Voltage

t

V1 = 3.3V

V2 = 1.8V

Voltage

t

V1 = 3.3V

V2 = 1.8V

a) V1 startup leading V2

b) Simultaneous tracking

÷

ø

ö

ç

è

æ

+

´

<

÷

ø

ö

ç

è

æ

+

1

4

R

3

R

56

.

1

1

2

R

1

R

÷

ø

ö

ç

è

æ

+

´

=

÷

ø

ö

ç

è

æ

+

1

4

R

3

R

56

.

1

1

2

R

1

R

2

R

2

R

1

R

4

R

3

R

4

R

56

.

1

1

1

V

2

V

+

´

+

´

=

R4

R3

V1

Output of external

DC DC converter

V2

1.8V/4A

V

IN

2.5V to 5.5V

PVIN

PVIN

EN

FB

C1

22µF

L1

1µH

C2

2 x 22µF

R1

200k

SW

TPS62095

SW

AVIN

R2

160k

SS

AGND

PG

VOS

DEF

CP

CN

C3

10nF

1

2

13

4

5

6

PGND PGND

7

8

9

10

11

12

3

14

15

16

TPS62095

www.ti.com

SLVSBD8A – APRIL 2014 – REVISED MAY 2014

Device Functional Modes (continued)

During startup the switch current limit is reduced to 1/3 of its typical current limit of 5.5A when the output voltage

is less than 0.6V. Once the output voltage exceeds typically 0.6V, the switch current limit is released to its

nominal value. Thus, the device provides a reduced load current of 1.8A when the output voltage is below 0.6V.

A small or no soft startup time may trigger this reduced switch current limit during startup, especially for larger

output capacitor applications. This is avoided by using a larger soft start up capacitance which extends the soft

startup time. See Short Circuit Protection (Hiccup-Mode) for details of the reduced current limit during startup.

7.4.2 Voltage Tracking

The SS pin can also be used to implement output voltage tracking with other supply rails, as shown in Figure 5.

Figure 5. Output Voltage Tracking

In voltage tracking applications, the resistance R4 should be set properly to achieve accurate voltage tracking by

taking 7.5

μA soft startup current into account. 4.3kΩ is a sufficient value for R4. The relationship between V1 and

V2 is shown in Equation 5. To achieve V1 startup leading V2, as shown in Figure 6, Equation 5 should be less

than 1. To achieve simultaneous tracking, Equation 5 should equal to 1.

(5)

Figure 6. Voltage Tracking Applications

Copyright © 2014, Texas Instruments Incorporated

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