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19-1153; Rev 0; 10/96
Dual, Current-Limited, High-Side P-Channel Switches with Thermal Shutdown
_______________General Description
The MAX894L/MAX895L smart, dual, low-voltage, P-channel, MOSFET power switches are intended for high-side load-switching applications. These switches operate with inputs from +2.7V to +5.5V, making them ideal for both 3V and 5V systems. Internal currentlimiting circuitry protects the input supply against overload. Thermal-overload protection limits power dissipation and junction temperature. The MAX894L/MAX895L's maximum current limits are 500mA and 250mA, respectively. The current limit through the switches is programmed with resistors from SET A/SET B to ground. When the switches are on, the quiescent supply current is a low 16 When the A. switches are off, the supply current decreases to 0.1 A. The MAX894L/MAX895L are available in an 8-pin SO package.
____________________________Features
o +2.7V to +5.5V Input Range o Programmable Current Limits o Low Supply Current: 16 IQ at VIN = 3.3V A 0.1 with Switch Off A o Thermal Shutdown
MAX894L/MAX895L
______________Ordering Information
PART* MAX894LC/D TEMP. RANGE 0C to +70C -40C to +85C 0C to +70C -40C to +85C PINPACKAGE Dice** 8 SO Dice** 8 SO CURRENT LIMIT 500mA 500mA 250mA 250mA
________________________Applications
PCMCIA Slots Access Bus Slots Portable Equipment
MAX894LESA MAX895LC/D MAX895LESA
*To order these units in tape and reel, add (-T) to the end of the part number. **Dice are tested at TA = +25C.
__________Typical Operating Circuit
__________________Pin Configuration
TOP VIEW
OUTPUT A 0.1F OUT A ONB ON/OFF
OUTPUT B 0.1F
OUT B
IN
INPUT 1F
OUT A 1 OUT B 2 SET A 3
8
ONB IN SET B GND
MAX894L MAX895L
SET A SET B
MAX894L MAX895L
7 6 5
RSET A
RSET B
ONA 4
SO
ON/OFF ONA GND
________________________________________________________________ Maxim Integrated Products
1
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Dual, Current-Limited, High-Side P-Channel Switches with Thermal Shutdown MAX894L/MAX895L
ABSOLUTE MAXIMUM RATINGS
IN to GND ...................................................................-0.3V to 6V ONA, ONB to GND .....................................................-0.3V to 6V SET A, SET B, OUT A, OUT B to GND ........-0.3V to (VIN + 0.3V) Maximum Continuous Switch Current MAX894L ..........................................................................0.75A MAX895L ........................................................................0.375A Continuous Power Dissipation (TA = +70C) SO (derate 5.88mW/C above +70C) .......................471mW Operating Temperature Range MAX89_LESA .................................................-40C to +85C Storage Temperature Range ...............................-65C to+150C Lead Temperature (soldering, 10sec) ..............................+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 = 3V, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER Operating Voltage Quiescent Current Off-Supply Current Off-Switch Current Undervoltage Lockout VIN = 5V, ONA = ONB = GND, IOUT A = IOUT B = 0 ONA = ONB = IN, VIN = VOUT A = VOUT B = 5.5V ONA = ONB = IN, VIN = 5.5V, VOUT A = VOUT B = 0 Rising edge, 1% hysteresis VIN = 4.5V On-Resistance VIN = 3.0V Current-Limit-Amplifier Threshold Maximum Output Current IOUT to ISET Current Ratio ONA, ONB Input Low Voltage ONA, ONB Input High Voltage ONA, ONB Input Leakage ISETA, ISETB Bias Current Slow-Current-Loop Response Time Fast-Current-Loop Response Time Turn-On Time Turn-Off Time VIN = 5V, IOUT = 250mA (MAX894L), 125mA (MAX895L) VIN = 3V, IOUT = 250mA (MAX894L), 125mA (MAX895L) 0.8 MAX894L MAX895L MAX894L MAX895L 1.178 2.0 CONDITION MIN 2.7 18 0.03 0.04 2.4 120 250 150 300 1.240 500 250 MAX894L, IOUT = 250mA MAX895L, IOUT = 125mA 945 910 2.0 2.4 0.01 0.5 0.5 5 2 100 150 1.2 20 200 1 3 3 1085 1050 1270 1235 0.8 TYP MAX 5.5 30 1 3 2.6 225 420 300 500 1.302 V mA A/A V V A A s s s s m UNITS V A A A V
VSET required to turn the switch off (Note 1) MAX894L MAX895L VOUT = 1.6V to 2.8V VIN = 2.7V to 5.5V VIN = 2.7V to 3.6V VIN = 4.5V to 5.5V V ONA = V ONB = 5.5V VSET A = 1.24V, ONA = 0, ONB = VIN, IOUT A = 0 VSET B = 1.24V, ONB = 0, ONA = VIN, IOUT B = 0 20% current overdrive, VCC = 5V
Note 1: Tested with IOUT = 50mA for the MAX894L and 25mA for the MAX895L, and VSET raised until VIN - VOUT 0.8V.
