General Description
The MAX4785–MAX4788 family of switches feature inter-
nal current limiting to prevent host devices from being
damaged due to faulty load conditions. These analog
switches have a low 0.7Ωon-resistance and operate
from a 2.3V to 5.5V input voltage range. They are avail-
able with guaranteed 50mA and 100mA current limits,
making them ideal for load-switching applications.
When the switch is on and a load is connected to the
port, a guaranteed blanking time of 14ms ensures that
the transient voltages settle down. If after this blanking
time the load current is greater than the current limit,
the MAX4785 and MAX4787 enter a latch-off state
where the switch is turned off and FLAG is issued to the
microprocessor. The switch can be turned on again by
cycling the power or the ON pin.
The MAX4786 and MAX4788 have an autoretry feature
where the switch turns off after the blanking time and
then continuously checks to see if the overload condi-
tion is present. The switch remains on after the overload
condition disappears.
The MAX4785 and MAX4787 are available in a tiny
space-saving 4-pin or 5-pin SC70 package. The
MAX4786 and MAX4788 are available only in the 4-pin
SC70 package. For higher current current-limiting
switches, refer to the MAX4789–MAX4794 and
MAX1693 data sheets.
Applications
PDAs and Palmtop Devices
Cell Phones
GPS Systems
Hand-Held Devices
Features
♦Guaranteed Current Limit: 50mA, 100mA
♦Thermal-Shutdown Protection
♦Reverse-Current Protection
♦0.7ΩOn-Resistance
♦14ms Guaranteed Blanking Time
♦FLAG Function (MAX4785/MAX4787)
♦65µA Supply Current
♦8µA Latch-Off Current (MAX4785/MAX4787)
♦0.01µA Shutdown Current
♦2.3V to 5.5V Supply Range
♦Undervoltage Lockout
♦Fast Current-Limit Response Time
♦Tiny SC70 Package
MAX4785–MAX4788
50mA/100mA Current-Limit Switches
________________________________________________________________ Maxim Integrated Products 1
Ordering Information
2.3V TO 5.5V
IN
OUT
FLAG
GND
ON
µP
TO EXTERNAL PORT
MAX4785
MAX4787
Typical Operating Circuit
19-2664; Rev 1; 4/03
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.
Selector Guide appears at end of data sheet.
PART
TEMP RANGE
PIN-
PACKAGE
TOP
MARK
MAX4785EXS-T
-40°C to +85°C
4 SC70-4
AGE
MAX4785EXK-T
-40°C to +85°C
5 SC70-5 ADL
MAX4786EXS-T
-40°C to +85°C
4 SC70-4 AGF
MAX4787EXS-T
-40°C to +85°C
4 SC70-4
AGG
MAX4787EXK-T
-40°C to +85°C
5 SC70-5
AND
MAX4788EXS-T
-40°C to +85°C
4 SC70-4
AGH
GND
ON
15INOUT
MAX4785
MAX4787
SC70
TOP VIEW
2
34
FLAG ON
14INOUT
MAX4785–
MAX4788
SC70
23GND
Pin Configurations
MAX4785–MAX4788
50mA/100mA Current-Limit Switches
2_______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VIN = 2.3V to 5.5V, TA= -40°C to +85°C, unless otherwise noted. Typical values are at VIN = 3.3V, TA= +25°C.) (Note 1)
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.
