TC9402 [TELCOM]
VOLTAGE-TO-FREQUENCY/FREQUENCY-TO-VOLTAGE CONVERTERS; 电压 - 频率/频率 - 电压转换器
| 型号： | TC9402 |
| 厂家： | 
TELCOM SEMICONDUCTOR, INC |
| 描述： | VOLTAGE-TO-FREQUENCY/FREQUENCY-TO-VOLTAGE CONVERTERS |
| 文件： | 总13页 (文件大小：155K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
3
TC9400
TC9401
TC9402
VOLTAGE-TO-FREQUENCY/FREQUENCY-TO-VOLTAGECONVERTERS
FEATURES
GENERAL DESCRIPTION
Voltage-to-Frequency
The TC9400/TC9401/TC9402 are low-cost voltage-to-
frequency (V/F) converters utilizing low power CMOS
technology. The converters accept a variable analog input
signal and generate an output pulse train whose frequency
is linearly proportional to the input voltage.
The devices can also be used as highly-accurate fre-
quency-to-voltage (F/V) converters, accepting virtually any
input frequency waveform and providing a linearly-propor-
tional voltage output.
■ Choice of Guaranteed Linearity:
TC9401.........................................................0.01%
TC9400.........................................................0.05%
TC9402.........................................................0.25%
■ DC to 100 kHz (F/V) or 1Hz to 100kHz (V/F)
■ Low Power Dissipation .......................... 27mW Typ
■ Single/Dual Supply Operation .................................
+ 8V to + 15V or ± 4V to ± 7.5V
A complete V/F or F/V system only requires the addition
of two capacitors, three resistors, and reference voltage.
■ Gain Temperature Stability .......... ± 25 ppm/°C Typ
■ Programmable Scale Factor
ORDERING INFORMATION
Frequency-to-Voltage
Linearity
(V/F)
Temperature
Range
■ Operation........................................... DC to 100 kHz
■ Choice of Guaranteed Linearity:
TC9401.........................................................0.02%
TC9400.........................................................0.05%
TC9402.........................................................0.25%
■ Programmable Scale Factor
Part No.
Package
TC9400COD 0.05%
14-Pin
0°C to +70°C
SOIC (Narrow)
TC9400CPD 0.05%
14-Pin
0°C to +70°C
Plastic DIP
14-Pin
CerDIP
14-Pin
Plastic DIP
14-Pin
CerDIP
14-Pin
TC9400EJD
TC9401CPD 0.01%
TC9401EJD 0.01%
TC9402CPD 0.25%
0.05%
– 40°C to +85°C
0°C to +70°C
APPLICATIONS
■ µP Data Acquisition
■ 13-Bit Analog-to-Digital Converters
■ Analog Data Transmission and Recording
■ Phase-Locked Loops
■ Frequency Meters/Tachometer
■ Motor Control
– 40°C to +85°C
0°C to +70°C
Plastic DIP
■ FM Demodulation
TC9402EJD
0.25%
14-Pin
– 40°C to +85°C
CerDIP
FUNCTIONAL BLOCK DIAGRAM
TC9400
Integrator
Capacitor
Integrator
OpAmp
Threshold
Detector
One
Shot
RIN
Input
Voltage
IIN
Pulse Output
÷2
Pulse/2 Output
Reference
Capacitor
IREF
Reference
Voltage
TC9400/1/2-5 11/6/96
TELCOM SEMICONDUCTOR, INC.
3-287
VOLTAGE-TO-FREQUENCY/
FREQUENCY-TO-VOLTAGECONVERTERS
TC9400
TC9401
TC9402
*Static-sensitive device. Unused devices must be stored in conductive
material. Protect devices from static discharge and static fields. Stresses
above those listed under Absolute Maximum Ratings may cause perma-
nent damage to the device. These are stress ratings only and functional
operation of the device at these or any other conditions above those
indicated in the operational sections of the specifications is not implied.
Exposure to Absolute Maximum Rating Conditions for extended periods
may affect device reliability.
ABSOLUTE MAXIMUM RATINGS*
VDD – VSS ................................................................. +18V
IIN ...........................................................................10mA
VOUT Max –VOUT Common..........................................23V
VREF – VSS ..............................................................– 1.5V
Storage Temperature Range ................ – 65°C to +150°C
Operating Temperature Range
C Device ................................................ 0°C to +70°C
E Device ........................................... – 40°C to +85°C
Package Dissipation (TA ≤ 70°C)
8-Pin CerDIP ..................................................800mW
8-Pin Plastic DIP.............................................730mW
8-Pin SOIC .....................................................470mW
Lead Temperature (Soldering, 10 sec) ................. +300°C
ELECTRICAL CHARACTERISTICS: VDD = +5V, VSS = – 5V, VGND = 0V, VREF = – 5V, RBIAS = 100kΩ,
Full Scale = 10kHz, unless otherwise specified. TA = +25°C, unless temperature range is specified (– 40°C to +85°C
for E device, 0°C to +70°C for C device).
