Datasheet

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POWER-DOWN MODES
V
OUT
Amplifier
Resistor
String
DAC
Power-Down
Circuitry
Resistor
Network
V
FB
DAC8551
SLAS429B – APRIL 2005 – REVISED OCTOBER 2006
power-down mode. There are three different options.
The output is connected internally to GND through a
The DAC8551 supports four separate modes of
1k Ω resistor, a 100k Ω resistor, or it is left
operation. These modes are programmable by
open-circuited (High-Z). The output stage is
setting two bits (PD1 and PD0) in the control
illustrated in Figure 49 .
register. Table 1 shows how the state of the bits
corresponds to the mode of operation of the device.
Table 1. Operating Modes
PD1 PD0
(DB17) (DB16) OPERATING MODE
0 0 Normal operation
– – Power-down modes
0 1 Output typically 1k Ω to GND
1 0 Output typically 100k Ω to GND
1 1 High-Z
When both bits are set to '0', the device works
Figure 49. Output Stage During Power-Down
normally with its typical current consumption of
200 µ A at 5V. However, for the three power-down
All analog circuitry is shut down when the
modes, the supply current falls to 200nA at 5V (50nA
power-down mode is activated. However, the
at 3V). Not only does the supply current fall, but the
contents of the DAC register are unaffected when in
output stage is also internally switched from the
power-down. The time to exit power-down is typically
output of the amplifier to a resistor network of known
2.5 µ s for V
DD
= 5V, and 5 µ s for V
DD
= 3V. See the
values. This configuration has the advantage that the
Typical Characteristics for more information.
output impedance of the device is known while it is in
17
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