MAXIM MAX4785EXK-T

19-2664; Rev 1; 4/03
50mA/100mA Current-Limit Switches
Applications
PDAs and Palmtop Devices
Cell Phones
Features
♦ Guaranteed Current Limit: 50mA, 100mA
♦ Thermal-Shutdown Protection
♦ Reverse-Current Protection
♦ 0.7Ω On-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
Ordering Information
PART
TEMP RANGE
PINPACKAGE
TOP
MARK
MAX4785EXS-T
-40°C to +85°C
4 SC70-4
MAX4785EXK-T
-40°C to +85°C
5 SC70-5
AGE
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
Selector Guide appears at end of data sheet.
GPS Systems
Typical Operating Circuit
Hand-Held Devices
2.3V TO 5.5V
Pin Configurations
TOP VIEW
IN
ON
OUT 1
GND 2
5 IN
OUT 1
MAX4785
MAX4787
MAX4785–
MAX4788
4 ON
FLAG 3
4 IN
GND 2
MAX4785
MAX4787
µP
FLAG
TO EXTERNAL PORT
OUT
3 ON
GND
SC70
SC70
________________________________________________________________ Maxim Integrated Products
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.
1
MAX4785–MAX4788
General Description
The MAX4785–MAX4788 family of switches feature internal current limiting to prevent host devices from being
damaged due to faulty load conditions. These analog
switches have a low 0.7Ω on-resistance and operate
from a 2.3V to 5.5V input voltage range. They are available 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 condition 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.
MAX4785–MAX4788
50mA/100mA Current-Limit Switches
ABSOLUTE MAXIMUM RATINGS
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
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 = 2.3V 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
Operating Voltage
VIN
Quiescent Current
IQ
CONDITIONS
VON = VIN, IOUT = 0, VIN = 2.3V to 5.0V
switch on
VIN = 5.0V to 5.5V
ILATCH
VON = VIN, after an overcurrent fault
(MAX4785/MAX4787)
Shutdown Current
ISHDN
VON = 0V
IFWD
Reverse Current Limit
IREV
ON Input Leakage
Undervoltage Lockout
65
UNITS
5.5
V
100
120
8
0.01
µA
1
µA
120
MAX4787/MAX4788
100
240
MAX4785/MAX4786
120
MAX4787/MAX4788
240
-1
Rising edge
0.01
1.8
Undervoltage Lockout Hysteresis
RON
ON Input Logic High Voltage
VIH
ON Input Logic Low Voltage
VIL
TA = +25°C, IOUT = 20mA
0.7
1
µA
ISINK = 1mA (MAX4785/MAX4787)
FLAG Output High Leakage
Current
VIN = V F LAG = 5.5V (MAX4785/MAX4787)
V
mV
1
1.3
2.0
FLAG Output Logic Low Voltage
mA
µA
2.2
TA = -40°C to +85°C, IOUT = 20mA
mA
+1
100
On-Resistance
µA
15
50
VON = 0V, VOUT = 0V
UVLO
MAX
MAX4785/MAX4786
VON = VIN or GND
Off Switch Leakage
TYP
2.3
Latch-Off Current (Note 2)
Forward Current Limit
MIN
Ω
V
0.8
V
0.4
V
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
2
_______________________________________________________________________________________
50mA/100mA Current-Limit Switches
(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
Blanking Time
CONDITIONS
tBLANK
MIN
Overcurrent fault, Figures 2, 3
Short-Circuit Current-Limit
Response Time
TYP
14
VON = VIN = 3.3V, short circuit applied to
OUT
Retry Time (Note 4)
UNITS
60
ms
5
MAX4786/MAX4788: overcurrent fault,
Figure 2
tRETRY
MAX
µs
98
420
ms
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.
Typical Operating Characteristics
(VIN = 3.3V, TA = +25°C, unless otherwise noted.)
