MPQ5069

– 7mΩ PROTECTION SWITCH WITH CURRENT MONITOR

MPQ5069 Rev. 1.1

www.MonolithicPower.com

12

11/19/2020

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OPERATION

The MPQ5069 protects circuitry on its output

from transients on its input. It also protects its

input

from

undesired shorts and transients

coming from its output. It provides an integrated

solution to monitor the input voltage, output

voltage, output current, and die temperature to

eliminate the need for an external current-sense

resistor, power MOSFET, and thermal sense

device.

Current Limit

The MPQ5069 provides a constant current limit

that can be programmed by an external resistor.

Once

the

device

reaches

its

current

limit

threshold, the internal circuit regulates the gate

voltage to hold the current in the MOSFET

constant. In order to limit the current, the gate-to-

source voltage needs to drop from 5V to about

1V. The typical response time is about 20µs, and

the output current may have a small overshoot

during this time period.

When the current limit triggers, the fault timer

starts. If the output current falls below the

current-limit threshold before the end of the fault

timeout period, the MPQ5069 resumes normal

operation. If the current limit duration remains

beyond the fault timeout period, the MOSFET

turns off. The subsequent behavior relates to the

AUTO pin configuration. If the temperature

reaches the thermal protection threshold during

the fault timeout period, the MOSFET turns off.

When the AUTO pin is floating, the part functions

in auto-retry mode for over-current protection.

The part enters latch-off mode when the AUTO

pin pulls to ground (once it detects an over-

current condition) and the duration exceeds the

preset value.

When the device reaches either its current limit

or its over-temperature threshold, the FLTB pin is

driven low with a 20

μs propagation delay to

indicate a fault. The desired current limit during

normal operation is a function of the external

current-limit resistor.

Short-Circuit Protection

If the load current increases rapidly due to a

short circuit, the current may significantly exceed

the current-limit threshold before the control loop

can respond. If the current reaches the 25A

secondary current limit level, a fast turn-off circuit

activates to turn off the MOSFET using a 100mA

pull-down gate discharge current (see Figure 2).

This limits the peak current through the switch to

limit the input voltage drop. The total short circuit

response time is about

200ns.

The FLTB

switches low once it reaches a 25A current limit,

and asserts low until the circuit resumes normal

operation.

Fault Timer and Restart

When the current reaches its over-current limit

threshold, a 200µA fault timer current source

charges the external capacitor (CT) at the TIMER

pin. If the current-limit state ceases before the

TIMER pin reaches 1.23V, the MPQ5069 returns

to normal operation mode and a low-value

resistor discharges CT after the TIMER voltage

reaches 1.23V. If the current-limit state continues

after the TIMER pin voltage reaches 1.23V, the

MOSFET switches off. The subsequent restart

procedure then depends on the selected retry

configuration.

If the AUTO pin connects to ground or is pulled

low, the MPQ5069 latches off. Restart the input

power

or cycle the EN

signal to resume

functioning.

Floating the AUTO pin or pulling it above 2.5V

causes the device to operate in hiccup mode

(see Figure 3). At the end of the fault timeout

period, the MOSFET turns off and a low-current

(0.5µA) sink discharges the external capacitor

(CT).

When the TIMER voltage reaches the low

threshold (0.2V), the part restarts. If the fault

condition remains, the fault timeout period and

restart timer repeat.