MP28162 – SINGLE-INDUCTOR, BUCK-BOOST CONVERTER WITH 1.5A MOSFETS

MP28162 Rev. 1.0

MonolithicPower.com

14

3/16/2023

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Under-Voltage Lockout (UVLO)

Under-voltage lockout (UVLO) protects the

device from operating at an insufficient VIN. The

MP28162

’s UVLO circuit monitors VCC. During

start-up, VIN must exceed its UVLO rising

threshold (VIN_UVLO_R) to support a sufficient VCC

and enable the IC. After the IC is enabled, VCC

is powered by VIN or VOUT, depending on which

value is higher. Thus, the IC can work even if

VIN drops to 1.2V, unless VCC drops to its UVLO

falling threshold (VCC_UVLO_F).

During start-up, if VCC has a biased voltage

from another power supply, the MP28162 can

work with a 1.2V VIN. If VIN is below 1.2V

significantly, SWA

’s on resistance (RDS(ON)) is

high, and the MP28162 cannot supply a large

amount of power to the output. If VIN drops to

0.69V, the MP28162 stops working.

VCC Power Supply

When the EN pin is high and VIN ramps up, VIN

charges VCC. If VIN exceeds VIN_UVLO_R, the

MP28162 begins working. All the MP28162

’s

internal circuits are supplied by VCC, which is

decoupled with a ceramic capacitor. After the

system starts up, VCC is powered internally by

the higher value between VIN or VOUT. If VCC is

powered by VOUT, the MP28162 does not shut

down until VIN drops to VIN_UVLO_F (0.69V) or VCC

drops

to

VCC_UVLO_F

(1.56V).

It

is

not

recommended to supply the MP28162 with VIN

below 1.2V, even if VCC has a biased voltage

due to SWA (P-MOSFET) having an RDS(ON) that

is too high when VIN is low. Even with a 1.2V VIN,

the load capability is weaker than the high input

condition due to the RDS(ON).

Internal Soft Start (SS)

When EN is high and VIN exceeds VIN_UVLO_R,

the MP28162 starts up with a soft-start (SS)

function. The internal SS signal ramps up and

controls the feedback VREF. After a blank time of

3.5ms, if VOUT does not rise to 60% of the

normal VOUT, or if VOUT is pulled down to 60% of

the normal VOUT due to an overload, then the

SS signal is pulled down to GND and hiccup

protection is triggered. During start-up or hiccup

recovery, an internal SS signal is clamped to

VFB + 0.3V if VOUT does not increase. This limit

can prevent a VOUT overshoot if the heavy load

disappears suddenly during start-up.

During start-up or recovery from hiccup, if there

is already some voltage on the output, this

voltage is discharged by the negative current

limit (-1A when the MP28162 operates in PWM

mode

regardless

of

the

MODE/SYNC

configuration) to reach the SS voltage (VSS).

VOUT then rises normally.

MODE/SYNC Configuration

The MP28162 can be configured to pulse-skip

mode or fixed-frequency PWM mode under

light-load conditions via the MODE/SYNC pin.

When

MODE/SYNC

is

pulled

high,

the

MP28162 operates in fixed-frequency PWM

mode. The current conducts while the IL

direction reverses. In this mode, the VOUT ripple

is below the ripple in power-save mode (PSM),

but the power loss is higher due to the high-

frequency switching.

When MODE/SYNC is pulled low, the MP28162

enters

PSM

automatically

when

the

load

decreases. In PSM, a group of switching pulses

are initiated when the internal VC_BUCK exceeds

the PSM threshold (where the group of pulses

starts with SWA and SWC on and ends with

SWB and SWD on). SWD turns off if the SWD

current flows from VOUT to SW2 in each period.

During start-up or short-circuit protection (SCP)

recovery,

the

MP28162

works

in

fixed-

frequency PWM mode, even if MODE/SYNC is

low. The negative IL is limited to about -1A,

which is the same in constant frequency mode.

Over-Current Protection (OCP) and Short-

Circuit Protection (SCP) with Two Current

Limits

The MP28162 has one switching peak current

limit (1.5A typically).

In overload or short-circuit conditions, VOUT

drops due to the switching current limit (ISW). If

VOUT drops below 60% of its normal output, the

MP28162 stops switching and recovers after