UVLO

VIN

VCC

SW Pin

Inductor

Current

SS Pin

t2

7.0V

2.5V

t1

LM2694

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SNVS444A – MAY 2006 – REVISED APRIL 2013

Figure 9. Startup Sequence

Functional Description

The LM2694 Step Down Switching Regulator features all the functions needed to implement a low cost, efficient

buck bias power converter capable of supplying at least 0.6A to the load. This high voltage regulator contains a

30V N-Channel buck switch, is easy to implement, and is available in the TSSOP-14 and the thermally enhanced

WSON-10 packages. The regulator’s operation is based on a constant on-time control scheme, where the on-

input voltage variations. The feedback control requires no loop compensation resulting in very fast load transient

response. The valley current limit detection circuit, internally set at 0.62A, holds the buck switch off until the high

current level subsides. This scheme protects against excessively high currents if the output is short-circuited

The LM2694 can be applied in numerous applications to efficiently regulate down higher voltages. Additional

duty cycle limiter.

Control Circuit Overview

The LM2694 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 (2.5V). If the FB voltage is below the

reference the buck switch is turned on for a time period determined by the input voltage and a programming

falls below the reference. 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 of 265 ns. Once regulation is

established, the off-times are longer.

Copyright © 2006–2013, Texas Instruments Incorporated

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