AD5429 Analog Devices, AD5429 Datasheet - Page 17

• Manufacturer Part Number: AD5429
• Description: Dual 8-Bit, High Bandwidth, Multiplying DAC with Serial Interface
• Manufacturer: Analog Devices

Specifications of AD5429

• Resolution (bits): 8bit
• Dac Update Rate: 2.47MSPS
• Dac Settling Time: 30ns
• Max Pos Supply (v): +5.5V
• Single-supply: Yes
• Dac Type: Current Out
• Dac Input Format: Ser,SPI

SINGLE-SUPPLY APPLICATIONS
Voltage-Switching Mode
Figure 40 shows the DACs operating in voltage-switching mode.
The reference voltage, V
is connected to AGND; and the output voltage is available at the
V
results in a positive output voltage, making single-supply operation
possible. The output from the DAC is voltage at a constant
impedance (the DAC ladder resistance). Therefore, an op amp
is necessary to buffer the output voltage. The reference input
no longer sees a constant input impedance; instead, it sees one
that varies with code. Therefore, the voltage input should be
driven from a low impedance source.
REF
A terminal. In this configuration, a positive reference voltage
IN
, is applied to the I
V
–5V
+
IN
5V
Figure 41. Positive Voltage Output with Minimum Components
V
OUT
ADR03
OUT
GND
NOTES
1. ADDITIONAL PINS OMITTED FOR CLARITY.
2. C1 PHASE COMPENSATION (1pF TO 2pF) MAY BE REQUIRED
–2.5V
1A pin; I
IF A1 IS A HIGH SPEED AMPLIFIER.
NOTES
1. ADDITIONAL PINS OMITTED FOR CLARITY.
2. C1 PHASE COMPENSATION (1pF TO 2pF) MAY BE REQUIRED
I
Figure 40. Single-Supply Voltage-Switching Mode
V
I
OUT
OUT
IN
IF A1 IS A HIGH SPEED AMPLIFIER.
1A
2A
R
V
FB
REF
8-/10-/12-BIT
A V
OUT
A
GND
V
V
DAC
DD
DD
8-/10-/12-BIT
DD
2A
GND
V
Rev. D | Page 17 of 28
= +5V
DD
DAC
V
REF
R
A
FB
I
I
OUT
OUT
A
1A
2A
Note that V
in the DAC ladder no longer have the same source-drain drive
voltage. As a result, their on resistance differs and degrades the
integral linearity of the DAC. Also, V
more than 0.3 V, or an internal diode turns on, causing the device
to exceed the maximum ratings. In this type of application, the
full range of multiplying capability of the DAC is lost.
Positive Output Voltage
The output voltage polarity is opposite to the V
dc reference voltages. To achieve a positive voltage output, an
applied negative reference to the input of the DAC is preferred
over the output inversion through an inverting amplifier because
of the resistor tolerance errors. To generate a negative reference,
the reference can be level-shifted by an op amp such that the V
and GND pins of the reference become the virtual ground and
−2.5 V, respectively, as shown in Figure 41.
R1
C1
R2
IN
is limited to low voltages because the switches
V
OUT
V
= 0V TO +2.5V
OUT
AD5429/AD5439/AD5449
IN
must not go negative by
REF
polarity for
OUT