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19-1223; Rev 0; 4/97
Current-Limited, High-Side P-Channel Switches with Thermal Shutdown
_______________General Description
The MAX891L/MAX892L smart, 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 current-limiting circuitry protects the input supply against overload. Thermaloverload protection limits power dissipation and junction temperatures. The MAX891L/MAX892L's maximum current limits are 500mA and 250mA, respectively. The current limit through the switch is programmed with a resistor from SET to ground. When the switch is on, the quiescent supply current is a low 13A. When the switch is off, the quiescent current decreases to 0.1A. The MAX891L/MAX892L are available in 8-pin MAX packages.
____________________________Features
o Ultra-Small MAX Package--Only 1.11mm High o 2.7V to 5.5V Input Range o Programmable Current Limit o Low 13A Quiescent Current at VIN = 3.3V, 0.1A Switch Off o Thermal Shutdown o FAULT Indicator Output o On-Resistances: 0.12 (MAX891L) 0.25 (MAX892L)
MAX891L/MAX892L
________________________Applications
PCMCIA Slots Access Bus Slots Portable Equipment
______________Ordering Information
PART MAX891LC/D MAX891LEUA* MAX892LC/D MAX892LEUA* TEMP. RANGE 0C to +70C -40C to +85C 0C to +70C -40C to +85C PINCURRENT PACKAGE LIMIT Dice** 8 MAX Dice** 8 MAX 500mA 500mA 250mA 250mA
* 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
INPUT IN IN FAULT 1F GND OUT OUTPUT 0.1F 100k IN 1 ON/OFF IN 2 ON 3 SET GND 4 5 SET 8 OUT
MAX891L MAX892L
OUT ON
MAX891L MAX892L
7 OUT 6 FAULT
MAX
________________________________________________________________ Maxim Integrated Products
1
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Current-Limited, High-Side P-Channel Switches with Thermal Shutdown MAX891L/MAX892L
ABSOLUTE MAXIMUM RATINGS
IN to GND ..................................................................-0.3V to 6V ON, FAULT to GND.................................................... -0.3V to 6V SET, OUT to GND ........................................-0.3V to (VIN + 0.3V) Maximum Continuous Switch Current MAX891L ..........................................................................0.75A MAX892L ........................................................................0.375A Continuous Power Dissipation (TA = +70C) MAX (derate 4.1mW/C above +70C) .......................330mW Operating Temperature Range MAX891LEUA/MAX892LEUA ............................-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, ON = GND, IOUT = 0mA ON = IN, VIN = VOUT = 5.5V ON = IN, VIN = 5.5V, VOUT = 0V Rising edge, 1% hysteresis VIN = 4.5V On-Resistance VIN = 3.0V Current-Limit-Amplifier Accuracy Maximum Output Current IOUT to ISET Current Ratio ON Input Low Voltage ON Input High Voltage ON Input Leakage ISET Bias Current FAULT Logic Output Low Voltage Slow-Current-Loop Response Time Fast-Current-Loop Response Time Turn-On Time Turn-Off Time IOUT = 250mA (MAX891L), or 125mA (MAX892L) VIN = 5V VIN = 5V VIN = 3V 0.8 MAX891L MAX892L MAX891L MAX892L 1.178 2.0 CONDITIONS MIN 2.7 13 0.02 0.02 2.3 120 250 150 300 1.240 500 250 MAX891L, IOUT = 250mA MAX892L, IOUT = 125mA 840 840 2.0 2.4 -1 0.01 0.5 0.05 5 2 100 150 2 20 200 1 3 0.4 1 965 965 1130 1130 0.8 TYP MAX 5.5 20 1 3 2.6 225 420 300 500 1.302 UNITS V A A A V m m V mA A/A V V A A V A s s s s
VSET required to turn the switch off (Note 1) MAX891L MAX892L 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 ON = 5.5V VSET = 1.24V, IOUT = 0mA ISINK = 1mA, VSET = 1.4V 20% current overdrive, VIN = 5V
FAULT Logic Output High Leakage V FAULT = 5.5V, VSET = 1V
2
_______________________________________________________________________________________
Current-Limited, High-Side P-Channel Switches with Thermal Shutdown
ELECTRICAL CHARACTERISTICS
