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MAX4914BELT-T

100mA/200mA/300mA Current-Limit Switches with Low Shutdown Reverse Current

Maxim Integrated 

100mA/200mA/300mA Current-Limit Switches

with Low Shutdown Reverse Current

Table 1. MAX4914B/MAX4915A/B/MAX4917A/B Switch Truth Table

ON

Low

High

High

High

FAULT

X

Undervoltage lockout

Thermal

Current limit

SWITCH ON/OFF

OFF

OFF

OFF immediately (tBLANK period does not apply)

OFF after tBLANK period has elapsed

ON during tBLANK period, OFF during tRETRY period for the

MAX4915A/MAX4917A (autoretry versions); cycle repeats

until fault is removed

SUPPLY CURRENT MODE

Shutdown

Shutdown

Latchoff

Latchoff

See the Autoretry

(MAX4915A/MAX4917A)

section

tBLANK

tRETRY

tBLANK

ON

SWITCH

STATUS

OFF

FLAG

STATUS

tBLANK

CURRENT

LIMIT

SHORT

CONDITION

REMOVED

Figure 2. MAX4915A/MAX4917A Autoretry Fault-Blanking Diagram

drain output transistor and requires an external pullup

resistor from FLAG to IN. During shutdown (VON < VIL),

the pulldown on the 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.

• VIN is below the UVLO threshold.

For the MAX4915A/MAX4917A (autoretry versions),

FLAG stays low until the overcurrent condition is

removed (See Figure 2).

Autoretry (MAX4915A/MAX4917A)

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 = 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.

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