APPLICATION INFORMATION

NC

NC

1GND

1IN

1IN

NC

NC

2GND

2IN

2IN

NC

NC

NC

NC

1FB/NC

1OUT

1OUT

NC

NC

NC

2OUT

2OUT

NC

NC

1

2

3

4

5

6

7

8

9

10

11

12

13

14

28

27

26

25

24

23

22

21

20

19

18

17

16

15

1EN

2EN

2RESET

1RESET

U1

TPS767D325

+

V

I/O

V

CORE

GND

2.5V

3.3V

C

33 F

3

m

C

33 F

2

m

C

1 F

1

m

C

1 F

0

m

5V

GND

R

100k

1

W

R

100k

2

W

PG

RESET toDSP

DSP

DEVICE OPERATION

TPS767D3xx

SLVS209H – JULY 1999 – REVISED AUGUST 2008......................................................................................................................................................... www.ti.com

The features of the TPS767D3xx family (low-dropout voltage, ultra low quiescent current, power-saving shutdown

mode, and a supply-voltage supervisor) and the power-dissipation properties of the TSSOP PowerPAD package

have enabled the integration of the dual LDO regulator with high output current for use in DSP and other multiple

voltage applications. Figure 25 shows a typical dual-voltage DSP application.

Figure 25. Dual-Voltage DSP Application

DSP power requirements include very high transient currents that must be considered in the initial design. This

design uses higher-valued output capacitors to handle the large transient currents.

The TPS767D3xx features very low quiescent current, which remain virtually constant even with varying loads.

Conventional LDO regulators use a pnp pass element, the base current of which is directly proportional to the

load current through the regulator (IB = IC/β). Close examination of the data sheets reveals that these devices are

typically specified under near no-load conditions; actual operating currents are much higher as evidenced by

typical quiescent current versus load current curves. The TPS767D3xx uses a PMOS transistor to pass current;

because the gate of the PMOS is voltage driven, operating current is low and invariable over the full load range.

The TPS767D3xx specifications reflect actual performance under load condition.

Another pitfall associated with the pnp pass element is its tendency to saturate when the device goes into

dropout. The resulting drop in

β forces an increase in I

B to maintain the load. During power-up, this translates to

large start-up currents. Systems with limited supply current may fail to start up. In battery-powered systems, it

means rapid battery discharge when the voltage decays below the minimum required for regulation. The

TPS767D3xx quiescent current remains low even when the regulator drops out, eliminating both problems.

10

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