(VIN = 3V, TA = -40C to +85C, unless otherwise noted.) (Note 2) PARAMETER Operating Voltage Quiescent Current Off-Supply Current Off-Switch Current Undervoltage Lockout VIN = 5V, ON = GND, IOUT = 0mA ON = IN, VIN = VOUT = 5.5V ON = IN, VIN = 5.5V, VOUT = 0V Rising edge, 1% hysteresis VIN = 4.5V On-Resistance On-Resistance Current-Limit-Amplifier Accuracy IOUT to ISET Current Ratio FAULT Logic Output Low Voltage Turn-On Time Turn-Off Time VIN = 3.0V MAX891L MAX892L MAX891L MAX892L 1.14 805 805 MAX891L, IOUT = 250mA MAX892L, IOUT = 125mA 2.0 CONDITIONS MIN 3.0 TYP MAX 5.5 50 2.2 8 2.9 225 420 300 500 1.34 1210 1210 0.4 200 0.25 20 UNITS V A A A V m m V A/A V s s
MAX891L/MAX892L
VSET required to turn the switch off (Note 1) VOUT = 1.6V to 2.8V ISINK = 1mA, VSET = 1.4V VIN = 5V VIN = 5V
Note 1: Tested with IOUT = 50mA for the MAX891L, 25mA for the MAX892L, and VSET raised until VIN - VOUT 0.8V. Note 2: Parameters to -40C are guaranteed by design, not production tested.
_______________________________________________________________________________________
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Current-Limited, High-Side P-Channel Switches with Thermal Shutdown MAX891L/MAX892L
__________________________________________Typical Operating Characteristics
(Typical Operating Circuit, TA = +25C, unless otherwise noted.)
QUIESCENT CURRENT vs. INPUT VOLTAGE
MAX981/2/3-01
QUIESCENT CURRENT vs. TEMPERATURE
MAX981/2/3-02
OFF-SUPPLY CURRENT vs. TEMPERATURE
MAX980-03
14 12 QUIESCENT CURRENT (A) 10 8 6 4 2 0 0 1 2 3 4 5 6 INPUT VOLTAGE (V)
14 13 QUIESCENT CURRENT (A) 12 11 10 9 8 7 -40 -20 0 20 40 60 80 VIN = 3V VIN = 5V
0.06 OFF-SUPPLY CURRENT (A) 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 LEAKAGE CURRENT vs. TEMPERATURE
MAX980-04
NORMALIZED ON-RESISTANCE vs. TEMPERATURE
ILOAD = 1/2ILIM 1.2 NORMALIZED RON IOUT/ISET RATIO 1.1 1.0 0.9 0.8 0.7 0.6
MAX980-05
IOUT/ISET RATIO vs. ILIMIT
MAX981/2/3-06
0.06 0.05 LEAKAGE CURRENT (A) 0.04 0.03 0.02 0.01 0 -40 -20 0 20 40 60 80
1.3
1400 1200 1000 800 600 400 200 0
100
-40
-20
0
20
40
60
80
100
0
20
40
60
80
100
120
140
TEMPERATURE (C)
TEMPERATURE (C)
ILIMIT (%)
NORMALIZED OUTPUT CURRENT vs. OUTPUT VOLTAGE
MAX890-06A
TURN-ON TIME vs. TEMPERATURE
MAX981/2/3-07
TURN-OFF TIME vs. TEMPERATURE
ILOAD = ILIM VIN = 5V 3 VIN = 3V tOFF (s) 2
MAX981/2/3-08
1.2 NORMALIZED OUTPUT CURRENT 1.0 0.8 0.6 0.4 0.2 VIN = 5V 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 -40 -20 0 20 40 60 80 VIN = 5V VIN = 3V ILOAD = ILIM
4
1
0 100 -40 -20 0 20 40 60 80 100 TEMPERATURE (C) TEMPERATURE (C)
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_______________________________________________________________________________________
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 (MAX891L, RL = 0.8)
A 5V
MAX891L/MAX892L
CURRENT-LIMIT RESPONSE (MAX891L, RL = 0.5)
5V
A
B
B
C
0A 0V
0A C 0V
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
SWITCH TURN-ON TIME
A
B
20s/div VIN = 5V, IOUT = ILIM A: VON, 2V/div B: VOUT, 2V/div
SWITCH TURN-OFF TIME
SWITCH TIMING CHARACTERISTICS
A A 0V B
0A
0V C 0V
B 0V 2s/div VIN = 5V, IOUT = ILIM A: VON, 2V/div B: VOUT, 2V/div
D 0V 50s/div VIN = 5V A: ILOAD, 0.1A/div B: VON, 5V/div C: VOUT, 5V/div D: VFAULT, 5V/div
_______________________________________________________________________________________
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Current-Limited, High-Side P-Channel Switches with Thermal Shutdown MAX891L/MAX892L
______________________________________________________________Pin Description
PIN 1, 2 3 4 5 6 7, 8 NAME IN ON GND SET FAULT OUT FUNCTION Input. P-channel MOSFET source. Bypass IN with a 1F capacitor to ground. Active-Low Switch On Input. A logic low turns the switch on. Ground Set Current-Limit Input. A resistor from SET to ground sets the current limit for the switch. See Setting the Current Limit section. Fault-Indicator Output. This open-drain output goes low when in current limit or when the die temperature exceeds +135C. Switch Output. P-channel MOSFET drain. Bypass OUT with a 0.1F capacitor to ground.
