TPS79301Q1,'79318Q1, '79325Q1

'79328Q1,'793285Q1,'79330Q1

TPS79333Q1,'793475Q1

SGLS162D − APRIL 2003 − REVISED SEPTEMBER 2007

www.ti.com

11

APPLICATION INFORMATION

POWER DISSIPATION AND JUNCTION TEMPERATURE

Specified regulator operation is assured 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, calculate the maximum allowable

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

P

D(max) +

T

J

max

* T

A

RθJA

Where:

(1)

The regulator dissipation is calculated using:

P

D +

V

I *

V

O

I

O

(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:

V

O +

V

ref

1

) R1

R2

(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 increases/decreases the feedback voltage and,

divider current at 50

µA, C1 = 15 pF for stability, and then calculate R1 using:

R1

+

V

O

V

ref

* 1

R2

(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:

C1

+

(R1

) R2)

(R1

R2)

(5)

The suggested value of this capacitor for several resistor ratios is shown in Figure 23. If this capacitor is not used (such

as in a unity-gain configuration) or if an output voltage <1.8 V is chosen, the minimum recommended output capacitor is

4.7

µF instead of 2.2 µF.