AD7243 Analog Devices, AD7243 Datasheet - Page 6

• Manufacturer Part Number: AD7243
• Description: LC2MOS 12-Bit Serial DACPORT
• Manufacturer: Analog Devices

AD7243
0 V, to allow full sink capability of 2.5 mA over the entire
output range and to eliminate the effects of negative offsets on
the transfer characteristic (outlined previously). A plot of the
output sink capability of the amplifier is shown in Figure 5.
DIGITAL INTERFACE
The AD7243 contains an input serial to parallel shift register
and a DAC latch. A simplified diagram of the input loading
SCLK
SYNC
LDAC
SDIN
CLR
3
2
0
*
1
= DON'T CARE
0
V
DCEN
SYNC
LDAC
SCLK
SDIN
SS
CLR
= –15V
2
OUTPUT VOLTAGE – Volts
4
t
2
DB15
V
SS
= 0V
*
RESET
6
DB14
COUNTER/
DECODER
÷
*
16
AUTO – UPDATE
CIRCUITRY
8
EN
DB13
t
1
*
10
GATING
SIGNAL
DB12
*
GATED
SCLK
circuitry is shown in Figure 6. Serial data on the SDIN input is
loaded to the input register under control of DCEN, SYNC and
SCLK. When a complete word is held in the shift register, it
may then be loaded into the DAC latch under control of
LDAC. Only the data in the DAC latch determines the analog
output on the AD7243.
The DCEN (daisy-chain enable) input is used to select either a
standalone mode or a daisy-chain mode. The loading format is
slightly different depending on which mode is selected.
Serial Data Loading Format (Standalone Mode)
With DCEN at Logic 0 the standalone mode is selected. In this
mode a low SYNC input provides the frame synchronization
signal which tells the AD7243 that valid serial data on the SDIN
input will be available for the next 16 falling edges of SCLK. An
internal counter/decoder circuit provides a low gating signal so
that only 16 data bits are clocked into the input shift register.
After 16 SCLK pulses the internal gating signal goes inactive
(high) thus locking out any further clock pulses. Therefore, ei-
ther a continuous clock or a burst clock source may be used to
clock in the data.
The SYNC input should be taken high after the complete 16-bit
word is loaded in.
t
4
DB11
MSB
t
5
INPUT SHIFT REGISTER (16 BITS)
DAC LATCH (12 BITS)
DB0
LSB
t
3
t
6
t
7
SDO
t
8
t
9