Datasheet
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 (I
B
= I
C
/ 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 Submit Documentation Feedback Copyright © 1999 – 2008, Texas Instruments Incorporated