LTC1594_1 Datasheet, PDF (11/24 Pages) Linear Technology – 4- and 8-Channel, Micropower Sampling 12-Bit Serial I/O A/D Converters

APPLICATIONS INFORMATION
t_CYC
CSMUX = CSADC = CS
CLK
t_suCS
LTC1594/LTC1598
D_IN
D_OUT
CH0 TO
CH7
ADCIN =
MUXOUT
COM = GND
EN
D1
D2
D0
Hi-Z
NULL
BIT
t_OFF
D0N‘T CARE
DUMMY CONVERSION
t_CONV
Figure 2. LTC1594/LTC1598 Operating Sequence Example: All Channels Off
Hi-Z
1594/98 F02
Data Transfer
The CLK synchronizes the data transfer with each bit
being transmitted on the falling CLK edge and captured
on the rising CLK edge in both transmitting and receiving
systems.
The LTC1594/LTC1598 first receive input data and then
transmit back the A/D conversion results (half duplex).
Because of the half duplex operation, D_IN and D_OUT may
be tied together allowing transmission over just 3 wires:
CS, CLK and DATA (D_IN/D_OUT).
Data transfer is initiated by a rising chip select (CS)
signal. After CS rises the input data on the D_IN pin is
latched into a 4-bit register on the rising edge of the clock.
More than four input bits can be sent to the D_IN pin
without problems, but only the last four bits clocked in
before CS falls will be stored into the 4-bit register. This
4-bit input data word will select the channel in the
multiplexer (see Input Data Word and Tables 1 and 2). To
ensure correct operation the CS must be pulled low
before the next rising edge of the clock.
Once the CS is pulled low, all channels are simulta-
neously switched off after a delay of t_OFF to ensure a
break-before-make interval, t_OPEN. After a delay of t_ON
(t_OFF + t_OPEN), the selected channel is switched on,
allowing the ADC in the chip to acquire input signal and
start the conversion (see Figures 1 and 2). After 1 null bit,
the result of the conversion is output on the D_OUT line.
The selected channel remains on, until the next falling
edge of CS. At the end of the data exchange CS should be
brought high. This resets the LTC1594/LTC1598 and
initiates the next data exchange.
CS
SHIFT MUX
ADDRESS IN
D_IN1
D_OUT1
t_SMPL + 1 NULL BIT
D_IN2
D_OUT2
SHIFT A/D CONVERSION
RESULT OUT
1594/98 AI01
Break-Before-Make
The LTC1594/LTC1598 provide a break-before-make
interval from switching off all the channels simulta-
neously to switching on the next selected channel once
CS is pulled low. In other words, once CS is pulled low,
15948fb
11