LP1111-00

Nov.-2017

Email: marketing@lowpowersemi.com

www.lowpowersemi.com

Page 6 of 8

Preliminary Datasheet

LP1111

Operation Information

The LP1111 is a single phase MOSFET driver for

driving two N-channel MOSFETs in a synchronous

buck converter topology. The LP1111 will operate

from 4.3V or 12V, but have been optimized for high

current multi-phase buck regulators that convert 12 V

rail directly to the core voltage required by complex

logic chips.

A single PWM input signal is all that is required to

properly drive the high-side and the low-side

MOSFETs. Each driver is capable of driving a 3nF

load at frequencies up to 1 MHz.

Low-Side Driver

The low-side driver is designed to drive a ground-

referenced low RDS(on) N-Channel MOSFET. The

voltage rail for the low-side driver is internally

connected to the VCC supply and PGND.

High-Side Driver

The high−side driver is designed to drive a floating

low RDS(on) N-channel MOSFET. The gate voltage

for the high side driver is developed by a bootstrap

circuit referenced to Switch Node (SWN) pin.

The bootstrap circuit is comprised of an external

diode, and an external bootstrap capacitor. When the

LP1111 are starting up, the SWN pin is at ground, so

the bootstrap capacitor will charge up to VCC

through the bootstrap diode. When the PWM input

goes high, the high-side driver will begin to turn on

the high-side MOSFET using the stored charge of

the bootstrap capacitor. As the high-side MOSFET

turns on, the SWN pin will rise. When the high-side

MOSFET is fully on, the switch node will be at 12 V,

and the BST pin will be at 12 V plus the charge of the

bootstrap capacitor (approaching 24V).The bootstrap

capacitor is recharged when the switch node goes

low during the next cycle.

Safety Timer and Overlap Protection Circuit

It is very important that MOSFETs in a synchronous

buck regulator do not both conduct at the same time.

Excessive shoot-through or cross conduction can

damage the MOSFETs, and even a small amount of

cross conduction will cause a decrease in the power

conversion efficiency.

The LP1111 prevent cross conduction by monitoring

the status of the external MOSFETs and applying the

appropriate amount of “ dead-time ” or the time

between the turn off of one MOSFET and the turn on

of the other MOSFET. When the PWM input pin goes

high, DRVL will go low after a propagation delay

(tpdlDRVL). The time it takes for the low-side

MOSFET to turn off (tfDRVL) is dependent on the

total charge on the low-side MOSFET gate. The

LP1111 monitor the gate voltage of both MOSFETs

and the switch node voltage to determine the

conduction status of the MOSFETs. Once the low−

side MOSFET is turned off an internal timer will delay

(tpdhDRVH) the turn on of the high-side MOSFET.

Likewise, when the PWM input pin goes low, DRVH

will go low after the propagation delay (tpdlDRVH).

The time to turn off the high-side MOSFET (tfDRVH)

is dependent on the total gate charge of the high −

side MOSFET. A timer will be triggered once the

high-side MOSFET has stopped conducting, to delay

(tpdhDRVL) the turn on of the low-side MOSFET.