MP2160 – 1.2A PEAK, 6V, 3.5MHz SYNCHRONOUS STEP-DOWN SWITCHER

MP2160 Rev. 1.03

www.MonolihicPower.com

9

7/5/2016

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

© 2016 MPS. All Rights Reserved.

OPERATION

MP2160 uses constant on-time control with

input voltage feed forward to stabilize the

switching frequency over full input range. At

light load, MP2160 employs a proprietary

control of low side switch and inductor current

to eliminate ringing on switching node and

improve efficiency.

Constant On-time Control

Compare to fixed frequency PWM control,

constant on-time control offers the advantage of

simpler control loop and faster transient response.

By using input voltage feed forward, MP2160

maintains a nearly constant switching frequency

across input and output voltage range. The on-

time of the switching pulse can be estimated as:

OUT

ON

IN

V

T0.285 s

V





To prevent inductor current run away during load

transient, MP2160 fixes the minimum off time to

be 30ns. However, this minimum off time limit will

not affect operation of MP2160 in steady state in

any way.

Light Load Operation

In light load condition, MP2160 uses a

proprietary control scheme to save power and

improve efficiency. The MP2160 will turn off the

low side switch when inductor current starts to

reverse. Then MP2160 works in discontinuous

conduction mode (DCM) operation.

For COT part, the efficiency can be improved if

using smaller inductor. That because smaller

inductor can transfer more energy in single on

pulse, and can save more driver loss.

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 MP2160 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 60ns. It is difficult to enter

DCM at light load. And using smaller inductor

can improve it and make it enter DCM easily.

Enable

When input voltage is greater than the under-

voltage lockout threshold (UVLO), typically 2.3V,

MP2160 can be enabled by pulling EN pin to

higher than 1.2V. Leaving EN pin float or pull

down to ground will disable MP2160. There is

an internal 1Meg Ohm resistor from EN pin to

ground.

Soft Start

MP2160 has built-in soft start that ramps up the

output voltage in a controlled slew rate,

avoiding overshoot at startup. The soft start

time is about 1.5ms typical.

Power GOOD Indicator

MP2160 has an open drain with 550kΩ pull-up

resistor pin for power good indicator PG. When

FB pin is within +/-10% of regulation voltage, i.e.

0.6V, PG pin is pulled up to VIN by the internal

resistor. If FB pin voltage is out of the +/-10%

window, PG pin is pulled down to ground by an

internal MOSFET. The MOSFET has a

Current limit

MP2160 has a typical 1.6A current limit for the

high side switch. When the high side switch hits

current limit, MP2160 will touch the hiccup

threshold until the current lower down. This will

prevent inductor current from continuing to build

up which will result in damage of the

components.

Short Circuit and Recovery

MP2160 enters short circuit protection mode

also when the current limit is hit, and tries to

recover from short circuit with hiccup mode. In

short circuit protection, MP2160 will disable

output power stage, discharge soft-start cap

and then automatically try to soft-start again. If

the short circuit condition still holds after soft-

start ends, MP2160 repeats this operation cycle

till short circuit disappears and output rises

back to regulation level.