Datasheet

Programming the TPS77x01 Adjustable LDO Regulator
V =V x(1+)
OUT ref
R
R
1
2
(1)
V
V
OUT
ref
1)xR-
2
R =(
1
(2)
IN
EN
GND
FB/NC
OUT
RESET/
PG
RESET orPGOutput
V
OUT
V
IN
0.1 Fm
250kW
TPS77x01
C
OUT
R
1
R
2
> 1.7V
< 0.9V
OUTPUTVOLTAGE
PROGRAMMINGGUIDE
R
1
R
2
UNIT
OUTPUT
VOLTAGE
2.5V
3.3V
3.6V
4.75V
121
196
226
332
110
110
110
110
kW
kW
kW
kW
Reset Indicator
Power-Good Indicator
TPS775xx, TPS776xx
SLVS232J – SEPTEMBER 1999 – REVISED MARCH 2009 .............................................................................................................................................. www.ti.com
The output voltage of the TPS77x01 adjustable regulator is programmed using an external resistor divider as
shown in Figure 25 . The output voltage is calculated using Equation 1 :
Where:
• V
ref
= 1.1834V typ (the internal reference voltage)
Resistors R
1
and R
2
should be chosen for approximately 10 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 R
2
= 110k Ω
to set the divider current at approximately 10 µ A and then calculate R
1
using Equation 2 :
Figure 25. TPS77x01 Adjustable LDO Regulator Programming
The TPS775xx features a RESET 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 RESET output transistor turns on, taking the signal low. The open-drain output requires a
pullup resistor. If not used, it can be left floating. RESET can be used to drive power-on reset circuitry or as a
low-battery indicator. RESET does not assert itself when the regulated output voltage falls outside the specified
2% tolerance, but instead reports an output voltage low relative to its nominal regulated value (refer to Timing
Diagram for start-up sequence).
The TPS776xx 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.
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