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19-2944; Rev 0; 8/03
450mA/500mA Current-Limit Switches
General Description
The MAX4795-MAX4798 family of switches feature internal current limiting to prevent damage to host devices due to faulty load conditions. These analog switches have a low 0.2 on-resistance and operate from a 2.0V to 4.5V input voltage range. They are available with guaranteed 450mA and 500mA current limits, making them ideal for SDIO and other load-switching applications. When the switch is on and a load is connected to the port, a guaranteed blanking time of 14ms ensures the transient voltages settle down. If after this blanking time, the load current is greater than the current limit, the MAX4795 and MAX4797 switches are turned off and FLAG is issued to the microprocessor. The switch can be turned on again by cycling the power or the ON input. The MAX4796 and MAX4798 have an autoretry feature where the switch turns off and issues a FLAG to the microprocessor 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 and FLAG deasserts. The MAX4795-MAX4798 are available in tiny, spacesaving, 5-pin SOT23 and 6-pin TDFN (3mm x 3mm) packages. o o o o o o o o o o o o o o
Features
Guaranteed Current Limit: 450mA and 500mA Thermal-Shutdown Protection Reverse-Current Protection 0.2 On-Resistance 14ms Guaranteed Blanking Time FLAG Function Autoretry (MAX4796/MAX4798) 80A Supply Current 6A Latchoff Current (MAX4795/MAX4797) 0.01A Shutdown Current +2V to +4.5V Supply Range Fast Current-Limit Response Time Tiny SOT23 and TDFN Packages UL Certification Pending
MAX4795-MAX4798
Ordering Information
PART MAX4795EUK-T MAX4795ETT* MAX4796EUK-T MAX4796ETT* MAX4797EUK-T MAX4797ETT* MAX4798EUK-T MAX4798ETT* TEMP RANGE -40C to +85C 40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C PINPACKAGE 5 SOT23-5 6 TDFN-EP** 5 SOT23-5 6 TDFN-EP** 5 SOT23-5 6 TDFN-EP** 5 SOT23-5 6 TDFN-EP** TOP MARK AEDI -- AEDJ -- AEDK -- AEDL --
Applications
SDIO PDAs and Palmtop Devices Cell Phones GPS Systems Hand-Held Devices
Typical Operating Circuit
+2.0V TO +4.5V
*Future product--contact factory for availability. **EP = Exposed pad. Selector Guide appears at end of data sheet.
Pin Configurations
TOP VIEW
IN ON P IN 1 GND 2 TO SDIO PORT OUT ON 3 5 OUT IN 1 OUT 2 4 FLAG N.C. 3 6 ON
MAX4795 MAX4796 MAX4797 MAX4798
GND
FLAG
MAX4795 MAX4796 MAX4797 MAX4798 SOT23
MAX4795 MAX4796 MAX4797 MAX4798 TDFN
5 GND 4 FLAG
________________________________________________________________ Maxim Integrated Products
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For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
450mA/500mA Current-Limit Switches MAX4795-MAX4798
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) 5-Pin SOT23 (derate 7.1mW/C above +70C)............571mW 6-Pin TDFN (derate 24.4mW/C above +70C) .........1951mW 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 = +2.0V to +4.5V, 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 Shutdown Current Forward Current Limit Reverse Current Limit ON Input Leakage Shutdown Forward Leakage Shutdown Reverse Leakage On-Resistance (Note 3) 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 