Applications information – Rainbow Electronics MAX5811 User Manual
Page 11
MAX5811
10-Bit Low Power 2-Wire Interface Serial,
Voltage-Output DAC
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11
data flow reverses following the address acknowledge
by the MAX5811. The device transmits the first byte of
data, waits for the master to acknowledge, then trans-
mits the second byte. Figure 7 shows an example read
data sequence.
I
2
C Compatibility
The MAX5811 is compatible with existing I
2
C systems.
SCL and SDA are high-impedance inputs; SDA has an
open drain that pulls the data line low during the ninth
clock pulse. The Typical Operating Circuit shows a typ-
ical I
2
C application. The communication protocol sup-
ports the standard I
2
C 8-bit communications. The
general call address is ignored. The MAX5811 address
is compatible with the 7-bit I
2
C addressing protocol
only. No 10-bit address formats are supported.
Digital Feedthrough Suppression
When the MAX5811 detects an address mismatch, the
serial interface disconnects the SCL signal from the
core circuitry. This minimizes digital feedthrough
caused by the SCL signal on a static output. The serial
interface reconnects the SCL signal once a valid
START condition is detected.
Applications Information
Powering the Device from an
External Reference
The MAX5811 uses the V
DD
as the DAC voltage refer-
ence. Any power-supply noise is directly coupled to the
device output. The circuit in Figure 8 uses a precision
voltage reference to power the MAX5811, isolating the
device from any power-supply noise. Powering the
MAX5811 in such a manner greatly improves overall
performance, especially in noisy systems. The
MAX6030 (3V, 75ppm/°C) or the MAX6050 (5V,
75ppm/°C) precision voltage references are ideal
choices due to the low power requirements of the
MAX5811.
Digital Inputs and Interface Logic
The MAX5811 2-wire digital interface is I
2
C and SMBus
compatible. The two digital inputs (SCL and SDA) load
the digital input serially into the DAC. Schmitt-trigger
buffered inputs allow slow-transition interfaces such as
S
A6
A5
A4
A3
A2
A1
A0
C3
C2
X
X
X
X
X
X
Sr
A6
A5
A4
A3
A2
A1
A0
MSB
LSB
MSB
LSB
LSB
MSB
ACK
ACK
ACK
D5
D4
D3
D2
D1
D0
X
X
MSB
LSB
ACK
ACK
P
R/W
= 1
X
X
PD1
PD0
D9
D8
D7
D6
MSB
LSB
DATA BYTES GENERATED BY MASTER DEVICE
DATA BYTES GENERATED BY MAX5811
ACK GENERATED BY
MASTER DEVICE
R/W
= 0
Figure 7. Read Word Data Sequence
V
DD
IN
GND
GND
OUT
OUT
MAX5811
MAX6030/
MAX6050
Figure 8. Powering the MAX5811 from an External Reference