XR-4151.PDF

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XR-4151
...the analog plus company
TM
Voltage-to-Frequency
Converter
June 1997-3
FEATURES
D
Single Supply Operation (+8V to +22V)
D
Pulse Output Compatible with All Logic Forms
D
Programmable Scale Factor (K)
D
Linearity
$0.05%
Typical-precision Mode
D
Temperature Stability
$100%
ppm/°C Typical
D
High Noise Rejection
D
Inherent Monotonicity
D
Easily Transmittable Output
D
Simple Full Scale Trim
D
Single-Ended Input, Referenced to Ground
D
Also Provides Frequency-to-Voltage Conversion
D
Direct Replacement for RC/RV/RM-4151
GENERAL DESCRIPTION
The XR-4151 is a device designed to provide a simple,
low-cost method for converting a DC voltage into a
proportional pulse repetition frequency. It is also capable
of converting an input frequency into a proportional output
ORDERING INFORMATION
Part No.
XR-4151P
XR-4151CP
XR-4151MD
APPLICATIONS
D
Voltage-to-Frequency Conversion
D
A/D and D/A Conversion
D
Data Transmission
D
Frequency-to-Voltage Conversion
D
Transducer Interface
D
System Isolation
voltage. The XR-4151 is useful in a wide range of
applications including A/D and D/A conversion and data
transmission.
Package
8 Lead 300 Mil PDIP
8 Lead 300 Mil PDIP
8 Lead 4.4mm EIAJ SOP
Operating
Temperature Range
-40°C to +85°C
0°C to +70°C
0°C to +70°C
BLOCK DIAGRAM
GND
4
V
CC
SCFA
8
2
INPV
TRSH
CSO
7
6
1
RC
Comp
One Shot
Switch
3
OUTL
5
Figure 1. Block Diagram
Rev. 2.01
E1979
EXAR Corporation, 48720 Kato Road, Fremont, CA 94538
z
(510) 668-7000
z
FAX (510) 668-7017
1
XR-4151
PIN CONFIGURATION
CSO
SCFA
OUTL
GND
1
2
3
4
8
7
6
5
V
CC
INPV
TRSH
RC
CSO
SCFA
OUTL
GND
1
2
3
4
8
7
6
5
V
CC
INPV
TRSH
RC
8 Lead PDIP (0.300”)
8 Lead SOP (EIAJ, 4.4mm)
PIN DESCRIPTION
Pin #
1
2
3
4
5
6
7
8
Symbol
CSO
SCFA
OUTL
GND
RC
TRSH
INPV
V
CC
I
I
I
O
Type
O
I
O
Description
Current Source Output.
Scale Factor Input.
Logic Output.
Supply Ground.
One Shot Timing Input.
Comparator Input.
Input Voltage.
Positive Supply.
Rev. 2.01
2
XR-4151
ELECTRICAL CHARACTERISTICS
Test Conditions: V
CC
= 15V, T
A
= +25°C, Unless Otherwise Specified
Parameter
Supply Current
XR-4151MD, CP
XR-4151P
Conversion Accuracy Scale Factor
XR-4151MD, CP
XR-4151P
Drift With Temperature
Drift With V
CC
XR-4151MD, CP
XR-4151P
Input Comparator
Offset Voltage
Offset Current
Input Bias Current
Common Mode Range
1
One-Shot
Threshold Voltage, Pin 5
Input Bias Current, Pin 5
Reset V
SAT
Current Source
Output Current
Change With Voltage
Off Leakage
Reference Voltage
Logic Output
V
SAT
V
SAT
Off Leakage
0.50
0.30
1.0
0.15
0.10
0.1
V
V
µA
Pin 3, 1=3.0mA
Pin 3, 1=2.0mA
1.70
2.5
50
2.08
138.7
1.0
0.15
1.9
µA
µA
nA
V
Pin 1, V=0, RS=14.0kΩ
Pin 1, V=0V to V=10V
Pin 1, V=0V
Pin 2
0.63
0.70
-500
0.5
0.667
-100
0.15
xV
CC
nA
V
Pin 5= 2.2mA
0
10
$100
-300
V
CC
-3
5
$50
-100
0 to V
CC
-2
mV
nA
nA
V
Min.
2.0
2.0
2.0
0.90
0.92
Max.
6.0
7.5
7.4
1.10
1.08
Typ.
