
AD5570
Asynchronous LDAC:
In this mode, LDAC is high while data is
being clocked in. The DAC output is updated by taking LDAC
low any time after SYNC has been taken high. The update now
occurs on the falling edge of LDAC.
Rev. 0 | Page 17 of 24
Figure 36 shows a simplified block diagram of the input loading
circuitry.
V
OUT
DAC
REGISTER
INPUT SHIFT
REGISTER
OUTPUT
I/V AMPLIFIER
LDAC
SDO
SDIN
16-BIT
DAC
V
REFIN
SYNC
0
Figure 36. Simplified Serial Interface Showing Input Loading Circuitry
TRANSFER FUNCTION
Table 6 shows the ideal input code to output voltage relationship
for the AD5570.
Table 6. Binary Code Table
Digital Input
MSB
LSB
1111
1111
1111
1111
1000
0000
0000
0001
1000
0000
0000
0000
0111
1111
1111
1111
0000
0000
0000
0000
Analog Output
V
OUT
+2 V
REF
× (32,767/32,768)
+2 V
REF
× (1/32,768)
0 V
2 V
REF
× (1/32,768)
2 V
REF
The output voltage expression is given by
]
65536
/
[
4
2
D
V
V
V
REFIN
REFIN
OUT
×
+
=
where:
D
is the decimal equivalent of the code loaded to the DAC.
V
REFIN
is the reference voltage available at the REFIN pin.
CLEAR (CLR)
CLR is an active low digital input that allows the output to be
cleared to 0 V. When the CLR signal is brought back high, the
output stays at 0 V until LDAC is brought low. The relationship
between LDAC and CLR is explained further in Table 7.
Table 7. Relationships among PD, CLR, and LDAC
PD
CLR
LDAC
Comments
0
x
x
PD has priority over LDAC and CLR. The
output remains at 0 V through an internal
20 k resistor. It is still possible to address
both the input register and DAC register
when the AD5570 is in power-down.
1
0
0
Data is written to the input register and
DAC register. CLR has higher priority over
LDAC; therefore, the output is at 0 V.
1
0
1
Data is written to the input register only.
The output is at 0 V and remains at 0 V,
when CLR is taken back high.
1
1
0
Data is written to the input register and
the DAC register. The output is driven to
the DAC level.
1
1
1
Data is written to the input register only.
The output of the DAC register is
unchanged.
POWER-DOWN (PD)
The power-down pin allows the user to place the AD5570 into a
power-down mode. When in this mode, power consumption is
at a minimum; the device consumes only 16 μA typically.
POWER-ON RESET
The AD5570 contains a power-on reset circuit that controls the
output during power-up and power-down. This is useful in
applications where the known state of the output of the DAC
during power-up is important. On power-up and power-down,
the output of the DAC, V
OUT
, is held at AGND.