R4

43k

R3

59k

V1

Output of external

DC DC converter

V2

1.5V/3A

Vin

2.5V to 6V

PVIN

PVIN

EN

FB

C1

10 F

m

L1

470nH

C2

22 F

m

R1

140k

SW

TPS62090

SW

Power Good

AVIN

R2

160k

SS

R3

500k

AGND

PG

VOS

FREQ

CP

CN

C3

10nF

1

2

3

4

5

6

PGND PGND

7

8

9

10

11

12

13

14

15

16

R3

R1

=

x 1.56

R4

R2

1.25V

R4 =

300μA

TPS62090, TPS62091

TPS62092, TPS62093

www.ti.com

SLVSAW2A – MARCH 2012 – REVISED MARCH 2012

Start-up Tracking (SS)

The softstart pin can also be used to implement output voltage tracking with other supply rails. The internal

reference voltage follows the voltage at the softstart pin with a fraction of 1.56 until the internal reference voltage

of 0.8 V is reached. The softstart pin can be used to implement output voltage tracking as shown in Figure 28.

Figure 28. Output Voltage Tracking

In Figure 28, the output V2 will track the voltage applied to V1. The voltage will track simultaneously when

following conditions are met:

(5)

As the fraction of R3/R4 becomes larger the voltage V1 will ramp up faster than V2 and if it gets smaller than the

ramp will be slower than V2. R4 needs to be determined first using Equation 6.

(6)

In the calculation of R4, 300 µA current is used to achieve sufficient accuracy by taking into account the typical

7.5 µA soft-start current. After determining R4, R3 can be calculated using Equation 5.

Short Circuit Protection (Hiccup-Mode)

The device is protected against hard short circuits to GND and over-current events. This is implemented by a two

level short circuit protection. During start-up and when the output is shorted to GND the switch current limit is

reduced to 1/3 of its typical current limit of 4.6 A. Once the output voltage exceeds typically 0.6 V the current limit

is released to its nominal value. The full current limit is implemented as a hiccup current limit. Once the internal

current limits is triggered 32 times the device stops switching and starts a new start-up sequence after a typical

delay time of 66 µS passed by. The device will go through these cycles until the high current condition is

released.

Output Discharge Function

To make sure the device starts up under defined conditions, the output gets discharged via the VOS pin with a

typical discharge resistor of 200

Ω whenever the device shuts down. This happens when the device is disabled

or if thermal shutdown, undervoltage lockout or short circuit hiccup-mode is triggered.

Power Good Output (PG)

The power good output is low when the output voltage is below its nominal value. The power good will become

high impedance once the output is within 5% of regulation. The PG pin is an open drain output and is specified to

typically sink up to 1 mA. This output requires a pull-up resistor to be monitored properly. The pull-up resistor

cannot be connected to any voltage higher than the input voltage of the device.

Copyright © 2012, Texas Instruments Incorporated

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