THIS DOCUMENT IS FOR MAINTENANCE
PURPOSES ONLY AND IS NOT
RECOMMENDED FOR NEW DESIGNS
MAY 1994
DS3008-2.0
ZN429E8/ZN429D
LOW COST 8-BIT D-A CONVERTER
The ZN429 is a monolithic 8-bit D-A converter
containing an R-2R ladder network of diffused resistors with
precision bipolar switches.
BIT 3
BIT 2
(MSB) BIT 1
ANALOG OUTPUT
V
REF
IN
NC
0V
1
2
3
4
5
6
7
14
13
12
ZN429E8
11
10
9
8
+V
CC
(+5V)
BIT 4
BIT 5
BIT 6
BIT 7
BIT 8 (LSB)
NC
FEATURES
s
Linearity Error
±
1
/
2
LSB
s
Single +5V Supply
s
Low Power Consumption 25mW Typical
s
Settling Time 1 Microsecond Typical
s
TTL and 5V CMOS Compatible
s
Designed for Low Cost Applications
ABSOLUTE MAXIMUM RATINGS
Supply voltage, V
CC
Max. voltage, logic and V
REF
inputs
Storage temperature range
+7.0V
+5.5V
-55
°
C to +125
°
C
DP14
NC
ANALOG OUTPUT
V
REF
IN
GROUND
BIT 8
BIT 7
GROUND
1
2
3
4
5
6
7
14
13
12
ZN429D
11
10
9
8
BIT 1
BIT 2
BIT 3
+V
CC
BIT 4
BIT 5
BIT 6
ORDERING INFORMATION
Ambient operating temperature
Package, ZN429D
Package, ZN429E8
-40
°
C to +85
°
C
MP14
DP14
MP14
Fig.1 Pin connections (not to scale) - top view
ZN429
ELECTRICAL CHARACTERISTICS
(at T
amb
= 25
°
C and V
CC
= +5V unless otherwise specified)
Parameter
Converter
Resolution
Accuracy
Non-linearity
Differential non-linearity
Settling time to 0.5LSB
Settling time to 0.5LSB
Offset voltage ZN429E8, ZN429D
V
OS
temperature coefficient
Full-scale output
Full-scale temp. coefficient
Non-linearity temp. coefficient
Analog output resistance
External reference voltage
Supply voltage
Supply current
High level input voltage
Low level input voltage
High level input current
V
CC
I
S
V
IH
V
IL
I
IH
R
O
V
OS
Symbol
Min.
Typ.
Max.
Units
Conditions
8
8
-
-
-
-
-
-
2.545
-
-
-
0
4.5
-
2.0
-
-
-
-
-
-
±
0.5
1.0
2.0
3.0
5
2.550
3
7.5
10
-
-
5
-
-
-
-
-
-
-
±
0.5
-
-
-
5.0
-
2.555
-
-
-
3.0
5.5
9
-
0.7
10
100
-0.18
bits
bits
LSB
LSB
µ
s
µ
s
mV
µ
V/
°
C
V
ppm/
°
C
ppm/
°
C
k
Ω
V
V
mA
V
V
µ
A
µ
A
mA
V
CC
= max.
V
I
= 2.4V
V
CC
= max.
V
I
= 5.5V
V
CC
= max.
V
I
= 0.3V
All bits ON
Ext. V
REF
= 2.56V
Ext. V
REF
= 2.560V
Relative to F.S.R.
Note 1
1 LSB step
All bits ON to OFF
or OFF to ON
All bits OFF
Low level input current
I
IL
-
NOTE 1: Monotonic over full temperature range.
INTRODUCTION
The ZN429 is an 8-bit D-A converter. It contains an
advanced design of R-2R ladder network and an array of
precision bipolar switches on a single monolithic chip.
The special design of the ladder network results in full
8-bit accuracy using normal diffused resistors.
The converter is of the voltage switching type and uses
an R-2R resistor ladder network as shown in Fig.3.
