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MAX4838EXT-T

Overvoltage Protection Controllers with Status FLAG

Maxim Integrated 

Overvoltage Protection Controllers with

Status FLAG

IN

5.5V

REGULATOR

2x CHARGE

PUMP

GATE DRIVER

GATE

GND

UVLO AND

OVLO

DETECTOR

CONTROL

LOGIC AND TIMER

FLAG

EN

MAX4838–

MAX4841

Figure 5. Functional Diagram

Detailed Description

The MAX4838–MAX4841 provide up to 28V overvoltage

protection for low-voltage systems. When the input volt-

age exceeds the overvoltage trip level, the MAX4838–

MAX4841 turn off a low-cost external N-channel FET(s)

to prevent damage to the protected components. An

internal charge pump (Figure 5) drives the FET gate for

a simple, robust solution.

Undervoltage Lockout (UVLO)

The MAX4838–MAX4841 have a fixed 3.25V typical

undervoltage lockout level (UVLO). When VIN is less

than the UVLO, the GATE driver is held low and FLAG

is asserted.

Overvoltage Lockout (OVLO)

The MAX4838/MAX4839 have a 7.4V typical overvolt-

age threshold (OVLO), and the MAX4840/MAX4841

have a 5.8V typical overvoltage threshold. When VIN is

greater than OVLO, the GATE driver is held low and

FLAG is asserted.

FLAG Output

The FLAG output is used to signal the host system

there is a fault with the input voltage. FLAG asserts

immediately to an overvoltage fault. FLAG is held low

for 50ms after GATE turns on before deasserting.

The MAX4839 and MAX4841 have a push-pull FLAG out-

put. The output high voltage is proportional to VIN for VIN

up to 5.5V, and fixed at 5.5V when VIN > 5.5V.

The MAX4838 and MAX4840 have an open-drain FLAG

output. Connect a pullup resistor from FLAG to the

logic I/O voltage of the host system.

EN Enable Input

EN is an active-low enable input on the MAX4838 and

MAX4840 only. Drive EN low or connect to ground to

enable normal device operation. Drive EN high to force

the external MOSFET(s) off. EN does not override an

OVLO or UVLO fault.

GATE Driver

An on-chip charge pump is used to drive GATE above

IN, allowing the use of low-cost N-channel MOSFETS.

The charge pump operates from the internal 5.5V

regulator.

The actual GATE output voltage tracks approximately

two times VIN until VIN exceeds 5.5V or the OVLO trip

level is exceeded, whichever comes first. The

MAX4838/MAX4839 have a 7.4V typical OVLO, there-

fore GATE remains relatively constant at about 10.5V

for 5.5V < VIN < 7.4V. The MAX4840/MAX4841 have a

5.8V typical OVLO, but this can be as low as 5.5V. The

MAX4840/MAX4841 in practice may never actually

achieve the full 10.5V GATE output. The GATE output

voltage as a function of input voltage is shown in the

Typical Operating Characteristics.

Device Operation

The MAX4838–MAX4841 have an on-board state

machine to control device operation. A flowchart is

shown in Figure 6. On initial power-up, if VIN < UVLO or

if VIN > OVLO, GATE is held at 0V, and FLAG is low.

If UVLO < VIN < OVLO and EN is low, the device enters

startup after a 50ms internal delay. The internal charge

pump is enabled, and GATE begins to be driven above

VIN by the internal charge pump. FLAG is held low dur-

ing startup until the FLAG blanking period expires, typi-

cally 50ms after the GATE starts going high. At this

point the device is in its on state.

At any time if VIN drops below UVLO, FLAG is driven

low and GATE is driven to ground.

6 _______________________________________________________________________________________

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