AD7945BRS Analog Devices Inc, AD7945BRS Datasheet - Page 14

• Manufacturer Part Number: AD7945BRS
• Description: IC DAC 12BIT MULTIPLYING 20SSOP
• Manufacturer: Analog Devices Inc

Specifications of AD7945BRS

• Mounting Type: Surface Mount
• Package / Case: 20-SSOP
• Rohs Status: RoHS non-compliant
• Settling Time: 600ns
• Number Of Bits: 12
• Data Interface: Parallel
• Number Of Converters: 1
• Voltage Supply Source: Single Supply
• Power Dissipation (max): 25µW
• Operating Temperature: -40°C ~ 85°C
• No. Of Pins: 20
• Peak Reflow Compatible (260 C): No
• No. Of Bits: 12 Bit
• Leaded Process Compatible: No
• Interface Type: Parallel
• Number Of Channels: 1
• Resolution: 12b
• Single Supply Voltage (typ): 5V
• Dual Supply Voltage (typ): Not RequiredV
• Architecture: R-2R
• Power Supply Requirement: Single
• Output Type: Current
• Integral Nonlinearity Error: ±0.5LSB
• Single Supply Voltage (min): 4.5V
• Single Supply Voltage (max): 5.5V
• Dual Supply Voltage (min): Not RequiredV
• Dual Supply Voltage (max): Not RequiredV
• Operating Temp Range: -40C to 85C
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 20
• Package Type: SSOP
• Lead Free Status / Rohs Status: Not Compliant

AD7943/AD7945/AD7948
BIPOLAR OPERATION
(Four-Quadrant Multiplication)
Figure 15 shows the standard connection diagram for bipolar
operation of the AD7943, AD7945 and AD7948. The coding is
offset binary as shown in Table IV. When V
the circuit performs four-quadrant multiplication. Resistors R1
and R2 are for gain error adjustment and are not needed in
many applications where the device gain error specifications are
adequate. To maintain the gain error specifications, resistors
R3, R4 and R5 should be ratio matched to 0.01%.
Suitable dual amplifiers for use with Figure 15 are the OP270
(low noise, low bandwidth, 15 kHz), the AD712 (medium
bandwidth, 200 kHz) or the AD827 (wide bandwidth, 1 MHz).
Table Digital Input
MSB
1111 1111 1111
1000 0000 0001
1000 0000 0000
0111 1111 1111
0000 0000 0001
0000 0000 0000
NOTE
Nominal LSB size for the circuit of Figure 15 is given by: V
V
IN
R1 20
Figure 15. Bipolar Operation (Four-Quadrant
Multiplication)
V
REF
NOTES
1. ONLY ONE DAC IS SHOWN FOR CLAIRITY.
2. DIGITAL INPUT CONNECTIONS ARE OMITTED.
3. C1 PHASE COMPENSATION (5 – 15pF) MAY BE REQUIRED
WHEN USING HIGH SPEED AMPLIFIER, A1.
LSB
Table IV. Bipolar (Offset Binary) Code
AD7943/45/48
DAC
RFB
R2 10
AGND
I
I
OUT1
OUT2
Analog Output
(V
+V
+V
+V
–V
–V
–V
OUT
REF
REF
REF
REF
REF
REF
SIGNAL GROUND
C1
(1/2048)
(2047/2048)
(2048/2048) = –V
as Shown in Figure 15)
(2047/2048)
(1/2048)
(0/2048) = 0
R4 20k
A1
IN
10k
R3
is an ac signal,
REF
(1/2048).
20k
R5
A2
REF
V
OUT
–14–
SINGLE SUPPLY APPLICATIONS
The “-B” versions of the devices are specified and tested for
single supply applications. Figure 16 shows the recommended
circuit for operation with a single +5 V to +3.3 V supply. The
I
applied to the V
0s loaded to the DAC) to 2.46 V (all 1s loaded). With 2.45 V
applied to the V
0s loaded) to 0.01 V (all 1s loaded). It is important when con-
sidering INL in a single-supply system to realize that most
single-supply amplifiers cannot sink current and maintain zero
volts at the output. In Figure 16, with V
quired sink current is 200 A. The minimum output voltage
level is 10 mV. Op amps like the OP295 are capable of main-
taining this level while sinking 200 A.
Figure 16 shows the I
by an amplifier. This is to maintain the bias voltage at 1.23 V
as the impedance seen looking into the I
This impedance is code dependent and varies from infinity (all
0s loaded in the DAC) to about 6 k minimum. The AD589
has a typical output resistance of 0.6
drive the terminals directly. However, this will cause a typical
linearity degradation of 0.2 LSBs. If this is unacceptable then
the buffer amplifier is necessary. Figure 9 shows the typical
linearity performance of the AD7943/AD7945/AD7948 when
used as in Figure 16 with V
OUT2
and AGND terminals are biased to 1.23 V. Thus, with 0 V
V
IN
V
REF
Figure 16. Single Supply System
REF
REF
V
DD
terminal, the output will go from 1.23 V (all
terminal, the output will go from 1.23 V (all
AD7943/45/48
AD589
5.6k
OUT2
DGND
+3.3V
DAC
RFB
+5V
and AGND terminals being driven
DD
SIGNAL GROUND
set at +3.3 V and V
A1
AGND
I
I
OUT1
OUT2
and it can be used to
REF
OUT2
C1
= 2.45 V the re-
A1
terminal changes.
A1: OP295
AD822
OP283
REF
V
= 0 V.
OUT
REV. B