MPM3530

– 55V, 3A, STEP-DOWN POWER MODULE

MPM3530 Rev. 1.0

www.MonolithicPower.com

12

9/21/2018

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© 2018 MPS. All Rights Reserved.

There is no internal pull-up or pull-down at EN,

so when it is floating, the EN status is uncertain.

EN is clamped internally using a 6.5V Zener

diode between EN and GND. Connecting EN to

a voltage source directly without any pull-up

resistor requires limiting the voltage amplitude

to

≤6V to prevent damage to the Zener diode.

EN can be connected to a higher voltage (such

as VIN) through a pull-up resistor if the system

does not have another logic signal acting as the

enable signal. If doing this, ensure that the pull-

up resistor is high enough to keep the sink

current flowing into EN below 150µA to avoid

damaging the Zener diode. For example, when

6.5V) ÷ 150μA = 37kΩ.

Soft Start (SS)

A soft start (SS)

is implemented in the

MPM3530 to ensure a smooth output voltage

during power-on and power-off. The soft-start

function also helps reduce inrush current during

start-up. The soft-start function is achieved by

ramping SS up slowly and using SS to override

the internal reference (REF) when SS - 900mV

is lower than REF. When SS - 900mV is higher

than REF, REF regains control. 900mV is the

offset voltage of SS, which means SS is

detected as 0 internally when it is lower than

900mV. To minimize the delay for SS to reach

0.9V, an internal pull-up circuit with about 30µA

of average current pulls SS up to 600mV. Then

use a 4µA constant current to charge SS until it

reaches 2.5V. When SS is in the range of 0.9 -

1.9V, it overrides REF as the reference voltage

of the error amplifier. During this period, the

output voltage ramps up from 0 to the regulated

value following the rise of SS.

An internal 4.7nF SS capacitor is used in the

MPM3530.

The

default

SS

time

can

be

estimated with Equation (1):

)

A

(

I

)

V

(

V

)

nF

(

C

)

ms

(

t

SS

REF

SS

SS







(1)

The default SS time is about 1.2ms. If a longer

SS time is needed, an external SS capacitor

can be added between SS and AGND. The

external capacitor value can be determined with

Equation (2):

)

nF

(

.

)

V

(

V

)

A

(

I

)

ms

(

T

)

nF

(

C

REF

SS

SS

SS

7

4









(2)

Over-Voltage Protection (OVP)

The MPM3530 monitors the feedback output

voltage

to

achieve

over-voltage

protection

MPM3530 switches to sleep mode, the HS-FET

turns off, and the LS-FET turns on to discharge

the output energy. The MPM3530 resumes

FET and LS-FET are turned off immediately.

Then both MOSFETs are latched, and the PG

signal is asserted to indicate the fault status.

Recycle EN or VIN to clear the protection.

Over-Current Protection (OCP)

The MPM3530 has cycle-by-cycle peak-current-

limit protection and valley-current detection

protection. The inductor current is monitored

during the HS-FET on state. If the inductor

current exceeds the current limit value set by

the LS-FET is turned on to discharge the

energy, and the inductor current decreases.

The HS-FET will not turn on again unless the

inductor valley current is below a certain current

threshold (valley current limit). This is useful for

preventing an inductor current runaway. Both

the peak current limit and the valley current limit

voltage is higher than 50% x REF, the current

limit value is at the normal value. If the

feedback output voltage is lower than 50% x

RFF, the current limit decreases to half the

normal value when the feedback output voltage

is zero. This feature is very useful for reducing

over-current

protection

(OCP)

thermal

dissipation, which may worsen when the output

voltage is shorted. It is also useful for reducing

high inrush current during start-up.

Under-Voltage Lockout (UVLO) Protection

The MPM3530 has an input under-voltage

lockout protection (UVLO). Assuming that EN is