Each 2R element is connected either to 0V or V
REF
by
transistor switches specially designed for low offset voltage
(typically 1mV).
Binary weighted voltages are produced at the output of
the R-2R ladder, the value depending on the digital number
applied to the bit inputs.
An external fixed or varying reference is required which
should have a slope resistance less than 2
Ω
.
Suggested external reference sources are the ZN404 or
one of the ZN458 range. Each ZN404 is capable of supplying
up to five ZN429 circuits and this is increased to ten for the
ZN458 range.
ZN429
Fig.3 The R-2R ladder network
APPLICATIONS
(1) Unipolar D-A Converter
The nominal output range of the ZN429 is 0 to V
REF IN
through a 10
Ω
resistance. Other output ranges can readily
be obtained by using an external amplifier.
The resulting full-scale range is given by
V
OUT FS
=
(
1 + R1
)
V
REF IN
= G.V
REF IN
R2
The impedance at the inverting input is R1//R2 and for
low drift with temperature this parallel combination should be
equal to the ladder resistance (10k
Ω
). The required nominal
values of R1 and R2 are given by
R1 = 10Gk
Ω
and R
2
= 10G/(G-1)k
Ω
.
Using these relationships a table of nominal resistance
values for R
1
and R
2
can be constructed for V
REF IN
= 2.5V.
Output Range
+5V
+10V
G
2
4
R
1
20k
Ω
40k
Ω
R
2
20k
Ω
13.33k
Ω
For gain setting R
1
is adjusted about its nominal value.
Practical circuit realisations (including amplifier stabilising
components) for +5 and +10V output ranges are given in
Fig.5. Settling time for a major transition is 2.5
µ
s typical.
Fig.4 Unipolar operation - basic circuit
ZN429
Fig.5 Unipolar operation - component values
UNIPOLAR ADJUSTMENT PROCEDURE
(i) Set all bits to OFF (LOW) and adjust zero until V
OUT
=
0.0000V.
(ii) Set all bits ON (HIGH) and adjust gain until V
OUT
=
FS - 1LSB.
(2) Bipolar D-A Converter
For bipolar operation the output from the ZN429 is offset
by half full-scale by connecting a resistor R3 between V
REF
IN
and the inverting input of the buffer amplifier (Fig.6).
When the digital input of the ZN429 is zero the analog
output is zero and the amplifier output should be -full-scale.
An input of all ones to the D-A will give a ZN429 output of
d
V
REF IN
and the amplifier output required is +full-scale. Also,
to match the ladder resistance the parallel combination of
R
1
, R
2
and R
3
should be 10k
Ω
.
The nominal values of R
1
, R
2
and R
3
which meet these
conditions are given by
R1 = 20GkΩ, R2 = 20G/(G-1)kΩ and R3 = 20kΩ.
where the resultant output range is
±G.V
REF IN
.
Assuming that V
REF IN
= 2.5V the nominal values of
resistors for
±5
and
±10V
output ranges are given in the
following table:
Output Range
±5V
±10V
G
2
4
R
1
40kΩ
80kΩ
R
2
40kΩ
26.67kΩ
R
3
20kΩ
20kΩ
UNIPOLAR SETTING UP POINTS
Output Range, +FS
+5V
+10V
1LSB = FS
256
LSB
19.5 mV
39.1mV
FS - 1LSB
4.9805V
9.9609V
UNIPOLAR LOGIC CODING
Input Code
(Binary)
11111111
11111110
11000000
10000001
10000000
01111111
01000000
00000001
00000000
Analog Output
(Nominal Value)
FS - 1LSB
FS - 2 LSB
3
/ FS
4
1
/
2
FS + 1LSB
1
/
2
FS
1
/ FS - 1LSB
2
1
/ FS
4
1LSB
0
Minus full scale (0FFSET) is set by adjusting R1 about
its nominal value relative to R3. Plus full-scale (GAIN) is set
by adjusting R2 relative to R1.
Settling time for a major transistion is 2.5µs typical.
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