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PG
OUT
OUT
7
6
5
IN
IN
EN
GND
3
16
14
13
V
I
C1
0.1 µF
PG
V
O
10 µF
+
TPS768xx
C
o
250 kΩ
V
O
 V
ref


1 
R1
R2

where:
V
ref
= 1.1834 V typ (the internal reference voltage)
(1)
R1 

V
O
V
ref
 1

 R2
(2)
OUTPUT
VOLTAGE
R1 R2
2.5 V
3.3 V
3.6 V
4.75 V
UNIT
33.2
53.6
61.9
90.8
30.1
30.1
30.1
30.1
kΩ
kΩ
kΩ
kΩ
OUTPUT VOLTAGE
PROGRAMMING GUIDE
V
O
V
I
PG
OUT
FB / NC
R1
R2
GND
EN
IN
≤ 0.9 V
≥ 1.7 V
TPS76801
PG
0.1 µF
250 kΩ
POWER-GOOD INDICATOR
TPS768xxQ
SLVS211L – JUNE 1999 – REVISED JANUARY 2006
APPLICATION INFORMATION (continued)
Figure 26. Typical Application Circuit (Fixed Versions)
The output voltage of the TPS76801 adjustable regulator is programmed using an external resistor divider as
shown in Figure 27 . The output voltage is calculated using:
Resistors R1 and R2 should be chosen for approximately 50- µ A divider current. Lower value resistors can be
used but offer no inherent advantage and waste more power. Higher values should be avoided as leakage
currents at FB increase the output voltage error. The recommended design procedure is to choose
R2 = 30.1 k Ω to set the divider current at 50 µ A and then calculate R1 using:
Figure 27. TPS76801 Adjustable LDO Regulator Programming
The TPS768xxQ features a power-good (PG) output that can be used to monitor the status of the regulator. The
internal comparator monitors the output voltage: when the output drops to between 92% and 98% of its nominal
regulated value, the PG output transistor turns on, taking the signal low. The open-drain output requires a pullup
resistor. If not used, it can be left floating. PG can be used to drive power-on reset circuitry or used as a
low-battery indicator. PG does not assert itself when the regulated output voltage falls out of the specified 2%
tolerance, but instead reports an output voltage low, relative to its nominal regulated value.
12
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