TPS780 datasheet(14/27 Pages) TI

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APPLICATION INFORMATION

Programming the TPS78001 Adjustable LDO

APPLICATION EXAMPLES

OUT

()

(1)

OUT

()

(2)

TPS780

GND

SET

OUT

1 F

4.2Vto5.5V

2.2Vto3.3V

Off

High=V

SET

OUT(LOW)

Low=V

SET

OUT(HIGH)

TPS78001

GND

OUT

1 F

(1+)

OUT

TPS780 Series

SBVS083C – JANUARY 2007 – REVISED MAY 2008 ....................................................................................................................................................... www.ti.com

Regulator

The TPS780 series of LDOs typically take less than

The output voltage of the TPS78001 adjustable

800

µs to transition from a lower voltage of 2.2V to a

regulator is programmed using an external resistor

higher voltage of 3.3V under an output load of

divider as shown in Figure 55. The output voltage

150mA; see Figure 51. Additionally, the TPS780

operating range is 1.2V to 5.1V, and is calculated

series

contain

active

pull-down

circuitry

that

using Equation 1:

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

Where:

undershoots are minimal under this load condition.

VFB = 1.216V typ (the internal reference voltage)

The TPS780 series typically take less than 800

µs to

transition from VSET low (3.3V to 2.2V), or VSET high

Resistors

R1 and

R2 should

chosen

for

(2.2V to 3.3V); see Figure 51 and Figure 52. Both

approximately 1.2

µA divider current. Lower value

output

states

the

TPS780

series

are

resistors

can

used

for

improved

noise

factory-programmable between 1.5V to 4.2V. Note

performance, but the solution consumes more power.

that during startup or steady-state conditions, it is

Higher resistor values should be avoided because

important that the EN pin and VSET pin voltages never

leakage current into/out of FB across R1/R2 creates

exceed VIN + 0.3V.

an offset voltage that artificially increases/decreases

the

feedback

voltage

and

thus

erroneously

decreases/increases VOUT. Table 2 lists several

common output voltages and resistor values. The

recommended design procedure is to choose R2 =

Ω to set the divider current at 1.2

µA, and then

calculate R1 using Equation 2:

Figure 54. Typical Application Circuit

The TPS780 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

Figure 55. TPS78001 Adjustable LDO Regulator

microprocessor

transition

quickly

into

Programming

operational state (wake up) without requiring a reload

of the states from external memory, or a reboot.

Table 2. Output Voltage Programming Guide

OUTPUT VOLTAGE

1.8V

0.499M

Ω

2.8V

1.33M

Ω

5.0V

3.16M

Ω

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