MP5018 –5V, 1A-5A CURRENT LIMIT SWITCH WITH REVERSE CURRENT BLOCKING

AND OUTPUT OVER-VOLTAGE CLAMP

MP5018 Rev. 1.02

www.MonolithicPower.com

11

3/23/2016

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© 2016 MPS. All Rights Reserved.

OPERATION

The MP5018 is designed to limit the inrush

current to the load when a circuit card inserts

into a live backplane power source, thereby

limiting the backplane’s voltage drop and the

dV/dt of the voltage to the load as well. It offers

an integrated solution to monitor the input

voltage, output voltage, output current, and die

temperature which eliminates the requirement

of external current sense power resistor, power

MOSFET and thermal sense device.

Under-Voltage Lockout (UVLO)

If the supply voltage is below the UVLO

threshold, the output is disabled, and the

EN/Fault line is driven low. When the supply

goes above the UVLO threshold, the output is

enabled and the EN/Fault is pulled high.

The nominal input supply voltage is 5V but

there are high energy transients during normal

operation or during hot swap. Those transients

depend on the parasitic inductance and

resistance of the wire along with capacitor at

diode is not used, E-Fuse must be able to

withstand this transient voltage. MP5018

integrates high voltage MOSFET up to 16V and

guarantee safe operation.

Fast Output over Voltage Clamp (OVP)

To protect the downstream loading when there

is a surge voltage at input, MP5018 provides an

accurate and fast comparator to monitor the

over voltage condition of output. If the output

voltage rises above the threshold (5.8V), the

gate of internal MOSFETs is quickly pulled

down and it’s regulated to a certain value to

maintain the output voltage clamped at 5.8V.

The fast loop response speed (10µs typical)

keeps the over voltage overshoot small.

Current Limit

The MP5018 provides a constant current limit

and the current limit can be programmed by

external resistor. Once the current limit

threshold is reached, the internal circuit will

regulate gate voltage to hold the current in

power FET constantly. In order to limit the

current, the gate to source voltage needs to be

regulated from 5V to around 1V. The typical

response time is about 10µs, during this period

the output current may have a small overshoot.

The desired current limit is a function of the

external current limit resistor.

MP5018 allows ILIMIT pin floating operation. If

ILIMIT pin is floating, the current limit will be set

as fixed 3A internally.

Reverse Current Blocking

The MP5018 integrates a pair of back-to-back

N channel MOSFETs for reverse current

protection. Once the reverse current limit

threshold (-1.2A) is reached and exceed 7μs

deglitch time, the internal circuit will shutdown

the pair of MOSFETs. Meanwhile, the EN/Fault

line is driven to middle level; reverse current is

totally blocked and this state continues until

VCC > VOUT-2mV. When VCC >VOUT-2mV,

part resumes normal operation with soft-start

control. Whenever the input voltage drops

below UVLO threshold, back-to-back MOSFETs

are turned off and the part is shut down;

therefore, there is no reverse current during this

condition.

Short Circuit Protection

If the load current increases rapidly due to short

circuit event, the current may exceed the

current limit threshold before control loop able

to respond. If the current reaches 12A

secondary current limit level, there is a fast turn

off circuit active to turn off the power FET with

100mA pull-down gate discharge current, as

shown in Figure 1. This can help to limit the

peak current through the switch, thus keep the

input voltage not drop too much. The total short

circuit response time is about 1µs. After the

FET is switched off, the part will restart. During

the restart process, if the short still exist,

MP5018 will regulate the gate voltage to hold

the current at normal current limit level.