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7101Q LOW-DROPOUT VOLTAGE REGULATORS Texas-Instruments
Texas Instruments Texas-Instruments
7101Q Datasheet PDF : 39 Pages
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TPS7101Q, TPS7133Q, TPS7148Q, TPS7150Q
TPS7101Y, TPS7133Y, TPS7148Y, TPS7150Y
LOW-DROPOUT VOLTAGE REGULATORS
SLVS092G NOVEMBER 1994 REVISED JANUARY 2003
APPLICATION INFORMATION
programming the TPS7101 adjustable LDO regulator (continued)
Resistors R1 and R2 should be chosen for approximately 7-µA divider current. A recommended value for R2
is 169 kwith R1 adjusted for the desired output voltage. Smaller resistors can be used, but offer no inherent
advantage and consume more power. Larger values of R1 and R2 should be avoided as leakage currents at
+ ǒ * Ǔ @ FB introduce an error. Solving equation 1 for R1 yields a more useful equation for choosing the appropriate
resistance:
R1
VO
Vref
1
R2
VI
0.1 µF
>2.7 V
<0.5V
TPS7101
IN
PG
EN
OUT
FB
GND
Power-Good
Indicator
250 k
VO
+
R1
R2
OUTPUT VOLTAGE
PROGRAMMING GUIDE
OUTPUT
VOLTAGE
R1
R2 UNIT
2.5 V
3.3 V
3.6 V
4V
5V
6.4 V
191 169
k
309 169
k
348 169
k
402 169
k
549 169
k
750 169
k
Figure 44. TPS7101 Adjustable LDO Regulator Programming
power-good indicator
The TPS71xx 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 as a low-battery
indicator. PG 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.
regulator protection
The TPS71xx PMOS-pass transistor has a built-in back diode that safely 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 TPS71xx also features internal current limiting and thermal protection. During normal operation, the
TPS71xx limits output current to approximately 1 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 165°C, thermal-protection circuitry shuts it down. Once the device has cooled, regulator
operation resumes.
28
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