3.5
4.5
4.5
1.00
1.00
$100
0.2
0.2
Unit
mA
mA
mA
kHz/V
kHz/V
ppm/°C
%/V
%/V
Conditions
8V < V
CC
< 15V
15V < V
CC
< 22V
15V < V
CC
< 22V
Circuit of
Figure 2,
V
I
=10V
RS=14.0K
Circuit of
Figure 2,
V
I
=10V
Circuit of
Figure 2,
V
I
=1.0V
8V < V
CC
< 18V
-0.9
0.9
Notes
1
Input Common Mode Range includes ground.
Bold face parameters
are covered by production test and guaranteed over operating temperature range.
Specifications are subject to change without notice
Rev. 2.01
3
XR-4151
ABSOLUTE MAXIMUM RATINGS
Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22V
Output Sink Current . . . . . . . . . . . . . . . . . . . . . . . 20mA
Internal Power Dissipation . . . . . . . . . . . . . . . . 500mW
Input Voltage . . . . . . . . . . . . . . . . . . . . . . -0.2V to +V
CC
Output Short Circuit to Ground . . . . . . . . . Continuous
SYSTEM DESCRIPTION
The XR-4151 is a precision voltage-to-frequency
converter featuring 0.05% conversion linearity (precision
mode), high noise rejection, monotonicity, and single
supply operation from 8V to 22V. An RC network on Pin 5
gets the maximum full wave frequency. Input voltage on
Pin 7 is compared with the voltage on Pin 6 (which is
generally controlled by the current source output, Pin 1).
Frequency output is proportioned to the voltage on Pin 7.
The current source is controlled by the resistance on Pin 2
(nominally 14kW with I = 1.9 V/R. The output is an open
collector at Pin 3.
PRINCIPLES OF OPERATION
Single Supply Mode Voltage-to-Frequency
Converter
In this application, the XR-4151 functions as a stand
alone voltage-to-frequency converter operating on a
single positive power supply. Refer to the functional block
diagram and
Figure 2,
the circuit connection for single
supply voltage-to-frequency conversion. The XR-4151
contains a voltage comparator, a one-shot, and a
precision switched current source. The voltage
comparator compares a positive input voltage applied at
pin 7 to the voltage at pin 6. If the input voltage is higher,
the comparator will fire the one-shot. The output of the
one-shot is connected to both the logic output and the
precision switched current source. During the one-shot
period, T, the logic output will go low and the current
source will turn on with current 1. At the end of the one
shot period the logic output will go high and the current
source will shut off. At this time the current source has
injected an amount of charge Q = I
O
T into the network
R
B
-C
B
. If this charge has not increased the voltage V
B
such that V
B
> V
I
, the comparator again fires the one-shot
and the current source injects another, Q, into the R
B
-C
B
network. This process continues until V
B
> V
I
. When this
condition is achieved, the current source remains off and
the voltage V
B
decays until V
B
is again equal to V
I
. This
completes one cycle. The VFC will now run in a steady
state mode. The current source charges the capacitor C
B
at a rate such that V
B
>V
I
. Since the discharge rate of
capacitor C
B
is proportional to V
B
/R
B
, the frequency at
which the system runs will be proportional to the input
voltage.
Rev. 2.01
4
XR-4151
V
CC
0.1µF
R
S
12K
5K
Voltage
V
I
Input
0.01µF
5
R
O
V
CC
6.8K
C
O
0.01µF
C
B
1µF
R
B
100K
4
1
100K
COMP
7
6
One
Shot
SW
R
L
5.1K
3
Frequency
fo
Output
2
C
S
8
V
L
XR-4151
fo
T
f0=KV
I
, Where K=0.486
T=1.1@R
O@
C
O
R
S
R
B@
R
O@
C
O
kHz
V
Figure 2. Voltage-to-Frequency Converter
TYPICAL APPLICATIONS
Single Supply Voltage-to-Frequency Converter
Figure 2
shows the simplest type of VFC that can be
made with the XR-4151. The input voltage range is from 0
to +10V, and the output frequency is from 0 to 10kHz. The
full scale frequency can be tuned by adjusting R
S
, the
output current set resistor. This circuit has the advantage
of being simple and low in cost, but it suffers from
inaccuracy due to a number of error sources. Linearity
error is typically 1%. A frequency offset will also be
introduced by the input comparator offset voltage. Also,
response time for this circuit is limited by the passive
integration network R
B
C
B
. For the component values
shown in
Figure 2,
response time for a step change input
from 0 to +10V will be 135msec. For applications which
require fast response time and high accuracy, use the
circuit of
Figure 3.
Rev. 2.01
5

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