MP5022C – 12V, 3

m

(

MP5022C Rev. 1.0

www.MonolithicPower.com

12

5/26/2016

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

© 2016 MPS. All Rights Reserved.

OPERATION

The MP5022C is designed to limit the inrush

current to the load when a circuit card is inserted

into a live backplane power source, limiting the

backplane’s voltage drop and the dV/dt of the

voltage to the load. The MP5022C provides an

integrated solution for

monitoring

the input

voltage, output voltage, output current, and die

temperature to eliminate the need for an external

current sense power resistor, power MOSFET,

and thermal sense device.

Current Limit

The MP5022C 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 power FET

constant. To limit the current, the gate-to-source

voltage must be regulated from 4V to around 1V.

The typical response time is about 20µs. The

output current may have a small overshoot

during this time period.

When the current limit is triggered, the fault timer

starts. If the output current falls below the current

limit threshold before the end of the fault timeout

period, the MP5022C resumes normal operation.

Otherwise, if the current-limit duration exceeds

the fault timeout period, the power FET is latched

off.

When the device reaches either its current limit

or over-temperature threshold, FLTB is driven

low with an 8

μs propagation delay to indicate a

fault.

The

desired

current

limit

at

normal

operation is a function of the external current-limit

resistor.

Short-Circuit Protection (SCP)

If the load current increases rapidly due to a

short circuit, the current may exceed the current-

limit threshold before the control loop can

respond. If the current reaches a 36A secondary

current-limit level, a fast turn-off circuit activates

to turn off the power FET 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.

When short-circuit protection is triggered, the

chip restarts to determine whether the overload

condition exists or not. If the short-circuit has

been induced by the input line transient, the part

works normally. If a real short circuit occurs, the

part latches off completely (see Figure 2 and

Figure 3).

FLTB switches low once it reaches a 36A current

limit and asserts low until the short circuit is

removed.

Fault Timer and Restart

When the current reaches its limit threshold, a

215µA fault timer current source charges the

limit state ceases before TIMER reaches 1.24V,

the MP5022C resumes normal operation mode

and releases TIMER immediately when the

current limit is removed. If the current limit state

lasts after the TIMER voltage reaches 1.24V, the

can be determined with Equation (1):

1.24

t

215

C

fault

T

⋅

=

(1)

capacitor yields a fault timer of 0.58ms.

This fault timer capacitor also determines the

insertion delay timer during start-up.