VOLTAGE-TO-FREQUENCY
TC9401
TC9400
TC9402
Parameter
Definition
Min Typ Max Min Typ Max Min Typ Max
Unit
Accuracy
Linearity 10 kHz
Output Deviation From Straight
Line Between Normalized Zero
and Full-Scale Input
—
—
0.004 0.01
0.04 0.08
± 25 ± 40
—
—
0.01 0.05
0.1 0.25
—
—
0.05 0.25
% Full
Scale
Linearity 100 kHz
Output Deviation From Straight
Line Between Normalized Zero
Reading and Full-Scale Input
0.25
0.5
% Full
Scale
Gain Temperature
Drift (Note 1)
Variation in Gain A Due to
Temperature Change
—
—
—
—
—
—
—
—
± 25 ± 40 — ± 50 ± 100 ppm/°C
Full Scale
Gain Variance
Variation From Ideal Accuracy
± 10
–
± 10
—
— ± 10
–
% of
Nominal
Zero Offset (Note 2)
Correction at Zero Adjust for Zero
Output When Input is Zero
± 10 ± 50
± 25 ± 50
± 10 ± 50 — ± 20 ± 100
mV
Zero Temperature
Drift (Note 1)
Variation in Zero Offset Due to
Temperature Change
± 25 ± 50
—
± 50 ± 100 µV/°C
Analog Input
IIN Full Scale
Full-Scale Analog Input Current to
Achieve Specified Accuracy
—
10
—
—
10
—
10
—
µA
IIN Overrange
Overrange Current
—
—
—
2
50
—
—
—
—
2
50
—
—
—
—
2
50
—
µA
Response Time
Settling Time to 0.1% Full Scale
Cycle
Digital Section
VSAT @ IOL = 10mA
Logic "0" Output Voltage (Note 3)
—
—
0.2
—
0.4
18
—
—
0.2 0.4
—
—
0.2
—
0.4
18
V
V
VOUT Max – VOUT
Common (Note 4)
Voltage Range Between Output
and Common
—
18
Pulse Frequency
Output Width
—
3
—
—
3
—
—
3
—
µsec
3-288
TELCOM SEMICONDUCTOR, INC.
VOLTAGE-TO-FREQUENCY/
FREQUENCY-TO-VOLTAGECONVERTERS
3
TC9400
TC9401
TC9402
ELECTRICAL CHARACTERISTICS: (Cont.) VDD = +5V, VSS = – 5V, VGND = 0, VREF = – 5V, RBIAS = 100kΩ,
Full Scale = 10kHz, unless otherwise specified. TA = +25°C, unless temperature range is specified – 40°C to +85°C for
E device, 0°C to +70°C for C device.
FREQUENCY-TO-VOLTAGE
TC9401
TC9400
TC9402
Parameter
Definition
Min Typ Max Min Typ Max Min Typ Max
Unit
Supply Current
IDD Quiescent
(Note 5)
Current Required From Positive
Supply During Operation
—
1.5
6
—
1.5
6
—
4
3
10
mA
ISS Quiescent
(Note 5)
Current Required From Negative
Supply During Operation
—
4
– 1.5 – 6
—
4
– 1.5 – 6
– 3 – 10
mA
V
VDD Supply
VSS Supply
Operating Range of Positive Supply
Operating Range of Negative Supply
—
—
7.5
—
—
7.5
—
—
7.5
– 4
– 7.5 – 4
– 7.5 – 4
– 7.5
V
Reference Voltage
VREF –VSS
Range of Voltage Reference Input
– 2.5
—
—
—
– 2.5
—
—
—
– 2.5
—
—
—
V
Accuracy
Nonlinearity (Note 10) Deviation From Ideal Transfer
Function as a Percentage
0.01 0.02
0.02 0.05
0.05 0.25
% Full
Scale
Full-Scale Voltage
Input Frequency
Frequency Range for Specified
10
—
—
100k 10
—
100k 10
—
100k
Hz
Range (Note 7 and 8) Nonlinearity
Frequency Input
Positive Excursion
Voltage Required to Turn
Threshold Detector On
0.4
– 0.4
—
VDD 0.4
– 2 – 0.4
—
—
5
VDD 0.4
—
VDD
– 2
—
V
Negative Excursion
Voltage Required to Turn
Threshold Detector Off
– 2 – 0.4 —
V
Minimum Positive
Pulse Width (Note 8)
Time Between Threshold
Crossings
5
—
—
—
—
—
—
—
—
—
—
—
—
5
µsec