IN, ON, FLAG, OUT to GND .....................................-0.3V to +6V
OUT Short Circuit to GND .................................Internally Limited
Continuous Power Dissipation (TA= +70°C)
4-Pin SC70 (derate 3.1mW/°C above +70°C)..............245mW
5-Pin SC70 (derate 3.1mW/°C above +70°C)..............247mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
PARAMETER
SYMBOL
CONDITIONS
MIN TYP MAX
UNITS
Operating Voltage VIN 2.3 5.5 V
VIN = 2.3V to 5.0V 65 100
Quiescent Current IQVON = VIN, IOUT = 0,
switch on VIN = 5.0V to 5.5V 120 µA
Latch-Off Current (Note 2) ILATCH VON = VIN, after an overcurrent fault
(MAX4785/MAX4787) 815µA
Shutdown Current ISHDN VON = 0V
0.01
1µA
MAX4785/MAX4786 50 120
Forward Current Limit IFWD MAX4787/MAX4788
100
240 mA
MAX4785/MAX4786 120
Reverse Current Limit IREV MAX4787/MAX4788 240 mA
ON Input Leakage VON = VIN or GND -1 +1 µA
Off Switch Leakage VON = 0V, VOUT = 0V
0.01
1µA
Undervoltage Lockout UVLO Rising edge 1.8 2.2 V
Undervoltage Lockout Hysteresis
100
mV
TA = +25°C, IOUT = 20mA 0.7 1
On-Resistance RON TA = -40°C to +85°C, IOUT = 20mA 1.3 Ω
ON Input Logic High Voltage VIH 2.0 V
ON Input Logic Low Voltage VIL 0.8 V
FLAG Output Logic Low Voltage
ISINK = 1mA (MAX4785/MAX4787) 0.4 V
FLAG Output High Leakage
Current VIN = V
F LAG = 5.5V (MAX4785/MAX4787) 1 µA
Thermal Shutdown
150
°C
Thermal-Shutdown Hysteresis 15 °C
DYNAMIC
Turn-On Time (Note 3) ON from low to high; IOUT = 10mA,
CL = 0.1µF 50 µs
Turn-Off Time (Note 3) ON from high to low; IOUT = 10mA,
CL = 0.1µF 30 ns
MAX4785–MAX4788
50mA/100mA Current-Limit Switches
_______________________________________________________________________________________ 3
Typical Operating Characteristics
(VIN = 3.3V, TA= +25°C, unless otherwise noted.)
Note 1: All parts are 100% tested at +25°C. Limits across the full temperature range are guaranteed by design and correlation.
Note 2: Latch-off current does not include the current flowing into FLAG.
Note 3: 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 4: Retry time is typically 7x the blanking time.
ELECTRICAL CHARACTERISTICS (continued)
(VIN = 2.3V to 5.5V, TA= -40°C to +85°C, unless otherwise noted. Typical values are at VIN = 3.3V, TA= +25°C.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN TYP MAX
UNITS
Blanking Time tBLANK Overcurrent fault, Figures 2, 3 14 60 ms
Short-Circuit Current-Limit
Response Time
VON = VIN = 3.3V, short circuit applied to
OUT 5µs
Retry Time (Note 4) tRETRY MAX4786/MAX4788: overcurrent fault,
Figure 2 98 420 ms
MAX4785–MAX4788
50mA/100mA Current-Limit Switches
4_______________________________________________________________________________________
CURRENT-LIMIT RESPONSE
MAX4785 toc11
40µs/div
VON
2V/div
IOUT
100mA/div
VIN
2V/div
COUT = 1µF VIN = 3.3V
CIN = 1µF
CURRENT-LIMIT RESPONSE
MAX4785 toc12
20µs/div
IOUT
100mA/div
VIN = VON
1V/div
COUT = 1µF
VIN = VON
CIN = 1µF
Typical Operating Characteristics (continued)
(VIN = 3.3V, TA= +25°C, unless otherwise noted.)
MAX4785–MAX4788
50mA/100mA Current-Limit Switches
_______________________________________________________________________________________ 5
Pin Description
SWITCH TURN-ON TIME RESPONSE
MAX4785 toc14
100µs/div
IOUT
10mA/div
VON
VIN = 3.3V
CURRENT-LIMIT RESPONSE
(OUT SHORTED TO GND)
MAX4785 toc13
40µs/div
VOUT
2V/div
IOUT
2A/div
VIN
2V/div
CIN = 1µF
COUT = 1µF
Typical Operating Characteristics (continued)
(VIN = 3.3V, TA= +25°C, unless otherwise noted.)
