Voltage

t

V

OUT1

V

OUT2

Voltage

t

V

OUT1

V

OUT2

a) Ratiometric Tracking

b) Coincidental Tracking

2

R

1

R

4

R

3

R

<

2

R

1

R

4

R

3

R

=

R2

V

OUT1

R1

TPS62097

V

OUT2

R4

R3

SS/TR

FB

A

5

.

7

V

8

.

0

C

t

TR

/

SS

SS

m

´

=

TPS62097

SLVSCD6 – DECEMBER 2015

www.ti.com

8.4.3 Soft Startup (SS/TR)

The TPS62097 programs its output voltage ramp rate with the SS/TR pin. Connecting an external capacitor to

SS/TR enables output soft startup to reduce inrush current from the input supply. The device charges the

capacitor voltage to the input supply voltage with a constant current of typically 7.5

μA. The FB pin voltage follows

the SS/TR pin voltage until the internal reference voltage of 0.8V is reached. The soft startup time is calculated

using Equation 3. Keep the SS/TR pin floating to set the minimum startup time.

(3)

An active pull-down circuit is connected to the SS/TR pin. It discharges the external soft startup capacitor in case

of disable, UVLO, thermal shutdown and HICCUP short circuit protection.

8.4.4 Voltage Tracking (SS/TR)

The SS/TR pin is externally driven by another voltage source to achieve output voltage tracking. The application

circuit is shown in Figure 4. From 0 V to 0.8 V, the internal reference voltage to the internal error amplifier follows

the SS/TR pin voltage. When the SS/TR pin voltage is above 0.8 V, the voltage tracking is disabled and the FB

pin voltage is regulated at 0.8 V. The device achieves ratiometric or coincidental (simultaneous) output tracking,

as shown in Figure 5.

Figure 4. Output Voltage Tracking

Figure 5. Voltage Tracking Options

The R2 value should be set properly to achieve accurate voltage tracking by taking 7.5 µA soft startup current

into account. 1 k

Ω or smaller is a sufficient value for R2.

For decreasing SS/TR pin voltage, the device doesn't sink current from the output when the device is in PSM. So

the resulting decreases of the output voltage may be slower than the SS/TR pin voltage if the load is light. When

driving the SS/TR pin with an external voltage, do not exceed the voltage rating of the SS/TR pin which is

10

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