www.ti.com

Power Dissipation and Junction Temperature

P

T

R

Q

JA

(1)

P

D

I

OUT

(2)

Programming the TPS79301 Adjustable LDO Regulator

V

1 )

R

1

R

2

(3)

R

1

+

V

OUT

V

REF

* 1

R

2

(4)

C

1

+

1

(R

(5)

TPS793xx

SLVS348K – JULY 2001 – REVISED OCTOBER 2007

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,

The maximum power dissipation limit is determined using Equation 1:

Where:

• T

• R

• T

The regulator dissipation is calculated using Equation 2:

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

protection circuit.

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 Equation 3:

Where:

• V

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

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 less than 1.8V, the value of this capacitor should be 100pF. For

voltages greater than 1.8V, the approximate value of this capacitor can be calculated as shown in Equation 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 less than 1.8V is chosen, then the

minimum recommended output capacitor is 4.7

μF instead of 2.2μF.

Copyright © 2001–2007, Texas Instruments Incorporated

Submit Documentation Feedback

9