MP2143 Rev. 1.07

www.MonolithicPower.com

11

7/4/2016

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© 2016 MPS. All Rights Reserved.

OPERATION

The MP2143 uses constant on-time control with

input-voltage feed-forward to stabilize the

switching frequency over its full input range. At

light load, the MP2143 employs a proprietary

control over the low-side MOSFET (LS-FET)

and inductor current to eliminate ringing on

switching node and to improve efficiency.

Constant On-Time Control

When compared to fixed-frequency PWM control,

constant on-time control offers a simpler control

loop and faster transient response. By using

input-voltage feed-forward, the MP2143 maintains

a nearly constant switching frequency across the

entire input and output voltage range. The

switching pulse ON time can be estimated as:

OUT

ON

IN

V

t0.833 s

V





To prevent inductor current runaway during the

load transient, the MP2143 has a fixed minimum

OFF time of 50ns. However, this minimum OFF

time limit does not affect the operation of the

MP2143 in steady state in any way.

Light Load Operation

In light load condition, the MP2143 uses a

proprietary control scheme to save power and

improve efficiency: It gradually ramps down the

LS-FET current to its minimum instead of

turning off the LS-FET immediately when the

inductor current starts to reverse. The gradual

current drop avoids ringing at the switching

node that always occurs in discontinuous

conduction mode (DCM) operation.

Considering the internal circuit propagation time,

the typical delay is 50ns. It means the inductor

current still fall after the ZCD is trigger in this

delay. If the inductor current falling slew rate is

fast (VOUT voltage is high or close to Vin), the

low side MOSFET is turned off and inductor

current may be negative. This phenomena will

cause MP2143 can not enter DCM operation. If

the DCM mode is required, the off time of low

side MOSFET in CCM should be longer than

100ns. For example, Vin is 3.6V and Vo is 3.3V,

the off time in CCM is 50ns. It is difficult to enter

DCM at light load. And using smaller inductor

can improve it and make it enter DCM easily.

Enable

When the input voltage exceeds the under-

voltage lockout (UVLO) threshold—typically

2.2V—the MP2143 is enabled by pulling the EN

pin above 1.2V. Leaving the EN pin floating or

grounded will disable the MP2143. There is an

internal 1MΩ resistor from the EN pin to ground.

Soft-Start/Stop

MP2143 has a built-in soft-start that ramps up

the output voltage at a constant slew rate that

avoids overshooting at startup. The soft-start

time is typically about 1ms. When disabled, the

MP2143 ramps down the internal reference

voltage to allow the load to linearly discharge

the output.

Power GOOD Indicator

MP2143 has an open drain with 500kΩ pull-up

resistor pin for power good (PG) indication.

When the FB pin is within ±10% of regulation

voltage (0.6V), the PG pin is pulled up to VIN by

the internal resistor. If the FB pin voltage is

outside the ±10% window, the PG pin is pulled

to ground by an internal MOSFET. The

100Ω.

Current limit

The MP2143 has a 4.8A current limit for the

high side switch (HS-FET). When the HS-FET

hits its current limit, the MP2143 enters hiccup

mode until the current drops to prevent the

inductor current from building and possibly

damaging the components.

Short Circuit and Recovery

The MP2143 also enters short-circuit protection

(SCP) mode when it hits the current limit, and

tries to recover from the short circuit by entering

hiccup mode. In SCP, the MP2143 disables the

output power stage, discharges a soft-start

capacitor,

and

then

enacts

a

soft-start

procedure. If the short-circuit condition still

holds after soft-start ends, the MP2143 repeats

this operation until the short circuit ceases and

output rises back to regulation level.