2
_______________________________________________________________________________________
Dual, Current-Limited, High-Side P-Channel Switches with Thermal Shutdown
ELECTRICAL CHARACTERISTICS (Note 2)
(VIN = 3V, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER Operating Voltage Quiescent Current Off-Supply Current Off-Switch Current Undervoltage Lockout VIN = 5V, ONA = ONB = GND, IOUT A = IOUT B = 0 ONA = ONB = IN, VIN = VOUT A = VOUT B = 5.5V ONA = ONB = IN, VIN = 5.5V, VOUT A = VOUT B = 0 Rising edge, 1% hysteresis VIN = 4.5V On-Resistance VIN = 3.0V Current-Limit-Amplifier Threshold IOUT to ISET Current Ratio Turn-On Time Turn-Off Time Note 2: Specifications to -40C are guaranteed by design, not production tested. MAX894L MAX895L MAX894L MAX895L 1.14 910 880 MAX894L, IOUT = 250mA MAX895L, IOUT = 125mA 2.0 CONDITION MIN 3.0 TYP MAX 5.5 50 2.2 8 2.9 250 420 300 500 1.34 1360 1315 200 0.25 20 V A/A s s m UNITS V A A A V
MAX894L/MAX895L
VSET_ required to turn the switch off (Note 1) VSET = 1.24V, VOUT = 1.6V to 2.8V VIN = 5V
_______________________________________________________________________________________
3
Dual, Current-Limited, High-Side P-Channel Switches with Thermal Shutdown MAX894L/MAX895L
__________________________________________Typical Operating Characteristics
(Typical Operating Circuit, TA = +25C, unless otherwise noted.)
QUIESCENT CURRENT vs. INPUT VOLTAGE
MAX894 TOC-01
QUIESCENT CURRENT vs. TEMPERATURE
MAX894 TOC-02
OFF-SUPPLY CURRENT vs. TEMPERATURE
MAX894 TOC-03
28 24 QUIESCENT CURRENT (A) 20 16 12 8 4 0 0 1 2 3 4 5 6 INPUT VOLTAGE (V) ONA = ONB = GND IOUT A = IOUT B = 0
24 QUIESCENT CURRENT (A) 22 20 18 16 14 12 -40 -20 0 20 40 60 80 VIN = 5V VIN = 3V
0.07 OFF-SUPPLY CURRENT (A) 0.06 0.05 0.04 0.03 0.02 0.01 0
100
-40
-20
0
20
40
60
80
100
TEMPERATURE (C)
TEMPERATURE (C)
OFF-SWITCH CURRENT vs. TEMPERATURE
MAX894 TOC-04
NORMALIZED ON-RESISTANCE vs. TEMPERATURE
IOUT = 1/2 ILIMIT
MAX894 TOC-05
IOUT/ISET vs. ILIMIT
1400 1200
MAX894 TOC-06
0.07 OFF-SWITCH CURRENT (A) 0.06 0.05 0.04 0.03 0.02 0.01 0 -40 -20 0 20 40 60 80
1.3 1.2 NORMALIZED RON 1.1 1.0 0.9 0.8 0.7 0.6
1600
IOUT/ISET RATIO
1000 800 600 400 200 0 0 20 40 60 80 100 120 140
100
-40
-20
0
20
40
60
80
100
TEMPERATURE (C)
TEMPERATURE (C)
ILIMIT (%)
NORMALIZED OUTPUT CURRENT vs. OUTPUT VOLTAGE
MAX894 TOC-06A
TURN-ON TIME vs. TEMPERATURE
MAX894 TOC-07
TURN-OFF TIME vs. TEMPERATURE
ILOAD = ILIMIT 6 5 tOFF (s) VIN = 5V
MAX894 TOC-08
1.4 NORMALIZED OUTPUT CURRENT VIN = 5V 1.2 1.0 0.8 0.6 0.4 0.2 0 0 1 2 3 4 5 6 OUTPUT VOLTAGE (V) ILIMIT
260 240 220 200 tON (s) 180 160 140 120 100 80 60
ILOAD = ILIMIT
7
VIN = 3V
4 3 2 VIN = 3V
VIN = 5V
1 0
-40
-20
0
20
40
60
80
100
-40
-20
0
20
40
60
80
100
TEMPERATURE (C)
TEMPERATURE (C)
4
_______________________________________________________________________________________
Dual, Current-Limited, High-Side P-Channel Switches with Thermal Shutdown
