TPS78101 Datasheet, PDF (13/26 Pages) Texas Instruments – 150mA, Low-Dropout Regulator, Ultralow-Power, IQ 1mA with Pin-Selectable, Dual-Level Output Voltage

TPS781 Series
www.ti.com ........................................................................................................................................................... SBVS102B – MARCH 2008 – REVISED MAY 2008
APPLICATION INFORMATION
APPLICATION EXAMPLES
The TPS781 series of LDOs typically take less than
800µs to transition from a lower voltage of 2.2V to a
higher voltage of 3.3V under an output load of
150mA; see Figure 45. Additionally, the TPS781
series contain active pull-down circuitry that
automatically pulls charge out of the voltage capacitor
to transition the output voltage from the higher
voltage to the lower voltage, even with no load
connected. Output voltage overshoots and
undershoots are minimal under this load condition.
The TPS781 series typically take less than 800µs to
transition from V_SET low (3.3V to 2.2V), or V_SET high
(2.2V to 3.3V); see Figure 45 and Figure 46. Both
output states of the TPS781 series are
factory-programmable between 1.5V to 4.2V. Note
that during startup or steady-state conditions, it is
important that the EN pin and V_SET pin voltages never
exceed V_IN + 0.3V.
4.2V to 5.5V
V_IN
IN
2.2V to 3.3V
OUT
V_OUT
1mF
1mF
TPS781
On
Off
EN
V_SET High = V_OUT(LOW)
V_SET Low = V_OUT(HIGH)
V_SET
GND
Figure 48. Typical Application Circuit
The TPS781 series is also used effectively in
dynamic voltage scaling (DVS) applications. DVS
applications are required to dynamically switch
between a high operational voltage to a low standby
voltage in order to reduce power consumption.
Modern multimillion gate microprocessors fabricated
with the latest sub-micron processes save power by
transitioning to a lower voltage to reduce leakage
currents while maintaining content. This architecture
enables the microprocessor to transition quickly into
an operational state (wake up) without requiring a
reload of the states from external memory, or a
reboot.
Programming the TPS78101 Adjustable LDO
Regulator
The output voltage of the TPS78101 adjustable
regulator is programmed using an external resistor
divider as shown in Figure 49. The output voltage
operating range is 1.2V to 5.1V, and is calculated
using Equation 1:
( ) ^VOUT ^{= V}FB ^´
1+
R₁
R₂
(1)
Where:
V_FB = 1.216V typ (the internal reference voltage)
Resistors R₁ and R₂ should be chosen for
approximately 1.2µA divider current. Lower value
resistors can be used for improved noise
performance, but the solution consumes more power.
Higher resistor values should be avoided as leakage
current into/out of FB across R₁/R₂ creates an offset
voltage that artificially increases/decreases the
feedback voltage and thus erroneously
decreases/increases V_OUT. Table 2 lists several
common output voltages and resistor values. The
recommended design procedure is to choose R₂ =
1MΩ to set the divider current at 1.2µA, and then
calculate R₁ using Equation 2:
( ) ^R1 ⁼
V_OUT
V_FB
-1
´ R₂
(2)
V_IN
IN
OUT
1mF
V_OUT
1mF
TPS78101
R₁
EN
FB
GND
R₂
V_OUT
=
V_FB
´
(1
+
R₁
R₂
)
Figure 49. TPS78101 Adjustable LDO Regulator
Programming
Table 2. Output Voltage Programming Guide
OUTPUT VOLTAGE
1.8V
2.8V
5.0V
R₁
0.499MΩ
1.33MΩ
3.16MΩ
R₂
1MΩ
1MΩ
1MΩ
Copyright © 2008, Texas Instruments Incorporated
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