Datasheet
®
9
ADS7845
single-ended mode, the converter’s reference voltage is
always the difference between the V
REF
and GND pins. In
differential mode, the reference voltage is the difference
between the currently enabled switches. See Tables I and II
and Figures 2 through 4 for more information. The last two
bits (PD1 - PD0) select the power- down mode as shown in
Table V. If both inputs are HIGH, the device is always
powered up. If both inputs are LOW, the device enters a
power-down mode between conversions. When a new con-
version is initiated, the device will resume normal operation
instantly—no delay is needed to allow the device to power
up and the very first conversion will be valid. There are two
power-down modes: one where PENIRQ is disabled and
one where it is enabled.
PD1 PD0 PENIRQ DESCRIPTION
0 0 Enabled Power-down between conversions. When each
conversion is finished, the converter enters a
LOW power mode. At the start of the next con-
version, the device instantly powers up to full
power. There is no need for additional delays to
assure full operation and the very first conversion
is valid. The LR– switch is on while in power-down.
0 1 Disabled Same as mode 00, except PENIRQ is disabled.
The LR– switch is off while in power-down mode.
1 0 Disabled Reserved for future use.
1 1 Disabled No power down between conversions, device is
always powered.
FIGURE 5. Conversion Timing, 24 Clocks per Conversion, 8-Bit Bus Interface. No DCLK Delay Required with Dedicated
Serial Port.
TABLE V. Power-Down Selection.
FIGURE 6. Conversion Timing, 16 Clocks per Conversion, 8-Bit Bus Interface. No DCLK Delay Required with Dedicated
Serial Port.
1
DCLK
CS
81
11
DOUT
BUSY
S
DIN
CONTROL BITS
S
CONTROL BITS
1098765 43210
11 10 9
81 18
t
ACQ
AcquireIdle Conversion Idle
1
DCLK
CS
81
11
DOUT
BUSY
DRIVERS 1 AND 2
(1)
(SER/DFR HIGH)
DRIVERS 1 AND 2
(1, 2)
(SER/DFR LOW)
(MSB)
(START)
(LSB)
A2S
ON
ON
OFF OFF
OFF OFF
DIN
A1 A0
MODE
SER/
DFR
PD1 PD0
1098765 4 3210 Zero Filled...
81 8
NOTES: (1) For Y Position, Driver 1 is ON and Driver 2 is OFF. For X Position, Driver 1 is OFF and Driver 2 is ON. LR
will turn on when power-down mode is entered and PD1, PD0 = 00
B
. (2) Drivers will remain on if power-down mode is
11
B
(no power down) until selected input channel, reference mode, or power-down mode is changed, or CS is HIGH.