____________________________Typical Operating Characteristics (continued)
(Typical Operating Circuit, TA = +25C, unless otherwise noted.) CURRENT-LIMIT RESPONSE (MAX894L, RL = 1) CURRENT-LIMIT RESPONSE (MAX894L, RL = 0.7)
MAX894L/MAX895L
A
5V
5V A
B B C 0A 0V
MAX894/895/896 TOC-9
0A C 0V
MAX894/895/896 TOC-10
2s/div CIN = 47F, COUT = 0.1F A: VIN, 500mV/div, AC coupled B: IOUT, 2A/div C: VOUT, 5V/div
1s/div CIN = 47F, COUT = 0.1F A: VIN, 500mV/div, AC coupled B: IOUT, 2A/div C: VOUT, 5V/div
LOAD-TRANSIENT RESPONSE (MAX894L)
A 0A
B 0V
MAX494/495/496 TOC-13
2ms/div
SWITCH TURN-ON TIME
VIN = 5V A: IOUT = 0 to 500mA, 0.2A/div B: VOUT RIPPLE, 200mV/div, AC COUPLED
SWITCH TURN-OFF TIME
A
A 0V
B
MAX894/895/896 TOC-11
B 0V 20s/div VIN = 5V, IOUT = ILIMIT A: VON, 2V/div B: VOUT, 2V/div VIN = 5V, IOUT = ILIMIT A: VON, 2V/div B: VOUT, 2V/div 2s/div
MAX894/895/896 TOC-12
_______________________________________________________________________________________
5
Dual, Current-Limited, High-Side P-Channel Switches with Thermal Shutdown MAX894L/MAX895L
______________________________________________________________Pin Description
PIN 1 2 3 4 5 6 7 8 NAME OUT A OUT B SET A ONA GND SET B IN ONB FUNCTION Switch A Output. P-channel MOSFET drain. Bypass OUT A with a 0.1 capacitor to ground. F Switch B Output. P-channel MOSFET drain. Bypass OUT B with a 0.1 capacitor to ground. F Set Current-Limit Input. A resistor from SET A to ground sets the current limit for switch A. See Setting the Current Limit section. Active-Low Switch A On Input. A logic low turns switch A on. Ground Set Current-Limit Input. A resistor from SET B to ground sets the current limit for switch B. See Setting the Current Limit section. Input, Switches A and B. P-channel MOSFET source. Bypass IN with a 1 capacitor to ground. F Active-Low Switch B On Input. A logic low turns switch B on.
IN
P P P P
OUT A OUT B
MAX894L MAX895L
ON REPLICA AMPLIFIER A
REPLICA AMPLIFIER B ON P
P SET B ON CURRENT-LIMIT AMPLIFIER B 1.24V
SET A RSET A ON CURRENT-LIMIT AMPLIFIER A 1.24V
RSET B
ONB GND ONA CONTROL CIRCUITRY
Figure 1. Functional Diagram
6
_______________________________________________________________________________________
Dual, Current-Limited, High-Side P-Channel Switches with Thermal Shutdown
_______________Detailed Description
The MAX894L/MAX895L P-channel MOSFET power switches limit output current to a user-programmed level. When the output current is increased beyond the set current level, the current also increases through the replica switch (IOUT/1050) (MAX895) and through RSET (Figure 1). The current-limit error amplifier compares the voltage across RSET to the internal 1.24V reference, and regulates the current back to the lesser of the programmed current limit (ILIMIT) or the maximum current limit (IMAX). These switches are not bidirectional; therefore, the input voltage must be higher than the output voltage.
