Datasheet
SLVS293D − NOVEMBER 2000 − REVISED MAY 2002
19
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
programming the TPS75501 adjustable LDO regulator
The output voltage of the TPS75501 adjustable regulator is programmed using an external resistor divider as
shown in Figure 28. The output voltage is calculated using:
V
O
+ V
ref
ǒ
1 )
R1
R2
Ǔ
(
9)
Where:
V
ref
= 1.224 V typ (the internal reference voltage)
Resistors R1 and R2 should be chosen for approximately 40-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 40 µA and then calculate R1 using:
R1 +
ǒ
V
O
V
ref
* 1Ǔ R2
(10)
V
O
V
I
OUT
FB
R1
R2
GND
EN
IN
≤ 0.7 V
≥ 2 V
TPS75501
1 µF
C
o
OUTPUT VOLTAGE
PROGRAMMING GUIDE
OUTPUT
VOLTAGE
R1 R2
2.5 V
3.3 V
3.6 V
UNIT
31.6
51
58.3
30.1
30.1
30.1
kΩ
kΩ
kΩ
Figure 28. TPS75501 Adjustable LDO Regulator Programming
regulator protection
The TPS755xx 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 TPS755xx also features internal current limiting and thermal protection. During normal operation, the
TPS755xx limits output current to approximately 10 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.