Datasheet

12ADS7835
®
logic.
DATA FORMAT
The ADS7835 output data is in Binary Two’s Complement
format as shown in Table III. This table shows the ideal
output code for the given input voltage and does not include
Figure 7 shows a timing diagram that might be used with a
typical digital signal processor such as a TI DSP. For the
Buffered Serial Port (BSP) on the TMS320C54X family,
CONV would tied to BFSX, CLK would be tied to BCLKX,
and DATA would be tied to BDR.
SPI/QSPI INTERFACING
Figure 8 shows the timing diagram for a typical Serial
Peripheral Interface (SPI) or Queued Serial Peripheral Inter-
face (QSPI). Such interfaces are found on a number of
microcontrollers from various manufacturers. CONV would
be tied to a general purpose I/O pin (SPI) or to a PCX pin
(QSPI), CLK would be tied to the serial clock, and DATA
would be tied to the serial input data pin such as MISO
(Master In Slave Out).
Note the time t
DRP
shown in Figure 8. This represents the
maximum amount of time between CONV going LOW and
the start of the conversion clock. Since CONV going LOW
places the S/H in the hold mode and because the hold
capacitor loses charge over time, there is a requirement that
time t
DRP
be met as well as the maximum clock period
D11
(MSB)
DATA
CLK
CONV
D10 D1
D0
(LSB)
231 4 13 14 15 16 1 2 3
D11
(MSB)
t
ACQ
t
DRP
FIGURE 8. Typical SPI/QSPI Interface Timing.
FIGURE 7. Typical DSP Interface Timing.
D11
(MSB)
DATA
CLK
CONV
D10 D1
D0
(LSB)
1215 16 3 12 13 14 15 16 1 2 3 4
D11
(MSB)
D10 D9
DESCRIPTION ANALOG INPUT DIGITAL OUTPUT
Full-Scale Input BINARY TWO’S
Range –V
REF
to +V
REF
(1)
COMPLEMENT
Least Significant Bit BINARY HEX
(LSB)
(2)
(–V
REF
to +V
REF
)/4096 CODE CODE
+Full Scale 2.49878V 0111 1111 1111 7FF
Mid-Scale 0V 0000 0000 0000 000
Mid-Scale –1LSB –0.00122V 1111 1111 1111 FFF
–Full Scale –2.49878V 1000 0000 0000 800
NOTES: (1) –2.5V to +2.5V when the internal reference is used. (2) 1.22mV
with a 2.5V reference.
TABLE III. Ideal Input Voltages and Output Codes.
the effects of offset, gain, or noise.
DSP INTERFACING