SUPPLY CURRENT
vs. TEMPERATURE
80
60
50
40
30
70
60
VIN = 3.3V
50
40
30
20
20
10
10
0
0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
-15
10
35
60
85
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
VON = VIN
VIN = 5V
VIN = 3.3V
-40
-15
10
35
60
SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
TEMPERATURE (°C)
SHUTDOWN SUPPLY CURRENT
vs. TEMPERATURE
SHUTDOWN LEAKAGE CURRENT
vs. TEMPERATURE
LATCH-OFF LEAKAGE CURRENT
vs. TEMPERATURE
0.1
0.01
0.001
-15
10
35
TEMPERATURE (°C)
60
85
VIN = 5V
0.1
0.01
VIN = 3.3V
0.001
0.0001
-40
85
MAX4785 toc06
1
100
LATCH-OFF LEAKAGE CURRENT (nA)
1
10
MAX4785-05
MAX4785-04
10
-40
-40
6.0
SHUTDOWN LEAKAGE CURRENT (nA)
2.0
SHUTDOWN SUPPLY CURRENT (nA)
VIN = 5V
LATCH-OFF (µA)
SUPPLY CURRENT (µA)
SUPPLY CURRENT (µA)
70
VON = VIN
MAX4785-02
VON = VIN
80
90
MAX4785-01
90
LATCH-OFF CURRENT
vs. TEMPERATURE
MAX4785 toc03
QUIESCENT SUPPLY CURRENT
vs. SUPPLY VOLTAGE
10
1
VIN = 5V
0.1
VIN = 3.3V
0.01
0.001
0.0001
-15
10
35
TEMPERATURE (°C)
60
85
-40
-15
10
35
60
85
TEMPERATURE (°C)
_______________________________________________________________________________________
3
MAX4785–MAX4788
ELECTRICAL CHARACTERISTICS (continued)
Typical Operating Characteristics (continued)
(VIN = 3.3V, TA = +25°C, unless otherwise noted.)
NORMALIZED ON-RESISTANCE
vs. TEMPERATURE
OUTPUT CURRENT
vs. OUTPUT VOLTAGE
250
OUTPUT CURRENT (mA)
0.8
0.6
0.4
150
100
MAX4785/MAX4786
50
0.2
0
0
-40
-15
10
35
60
85
VIN - VOUT (V)
SWITCH TURN-ON/OFF TIMES
vs. TEMPERATURE
FLAG-BLANKING TIMEOUT
vs. TEMPERATURE
VCC = 3.3V
45
FLAG-BLANKING TIME (ms)
ILOAD = 10mA
VCC = 5V
0.1
OFF
0.01
50
MAX4785 toc09
ON
1
0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 3.0 3.3
TEMPERATURE (°C)
100
10
MAX4787/MAX4788
200
MAX4785 toc10
NORMALIZED RON
1.0
MAX4785 toc08
VCC = 3.3V
1.2
300
MAX4785-07
1.4
TURN-ON/OFF TIMES (µs)
MAX4785–MAX4788
50mA/100mA Current-Limit Switches
40
35
30
25
0.001
-40
-15
10
35
60
20
85
-40
TEMPERATURE (°C)
10
35
60
CURRENT-LIMIT RESPONSE
MAX4785 toc11
VIN = 3.3V
CIN = 1µF
MAX4785 toc12
VIN
2V/div
VIN = VON
1V/div
VON
2V/div
IOUT
100mA/div
40µs/div
4
85
TEMPERATURE (°C)
CURRENT-LIMIT RESPONSE
COUT = 1µF
-15
VIN = VON
CIN = 1µF
COUT = 1µF
20µs/div
_______________________________________________________________________________________
IOUT
100mA/div
50mA/100mA Current-Limit Switches
CURRENT-LIMIT RESPONSE
(OUT SHORTED TO GND)
SWITCH TURN-ON TIME RESPONSE
MAX4785 toc13
CIN = 1µF
COUT = 1µF
MAX4785 toc14
VIN = 3.3V
VIN
2V/div
VON
VOUT
2V/div
IOUT
10mA/div
IOUT
2A/div
40µs/div
100µs/div
FLAG-BLANKING RESPONSE
SWITCH TURN-OFF TIME RESPONSE
MAX4785 toc16
MAX4785 toc15
VIN = 3.3V
VON
2V/div
VIN
2V/div
VON
2V/div
FLAG
2V/div
IOUT
10mA/div
IOUT
100mA/div
4ms/div
100ns/div
Pin Description
PIN
NAME
FUNCTION
SC70
SC70
1
1
OUT
Switch Output. Bypass with a 0.1µF capacitor to ground.
2
2
GND
Ground
—
3
FLAG
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.
3
4
ON
Active-High Switch-On Input. A logic high turns the switch on.
