10.3 System Examples

10.3.1 Fixed Output Voltage Versions

Versions with an internally fixed output voltage allow you to remove the external feedback voltage divider. This

not only allows you to reduce the total solution size but also provides higher accuracy as there is no additional

error caused by the external resistor divider. The FB pin must be tied to the output voltage directly as shown in

Figure 10-57. Independent of that, the application shown runs with an internally defined switching frequency of

2.25 MHz by connecting COMP/FSET to GND.

L

0.56

H

m

MODE/SYNC

SW

FB

VIN

V

IN

2.75 V -

V

6

C

IN

22 mF

C

OUT

1 x 22

F

m

+ 10

F

m

TPS62812x-Q1

EN

V

OUT

GND

PG

SS/TR

COMP/FSET

C

SS

R

3

Figure 10-57. Schematic for Fixed Output Voltage Versions

10.3.2 Voltage Tracking

The TPS6281x-Q1 follows the voltage applied to the SS/TR pin. A voltage ramp on SS/TR to 0.6 V ramps the

output voltage according to the 0.6 V feedback voltage.

Tracking the 3.3 V of device 1, such that both rails reach their target voltage at the same time, requires a resistor

divider on SS/TR of device 2 equal to the output voltage divider of device 1. The output current of 2.5 µA on

the SS/TR pin causes an offset voltage on the resistor divider formed by R5 and R6. The equivalent resistance

of R5 // R6, so it must be kept below 15 kΩ. The current from SS/TR causes a slightly higher voltage across R6

than 0.6 V, which is desired because device 2 switches to its internal reference as soon as the voltage at SS/TR

is higher than 0.6 V.

In case both devices must run in forced PWM mode, TI recommends to tie the MODE pin of device 2 to the

output voltage or the power good signal of device 1, the master device. The TPS6281x-Q1 has a duty cycle

limitation defined by the minimum on-time. For tracking down to low output voltages, device 2 cannot follow after

the minimum duty cycle is reached. Enabling PFM mode while tracking is in progress allows you to ramp down

the output voltage close to 0 V.

TPS62810-Q1, TPS62811-Q1, TPS62812-Q1, TPS62813-Q1

SLVSDU1J – AUGUST 2018 – REVISED MARCH 2023

www.ti.com

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