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MAX4785

50mA/100mA Current-Limit Switches

Maxim Integrated 

50mA/100mA Current-Limit Switches

LOAD

CURRENT

ON

SWITCH

STATUS

OFF

ON PIN

VOLTAGE

tBLANK

tBLANK

FLAG

PIN STATUS

tBLANK

(a)

tBLANK

LOAD

CURRENT

ON

SWITCH

STATUS

OFF

IN PIN

VOLTAGE

UVLO

FLAG

PIN STATUS

(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.

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:

CMAX < IFWD_MIN

× tBLANK _MIN

VIN

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:

PMAX

=

VIN_MAX × IOUT _MAX ×

tRETRY + tBLANK

tBLANK

= 161mW

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.

PART

MAX4785EXS

MAX4785EXK

MAX4786EXS

MAX4787EXS

MAX4787EXK

MAX4788EXS

CURRENT

LIMIT (mA)

50

50

50

100

100

100

Selector Guide

FLAG

FUNCTION

No

Yes

No

No

Yes

No

AUTO-

RETRY

No

No

Yes

No

No

Yes

8 _______________________________________________________________________________________

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