MP5017 – 3V-5.5V, 1A-5A PROGRAMMABLE CURRENT LIMIT SWITCH

MP5017 Rev.1.0

www.MonolithicPower.com

12

10/15/2015

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OPERATION

The MP5017 is designed to limit the inrush

current to the load when a circuit card is

inserted into a live backplane power source.

This limits the backplane’s voltage drop, as well

as the DV/DT of the voltage to the load. It offers

an integrated solution that monitors the input

voltage, output voltage, output current, and die

temperature, eliminating the need for an

external current sense power resistor, power

MOSFET, and thermal sense device.

Under-Voltage Lockout (UVLO)

The nominal input supply voltage is 5V, but high

energy transients can occur during normal

operation or hot swaps. These transients

depend on the parasitic inductance, resistance

of the wire, and the capacitor at VCC. If the

power clamp (TVS, Tranzorb) is not used, the

E-Fuse must be able to withstand this transient

voltage. The MP5017 uses a high-voltage

MOSFET of up to 16V and a high-voltage circuit

on VCC to guarantee safe operation.

SAS/OV Control

SAS/OV can control the part during start-up and

shutdown. Floating or pulling SAS/OV low

enables the part; pulling it high disables the part.

It also can be used as an input OVP control.

The input OVP limit can be set by a divider from

VCC to SAS/OV (see Figure 2). When the

SAS/OV voltage exceeds 1.25V, the part shuts

down. When the voltage drops below 1.21V or

SAS/OV is floated, the part is enabled again.

Figure 2: Adjustable Input OVP

Soft Start (SS)

The rise time is a function of the capacitor

calculated with Equation (1):

()

SS

DV / DT

1V C

nF

t(ms)

6.5 A

×

=

μ

(1)

For example, a 47nF capacitor generates a

soft-start time of approximately 7.2ms.

Fast Output Over-Voltage Protection (OVP)

The MP5017 uses an output OVP function to

protect the downstream loading when there is a

voltage surge at the input. An accurate and fast

comparator monitors the over-voltage condition

on the output. If the output voltage rises above

the threshold (typically 5.8V), the gate of the

internal MOSFET is pulled down quickly and is

regulated to a specific value to keep the output

voltage clamped at 5.8V. The rapid loop

response speed (typically 10µs) keeps the over-

voltage overshoot small.

Current Limit

The MP5017 provides a constant current limit,

which can be programmed by an external

resistor. Once the current limit threshold is

reached, the internal circuit regulates the gate

voltage to hold the current in the power FET. 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.

Reverse Current Blocking

The MP5017 uses a pair of back-to-back N-

channel

MOSFETs

for

reverse

current

protection. Once the reverse current limit

threshold (-50mA) is reached and exceeds the

80µs deglitch time, the internal circuit pulls the

gate voltage down to shut down the MOSFETs.

If the reverse current reaches the -1A threshold,

the part shuts the MOSFETs down immediately

to prevent VOUT from being pulled down.

reverse current limit. The reverse current is