_______________Detailed Description
The MAX891L/MAX892L 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 is also increased through the replica switch (I OUT /965) 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.
P
IN
MAX891L MAX892L
OUT P
FAULT
N
REPLICA AMPLIFIER ON P SET ON CURRENT-LIMIT AMPLIFIER 1.24V
Setting the Current Limit
The MAX891L/MAX892L feature internal current-limiting circuitry with maximum programmable values (IMAX) of 500mA and 250mA, respectively. For best performance, set the current limit (I LIMIT ) between 0.2IMAX ILIMIT IMAX. This current limit remains in effect throughout the input supply-voltage range. Program the current limit with a resistor (R SET) from SET to ground (Figure 2) as follows: ISET = ILIMIT / IRATIO RSET = 1.240 / ISET where ILIMIT is the desired current limit, and IRATIO is the IOUT to ISET current ratio (965).
ON CONTROL CIRCUITRY
RSET
HOT GND
Figure 1. Functional Diagram
Short-Circuit Protection
The MAX891L/MAX892L are short-circuit-protected switches. In the event of an output short circuit or current-overload condition, the current through the 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.
V t For a high DS/ 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 ILIMIT. When the fault condition is removed, the current limit is set back to ILIMIT. Refer to the CurrentLimit Response graphs in the Typical Operating Characteristics.
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_______________________________________________________________________________________
Current-Limited, High-Side P-Channel Switches with Thermal Shutdown
Output Capacitor
Connect a 0.1F capacitor from OUT to GND. One function of this capacitor is to prevent inductive parasitics from pulling OUT negative during turn-off.
MAX891L MAX892L
SET RSET GND
MAX891L/MAX892L
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 to reduce 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 dissipates and channels heat away. Calculate maximum power as follows: P = I2LIM x RON where RON is the on-resistance of the switch. When the output is short circuited, 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 dissipate additional heat.
Figure 2. Setting the Current Limit
Thermal Shutdown
The MAX891L/MAX892L 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 will cycle on and off, resulting in a pulsed output.
Fault Indicator
The MAX891L/MAX892L provide a fault output (FAULT). This open-drain output goes low when in current limit or when the die temperature exceeds +135C. During start-up, FAULT is low until the switch is fully on and no over-current condition exists. A 100k pull-up resistor from FAULT to IN provides a logic-control signal.
___________________Chip Information
TRANSISTOR COUNT: 396 SUBSTRATE CONNECTED TO GND
__________Applications Information
Input Capacitor
To limit input voltage drop during momentary output short-circuit conditions, connect a capacitor from IN to GND. A 1F ceramic capacitor is adequate for most applications; however, higher capacitor values further reduce voltage drop at the input.
_______________________________________________________________________________________
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Current-Limited, High-Side P-Channel Switches with Thermal Shutdown MAX891L/MAX892L
__________________________________________________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.
________________________________________________________Package Information
8LUMAXD.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.
8 ___________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600 (c) 1997 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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