SET
MAX894L/MAX895L
MAX894L MAX895L
GND
RSET
Figure 2. Setting the Current Limit
__________Applications Information
Input Capacitor
To limit input voltage drop during momentary output short-circuit conditions, place a capacitor from IN to GND. A 1 ceramic capacitor is adequate for most F applications; however, higher capacitor values further reduce voltage drop at the input.
Setting the Current Limit
The MAX894L/MAX895L feature internal current-limiting circuitry with maximum programmable values (IMAX) of 500mA, and 250mA, respectively. For best performance, set the current limit (ILIMIT) between 0.2IMAX I LIMIT I MAX . This current limit remains in effect throughout the input supply-voltage range. Program the current limit with a resistor (RSET_) connected from SET_ to ground (Figure 2) as follows: ISET = ILIMIT / IRATIO RSET = 1.24V / ISET = (1.24V x IRATIO) / ILIMIT where ILIMIT is the desired current limit for either switch and IRATIO is the IOUT to ISET current ratio (1085mA for the MAX894L and 1050mA for the MAX895L.
Output Capacitor
Connect a 0.1 capacitor from OUT to GND. This F capacitor prevents inductive parasitics from pulling OUT negative during turn-off.
Layout and Thermal-Dissipation Consideration
To take full advantage of the switch-response time to output short-circuit conditions, it is very important to keep all traces as short as possible, reducing the effect of undesirable parasitic inductance. Place input and output capacitors as close as possible to the device (no more than 5mm). Under normal operating conditions, the package can dissipate and channel heat away. Calculate the maximum power as follows: P = I2LIMITA x R ONA + I2LIMITB x R ONB where R ONA and R ONB are the on-resistances of switches A and B, respectively. When one or both outputs are short circuited, the voltage drop across the switch equals the input supply. Hence, the power dissipated across the switch increases, as does the die temperature. If the fault condition is not removed, the thermal-overload-protection circuitry turns the switch off until the die temperature falls by 10C. A ground plane in contact with the device helps to further dissipate heat.
Short-Circuit Protection
The MAX894L/MAX895L are short-circuit-protected switches. In the event of an output short circuit or current-overload condition, the current through either switch is limited by the internal current-limiting error amplifier to 1.5 x ILIMIT. When the fault condition is removed, the replica error amplifier sets the current limit back to ILIMIT. For a high VDS/t during an output short-circuit condition, the switch turns off and disconnects the input supply from the output. The current-limiting amplifier then slowly turns the switch on with the output current limited to 1.5 x ISET. When the fault condition is removed, the current limit is set back to ILIMIT. Refer to Output Short-Circuit Fast-Loop Response and Output Short-Circuit Slow-Loop Response in the Typical Operating Characteristics.
Thermal Shutdown
The MAX894L/MAX895L feature thermal shutdown. The switch turns off when the junction temperature exceeds +135C. Once the device cools by 10C, the switch turns back on. If the fault short-circuit condition is not removed, the switch cycles on and off, resulting in a pulsed output.
_______________________________________________________________________________________
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Dual, Current-Limited, High-Side P-Channel Switches with Thermal Shutdown MAX894L/MAX895L
___________________Chip Information
TRANSISTOR COUNT: 453 SUBSTRATE CONNECTED TO GND.
__________________________________________________Tape-and-Reel Information
4.0 0.1 1.0 0.1 1.5 +0.1/-0.0 DIAMETER 2.0 0.05 1.75 0.1 A
3.5 0.05 2.2 0.1
8.0 0.3
0.5 RADIUS TYPICAL Bo 0.30 0.05 0.8 0.05 0.30R MAX.
4.0 0.1
A0 A
1.0 MINIMUM
Ko
Ao = 3.1mm 0.1 Bo = 2.7mm 0.1 Ko = 1.2mm 0.1
NOTE: DIMENSIONS ARE IN MM. AND FOLLOW EIA481-1 STANDARD.
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.
8 ___________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600 (c) 1996 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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