TPS767D3xx
SLVS209H–JULY 1999–REVISED AUGUST 2008......................................................................................................................................................... www.ti.com
APPLICATION INFORMATION
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.
U1
R1
R2
TPS767D325
100kW
100kW
PG
1RESET
NC
1
28
27
26
25
24
23
22
21
20
19
18
17
16
NC
NC
NC
2
RESET to DSP
1GND
3
4
1FB/NC
1OUT
1OUT
1EN
1IN
5
5V
DSP
1IN
6
2.5V
VCORE
C0
2RESET
NC
NC
7
1mF
NC
8
NC
NC
2GND
9
10
11
12
13
2EN
2IN
2IN
NC
2OUT
2OUT
NC
C
+
3
33mF
NC
NC
14
15
3.3V
VI/O
C1
C2
1mF
33mF
GND
GND
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.
DEVICE OPERATION
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 IB 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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