Turn-Off Time Blanking Time Short-Circuit Current-Limit Response Time Retry Time tRETRY tBLANK VON from low to high; IOUT = 10mA, CL = 0.1F (Note 4) VON from high to low; IOUT = 10mA, CL = 0.1F (Note 4) Overcurrent fault; Figures 2, 3 VON = VIN, short circuit applied to OUT MAX4796/MAX4798, Figure 2 (Note 5) 210 14 5 900 120 100 60 s ns ms s ms RON VIH VIL ISINK = 1mA VIN = V F LAG = VON = 4.5V 150 15 VON = 0V, VOUT = 0V VON = 0V, VIN = 2V, VOUT = 4.5V MAX4795/MAX4796, ILOAD = 100mA MAX4797/MAX4798, ILOAD = 100mA VIN = +2V to +3.6V VIN > 3.6V 1.4 2 0.5 0.4 1 0.2 0.18 SYMBOL VIN IQ ILATCH ISHDN VON = VIN, IOUT = 0, switch on VON = VIN, after an overcurrent fault (MAX4795/MAX4797) (Note 2) VON = 0V MAX4795/MAX4796, VIN = 3.3V, VOUT = GND MAX4797/MAX4798, VIN = 3.3V, VOUT = GND MAX4795/MAX4796 MAX4797/MAX4798 -1 0.01 450 500 VIN = +3.3V VIN = +3.3V CONDITIONS MIN 2.0 80 6 0.03 TYP MAX 4.5 125 10 1 720 800 720 800 +1 1 1 0.4 0.36 UNITS V A A A mA mA A A A V V V A C C
All parts are 100% tested at +25C. Electrical limits across the full temperature range are guaranteed by design and correlation. Latch-off current does not include the current flowing into FLAG. TDFN packages are guaranteed by design. 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 5: Retry time is typically 15 times the blanking time. 2 _______________________________________________________________________________________ Note 1: Note 2: Note 3: Note 4:
450mA/500mA Current-Limit Switches
Typical Operating Characteristics
(VIN = 3.3V, TA = +25C, unless otherwise noted.)
MAX4795-MAX4798
QUIESCENT SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX4795 toc01
SUPPLY CURRENT vs. TEMPERATURE
MAX4795 toc02
LATCH-OFF CURRENT vs. TEMPERATURE
9 LATCH-OFF CURRENT (A) 8 7 6 5 4 3 2 1 VON = VIN
MAX4795 toc03
160 140 SUPPLY CURRENT (A) 120 100 80 60 40 20 0
VON = VIN
100
10
VON = VIN
90 SUPPLY CURRENT (A)
80
70
60
50 2.0 2.5 3.0 3.5 4.0 4.5 -40 -15 10 35 60 85 SUPPLY VOLTAGE (V) TEMPERATURE (C)
0 -40 -15 10 35 60 85 TEMPERATURE (C)
SHUTDOWN SUPPLY CURRENT vs. TEMPERATURE
MAX4795 toc04
SHUTDOWN LEAKAGE CURRENT vs. TEMPERATURE
MAX4795 toc05
LATCH-OFF LEAKAGE CURRENT vs. TEMPERATURE
LATCH-OFF LEAKAGE CURRENT (nA)
MAX4795 toc06
100 SHUTDOWN SUPPLY CURRENT (nA)
10 SHUTDOWN SUPPLY CURRENT (nA)
VON = 0V, VOUT = 0V
100 10 1 0.1 0.01 0.001
10
1
1
0.1
0.1
0.01
0.01 0.001 -40 -15 10 35 60 85 TEMPERATURE (C)
0.001 -40 -15 10 35 60 85 TEMPERATURE (C)
0.0001 -40 -15 10 35 60 85 TEMPERATURE (C)
SHUTDOWN REVERSE LEAKAGE CURRENT vs. TEMPERATURE
VON = 0V, VOUT = 4.5V
MAX4795 toc07
NORMALIZED ON-RESISTANCE vs. TEMPERATURE
MAX4795 toc08
OUTPUT CURRENT vs. OUTPUT VOLTAGE
900 800 OUTPUT CURRENT (mA) 700 600 500 400 300 200 MAX4795/MAX4796 MAX4797/MAX4798
MAX4795 toc09
10 SHUTDOWN LEAKAGE CURRENT (nA)
1.4 1.2 NORMALIZED RON () 1.0 0.8 0.6 0.4 0.2 0
1000
1
0.1
0.01
0.001
100 0 -40 -15 10 35 60 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)
0.0001 -40 -15 10 35 60 85 TEMPERATURE (C)
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450mA/500mA Current-Limit Switches MAX4795-MAX4798
Typical Operating Characteristics (continued)
(VIN = 3.3V, TA = +25C, unless otherwise noted.)