PIN
SC70 SC70 NAME FUNCTION
11OUT Switch Output. Bypass with a 0.1µF capacitor to ground.
22GND Ground
—3FLAG
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.
34ON Active-High Switch-On Input. A logic high turns the switch on.
45IN Input. Bypass with a 0.1µF ceramic capacitor to ground.
FLAG-BLANKING RESPONSE
MAX4785 toc16
4ms/div
FLAG
2V/div
IOUT
100mA/div
VIN
2V/div
VON
2V/div
SWITCH TURN-OFF TIME RESPONSE
MAX4785 toc15
100ns/div
VON
2V/div
IOUT
10mA/div
VIN = 3.3V
MAX4785–MAX4788
Detailed Description
The MAX4785–MAX4788 are forward/reverse current-
limited switches that operate from a 2.3V to 5.5V input
voltage range and guarantee a 50mA and 100mA mini-
mum current-limit threshold for different options. The
voltage drop across an internal sense resistor is com-
pared 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 MAX4786 and MAX4788 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 pre-
sent, the switch remains on.
The MAX4785 and MAX4787 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.
The undervoltage lockout (UVLO) circuit prevents erro-
neous switch operation when the input voltage goes too
low during startup conditions.
Reverse-Current Protection
The MAX4785–MAX4788 limit the reverse current (VOUT
to VIN) from exceeding the maximum IREV value. The
switch is shut off and FLAG is asserted (MAX4785/
MAX4787) if the reverse current-limit condition persists
for more than the blanking time. This feature prevents
excessive reverse currents from flowing through the
device.
Switch-On/Off Control
Toggle ON high to enable the current-limited switches.
The switches are continuously on, only if VIN exceeds
the UVLO threshold (typically 2V) and there is no fault.
When a forward/reverse current fault is preset or the die
exceeds the thermal-shutdown temperature of +150°C,
OUT is internally disconnected from IN and the supply
current decreases to 8µA (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 0.01µA. Table 1 illustrates
the ON/OFF state of the MAX4785–MAX4788 current-
limit switches.
50mA/100mA Current-Limit Switches
6_______________________________________________________________________________________
N
BLANKING TIME
CIRCUITRY
REVERSE-CURRENT
DETECTOR
FORWARD CURRENT
DETECTOR
N
+2.0V
FLAG
OUT
IN
ON
GND
MAX4785/MAX4787
ONLY
LOGIC
AUTO-
RETRY MAX4785–MAX4788
UNDERVOLTAGE
LOCKOUT
Figure 1. MAX4785–MAX4788 Functional Diagram
FLAG
Indicator
The MAX4785 and MAX4787 feature a latched fault out-
put, FLAG. Whenever a fault is activated, it latches
FLAG output low and also turns the switch off. FLAG is
an open-drain output transistor and requires an exter-
nal pullup resistor from FLAG to IN. During shutdown
(ON is low), the pulldown on FLAG output is released in
order to limit power dissipation. FLAG goes low when
any of the following conditions occur:
•The die temperature exceeds the thermal-shutdown
temperature limit of +150°C.
•The device is in current limit for more than the fault-
blanking period.
•V
IN is below UVLO threshold.
Autoretry (MAX4786/MAX4788)
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. 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.
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 =
ILOAD ✕tBLANK/(tBLANK + tRETRY). With a typical
tBLANK = 37ms and typical tRETRY = 259ms, the duty
cycle is 12%, which results in an 88% power savings
over the switch being on the entire time. The duty cycle
is consistent across the process and devices.
Latch Off (MAX4785/MAX4787)
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 if the over-
current condition continues up to the end of the blank-
ing time. Reset the switch by either toggling ON (Figure
3a) or cycling the input voltage below UVLO, typically
2V (Figure 3b).
Fault Blanking
The MAX4785–MAX4788 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, the MAX4785 and
MAX4787s’ 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 and input voltage drops below the
UVLO threshold cause FLAG to assert immediately and
do not wait for the blanking time.
