MP5403

– CONFIGURABLE 2.7V-6V MINI PMIC WITH DUAL 2.5A/3.5A BUCK,

ONE LOAD SWITCH, AND INPUT POWER SUPERVISORY

MP5403 Rev. 1.0

www.MonolithicPower.com

16

9/20/2016

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

© 2016 MPS. All Rights Reserved.

OPERATION

The MP5403 has two step-down regulators and

one load switch integrated into an ultra-small

UTQFN-20 package. The two buck regulators

are able to run up to 3.5A and 2.5A of load

current, respectively. With a peak current mode

control scheme and an interleaving PWM clock,

the MP5403 minimizes the input voltage ripple

and achieves a fast dynamic load response.

The load switch has 3A and only 20

mΩ of

loss, and provides tight regulation with a high

load current. The load switch can also clamp

compact solid-state drives (SSD), portable

instruments, and battery-powered devices.

Peak-Current Mode Control

The two buck regulators of the MP5403 operate

at an 180° phase shift to reduce the input

current ripple and the required input capacitor.

In continuous conduction mode (CCM), two

internal clocks control the switching behavior.

The high-side MOSFET (HS-FET) turns on at

the corresponding

clock’s rising edge. The two

high-side switch current increases and reaches

the internal compensation voltage, the high-side

switch is turned off, and the low-side switch is

turned on to conduct current.

Figure 2: Phase Shift

The switching frequency is 1.5MHz, typically,

running in CCM. With a lower input voltage, the

switching frequency falls and works with a large

duty cycle and a fixed off-time mode.

Light-Load Operation

In light load mode, the MP5403 uses a

proprietary control scheme to save power and

improve efficiency. The MP5403 turns off the

low-side switch when the inductor current

begins reversing. The MP5403 then works in

discontinuous

conduction

mode

(DCM)

operation. With light-load mode control, the

switching loss can be greatly reduced due to

the lower switching frequency.

A zero-current cross detection (ZCD) circuit is

used to detect if the inductor current begins

reversing.

Considering

the

internal

circuit

propagation time, the typical delay is 50ns. This

means that the inductor current continues

falling after ZCD is triggered in this delay. If the

high or close to VIN), the low-side MOSFET

(LS-FET) is turned off, and the inductor current

may be negative. This prevents the MP5403

from entering DCM operation. If DCM operation

is required, the off time of the LS-FET in CCM

should be longer than 100ns. For example, if

in CCM is 37ns. It is difficult to enter DCM at

light load. Using a smaller inductor can improve

this and make it easier to enter DCM.

Enable (EN)

When VIN1 is greater than the under-voltage

lockout (UVLO) threshold (typically 2.5V), the

regulators or the load switch can be enabled by

pulling its EN pins above the EN UVLO

threshold. Leave the EN pins floating or pull the

EN pins down to ground to disable the

corresponding channel. There is an internal

2M

Ω resistor from the EN pins to ground. There

is a delay of about 100µs for the VIN1 and VIN2

enable start-up. The VIN3 enable start-up delay

is shorter (around 70µs).

Soft Start (SS) and Output Discharge

The MP5403 has a built-in soft start (SS) that

ramps up the output voltage at a controlled slew

rate to prevent overshooting at start-up for both

step-down regulators and the load switch. For

the step-down regulator, the soft-start time is

about 500µs, typically. For the load switch, the

soft-start time is set to around 350µs. When the

regulators are disabled, the internal discharge