LP1115AQVF datasheet(7/10 Pages) POWER

7 / 10 page

LP1115-01

Dec.-2019

Email: marketing@lowpowersemi.com

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Page 7 of 10

Preliminary Datasheet

LP1115

Operation Information (Full Bridge Driver)

The Full Bridge Driver part of LP1115 is a single

phase MOSFET driver for driving two N-channel

MOSFETs in a synchronous buck converter topology.

The LP1115 will operate from 5V or 12V, but have

been optimized for high current multi-phase buck

regulators that convert 12V 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.

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 (SW) pin.

The bootstrap circuit is comprised of an external

diode, and an external bootstrap capacitor. When the

LP1115 are starting up, the SW 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 SW pin will rise. When the high-side

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

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

bootstrap capacitor (approaching 24V).The bootstrap

capacitor is recharged when the switch node goes

low during the next cycle.

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 GND.

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 LP1115 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 LP1115 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.

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