P1

P2

N2

+

-

VIN

Load

SW1

SW2

LM3668-Q1

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SNVSA84A – APRIL 2015 – REVISED MAY 2015

Feature Description (continued)

Figure 7. Simplified Circuit for Boost Operation

7.3.3 Internal Synchronous Rectification

While in PWM mode, the LM3668-Q1 uses an internal MOSFET as a synchronous rectifier to reduce rectifier

forward voltage drop and associated power loss. Synchronous rectification provides a significant improvement in

efficiency whenever the output voltage is relatively low compare to the voltage drop across an ordinary rectifier

diode.

7.3.4 Current Limit Protection

The LM3668-Q1 has current limit protection to prevent excessive stress on itself and external components during

overload conditions. The internal current limit comparator will disable the power device at a typical switch peak

current limit of 1.85 A (typ.).

7.3.5 Undervoltage Protection

The LM3668-Q1 has an UVP comparator to turn the power device off in case the input voltage or battery voltage

is too low . The typical UVP threshold is around 2 V.

7.3.6 Short Circuit Protection

When the output of the LM3668-Q1 is shorted to GND, the current limit is reduced to about half of the typical

current limit value until the short is removed.

7.3.7 Shutdown

When the EN pin is pulled low, P1 and P2 are off; N1 and N2 are turned on to pull SW1 and SW2 to ground.

7.3.8

Thermal Shutdown

The LM3668-Q1 has an internal thermal shutdown function to protect the die from excessive temperatures. The

thermal shutdown trip point is typically 150°C; normal operation resumes when the temperature drops below

125°C.

7.3.9 Start-Up

The LM3668-Q1 has a soft-start circuit that smooth the output voltage and ramp current during start-up. During

start-up the bandgap reference is slowly ramped up and switch current limit is reduced to half the typical value.

thereby depends on the output capacitor and load current demanded at start-up. It is not recommended to start

up the device at full load while in soft-start.

Copyright © 2015, Texas Instruments Incorporated

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Product Folder Links: LM3668-Q1