Datasheet
C1 +
(
3 10
5
)
(
R1 ) R2
)
(
R1 R2
)
(
pF
)
V
OUT
+ V
REF
ǒ
1 )
R1
R2
Ǔ
R1 +
ǒ
V
OUT
V
REF
* 1
Ǔ
R2
V
OUT
1.225 V
1.5 V
2.5 V
3.0 V
3.3 V
4.75 V
R1/R3
Short
7.15 kΩ
31.6 kΩ
43.2 kΩ
49.9 kΩ
86.6 kΩ
R2/R4
Open
30.1 kΩ
30.1 kΩ
30.1 kΩ
30.1 kΩ
30.1 kΩ
Output Voltage Programming Guide
C1/C2
Open
100 pF
22 pF
15 pF
15 pF
15 pF
TPS71202
GND
EN2
FB2NR
IN OUT1
FB1
EN1
OUT2
V
IN
V
OUT1
V
OUT2
0.1
µ
F
2.2
µ
F
2.2
µ
F
0.01
µ
F
C1
R1
C2
R3
R2
R4
TPS71202, TPS71219
TPS71229, TPS71247
TPS71256, TPS71257
SBVS049D –MAY 2004–REVISED AUGUST 2010
www.ti.com
PROGRAMMING THE TPS71202
ADJUSTABLE LDO REGULATOR
(3)
The output voltage of the TPS71202 dual adjustable
blank
regulator is programmed using an external resistor
The suggested value of this capacitor for several
divider, as shown in Figure 25. The output voltage is
resistor ratios is shown in Figure 25. If this capacitor
calculated using Equation 1:
is not used (such as in a unity-gain configuration) or if
an output voltage ≤ 1.8 V is chosen, then the
(1)
minimum recommended output capacitor is 4.7 mF
instead of 2.2 mF.
where V
REF
= 1.225 V (the internal reference
voltage).
DROPOUT VOLTAGE
Resistors R2 and R4 should be chosen for
The TPS712xx uses a PMOS pass transistor to
approximately a 40 mA divider current. Lower value
achieve extremely low dropout. When (V
IN
- V
OUT
) is
resistors can be used for improved noise
less than the dropout voltage (V
DO
), the PMOS pass
performance, but will consume more power. Higher
device is in its linear region of operation and the
values should be avoided because leakage current at
input-to-output resistance is the R
DS, ON
of the PMOS
FB increases the output voltage error. The
pass element. Dropout voltages at lower currents can
recommended design procedure is to choose R2 =
be approximated by calculating the effective R
DS, ON30.1 kΩ to set the divider current at 40 mA, and then
of the pass element and multiplying that resistance by
calculate R1 using Equation 2:
the load current. R
DS, ON
of the pass element can be
obtained by dividing the dropout voltage by the rated
output current. For the TPS71256, the R
DS, ON
of the
(2)
pass element is 84 mΩ. The dropout voltage of the
To improve the stability and noise performance of the
TPS712xx will be less for higher output voltage
adjustable version, a small compensation capacitor
versions. This is because the PMOS pass element
can be placed between OUT and FB.
will have lower on-resistance due to increased gate
drive.
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 Equation 3:
Figure 25. TPS71202 Adjustable LDO Regulator Programming
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