S

Q

Q

R

+

CSN

CSP

K1

One-

Shot

+

+

+

–

Σ

+

–

PWM

Comparator

+

Integrator

+

–

UDG-12133

B

C

A

TPS51312

SLUSB57 – SEPTEMBER 2012

www.ti.com

APPLICATION INFORMATION

Functional Overview

TPS51312 is a D-CAP2 mode adaptive on time converter with internal integrator. Monolithically integrate high

side and low side FET supports output current to a maximum of 3-ADC. The converter automatically runs in

discontinuous conduction mode to optimize light load efficiency. A switching frequency of 900 kHz enables

optimization of the power train for the cost, size and efficiency performance of the design.

PWM Operation

The PWM operation is comprised of three separate loops, A, B and C as shown in Figure 9.

Figure 9. ¾PWM Operation

Internal Current Loop (A)

Loop A is the internal current loop. The current information is sampled, divided and averaged at the SW node.

The RC time constant and the gain of the current sense amplifier is chosen to cover the wide range of power

stage design intended for this application.

Internal Voltage Loop (B)

Loop B is the internal voltage loop. The feedback voltage information is compared to the voltage reference at the

phase margin at the desired crossover frequency.

8

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