make changes to the specifications without notice. Please contact Cherry Semiconductor Corporation for the latest available information.
(c) 1999 Cherry Semiconductor Corporation
Rev. 5/4/99

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