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PDF ( 数据手册 , 数据表 ) DAC0808LCN

零件编号 DAC0808LCN
描述 8-Bit D/A Converter
制造商 National Semiconductor
LOGO National Semiconductor LOGO 


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DAC0808LCN 数据手册, 描述, 功能
January 1995
DAC0808 DAC0807 DAC0806 8-Bit D A Converters
General Description
The DAC0808 series is an 8-bit monolithic digital-to-analog
converter (DAC) featuring a full scale output current settling
time of 150 ns while dissipating only 33 mW with g5V sup-
plies No reference current (IREF) trimming is required for
most applications since the full scale output current is typi-
cally g1 LSB of 255 IREF 256 Relative accuracies of bet-
ter than g0 19% assure 8-bit monotonicity and linearity
while zero level output current of less than 4 mA provides
8-bit zero accuracy for IREFt2 mA The power supply cur-
rents of the DAC0808 series are independent of bit codes
and exhibits essentially constant device characteristics over
the entire supply voltage range
The DAC0808 will interface directly with popular TTL DTL
or CMOS logic levels and is a direct replacement for the
MC1508 MC1408 For higher speed applications see
DAC0800 data sheet
Features
Y Relative accuracy g0 19% error maximum (DAC0808)
Y Full scale current match g1 LSB typ
Y 7 and 6-bit accuracy available (DAC0807 DAC0806)
Y Fast settling time 150 ns typ
Y Noninverting digital inputs are TTL and CMOS compati-
ble
Y High speed multiplying input slew rate 8 mA ms
Y Power supply voltage range g4 5V to g18V
Y Low power consumption 33 mW g5V
Block and Connection Diagrams
Dual-In-Line Package
Order Number
DAC0808 DAC0807
or DAC0806
See NS Package
Number J16A
M16A or N16A
TL H 5687 – 1
Small-Outline Package
TL H 5687 – 2
Ordering Information
Top View
TL H 5687 – 13
ACCURACY OPERATING TEMPERATURE
RANGE
J PACKAGE (J16A)
ORDER NUMBERS
N PACKAGE (N16A)
SO PACKAGE (M16A)
DAC0808LCN MC1408P8
7-bit
6-bit
0 CsTAsa75 C
0 CsTAsa75 C
DAC0807LCJ MC1408L7 DAC0807LCN MC1408P7
DAC0806LCJ MC1408L6 DAC0806LCN MC1408P6
Note Devices may be ordered by using either order number
DAC0808LCM
DAC0807LCM
DAC0806LCM
C1995 National Semiconductor Corporation TL H 5687
RRD-B30M115 Printed in U S A







DAC0808LCN pdf, 数据表
Application Hints (Continued)
A negative reference voltage may be used if R14 is ground-
ed and the reference voltage is applied to R15 as shown in
Figure 8 A high input impedance is the main advantage of
this method Compensation involves a capacitor to VEE on
pin 16 using the values of the previous paragraph The neg-
ative reference voltage must be at least 4V above the VEE
supply Bipolar input signals may be handled by connecting
R14 to a positive reference voltage equal to the peak posi-
tive input level at pin 15
When a DC reference voltage is used capacitive bypass to
ground is recommended The 5V logic supply is not recom-
mended as a reference voltage If a well regulated 5V sup-
ply which drives logic is to be used as the reference R14
should be decoupled by connecting it to 5V through another
resistor and bypassing the junction of the 2 resistors with
0 1 mF to ground For reference voltages greater than 5V a
clamp diode is recommended between pin 14 and ground
If pin 14 is driven by a high impedance such as a transistor
current source none of the above compensation methods
apply and the amplifier must be heavily compensated de-
creasing the overall bandwidth
OUTPUT VOLTAGE RANGE
The voltage on pin 4 is restricted to a range of b0 55 to
0 4V when VEE e b5V due to the current switching meth-
ods employed in the DAC0808
The negative output voltage compliance of the DAC0808 is
extended to b5V where the negative supply voltage is more
negative than b10V Using a full-scale current of 1 992 mA
and load resistor of 2 5 kX between pin 4 and ground will
yield a voltage output of 256 levels between 0 and
b4 980V Floating pin 1 does not affect the converter
speed or power dissipation However the value of the load
resistor determines the switching time due to increased volt-
age swing Values of RL up to 500X do not significantly
affect performance but a 2 5 kX load increases worst-case
settling time to 1 2 ms (when all bits are switched ON) Refer
to the subsequent text section on Settling Time for more
details on output loading
OUTPUT CURRENT RANGE
The output current maximum rating of 4 2 mA may be used
only for negative supply voltages more negative than b8V
due to the increased voltage drop across the resistors in the
reference current amplifier
ACCURACY
Absolute accuracy is the measure of each output current
level with respect to its intended value and is dependent
upon relative accuracy and full-scale current drift Relative
accuracy is the measure of each output current level as a
fraction of the full-scale current The relative accuracy of the
DAC0808 is essentially constant with temperature due to
the excellent temperature tracking of the monolithic resistor
ladder The reference current may drift with temperature
causing a change in the absolute accuracy of output cur-
rent However the DAC0808 has a very low full-scale cur-
rent drift with temperature
The DAC0808 series is guaranteed accurate to within g
LSB at a full-scale output current of 1 992 mA This corre-
sponds to a reference amplifier output current drive to the
ladder network of 2 mA with the loss of 1 LSB (8 mA) which
is the ladder remainder shunted to ground The input current
to pin 14 has a guaranteed value of between 1 9 and 2 1
mA allowing some mismatch in the NPN current source
pair The accuracy test circuit is shown in Figure 4 The 12-
bit converter is calibrated for a full-scale output current of
1 992 mA This is an optional step since the DAC0808 accu-
racy is essentially the same between 1 5 and 2 5 mA Then
the DAC0808 circuits’ full-scale current is trimmed to the
same value with R14 so that a zero value appears at the
error amplifier output The counter is activated and the error
band may be displayed on an oscilloscope detected by
comparators or stored in a peak detector
Two 8-bit D-to-A converters may not be used to construct a
16-bit accuracy D-to-A converter 16-bit accuracy implies a
total error of g of one part in 65 536 or g0 00076%
which is much more accurate than the g0 019% specifica-
tion provided by the DAC0808
MULTIPLYING ACCURACY
The DAC0808 may be used in the multiplying mode with
8-bit accuracy when the reference current is varied over a
range of 256 1 If the reference current in the multiplying
mode ranges from 16 mA to 4 mA the additional error con-
tributions are less than 1 6 mA This is well within 8-bit accu-
racy when referred to full-scale
A monotonic converter is one which supplies an increase in
current for each increment in the binary word Typically the
DAC0808 is monotonic for all values of reference current
above 0 5 mA The recommended range for operation with
a DC reference current is 0 5 to 4 mA
SETTLING TIME
The worst-case switching condition occurs when all bits are
switched ON which corresponds to a low-to-high transition
for all bits This time is typically 150 ns for settling to within
g LSB for 8-bit accuracy and 100 ns to LSB for 7 and
6-bit accuracy The turn OFF is typically under 100 ns
These times apply when RL s 500X and CO s 25 pF
Extra care must be taken in board layout since this is usually
the dominant factor in satisfactory test results when mea-
suring settling time Short leads 100 mF supply bypassing
for low frequencies and minimum scope lead length are all
mandatory
8














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