LM34919C-Q1 Datasheet, PDF (12/29 Pages) Texas Instruments – LM34919C-Q1 Ultra Small 50V, 600 mA Constant On-Time Buck Switching Regulator

LM34919C-Q1
SNVS831A – SEPTEMBER 2013 – REVISED DECEMBER 2013
VIN
www.ti.com
EN
VCC
UVLO
PGD
SS
SW
FB
VOUT
tt1t
tt2t
Figure 6. Start-Up Sequence
Functional Description
Device Information
The LM34919C Step Down Switching Regulator features all the functions needed to implement a low cost,
efficient buck bias power converter capable of supplying 600 mA to the load. This high voltage regulator is easy
to implement and is available in DSBGA and WSON packages. The regulator’s operation is based on a constant
on-time control scheme, where the on-time is determined by V_IN. This feature allows the operating frequency to
remain relatively constant with load and input voltage variations. The feedback control requires no loop
compensation resulting in fast load transient response. The valley current limit detection circuit, internally set at
0.64 A, holds the buck switch off until the high current level subsides. This scheme protects against excessively
high current if the output is short-circuited when V_IN is high.
The LM34919C can be applied in numerous applications to efficiently step down higher voltages. Additional
features include: Thermal shutdown, V_CC undervoltage lockout, gate drive undervoltage lockout, maximum duty
cycle limiter, power good, and enable.
Control Circuit Overview
The LM34919C buck DC-DC regulator employs a control scheme based on a comparator and a one-shot on-
timer, with the output voltage feedback (FB) compared to an internal reference (2.52 V). If the FB voltage is
below the reference the N-channel buck switch is turned on for a time period determined by the input voltage and
a programming resistor R_ON. Following the on-time the switch remains off until the FB voltage falls below the
reference but not less than the minimum off-time. The buck switch then turns on for another on-time period.
Typically, during start-up, or when the load current increases suddenly, the off-times are at the minimum. Once
regulation is established, in steady state operations, the off-times are longer and automatically adjust to produce
the SW pin duty cycle required for output regulation.
12
Submit Documentation Feedback
Product Folder Links: LM34919C-Q1
Copyright © 2013, Texas Instruments Incorporated