Datasheet

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PROGRAMMING THE TPS71202
C1 
(
3  10
5
)

(
R1  R2
)
(
R1  R2
)
(
pF
)
(3)
V
OUT
 V
REF


1 
R1
R2

(1)
DROPOUT VOLTAGE
R1 

V
OUT
V
REF
 1

 R2
(2)
V
OUT2
1.225 V
1.5 V
2.5 V
3.0 V
3.3 V
4.75 V
R1
Short
7.15 kΩ
31.6 kΩ
43.2 kΩ
49.9 kΩ
86.6 kΩ
R2
Open
30.1 kΩ
30.1 kΩ
30.1 kΩ
30.1 kΩ
30.1 kΩ
Output Voltage Programming Guide
C1
Open
100 pF
22 pF
15 pF
15 pF
15 pF
TPS71334
GND
NR FB2
IN OUT1
EN1 OUT2
EN2 RESET
V
IN
V
OUT1
V
OUT2
0.1
µ
F
2.2
µ
F
2.2
µ
F
C1
0.01
µ
F
R1
R2
TPS71319
TPS71334
SBVS055A – DECEMBER 2004 – REVISED JANUARY 2005
ADJUSTABLE LDO REGULATOR
The output voltage of the TPS71202 dual adjustable
The suggested value of this capacitor for several
regulator is programmed using an external resistor
resistor ratios is shown in Figure 25 . If this capacitor
divider, as shown in Figure 24 . The output voltage is
is not used (such as in a unity-gain configuration) or if
calculated using Equation 1 :
an output voltage ≤ 1.8 V is chosen, then the
minimum recommended output capacitor is 4.7 µF
instead of 2.2 µF.
where V
REF
= 1.225 V (the internal reference volt-
age).
The TPS713xx uses a PMOS pass transistor to
Resistors R2 and R4 should be chosen for approxi-
achieve extremely low dropout. When (V
IN
- V
OUT
) is
mately a 40 µA divider current. Lower value resistors
less than the dropout voltage (V
DO
), the PMOS pass
can be used for improved noise performance, but will
device is in its linear region of operation and the
consume more power. Higher values should be
input-to-output resistance is the R
DS, ON
of the PMOS
avoided because leakage current at FB increases the
pass element. Dropout voltages at lower currents can
output voltage error. The recommended design pro-
be approximated by calculating the effective R
DS, ON
cedure is to choose R2 = 30.1 k Ω to set the divider
of the pass element and multiplying that resistance by
current at 40 µA, and then calculate R1 using
the load current. R
DS, ON
of the pass element can be
Equation 2 :
obtained by dividing the dropout voltage by the rated
output current. For the TPS71334, the R
DS, ON
of the
pass element is 84 m Ω . The dropout voltage of the
TPS713xx will be less for higher output voltage
versions. This is because the PMOS pass element
To improve the stability and noise performance of the
will have lower on-resistance due to increased gate
adjustable version, a small compensation capacitor
drive.
can 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 approxi-
mate value of this capacitor can be calculated as
Equation 3 :
Figure 25. TPS71334 Adjustable LDO Regulator Programming
10