Datasheet

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APPLICATION INFORMATION
PROGRAMMING THE TPS75901 ADJUSTABLE LDO REGULATOR
V
O
 V
ref


1 
R1
R2

Where:
V
ref
= 1.224 V typ (the internal reference voltage)
(9)
R1 

V
O
V
ref
 1

 R2
(10)
V
O
V
I
OUT
FB
R1
R2
GND
EN
IN
≤ 0.7 V
≥ 2 V
TPS75901
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
REGULATOR PROTECTION
INPUT CAPACITOR
TPS75901, TPS75915
TPS75918, TPS75925, TPS75933
SLVS318E – DECEMBER 2000 – REVISED MARCH 2004
The output voltage of the TPS75901 adjustable regulator is programmed using an external resistor divider as
shown in Figure 28 . The output voltage is calculated using:
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:
Figure 28. TPS75901 Adjustable LDO Regulator Programming
The TPS759xx 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 TPS759xx also features internal current limiting and thermal protection. During normal operation, the
TPS759xx 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.
For a typical application, a ceramic input bypass capacitor (0.22 µF-1 µF) is recommended to ensure device
stability. This capacitor should be as close as possible to the input pin. Due to the impedance of the input supply,
large transient currents will cause the input voltage to droop. If this droop causes the input voltage to drop below
the UVLO threshold, the device will turn off. Therefore, it is recommended that a larger capacitor be placed in
parallel with the ceramic bypass capacitor at the regulator's input. The size of this capacitor depends on the
output current, response time of the main power supply, and the main power supply's distance to the regulator.
At a minimum, the capacitor should be sized to ensure that the input voltage does not drop below the minimum
UVLO threshold voltage during normal operating conditions.
20