C1 +

(R1 x R2)

R1 +

V

O

V

ref

* 1

R2

V

O +

V

ref

1 )

R1

R2

P

D +

V

I *

V

O

I

O

P

D(max) +

T

J

max * TA

RθJA

TPS79301-Q1, TPS79318-Q1, TPS79325-Q1

TPS79328-Q1, TPS793285-Q1, TPS79330-Q1

TPS79333-Q1, TPS793475-Q1

www.ti.com

SGLS162H – APRIL 2003 – REVISED JANUARY 2013

Power Dissipation and Junction Temperature

Specified regulator operation is ensured to a junction temperature of 125°C; the maximum junction temperature

should be restricted to 125°C under normal operating conditions. This restriction limits the power dissipation the

regulator can handle in any given application. To ensure the junction temperature is within acceptable limits,

The maximum power dissipation limit is determined using the following equation:

(1)

Where:

R

The regulator dissipation is calculated using:

(2)

Power dissipation resulting from quiescent current is negligible. Excessive power dissipation triggers the thermal

protection circuit.

Programming the TPS79301 Adjustable LDO Regulator

The output voltage of the TPS79301 adjustable regulator is programmed using an external resistor divider as

shown in Figure 23. The output voltage is calculated using:

(3)

Where:

Resistors R1 and R2 should be chosen for approximately 50-

μA divider current. Lower-value resistors can be

used for improved noise performance, but the solution consumes more power. Higher resistor values should be

avoided as leakage current into/out of FB across R1/R2 creates an offset voltage that artificially

design procedure is to choose R2 = 30.1 k

Ω to set the divider current at 50 μA, C1 = 15 pF for stability, and then

calculate R1 using:

(4)

In order to improve the stability of the adjustable version, it is suggested that a small compensation capacitor be

placed between OUT and FB. For voltages <1.8 V, the value of this capacitor should be 100 pF. For voltages

>1.8 V, the approximate value of this capacitor can be calculated as:

(5)

The suggested value of this capacitor for several resistor ratios is shown in the table below. If this capacitor is

not used (such as in a unity-gain configuration) or if an output voltage <1.8 V is chosen, then the minimum

recommended output capacitor is 4.7

μF instead of 2.2 μF.

Copyright © 2003–2013, Texas Instruments Incorporated

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