4
5
IN
Input. Bypass with a 0.1µF ceramic capacitor to ground.
_______________________________________________________________________________________
5
MAX4785–MAX4788
Typical Operating Characteristics (continued)
(VIN = 3.3V, TA = +25°C, unless otherwise noted.)
MAX4785–MAX4788
50mA/100mA Current-Limit Switches
REVERSE-CURRENT
DETECTOR
MAX4785/MAX4787
ONLY
FLAG
BLANKING TIME
CIRCUITRY
N
FORWARD CURRENT
DETECTOR
N
IN
ON
UNDERVOLTAGE
LOCKOUT
OUT
+2.0V
LOGIC
GND
AUTORETRY
MAX4785–MAX4788
Figure 1. MAX4785–MAX4788 Functional Diagram
Detailed Description
The MAX4785–MAX4788 are forward/reverse currentlimited switches that operate from a 2.3V to 5.5V input
voltage range and guarantee a 50mA and 100mA 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 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 present, 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 erroneous switch operation when the input voltage goes too
low during startup conditions.
6
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 currentlimit switches.
_______________________________________________________________________________________
50mA/100mA Current-Limit Switches
ON
FAULT
Low
X
OFF
Shutdown
High
Undervoltage lockout
OFF
Shutdown
High
Thermal
High
Current limit
SWITCH ON/OFF
SUPPLY CURRENT MODE
OFF immediately (tBLANK period does not apply)
Latch off
OFF after tBLANK period has elapsed
Latch off
ON during tBLANK period, OFF during tRETRY period for the
MAX4786 and MAX4788; cycle repeats until fault is removed
See the Autoretry section
FLAG Indicator
The MAX4785 and MAX4787 feature a latched fault output, 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 external 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 faultblanking period.
• VIN 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 =
I LOAD ✕ t BLANK /(t BLANK + t RETRY ). 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
tBLANK
tRETRY
tBLANK
tBLANK
CURRENT
LIMIT
LOAD
CURRENT
SHORT
CONDITION
REMOVED
ON
SWITCH
STATUS
OFF
Figure 2. MAX4786/MAX4788 Autoretry Fault Blanking Diagram
resets if the overcurrent condition disappears before
tBLANK has elapsed. The switch is shut off if the overcurrent condition continues up to the end of the blanking 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 feature to protect the devices from overheating. The switch
turns off and FLAG goes low immediately (no fault blanking) when the junction temperature exceeds +150°C.
_______________________________________________________________________________________
7
MAX4785–MAX4788
Table 1. MAX4785–MAX4788 Switch Truth Table
MAX4785–MAX4788
50mA/100mA Current-Limit Switches
tBLANK
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:
tBLANK
LOAD
CURRENT
ON
SWITCH
STATUS
CMAX <
OFF
ON PIN
VOLTAGE
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.
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:
FLAG
PIN STATUS
(a)
tBLANK
tBLANK
LOAD
CURRENT
ON
SWITCH
STATUS
IN PIN
VOLTAGE
IFWD _ MIN × tBLANK _ MIN
VIN
OFF
UVLO
PMAX =
FLAG
PIN STATUS
VIN _ MAX × IOUT _ MAX × tBLANK
= 161mW
tRETRY + tBLANK
where VIN = 5.5V, IOUT = 240mA, tBLANK = 14ms, and
tRETRY = 98ms.
(b)
Figure 3. MAX4785/MAX4787 Latch Off Fault Blanking
The switches with autoretry feature turn back on when
the device temperature drops approximately 15°C. The
switches with latchoff feature require ON cycling.
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 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.
Applications Information
Selector Guide
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 recommended 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
8
PART
CURRENT
LIMIT (mA)
FLAG
FUNCTION
AUTORETRY
MAX4785EXS
50
No
No
MAX4785EXK
50
Yes
No
MAX4786EXS
50
No
Yes
MAX4787EXS
100
No
No
MAX4787EXK
100
Yes
No
MAX4788EXS
100
No
Yes
_______________________________________________________________________________________
50mA/100mA Current-Limit Switches
SC70, 4L.EPS
Chip Information
TRANSISTOR COUNT: 1659
PROCESS: BiCMOS
_______________________________________________________________________________________
9
MAX4785–MAX4788
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.)
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
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
© 2003 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.