AD7937BRZ Analog Devices Inc, AD7937BRZ Datasheet - Page 4

• Manufacturer Part Number: AD7937BRZ
• Description: 12-Bit Current Output DAC +5V Supply.
• Manufacturer: Analog Devices Inc

Specifications of AD7937BRZ

• Settling Time: 1µs
• Number Of Bits: 12
• Data Interface: Parallel
• Number Of Converters: 2
• Voltage Supply Source: Single Supply
• Power Dissipation (max): 24mW
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-SOIC (7.5mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD7937
Pin
1
2
3
4
5
6–11
13, 14
12
15
16
17
18
19
20
21
22
23
24
CIRCUIT INFORMATION – D/A SECTION
The AD7937 contains two identical 12-bit multiplying D/A
converters. Each DAC consists of a highly stable R-2R ladder
and 12 N-channel current steering switches. Figure 2 shows a
simplified D/A circuit for DAC A. In the R-2R ladder, binary
weighted currents are steered between I
current flowing in each ladder leg is constant, irrespective of
switch state. The feedback resistor R
(see Figures 4 and 5) to convert the current flowing in I
a voltage output.
Mnemonic
AGNDA
I
R
V
CS
DB0–DB7
DGND
A0
A1
CLR
WR
UPD
V
V
R
I
AGNDB
OUTA
OUTB
FBA
REFA
DD
REFB
FBB
PIN FUNCTION DESCRIPTIONS
AGNDA
V
DGND
PIN CONFIGURATION
I
R
OUTA
REFA
DB0
DB1
DB2
DB3
DB4
DB5
FBA
CS
12
10
11
1
2
3
4
5
6
7
8
9
registers.
registers.
15 V, with ± 10% tolerance.
Description
Analog Ground for DAC A.
Current output terminal of DAC A.
Feedback resistor for DAC A.
Reference input to DAC A.
Chip Select Input Active low.
Eight data inputs, DB0–DB7.
Digital Ground.
Address Line 0.
Address Line 1.
Clear Input. Active low. Clears all
Write Input. Active low.
Updates DAC Registers from inputs
Power supply input. Nominally 5 V to
Reference input to DAC B.
Feedback resistor for DAC B.
Current output terminal of DAC B.
Analog Ground for DAC B.
(Not to Scale)
TOP VIEW
AD7937
SOIC
FBA
24
23
22
21
20
19
18
17
16
15
14
13
is used with an op amp
OUTA
AGNDB
I
R
V
V
UPD
WR
CLR
A1
A0
DB7
DB6
OUTB
REFB
DD
FBB
and AGNDA. The
OUTA
to
EQUIVALENT CIRCUIT ANALYSIS
Figure 3 shows the equivalent circuit for one of the D/A con-
verters (DAC A) in the AD7937. A similar equivalent circuit
can be drawn for DAC B.
C
and varies from about 50 pF to 100 pF with digital input code.
The current source I
leakages and approximately doubles every 10°C. R
lent output resistance of the device which varies with input code.
DIGITAL CIRCUIT INFORMATION
The digital inputs are designed to be both TTL and 5 V CMOS
compatible. All logic inputs are static protected MOS gates with
typical input currents of less than 1 nA.
CLR UPD CS WR A1 A0 Function
1
1
0
1
1
1
1
1
1
NOTE: X = Don’t care
OUT
is the output capacitance due to the N-channel switches
V
1
1
X
1
1
1
1
0
0
REFA
V
REFA
1
X
X
0
0
0
0
1
0
R
Table I. AD7937 Truth Table
X
1
X
0
0
0
0
0
0
2R
S11
LKG
R
D.V
X
X
X
0
0
1
1
X
X
R
is composed of surface and junction
REF
2R
S10
X
X
X
0
1
0
1
X
X
R
R
O
No Data Transfer
No Data Transfer
All Registers Cleared
DAC A LS Input Register
Loaded with DB7–DB0 (LSB)
DAC A MS Input Register
Loaded with DB3 (MSB)–DB0
DAC B LS Input Register
Loaded with DB7–DB0 (LSB)
DAC B MS Input Register
Loaded with DB3 (MSB)–DB0
DAC A, DAC B Registers
Updated Simultaneously from
Input Registers
DAC A, DAC B Registers are
Transparent
2R
S0
I
LKG
2R
R
R
C
R
I
AGNDA
OUT
OUTA
FBA
O
R
I
AGNDA
is the equiva-
OUTA
FBA