COMP

FB

GM Amplifier

Vref

SW

SW

GateDriverof

Power

Transistor

IN

SS

PWM

Generator

Currentlimit

and

SoftStart

t

Generator

OFF

t

ON

PGND

BiasVref = 1.238V

UVLO

ThermalShutdown

AGND

EN

FREQ

TPS61087

SLVS821C – MAY 2008 – REVISED JULY 2013

www.ti.com

DETAILED DESCRIPTION

Figure 13. Block Diagram

The boost converter is designed for output voltages up to 18.5 V with a switch peak current limit of 3.2 A

minimum. The device, which operates in a current mode scheme with quasi-constant frequency, is externally

compensated for maximum flexibility and stability. The switching frequency is selectable between 650 kHz and

1.2 MHz and the minimum input voltage is 2.5 V. To limit the inrush current at start-up a soft-start pin is

available.

TPS61087 boost converter’s novel topology using adaptive off-time provides superior load and line transient

responses and operates also over a wider range of applications than conventional converters.

The selectable switching frequency offers the possibility to optimize the design either for the use of small sized

components (1.2 MHz) or for higher system efficiency (650 kHz). However, the frequency changes slightly

thus on the on-time (the off-time remains constant).

The converter operates in continuous conduction mode (CCM) as soon as the input current increases above half

the ripple current in the inductor, for lower load currents it switches into discontinuous conduction mode (DCM). If

the load is further reduced, the part starts to skip pulses to maintain the output voltage.

8

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