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PDF SP7514BN Data sheet ( Hoja de datos )
| Número de pieza | SP7514BN | |
| Descripción | 14-Bit Multiplying DACs | |
| Fabricantes | Sipex | |
| Logotipo |  |
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®
s Monolithic Construction
s 14–Bit Resolution
s 0.003% Non-Linearity
s Four-Quadrant Multiplication
s Latch-up Protected
s Low Power - 30mW
s Single +15V Power Supply
HS3140/SP7514
14-Bit Multiplying DACs
DESCRIPTION…
The SP7514 and HS3140 are precision 14-bit multiplying DACs, that provide four-quadrant
multiplication. Both parts accept both AC and DC reference voltages. The SP7514 is available
for use in commercial and industrial temperature ranges, packaged in a 20-pin SOIC. The
HS3140 is available in commercial and military temperature ranges, packaged in a 20-pin
side-brazed DIP.
VREF 19
15 EQUAL
SECTIONS
96k 96k
GND
VDD
3
18
4 to 16 DECODE
45 67
BIT 1 BIT 2 BIT 3 BIT 4
(MSB)
SP7514S,PH7S5311440
48k
96k 96k
2
I OUT2
17
BIT 14
LSB
6k
20
R FEEDBACK
1 I OUT1
SWITCHES ARE
SHOWN IN THE
HIGH STATE
HS3140/SP7514
HS3140/SP7514 14-Bit Multiplying DACs
1
© Copyright 2000 Sipex Corporation
1 page  
2 - 1(MSB)
0
0
1
1
2 -2
0
1
0
1
Output
0
1/4 Full-Scale
1/2 Full-Scale
3/4 Full-Scale
Table 1. Contribution of the two MSB's
400Ω
V REF
470Ω
V DD
DIGITAL
INPUTS
SP7514
HS3140
RFEEDBACK
I O1
I O2
200Ω
ROS
-
A
+
V OUT
accuracy required of any switch for a given overall
converter accuracy.
With the decoded converter described above, a 1%
change in any of the converter’s switches will affect
the output by no more than 0.25% of full-scale as
compared to 0.5% for a conventional converter. In
other words the conventional D/A converter can be
made less sensitive to the quality of its individual bits
by decoding.
In the SP7514/HS3140 the first four MSB’s are
decodedinto16levelswhichdrive15equallyweighted
current sources. The sensitivity of each switch on the
output is reduced by a factor of 8. Each of the 15
sources contributes 6.25% output change rather than
an MSB change of 50% for the common approach.
Following the decoded section of the DAC a standard
binary weighted R-2R approach is used. This divides
each of the 16 levels (or 6.25% of F.S.) into 4096
discrete levels (the 12 LSB’s).
Output Capacitance
The SP7514/HS3140 have very low output capaci-
tance(CO).ThisisspecifiedbothwithallswitchesON
and all switches OFF. Output capacitance varies from
50pF to 100pF over all input codes. This low capaci-
tance is due in part to the decoding technique used.
Smaller switches are used with resulting less capaci-
tance. Three important system characteristics are
affected by CO and ∆CO; namely digital feedthrough,
TRANSFER FUNCTION (N=14)
BINARY INPUT UNIPOLAR OUTPUT BIPOLAR OUTPUT
111...111
100...001
100...000
011...111
000…001
000...000
–VREF (1 - 2–N)
–VREF (1/2 + 2–N)
–VREF /2
–VREF (1/2 – 2–N)
–VREF (2(N – 1))
0
–VREF (1 – 2 –(N – 1))
–VREF (2 –(N – 1))
0
VREF (2 )–(N – 1)
VREF (1 – 2 –(N – 1))
VREF
Table 2. Transfer Function
GND
Figure 2. Unipolar Operation
settlingtime,andbandwidth.TheDACoutputequiva-
lent circuit can be represented as shown in Figure 1.
Digital feedthrough is the change in analog output due
to the toggling conditions on the converter input data
lines when the analog input VREF is at 0V. The
SP7514/HS3140 very low CO and therefore will yield
low digital feedthrough. Inputs to the DAC can be
buffered.Thisinputlatchwithmicroprocessorcontrol
is shown in Figure 4.
SettlingtimeisdirectlyaffectedbyCO.InFigure1,CO
combines with Rf to add a pole to the open loop
response, reducing bandwidth and causing excessive
phase shift - which could result in ringing and/or
oscillation. A feedback capacitor, Cf must be added to
restore stability. Even with Cf, there is still a zero-pole
mismatch due to RiCO which is code dependent. This
code dependent mismatch is minimized when CORi =
RfCf. However Cf must now be made larger to
compensate for worst case ∆RiCO - resulting in re-
ducedbandwidthandincreasedsettlingtime.Withthe
SP7514/HS3140, small values for Cf must be used.
400Ω
V REF
470Ω
V DD
200Ω
R FEEDBACK
I O1
DIGITAL
INPUTS
SP7514
HS3140
4KΩ
4KΩ
IO2
GND
ROS2 R
R OS2
-
A2
+
R OS1
-
A1
+ VOUT
V OUT1
A1, A2 , OP-07
Figure 3. Bipolar Operation
HS3140/SP7514
HS3140/SP7514 14-Bit Multiplying DACs
5
© Copyright 2000 Sipex Corporation
5 Page | ||
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