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MAX4995ALAUT

50mA to 600mA Programmable Current-Limit Switches

Maxim Integrated 

50mA to 600mA Programmable

Current-Limit Switches

Detailed Description

The MAX4995A/MAX4995AF/MAX4995AL/MAX4995B/

MAX4995C programmable current-limit switches oper-

ate from +1.7V to +5.5V and provide internal current

limiting adjustable from 50mA to 600mA. These devices

feature a fixed blanking time and a FLAG output that

notifies the processor when a fault condition is present.

Programmable Current Limit

A resistor from SETI to GND programs the current limit

for the switch (see the Setting the Current Limit sec-

tion). If the output current exceeds the current limit for a

time equal to or longer than tBLANK, the output flag

asserts and the MAX4995A/MAX4995AF/MAX4995AL

enter the autoretry mode. The MAX4995B latches off

the switch, and the MAX4995C enters the continuous

current-limit mode.

Autoretry (MAX4995A/MAX4995AF/

MAX4995AL)

When the forward current reaches the current-limit

threshold, the tBLANK timer begins counting (Figure 2).

FLAG asserts if the overcurrent-limit condition is pre-

sent for tBLANK. The timer resets if the overcurrent con-

dition disappears before the blanking time (tBLANK) has

elapsed. A retry time delay (tRETRY) starts immediately

after the blanking time has elapsed and during that

time, the switch latches off. At the end of tRETRY, the

switch turns on again. If the fault still exists, the cycle

repeats. If the fault has been removed, the switch stays

on. During this cycle, FLAG stays low. In autoretry if

the thermal power rating of the package is exceeded,

the MAX4995A/MAX4995AF/MAX4995AL go into ther-

mal shutdown.

The autoretry feature saves system power in case of an

overcurrent or short-circuit condition. During tBLANK

time when the switch is on, the supply current is held at

the current limit. During time tRETRY when the switch is

off, the current through the switch is zero. Thus, the

average output current is much less than the pro-

grammed current limit. Calculate the average output

current using the following equation:

ILOAD = ILIM [tBLANK/(tBLANK + tRETRY)]

With a typical tBLANK = 16.3ms and typical tRETRY =

524ms, the duty cycle is 3%, resulting in a 97% power

savings over the switch being on the entire time.

Table 1. Switch Truth Table

MAX4995_/

MAX4995AF

ON

0

1

MAX4995AL

ON

1

0

SWITCH

STATUS

Off

On

Latchoff (MAX4995B)

When the forward current reaches the current-limit

threshold, the tBLANK timer begins counting (Figure 3).

FLAG asserts if an overcurrent-limit condition is present

for greater than tBLANK time. The timer resets if the over-

current condition disappears before tBLANK has

elapsed. The switch turns off if the overcurrent condition

continues beyond the blanking time. Reset the switch

by either toggling the control logic (ON) or cycling the

input voltage. If the thermal power rating of the pack-

age is exceeded during tBLANK, the MAX4995B goes

into thermal shutdown.

Continuous Current Limit (MAX4995C)

When the forward current reaches the forward current-

limit threshold, the MAX4995C limits the output current

to the programmed current limit. FLAG asserts if the

current limit is present for tBLANK and deasserts when

the overload condition is removed. In this mode, if the

thermal power rating of the package is exceeded, the

MAX4995C goes into thermal shutdown.

Switch-On/Off Control

The ON input for the MAX4995_/MAX4995AF and ON

input for the MAX4995AL control the switch; see Table

1. Toggle ON for the MAX4995B to reset the fault condi-

tion once the short current is detected and the device

shuts down.

Reverse-Current Protection

The MAX4995 features a reverse-current protection cir-

cuit that limits the backflow current to 10µA when the

output voltage exceeds the input voltage by 110mV

(typ). The switch turns off and FLAG asserts without

waiting for tBLANK to elapse. The switch turns back on

and FLAG deasserts when the output voltage drops

below the detecting threshold by 10mV (typ).

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