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19-1450; Rev 0; 7/99
1.2A, Current-Limited, High-Side P-Channel Switch with Thermal Shutdown
General Description
The MAX893L smart, low-voltage, P-channel, MOSFET power switch is intended for high-side load-switching applications. This switch operates with inputs from +2.7V to +5.5V, making it ideal for both +3V and +5V systems. Internal current-limiting circuitry protects the input supply against overload. Thermal overload protection limits power dissipation and junction temperature. The MAX893L's maximum programmed current limit is 1.2A. The typical short-circuit current is 1.5 times the programmed current; therefore, a 1.2A programmed limit will result in a 1.8A short-circuit current limit. The current limit through the switch is programmed with a resistor from SET to ground. The quiescent supply current is a low 13A. When the switch is off, the supply current decreases to 0.1A. The MAX893L is available in an 8-pin SO package.
____________________________Features
o +2.7V to +5.5V Input Range o Programmable Current Limit 0.2A to 1.2A Range 20% Accuracy o 1.2A Continuous Load Current o 1.8A Short-Circuit Current o Low Quiescent Current 13A at VIN = 3.3V 0.1A with Switch Off o Thermal Shutdown o FAULT Indicator Output o 0.07 On-Resistance
MAX893L
________________________Applications
USB Ports USB Hubs PCMCIA Slots Access Bus Slots Portable Equipment
PART MAX893LESA
Ordering Information
TEMP. RANGE -40C to +85C PIN-PACKAGE 8 SO
Typical Operating Circuit
Pin Configuration
TOP VIEW
INPUT IN IN 100k FAULT 1F GND ON SET RSET ON/OFF IN 2 ON 3 GND 4 OUT OUTPUT 0.1F* IN 1 8 FAULT
MAX893L
OUT
MAX893L
7 OUT 6 OUT 5 SET
SO *USB SPECIFICATIONS REQUIRE HIGHER CAPACITANCE.
________________________________________________________________ Maxim Integrated Products
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1.2A, Current-Limited, High-Side P-Channel Switch with Thermal Shutdown MAX893L
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 Short-Circuit Switch Current .............2.0A Continuous Power Dissipation (TA = +70C) SO (derate 5.88mW/C above +70C) .........................471mW Operating Temperature Range MAX893LESA ...................................................-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 On-Resistance Current-Limit-Amplifier Threshold Maximum Programmable Continuous Output Current Limit Short-Circuit Current IOUT to ISET Current Ratio ON Input Voltage Low ON Input Voltage High ON Input Leakage Current ISET Bias Current FAULT Logic Output Voltage Low FAULT Logic Output High Leakage Current Slow Current-Loop Response Time Fast Current-Loop Response Time Turn-On Time Turn-Off Time VIN = 5V, IOUT = 500mA VIN = 3V, IOUT = 500mA VIN = 5V, IOUT = 500mA 2 IOUT = 500mA, VOUT > 1.6V 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 = 0; VIN = VOUT ISINK = 1mA, VSET = 1.4V V FAULT = 5.5V, VSET = 1V 20% current overdrive, VIN = 5V 0.05 5 2 80 115 4 200 2.0 2.4 0.01 0.5 1 3 0.4 1 920 VIN = 5V, ON = GND, IOUT = 0 ON = IN, VIN = VOUT = 5.5V ON = IN, VIN = 5.5V, VOUT = 0 Rising edge, 1% hysteresis VIN = 4.5V VIN = 3.0V VSET required to turn the switch off (Note 1) 1.178 2.0 CONDITIONS MIN 2.7 13 0.03 0.04 2.4 70 88 1.240 1.2 1.8 1080 1250 0.8 TYP MAX 5.5 20 1 15 2.6 125 160 1.302 UNITS V A A A V m V A A A/A V V A A V A s s s s
2
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1.2A, Current-Limited, High-Side P-Channel Switch 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 On-Resistance Current-Limit-Amplifier Threshold IOUT to ISET Current Ratio FAULT Logic Output Voltage Low Turn-On Time Turn-Off Time VIN = 5V, ON = GND, IOUT = 0 ON = IN, VIN = VOUT = 5.5V ON = IN, VIN = 5.5V, VOUT = 0 Rising edge, 1% hysteresis VIN = 4.5V VIN = 3.0V VSET required to turn the switch off (Note 1) IOUT = 500mA, VOUT > 1.6V ISINK = 1mA, VSET = 1.4V VIN = 5V, IOUT = 500mA VIN = 5V, IOUT = 500mA 1 1.14 865 2.0 CONDITIONS MIN 3.0 TYP MAX 5.5 30 2.2 15 2.9 125 160 1.34 1300 0.4 200 20 UNITS V A A A V m V A/A V s s
MAX893L
Note 1: Tested with IOUT = 100mA and VSET raised until VIN - VOUT 0.8V. Note 2: Specifications to -40C are guaranteed by design, not production tested.