FORWARD CURRENT LIMIT vs. SUPPLY VOLTAGE
MAX4795 toc10
SWITCH TURN-ON/OFF TIMES vs. TEMPERATURE
ILOAD = 10mA ON 10 1 0.1 0.01 0.001 OFF
MAX4795 toc11
FLAG-BLANKING TIMEOUT vs. TEMPERATURE
MAX4795 toc12
650 OUT = GND FORWARD CURRENT LIMIT (mA) 625 MAX4797/MAX4798 600 575 550 MAX4795/MAX4796 525 500 2.0 2.5 3.0 3.5 4.0
1000 100 TURN-ON/OFF TIMES (s)
50 FLAG-BLANKING TIMEOUT (ms) 45 40 35 30 25 20
4.5
-40
-15
10
35
60
85
-40
-15
10
35
60
85
SUPPLY VOLTAGE (V)
TEMPERATURE (C)
TEMPERATURE (C)
MAX4797/MAX4798 CURRENT-LIMIT RESPONSE
MAX4795 toc13
MAX4797/MAX4798 CURRENT-LIMIT RESPONSE
MAX4795 toc14
CURRENT-LIMIT RESPONSE (OUT SHORTED TO GND)
MAX4795 toc15
3.3V 3.3V 3V VIN 2V/div VON 2V/div IOUT 200mA/div VIN = 3.3V COUT = 1F CIN = 1F VSEL = 3.3V 40s/div VIN = VON COUT = 1F CIN = 1F 40s/div VIN = VON 1V/div 0V 3.3V
VIN 2V/div
0V 3.3V
0V IOUT 200mA/div
0V
VOUT 2V/div
0V
CIN = 1F COUT = 1F 0V 4s/div
IOUT 5A/div
0V
0V
MAX4797/MAX4798 REVERSE CURRENT LIMIT
MAX4795 toc16
SWITCH TURN-ON TIME RESPONSE
MAX4795 toc17
3V 0V 3V
VIN 2V/div VOUT 2V/div
3V
VIN = 3.3V
VON 1V/div
0V 0V 0V CIN = 1F COUT = 1F 200s/div IOUT 1A/div 0V IOUT 10mA/div
20s/div
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450mA/500mA Current-Limit Switches
Typical Operating Characteristics (continued)
(VIN = 3.3V, TA = +25C, unless otherwise noted.)
MAX4797/MAX4798 FLAG-BLANKING RESPONSE (OVERLOAD CONDITION)
MAX4795 toc19
MAX4795-MAX4798
SWITCH TURN-OFF TIME RESPONSE
MAX4795 toc18
3.3V VON 1V/div
3.3V
VIN 2V/div
0V 3.3V
VOUT 2V/div
0V IOUT 10mA/div
0V 3.3V 0V VIN = 3.3V CIN = 1F COUT = 1F 0V 40ns/div 10ms/div VFLAG 2V/div IOUT 500mA/div
0V
Pin Description
PIN SOT23 1 2 3 TDFN 1 5 6 NAME IN GND ON FUNCTION Input. Bypass with a 0.1F ceramic capacitor to ground. Ground Active-High Switch On Input. A logic high turns the switch on. 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. Switch Output. Bypass with a 0.1F ceramic capacitor to ground. No Connection. Not internally connected.
IN FORWARD-CURRENT DETECTOR REVERSE-CURRENT DETECTOR FLAG BLANKING TIME CIRCUITRY
N
OUT
ON
4
4
FLAG
LOGIC AUTORETRY
GND
MAX4795-MAX4798
5 --
2 3
OUT N.C.
Figure 1. Functional Diagram
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450mA/500mA Current-Limit Switches MAX4795-MAX4798
Detailed Description
The MAX4795-MAX4798 are forward/reverse currentlimited switches that operate from a 2V to 4.5V input voltage range and guarantee a 450mA and 500mA 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 MAX4796 and MAX4798 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 MAX4795 and MAX4797 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.
FLAG Indicator
The MAX4795-MAX4798 feature a latched output (FLAG). Whenever an overcurrent condition is encountered, the MAX4795/MAX4797 latch FLAG low and turn the switch off. The MAX4796/MAX4798 latch FLAG low and keep it low until the overcurrent condition is removed. During this time, the switch cycles on and off in the autoretry mode. When the overcurrent condition is removed, FLAG deasserts and the switch turns on (Figure 2). 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 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. * The switch is in autoretry.
