LP6255 datasheet(9/10 Pages) POWER

9 / 10 page

LP6255-02

Feb.-2014

Email: marketing@lowpowersemi.com

www.lowpowersemi.com

Page 9 of 10

Preliminary Datasheet

LP6255

The LDR and HDR outputs are controlled with an

adaptive dead-time methodology which ensures that

both outputs are never enabled at the same time.

When the controller commands LDR to be enabled,

the adaptive dead-time logic first disables HDR and

waits for HDR-LX voltage to drop. LDR is then

enabled after a small delay (HDR Fall to LDR Rise

Delay). Similarly, the HDR turn-on is delayed until

the LDR voltage has discharged. HDR is then

enabled after a small delay (LDR Fall to HDR Rise

Delay). This technique ensures adequate dead-time

for any size N-channel MOSFET or parallel MOSFET

configurations especially when VIN is supplied by a

higher external voltage source. Use caution when

adding series gate resistors, as this may decrease

the effective dead-time.

Care should be exercised in selecting the N-channel

MOSFET devices threshold voltage. During startup

at low input voltages, the low-side N-channel

MOSFET's gate plateau voltage should be

sufficiently low to completely enhance the N-channel

MOSFET device. If the low-side MOSFET drive

voltage is lower than the low-side MOSFET gate

plateau voltage during startup, the regulator may not

start properly and it may operate at the maximum

duty cycle in a high power dissipation state.

Cycle-by-Cycle Current Limit

The LP6255 features a peak cycle-by-cycle current

limit function. If the VIN to CS voltage exceeds the

100mV cycle-by-cycle current limit threshold, the

current limit comparator immediately terminates the

LDR output. For the case where the inductor current

overshoots the desired limit, such as inductor

saturation, the current limit comparator blocks LDR

pulses until the current has decayed below the

current limit threshold. Peak inductor current in

current limit can be calculated as follows:

PEAK

100



Thermal Protection

Internal thermal shutdown circuitry is provided to

protect the controller in the event the maximum

junction temperature is exceeded. When activated,

typically at 150℃, the controller is forced into a

low-power shutdown mode, disabling the output

drivers, disconnection switch and the VIN regulator.

This feature is designed to prevent overheating and

destroying the device.

LP6255 数据表(PDF) 9 Page - Lowpower Semiconductor inc

LP6255 数据表(HTML) 9 Page - Lowpower Semiconductor inc

Html Pages

1 2 3 4 5 6 7 8 9 10

数据表下载