_______________________________________________________________________________________
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1.2A, Current-Limited, High-Side P-Channel Switch with Thermal Shutdown MAX893L
__________________________________________Typical Operating Characteristics
(TA = +25C, unless otherwise noted.)
QUIESCENT CURRENT vs. INPUT VOLTAGE
MAX89L toc01
QUIESCENT CURRENT vs. TEMPERATURE
VIN = 5V 13 QUIESCENT CURRENT (A) VIN = 3V 12 11 10 9 8 0.001 -40 -20 0 20 40 60 80 100 -40 -20
MAX89L toc02
OFF-SUPPLY CURRENT vs. TEMPERATURE
MAX893L toc03
14 12 QUIESCENT CURRENT (A) 10 8 6 4 2 0 0 1 2 3 4 5 6 INPUT VOLTAGE (V) ON = GND IOUT = 0
14
10
OFF-SUPPLY CURRENT (nA)
1
0.1
0.01
0
20
40
60
80
100
TEMPERATURE (C)
TEMPERATURE (C)
OFF-SWITCH CURRENT vs. TEMPERATURE
MAX893L toc04
NORMALIZED ON-RESISTANCE vs. TEMPERATURE
MAX893L toc05
IOUT/ISET RATIO vs. ILIMIT
MAX89L toc06
1000
1.3 1.2 NORMALIZED RON 1.1 1.0 0.9 0.8 IOUT = 1/2 ILIMIT VIN = 5V
1400 1200 IOUT/ISET RATIO 1000 800 600 400 200 0
OFF-SWITCH CURRENT (nA)
100
10
1
0.1 0.7 0.01 -40 -20 0 20 40 60 80 100 TEMPERATURE (C) 0.6 -40 -20 0 20 40 60 80 100 TEMPERATURE (C)
0
20
40
60
80
100
120
140
ILIMIT (%)
NORMALIZED OUTPUT CURRENT vs. OUTPUT VOLTAGE
MAX893L toc07
TURN-ON TIME vs. TEMPERATURE
MAX893L toc08
TURN-OFF TIME vs. TEMPERATURE
ILOAD = ILIMIT 5 4 tOFF (s) 3 2 1 0 -40 -20 0 20 40 60 80 100 TEMPERATURE (C) VIN = 3V VIN = 5V
MAX893L toc09
1.4 NORMALIZED OUTPUT CURRENT 1.2 1.0 0.8 0.6 0.4 ILIMIT = 1.2A
150 140 130 120 tON (s) 110 100 90 VIN = 5V 80 ILOAD = ILIMIT VIN = 3V
6
0.2 VIN = 5V 0 0 1 2 3 4 5 6 OUTPUT VOLTAGE (V)
70 60 -40 -20 0 20 40 60 80 100 TEMPERATURE (C)
4
_______________________________________________________________________________________
1.2A, Current-Limited, High-Side P-Channel Switch with Thermal Shutdown
____________________________Typical Operating Characteristics (continued)
(TA = +25C, unless otherwise noted.)
MAX893L
OUTPUT OVERLOAD (SLOW-LOOP RESPONSE)
MAX893L toc10
OUTPUT SHORT CIRCUIT (FAST-LOOP RESPONSE)
A
MAX893L toc11
A
C 0V
C VOUT 0V
B 0A
B IOUT 0V 2s/div CIN = 100F, COUT = 0.1F A: VIN, 1V/div, AC-COUPLED B: IOUT, 1A/div C: VOUT, 5V/div 2s/div CIN = 100F, COUT = 0.1F A: VIN, 1V/div, AC-COUPLED B: IOUT, 2A/div C: VOUT, 5V/div
SWITCH TURN-ON TIME
MAX893L toc13
SWITCH TURN-OFF TIME
MAX893L toc14
A 0V A 0V
B 0V
B 0V 20s/div VIN = 5V, IOUT = ILIMIT/2 A: VON, 2V/div B: VOUT, 2V/div
1s/div VIN = 5V, IOUT = ILIMIT/2 A: VON, 2V/div B: VOUT, 2V/div
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1.2A, Current-Limited, High-Side P-Channel Switch with Thermal Shutdown MAX893L
Pin Description
PIN 1, 2 3 4 5 6, 7 8 NAME IN ON GND SET OUT FAULT 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. RSET = 1.34 * 103 / ILIMIT, where ILIMIT is the desired current limit in amperes. Switch Output. P-channel MOSFET drain. Bypass OUT with a 0.1F capacitor to ground. Fault-Indicator Output. This open-drain output goes low when in current limit or when the die temperature exceeds +165C.
