LP6255 datasheet(8/10 Pages) POWER

8 / 10 page

LP6255-02

Feb.-2014

Email: marketing@lowpowersemi.com

www.lowpowersemi.com

Page 8 of 10

Preliminary Datasheet

LP6255

Application Information

The LP6255 wide input range synchronous boost

controller features all of the functions necessary to

implement a highly efficient synchronous boost

regulator. The regulator control method is based

upon peak current mode control. Peak current mode

control provides inherent line feed-forward and ease

of loop compensation. This highly integrated

controller provides strong high-side and low-side

N-channel

MOSFET

drivers.

The

switching

frequency is user programmable up to 1MHz, by a

single resistor connected to ground. The LP6255

contains an internal high voltage regulator that

provides typical 5V the controller and N-channel

MOSFET drivers. The input of the VIN regulator can

be connected to a voltage source as high as 30V.

The control mode of high-side synchronous switch

can be configured as either forced PWM (FPWM) or

diode emulation mode. Fault protection features

include cycle-by-cycle current limiting, hiccup mode

over load protection, hiccup mode short circuit

protection, thermal shutdown. Hiccup mode short

circuit protection minimizes power dissipation during

prolonged output short condition. The device is

available in 20-pin QFN package featuring an

exposed pad to aid in thermal dissipation.

Setting the Output Voltage

Set the output voltage by selecting the resistive

voltage divider ratio. The voltage divider drops the

output voltage to the 1.31V feedback voltage. Use a

10K resistor for R2 of the voltage divider. Determine

the high-side resistor R1 by the equation:

VOUT = ( R1 / R2 + 1 ) × VFB

Oscillator and Clock Synchronization

The LP6255 switching frequency is programmable

by a single external resistor connected between the

RT pin and the GND pin. The resistor should be

located very close to the device and connected

directly to the RT and GND pin. To set a desired

switching frequency (fLX), the resistor value can be

programmed as below.

PWM Comparator

The PWM comparator compares the sum of sensed

inductor current and slope compensation ramp to the

voltage at the COMP pin through a 1.2V internal

COMP to PWM voltage drop and terminates the

present cycle when the sum of sensed inductor

current and slope compensation ramp is greater than

VCOMP

HDR and LDR Drivers

The LP6255 contains two strong N-channel

MOSFET gate drivers and a high-side level shifter to

drive the external N-channel MOSFET switches. The

high-side gate driver works in conjunction with an

external bootstrap diode DBST, and bootstrap

capacitor CBST. During the on-time of the low-side

N-channel MOSFET driver, the LX pin voltage is

approximately 0V and the CBST is charged from VIN

through the DBST. A 0.1μF or larger ceramic

capacitor, connected with short traces between the

BST and LX pin, is recommended.

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