AD652BQ Просмотр технического описания (PDF) - Analog Devices
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AD652BQ Datasheet PDF : 28 Pages
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AD652
+VS
20kΩ
CINT
VIN
±5V
AD652
SYNCHRONOUS
VOLTAGE-TO-
1
FREQUENCY
CONVERTER
2
3
4
5
6
20kΩ
7
1mA
8
–VS
5V
REFERENCE
16
15
14
13
ONE
12
SHOT
11
10
Q CK
9
AND D "D"
Q FLOP
ANALOG
GND
RL
5V
CLOCK
COS
DIGITAL
GND
FREQ
OUT
Figure 10. Bipolar Offset
SVFC CONNECTION FOR BIPOLAR INPUT VOLTAGES
A bipolar input voltage of ±5 V can be accommodated by
injecting a 250 µA current into Pin 5 (see Figure 10). A −5 V
signal provides a zero sum current at the integrator summing
junction, which results in a zero-output frequency; a +5 V signal
provides a 0.5 mA (full-scale) sum current, which results in the
full-scale output frequency.
Using an external resistor to inject the offset current has some
effect on the bipolar offset temperature coefficient. The ideal
transfer curve with bipolar inputs is shown in Figure 11. The
user actually has four options to use in injecting the bipolar
offset current into the inverting input of the op amp:
1. Use an external resistor for ROS and the internal 20 kΩ
resistor for RIN (as shown in Figure 10).
2. Use the internal 20 kΩ resistor as ROS and an external RIN.
3. Use two external resistors.
4. Use two internal resistors for RIN and ROS (available on
PLCC version only).
Option 4 provides the closest to the ideal transfer function as
diagrammed in Figure 11. Figure 12 shows the effects of the
transfer relation on the other three options. In the first case, the
slope of the transfer function is unchanged with temperature.
However, VZERO (the input voltage required to produce an output
frequency of 0 Hz) and FZERO (the output frequency when
VIN = 0 V) changes as the transfer function is displaced parallel
to the voltage axis with temperature. In the second case, FZERO
remains constant, but VZERO changes as the transfer function
rotates about FZERO with temperature changes. In the third case,
with two external resistors, the VZERO point remains invariant
while the slope and offset of the transfer function change with
temperature. If selecting this third option, the user should select
low drift, matched resistors.
VREF
ROS
RIN
VIN
FOUT
IDEAL
TRANSFER
RELATION
FZERO
–5V
VZERO
VIN
+5V
Figure 11. Ideal Bipolar Input Transfer Curve over Temperature
FOUT
CASE 1
RIN ∼ INTERNAL
ROS ∼ EXTERNAL
IDEAL
TEMPERATURE
PERTURBED
FZERO TRANSFER
VIN
–5V
VZERO
CASE 2
RIN ∼ EXTERNAL
ROS ∼ INTERNAL
FOUT
IDEAL
TEMPERATURE
PERTURBED
FZERO
VIN
VZERO –5V
FOUT
CASE 3
RIN ∼ EXTERNAL
ROS ∼ EXTERNAL
IDEAL
–5V VZERO
TEMPERATURE
PERTURBED
FZERO
VIN
Figure 12. Actual Bipolar Input Transfer over Temperature
Rev. C | Page 10 of 28
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