dac-1508a Analog Devices, Inc., dac-1508a Datasheet - Page 5

• Manufacturer Part Number: dac-1508a
• Description: 8-bit Multiplying D/a Converters
• Manufacturer: Analog Devices, Inc.

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TRANSIENT RESPONSE AND SETTLING
TIME TEST CIRCUIT
USE
GENERAL
The reference amplifier provides a voltage at Pin 14 for
converting the reference voltage to a current. and a turn-
around
REFERENCE A MPLIFIERDRIVEAND COMPENSATION
reference amplifier input current, 114, m ust always flow into
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A2
A3
A4
AS
A7
A8
WITH CURRENT -TO-VOLTAGE CONVERTING OP AMP
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circuit or current mirror for feeding the ladder. The
THEORETICALVo
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ADJUST VREF R15 OR RO SO THAT Vo WITH ALL DIGITAL
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INPUTS AT HIGH LEVEL IS EQUAL TO 9.961 VOLTS.
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91 DAC-1408A
EO FOR SETTLING
(ALL BITS SWITCHED LOW TO HIGH)
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INFORMATION
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TIME MEASUREMENT
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16
AND APPLICATION NOTES
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R15
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DAC-1508A11408A 8-BIT MULTIPLYING DIA CONVERTERS
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11-119
A negative reference voltage may be used if R14 is grounded
and the reference voltage is applied to R15 as shown. A high
the values of the previous paragraph. The negative reference
voltage must be at least 4.0V above the VEE supply. Bipolar
full current 114.For bipolar reference signals, as in the
corresponding to the minimum input level. It is possible to
eliminate R15 with only a small sacrifice in accuracy and
temperature drift.
The compensation capacitor value must be increased with
values of 1.0, 2.5 and 5.0kn, minimum capacitor values are 15.
37, and 75pF. The capacitor may be tied to either VEEor
ground, but using VEEincreases negative supply rejection.
input impedance is the main advantage of this method.
Compensation involves a capacitor to VEEon Pin 16, using
input signals may be handled by connecting R14to a positive
reference voltage equal to the peak positive input level at
Pin 15.
When a DC reference voltage is used. capacitive bypass to
ground is recommended as a reference voltage. If a well
+ 5.0Vthrough another resistor and bypassing the junction of
the two resistors with 0.1~F to ground. For reference voltages
greater than 5.0Y. a clamp diode is recommended between
Pin 14 regardless of the setup method or reference voltage
polarity. Connections for a positive voltage are shown on the
preceding page. The reference voltage source supplies the
multiplying mode, R15 can be tied to a negative voltage
increases in R14 to maintain proper phase margin; for R14
regulated 5.0Vsupply, which drives logic is to be used as the
reference, R14 should be decoupled by connecting it to
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,
decreasing the overall bandwidth.
OUTPUT
The voltage on Pin 4 is restricted to a range of -0.6V to +0.5V
when VEE
employed in the DAC-1508A-8.
The negative output voltage compliance of the DAC-1508A-8
is extended to -5.0V where the negative supply voltage is
more negative than -10V. Using a full-scale current of
will yield a voltage output of 256 levels between 0 and
-4.980V. The value of the load resistor determines the
switching time due to increased voltage swing. Values of RL
2.5kn load increases "worst case" settling time to 1.2~s
section of Settling Time for more details on output loading.
The output current maximum rating of 4.2mA may be used
1.992mAand load resistor of 2.5kn between Pin 4 and ground
up to 500n do not significantly affect performance but a
(when all bits are switched on). Refer to the subsequent text
OUTPUT CURRENT RANGE
only for negative supply voltages more negative than -7.0V,
due to the increased voltage drop across the resistors in the
reference current amplifier.
VOLTAGERANGE
=
-5V due to the current switching methods
8/87, Rev. A1
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