Thermal Shutdown
The MAX4785–MAX4788 have a thermal shutdown fea-
ture to protect the devices from overheating. The switch
turns off and FLAG goes low immediately (no fault blank-
ing) when the junction temperature exceeds +150°C.
MAX4785–MAX4788
50mA/100mA Current-Limit Switches
_______________________________________________________________________________________ 7
ON FAULT SWITCH ON/OFF
SUPPLY CURRENT MODE
Low X OFF Shutdown
High
Undervoltage lockout
OFF Shutdown
High Thermal OFF immediately (tBLANK period does not apply) Latch off
OFF after tBLANK period has elapsed Latch off
High Current limit ON during tBLANK period, OFF during tRETRY period for the
MAX4786 and MAX4788; cycle repeats until fault is removed
See the Autoretry section
Table 1. MAX4785–MAX4788 Switch Truth Table
LOAD
CURRENT
SWITCH
STATUS
tBLANK
OFF
ON
tRETRY
CURRENT
LIMIT
SHORT
CONDITION
REMOVED
tBLANK tBLANK
Figure 2. MAX4786/MAX4788 Autoretry Fault Blanking Diagram
MAX4785–MAX4788
The switches with autoretry feature turn back on when
the device temperature drops approximately 15°C. The
switches with latchoff feature 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 0.1µF ceramic capacitor is adequate for most
applications; however, higher capacitor values further
reduce the voltage drop at the input and are recom-
mended for lower voltage applications.
Output Capacitance
Connect a 0.1µF capacitor from OUT to GND. This
capacitor helps prevent inductive parasitics from
pulling OUT negative during turn-off, thus preventing
the MAX4785–MAX4788 from tripping erroneously. If
the load capacitance is too large, then current may not
have enough time to charge the capacitance 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:
Layout and Thermal Dissipation
To optimize 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).
IN and OUT pins must be connected with short traces
to the power bus.
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 maxi-
mum 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:
where VIN = 5.5V, IOUT = 240mA, tBLANK = 14ms, and
tRETRY = 98ms.
Attention must be given to the MAX4785 and MAX4787
where the latch-off condition must be manually reset by
toggling ON from high to low. If the latch-off time dura-
tion 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.
PVI t
tt mW
MAX IN MAX OUT MAX BLANK
RETRY BLANK
=××
+=
__
161
CIt
V
MAX FWD MIN BLANK MIN
IN
<×
__
50mA/100mA Current-Limit Switches
8_______________________________________________________________________________________
LOAD
CURRENT
SWITCH
STATUS
tBLANK tBLANK
OFF
ON
ON PIN
VOLTAGE
(a)
(b)
UVLO
FLAG
PIN STATUS
LOAD
CURRENT
SWITCH
STATUS OFF
ON
IN PIN
VOLTAGE
FLAG
PIN STATUS
tBLANK tBLANK
Figure 3. MAX4785/MAX4787 Latch Off Fault Blanking
Selector Guide
PART CURRENT
LIMIT (mA)
FLAG
FUNCTION
AUTO-
RETRY
MAX4785EXS
50 No No
MAX4785EXK
50 Yes No
MAX4786EXS
50 No Yes
MAX4787EXS
100 No No
MAX4787EXK
100 Yes No
MAX4788EXS
100 No Yes
MAX4785–MAX4788
50mA/100mA Current-Limit Switches
_______________________________________________________________________________________ 9
SC70, 4L.EPS
PACKAGE OUTLINE, 4L SC70
21-0098
1
1
C
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.)
Chip Information
TRANSISTOR COUNT: 1659
PROCESS: BiCMOS
MAX4785–MAX4788
50mA/100mA Current-Limit Switches
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.
10 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
©2005 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products, Inc.
Package Information (continued)
(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.)
SC70, 5L.EPS
PACKAGE OUTLINE, 5L SC70
21-0076
1
1
C