TPS77401-EP Datasheet, PDF (17/23 Pages) Texas Instruments – 250-mA LDO VOLTAGE REGULATOR WITH POWER-GOOD OUTPUT

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TPS77401-EP
250-mA LDO VOLTAGE REGULATOR
WITH POWER-GOOD OUTPUT
SLVS702 – OCTOBER 2006
APPLICATION INFORMATION (continued)
Programming the TPS77401 Adjustable LDO Regulator
The output voltage of the TPS77401 adjustable regulator is programmed using an external resistor divider as
shown in Figure 24. The output voltage is calculated using:
ǒ Ǔ VO + Vref
1
)
R1
R2
(1)
Where:
V_ref = 1.1834 V typ (the internal reference voltage)
Resistors R1 and R2 should be chosen for approximately 50-µA 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 kΩ
to set the divider current at 50 µA and then calculate R1 using:
ǒ Ǔ R1 +
VO
Vref
*
1
R2
(2)
V_I
0.1 µF
TPS77401
IN
PG
EN
OUT
FB/SENSE
GND
PG Output
250 kΩ
V_O
R1
C_O
R2
OUTPUT VOLTAGE
PROGRAMMING GUIDE
OUTPUT
VOLTAGE
2.5 V
3.3 V
3.6 V
R1 R2 UNIT
33.5 30.1 kΩ
53.8 30.1 kΩ
61.5 30.1 kΩ
NOTE: To reduce noise and prevent
oscillation, R1 and R2 need to be as close
as possible to the FB/SENSE terminal.
Figure 24. TPS77401 Adjustable LDO Regulator Programming
Regulator Protection
The TPS77401 PMOS-pass transistor has a built-in back diode that conducts reverse currents when the input
voltage drops below the output voltage (e.g., during power down). Current is conducted from the output to the
input and is not internally limited. When extended reverse voltage is anticipated, external limiting may be
appropriate.
The device also features internal current limiting and thermal protection. During normal operation, the TPS77401
limits output current to approximately 0.9 A. 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. If the temperature of the
device exceeds 150°C (typ), thermal-protection circuitry shuts it down. Once the device has cooled below 130°C
(typ), regulator operation resumes.
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