EVAL-AD5429EB View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
EVAL-AD5429EB
Analog Devices
'EVAL-AD5429EB' PDF : 32 Pages View PDF
AD5429/AD5439/AD5449
BIPOLAR OPERATION
In some applications, it might be necessary to generate full
4-quadrant multiplying operation or a bipolar output swing.
This can be easily accomplished by using another external
amplifier and three external resistors, as shown in Figure 38.
When VIN is an ac signal, the circuit performs 4-quadrant
multiplication. When connected in bipolar mode, the output
voltage is
( ) VOUT = VREF × D /2n−1 − VREF
where D is the fractional representation of the digital word
loaded to the DAC, and n is the number of bits.
D = 0 to 255 (AD5429)
= 0 to 1023 (AD5439)
= 0 to 4095 (AD5449)
Table 6 shows the relationship between digital code and the
expected output voltage for bipolar operation with the AD5429.
Table 6. Bipolar Code Table
Digital Input
Analog Output (V)
1111 1111
+VREF (2047/2048)
1000 0000
0
0000 0001
−VREF (2047/2048)
0000 0000
−VREF (2048/2048)
STABILITY
In the I-to-V configuration, the IOUT of the DAC and the
inverting node of the op amp must be connected as closely as
possible, and proper PCB layout techniques must be employed.
Because every code change corresponds to a step function, gain
peaking can occur, if the op amp has limited GBP and there is
excessive parasitic capacitance at the inverting node. This
parasitic capacitance introduces a pole into the open loop
response, which can cause ringing or instability in the closed-
loop applications circuit.
As shown in Figure 37 and Figure 38, an optional compensation
capacitor, C1, can be added in parallel with RFB for stability. Too
small a value of C1 can produce ringing at the output, while too
large a value can adversely affect the settling time. C1 should be
found empirically, but 1 pF to 2 pF is generally adequate for the
compensation.
VREF ±10V
R3
20kΩ
VDD
R2
VDD
RFBA
R1
VREF
AD5429/
AD5439/
AD5449
IOUT1A
IOUT2A
SYNC SCLK SDIN GND
C1
A1
R4
10kΩ
R5
20kΩ
A2
VOUT = –VREF TO +VREF
µCONTROLLER
AGND
NOTES:
1. R1 AND R2 USED ONLY IF GAIN ADJUSTMENT IS REQUIRED.
ADJUST R1 FOR VOUT = 0V WITH CODE 10000000 LOADED TO DAC.
2. MATCHING AND TRACKING IS ESSENTIAL FOR RESISTOR PAIRS
R3 AND R4.
3. C1 PHASE COMPENSATION (1pF TO 2pF) MAY BE REQUIRED,
IF A1/A2 IS A HIGH SPEED AMPLIFIER.
4. DAC B AND ADDITIONAL PINS OMITTED FOR CLARITY.
Figure 38. Bipolar Operation
Rev. 0 | Page 16 of 32
Share Link: 