Thermal

Shutdown

Undervoltage

Lockout

Gate Driver

PWM Control

Over Voltage

Protection &

Short Circuit

Protection

1

3

6

8

Logic

5

EA

SW

EN

FB

AGND

VOUT

VIN

VREF

2

Valley Current

Sense

Soft Startup

VOUT

7

SW

VOUT

VIN

8

TPS61021

SLVSD21B – NOVEMBER 2015 – REVISED MARCH 2016

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7 Detailed Description

7.1 Overview

The TPS61021 synchronous step-up converter is designed to operate from an input voltage supply range

between 0.5 V and 4.4 V with 3-A valley switch current limit. The TPS61021 typically operates at a quasi-

constant frequency pulse width modulation (PWM) at moderate to heavy load currents. The switching frequency

is 2.0 MHz when the input voltage is above 1.8 V. The switching frequency reduces down to 1.0 MHz when the

input voltage goes down from 1.8 V to 1.2 V. At light load currents, the TPS61021 converter operates in power-

save mode with pulse frequency modulation (PFM). During PWM operation, the converter uses adaptive constant

on-time valley current mode control scheme to achieve excellent line/load regulation and allows the use of a

small inductor and ceramic capacitors. Internal loop compensation simplifies the design process while minimizing

the number of external components.

7.2 Functional Block Diagram

7.3 Feature Description

7.3.1 Under-Voltage Lockout

The TPS61021 has a built-in under-voltage lockout (UVLO) circuit to ensure the device working properly. When

the input voltage is above the UVLO rising threshold of 0.9 V, the TPS61021 can be enabled to boost the output

voltage. After the TPS61021 starts up and the output voltage is above 1.6 V, the TPS61021 can work with the

input voltage as low as 0.5 V.