Detailed Description
The MAX893L P-channel MOSFET power switch limits output current to a programmed level. When the output current is increased beyond the programmed current limit, or 1.2A (IMAX), the current also increases through the replica switch (I OUT / 1080) and through R SET (Figure 1). The current-limit error amplifier compares the voltage across RSET to the internal 1.24V reference, and regulates the current to the programmed current limit (ILIMIT). This switch is not bidirectional; therefore, the input voltage must be higher than the output voltage.
IN P OUT
MAX893L
FAULT P
N
REPLICA AMPLIFIER ON P SET ON CURRENT-LIMIT AMPLIFIER 1.24V
Setting the Current Limit
The MAX893L features internal current-limiting circuitry with a maximum programmable value (IMAX) of 1.2A. For best performance, set the current limit (I LIMIT ) between 0.2A ILIMIT 1.2A. 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 / 1080 RSET = 1.24V / ISET = 1.34 * 103 / ILIMIT where ILIMIT is the desired current limit.
ON CONTROL CIRCUITRY
RSET
HOT GND
Figure 1. Functional Diagram
Short-Circuit Protection
The MAX893L is a short-circuit protected switch. In the event of an output short circuit or a current overload condition, the current through the switch is limited by the internal current-limiting error amplifier to 1.5 * ILIMIT. The short-circuit current is typically 1.8A for a programmed current limit of 1.2A. When the short-circuit condition is removed, the replica error amplifier will set 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 * ILIMIT. When the short-circuit condition is removed, the current limit is set back to ILIMIT. See Output ShortCircuit (Fast-Loop Response) and Output Overload (Slow-Loop Response) in the Typical Operating Characteristics.
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_______________________________________________________________________________________
1.2A, Current-Limited, High-Side P-Channel Switch with Thermal Shutdown MAX893L
INPUT VOLTAGE +5V
IN
OUT
VOUT
MAX893L
SET RSET GND BLANKED SIGNAL TO P 100k R 100k C 0.1F
MAX893L
ON/OFF FAULT GND SET RSET
Figure 2. Setting the Current Limit
Figure 3. Fault-Blanking Circuit
Thermal Shutdown
The MAX893L features thermal shutdown. The switch turns off when the junction temperature exceeds +165C. Once the device cools by 10C, the switch turns back on. If the fault condition is not removed, the switch will cycle on and off, resulting in a pulsed output.
Output Capacitor
Connect a 0.1F capacitor from OUT to GND to prevent inductive parasitics from pulling OUT negative during turn-off.
Layout and Thermal-Dissipation Considerations
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 to the device as possible (no more than 5mm). Under normal operating conditions, the package can dissipate and channel heat away. Calculate the maximum power as follows: P = (ILIMIT)2 * RON where RON is the on-resistance of the switch. When the output is 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-shutdown protection circuitry turns the switch off until the die temperature falls by 10C. A ground plane in contact with the device will help dissipate additional heat.
Fault Indicator
The MAX893L provides a fault output (FAULT). This open-drain output goes low when in current limit or when the die temperature exceeds +165C. A 100k pull-up resistor from FAULT to IN provides a logiccontrol signal.
Fault Blanking
During start-up in USB applications, the MAX893L charges the relatively large USB capacitance. This may activate an unwanted fault signal if the charging current exceeds the programmed current limit. To "blank out" this start-up fault signal, add a simple lowpass RC delay circuit as shown in Figure 3. This circuit provides a 10ms delay.
Applications Information
Input Capacitor
To limit the input voltage drop during momentary output short-circuit conditions, connect a capacitor no more than 5mm from IN to GND. A 1F ceramic capacitor will be adequate for most applications; however, higher capacitor values will further reduce the voltage drop at the input.
Chip Information
TRANSISTOR COUNT: 340
_______________________________________________________________________________________
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1.2A, Current-Limited, High-Side P-Channel Switch with Thermal Shutdown MAX893L
________________________________________________________Package Information
SOICN.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) 1999 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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