Datasheet
www.ti.com
Programming the TPS79301 Adjustable LDO Regulator (continued)
R1 +
ǒ
V
O
V
ref
* 1
Ǔ
R2
(4)
C1 +
(3 x 10
–7
) x (R1 ) R2)
(R1 x R2)
(5)
22 pF
15 pF
15 pF
OUTPUT VOLTAGE
PROGRAMMING GUIDE
OUTPUT
VOLTAGE
R1 R2
2.5 V
3.3 V
3.6 V
C1
31.6 kΩ
51 kΩ
59 kΩ
30.1 kΩ
30.1 kΩ
30.1 kΩ
V
O
V
I
OUT
FB
R1
R2
GND
EN
IN
≤ 0.7 V
≥ 2 V
TPS79301
1 µF
BYPASS
0.01 µF
1 µF
C1
Regulator Protection
TPS79301-EP , , TPS79318-EP , , TPS79325-EP , , TPS79328-EP
TPS793285-EP , TPS79330-EP , TPS79333-EP , TPS793475-EP
SGLS163B – APRIL 2003 – REVISED NOVEMBER 2006
APPLICATION INFORMATION (continued)
Resistors R1 and R2 should be chosen for approximately 50- µ A 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, thus, erroneously decreases/increases V
O
. The recommended
design procedure is to choose R2 = 30.1 k Ω to set the divider current at 50 µ A, C1 = 15 pF for stability, and then
calculate R1 using:
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:
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 µ F instead of 2.2 µ F.
Figure 23. TPS79301 Adjustable LDO Regulator Programming
The TPS793xx features internal current limiting and thermal protection. During normal operation, the TPS793xx
limits output current to approximately 400 mA. When current limiting engages, the output voltage scales back
linearly until the overcurrent condition ends. While current limiting is designed to prevent gross device failure,
care should be taken not to exceed the power dissipation ratings of the package or the absolute maximum
voltage ratings of the device. If the temperature of the device exceeds approximately 165 ° C, thermal-protection
circuitry shuts it down. Once the device has cooled down to below approximately 140 ° C, regulator operation
resumes.
12
Submit Documentation Feedback