Reverse-Current Protection
The MAX4795-MAX4798 limit the reverse current (VOUT to VIN) from exceeding the maximum IREV value. The switch is shut off and FLAG is asserted if the reverse current-limit condition persists for more than the blanking time. This feature prevents excessive reverse currents from flowing through the device.
tBLANK tRETRY tBLANK tBLANK CURRENT LIMIT SHORT CONDITION REMOVED
Switch-On/Off Control
Toggle ON high to enable the current-limited switches. The switches are continuously on if there is no fault. When a forward/reverse current fault is present 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 MAX4795-MAX4798 current-limit switches.
ON SWITCH STATUS OFF
FLAG PIN STATUS
Figure 2. MAX4796/MAX4798 Autoretry Fault-Blanking Diagram
Table 1. MAX4795-MAX4798 Switch Truth Table
ON Low High High FAULT X Thermal Current limit OFF OFF immediately (tBLANK period does not apply) OFF after tBLANK period has elapsed ON during tBLANK period, OFF during tRETRY period for the MAX4796 and MAX4798; cycle repeats until fault is removed SWITCH ON/OFF SUPPLY CURRENT MODE Shutdown Latchoff Latchoff See the Autoretry section
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450mA/500mA Current-Limit Switches
Autoretry (MAX4796/MAX4798)
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 and FLAG asserts. 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 and FLAG deasserts. 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 = 555ms, the duty cycle is 6%, which results in a 94% power savings over the switch being on the entire time. The duty cycle is consistent across the process and devices.
MAX4795-MAX4798
tBLANK
tBLANK
LOAD CURRENT ON SWITCH STATUS ON PIN VOLTAGE
OFF
FLAG PIN STATUS
(a) tBLANK LOAD CURRENT tBLANK
ON SWITCH STATUS
Latchoff (MAX4795/MAX4797)
When the forward or reverse current-limit threshold is exceeded, tBLANK timer begins counting. The timer resets if the overcurrent condition disappears before tBLANK has elapsed. The switch is shut off and FLAG asserts if the overcurrent condition continues up to the end of the blanking time. Reset the switch by either toggling ON (Figure 3) or cycling the input voltage.
OFF
IN PIN VOLTAGE FLAG PIN STATUS
Fault Blanking
The MAX4795-MAX4798 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, 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 causes FLAG to assert immediately and does not wait for the blanking time.
Figure 3. MAX4795/MAX4797 Latch-Off Fault Blanking
turns off and FLAG goes low immediately (no fault blanking) when the junction temperature exceeds +150C. The switches with autoretry turn back on when the device temperature drops approximately 15C. The switches with latchoff 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.
Thermal Shutdown
The MAX4795-MAX4798 have a thermal-shutdown feature to protect the devices from overheating. The switch
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450mA/500mA Current-Limit Switches MAX4795-MAX4798
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 the MAX4795-MAX4798 from tripping erroneously. If the load capacitance is too large, then current may not have enough time to charge the capacitor 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 < IFWD _ MIN x tBLANK _ MIN VIN 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 tRETRY + tBLANK = 211mW
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.
where VIN = 4.5V, IOUT = 750mA, tBLANK = 14ms, and tRETRY = 210ms. Attention must be given to the MAX4795 and MAX4797 where the latchoff condition must be manually reset by toggling ON from high to low. If the latchoff 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.
Chip Information
TRANSISTOR COUNT: 2539 PROCESS: BiCMOS
Selector Guide
PART MAX4795EUK-T MAX4795ETT MAX4796EUK-T MAX4796ETT MAX4797EUK-T MAX4797ETT MAX4798EUK-T MAX4798ETT CURRENT LIMIT (mA) 450 450 450 450 500 500 500 500 AUTORETRY No No Yes Yes No No Yes Yes
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450mA/500mA 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.)
MAX4795-MAX4798
PACKAGE OUTLINE, SOT-23, 5L
21-0057
E
1 1
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 _____________________ 9 (c) 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
SOT-23 5L .EPS

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