MP2236C

– 18V, 6A, FCCM SYNCHRONOUS STEP-DOWN CONVERTER

MP2236C Rev. 1.0

MonolithicPower.com

13

3/16/2022

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© 2022 MPS. All Rights Reserved.

Over-Current Protection (OCP) and Hiccup

Mode

The

MP2236C

offers

cycle-by-cycle,

over-

current (OC) limiting control. The current-limit

circuit employs a low-side (LS) valley current-

sensing algorithm. The MP2236C uses the LS-

FET on resistance (RDS(ON)) as a current-

sensing element for valley-current limiting.

When the LS-FET turns on, the inductor current

(IL) is monitored by the voltage between GND

and SW. As the positive current-sensing node,

GND

must

be

connected

to

the

bottom

MOSFET

’s source terminal. PWM cannot

initiate a new cycle until IL falls to the valley

threshold.

After the cycle-by-cycle OC limit is reached,

VOUT drops until it is below the under-voltage

(UV) threshold. There are two UV thresholds:

UV1 (80%) and UV2 (60%). Once UV1 and OC

are both triggered, the MP2236C waits for 30

cycles. If OC exits after 31 cycles, then the

MP2236C enters hiccup mode to periodically

restart the part with a 12.5% duty cycle. If UV2

and OC are triggered, then the MP2236C

enters hiccup mode after three cycles. This

protection mode is especially useful when the

output is dead-shorted to ground. The average

short-circuit

current

is

greatly

reduced

to

alleviate

thermal

issues

and

protect

the

regulator. Once the OC condition is removed,

the MP2236C exits hiccup mode and resumes

normal operation.

Thermal Shutdown

Thermal shutdown prevents the chip from

operating at exceedingly high temperatures. If

the silicon die temperature exceeds 150°C, the

entire chip shuts down. Once the temperature

drops

below

its

lower

threshold

(typically

130°C), the chip is enabled again.

Floating

Driver

and

Bootstrap

(BST)

Charging

An external bootstrap (BST) capacitor (CBST)

powers the floating power MOSFET driver,

which has its own UVLO protection. The UVLO

rising

threshold

is

1.2V,

with

a

150mV

hysteresis.

The

CBST

voltage

is

regulated

internally by VIN through D1, M1, C4, L1, and

C2 (see Figure 3).

Figure 3: Internal BST Charging Circuit

If VIN - VSW exceeds 3.3V, then U1 regulates M1

to maintain a 3.3V BST voltage across C4.

Start-Up and Shutdown

If both VIN and EN exceed their respective

thresholds, the chip starts up. The reference

block starts first, generating a stable VREF and

current, and then the internal regulator is

enabled. The regulator provides a stable supply

for the remaining circuitries.

Three events can shut down the chip: EN low,

VIN low, and thermal shutdown. During the

shutdown procedure, the signaling path is

blocked first to avoid any fault triggering. Then

the internal supply rail is pulled down.