µsec
MΩ
Minimum Negative
Pulse Width (Note 8)
Time Between Threshold
Crossings
—
0.5
10
0.5
10
0.5
10
Input Impedance
—
—
Analog Outputs
Output Voltage
(Note 9)
Voltage Range of Op Amp Output
for Specified Nonlinearity
—
2
VDD – 1
—
—
2
VDD – 1
—
—
2
VDD – 1
—
—
V
Output Loading
Resistive Loading at Output of
Op Amp
—
—
—
—
—
kΩ
Supply Current
IDD Quiescent
(Note 10)
Current Required From Positive
Supply During Operation
—
1.5
6
—
4
1.5
6
—
4
3
10
mA
ISS Quiescent
(Note 10)
Current Required From Negative
Supply During Operation
—
4
– 1.5 – 6
– 1.5 – 6
– 3 – 10
mA
V
VDD Supply
VSS Supply
Operating Range of Positive Supply
Operating Range of Negative Supply
—
—
7.5
—
—
7.5
—
—
7.5
– 4
– 7.5 – 4
– 7.5 – 4
– 7.5
V
Reference Voltage
VREF –VSS
Range of Voltage Reference Input
– 2.5
—
—
– 2.5
—
—
– 2.5 —
—
V
6. 10Hz to 100kHz.; Guaranteed, Not Tested
NOTES: 1. Full temperature range. Guaranteed, Not Tested.
2. IIN = 0.
7. 5µsec minimum positive pulse width and 0.5 µsec minimum
negative pulse width.
8. tR = tF = 20 nsec.
3. Full temperature range, IOUT = 10mA.
4. IOUT = 10µA.
5. Threshold Detect = 5V, Amp Out = 0V, Full Temperature
Range
9. RL ≥ 2kΩ.; Tested @ 10kΩ
10. Full temperature range, VIN = – 0.1V.
TELCOM SEMICONDUCTOR, INC.
3-289
VOLTAGE-TO-FREQUENCY/
FREQUENCY-TO-VOLTAGECONVERTERS
TC9400
TC9401
TC9402
PIN CONFIGURATIONS
14-Pin Plastic DIP/CerDIP
14-Pin SOIC (Narrow)
I
I
BIAS
14
13
12
V
1
2
3
4
5
6
7
V
DD
BIAS
1
2
3
4
5
6
7
14
13
12
DD
ZERO ADJ
ZERO ADJ
NC
NC
I
I
IN
AMPLIFIER OUT
IN
AMPLIFIER OUT
TC9400
TC9401
TC9402
V
TC9400
TC9401
TC9402
V
SS
11 THRESHOLD DETECTOR
10 FREQ/2 OUT
SS
11 THRESHOLD DETECTOR
10 FREQ/2 OUT
V
OUT
GND
V
OUT
GND
REF
REF
9
8
OUTPUT COMMON
PULSE FREQ OUT
9
8
OUTPUT COMMON
PULSE FREQ OUT
V
V
REF
REF
NC = NO INTERNAL CONNECTION
PIN DESCRIPTIONS
Pin No.
Symbol
Description
1
IBIAS
ThispinsetsbiascurrentintheTC9400. ConnecttoVSS througha100kΩ resistor.
See text.
2
3
4
5
6
7
8
Zero Adj
IIN
Low frequency adjustment input. See text.
Input current connection for the V/F converter.
Negative power supply voltage connection, typically – 5V.
Reference capacitor connection.
VSS
VREFOUT
GND
Analog ground.
VREF
Voltage reference input, typically – 5V.
Pulse Freq Out
Frequency output. This open drain output will pulse LOW each time the Freq
threshold detector limit is reached. The pulse rate is proportional to input voltage.
9
Output Common
Freq/2 Out
Source connection for the open drain output FETs. See text.
10
This open drain output is a square wave at one half the frequency of the pulse
output (pin 8). Output transitions of this pin occur on the rising edge of pin 8.
11
12
13
14
Threshold Detect
Amplifier Out
NC
Inputtothethresholddetector. ThispinisthefrequencyinputduringF/Voperation.
Output of the integrator amplifier.
No internal connection
VDD
Positive power supply connection, typically +5V.
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VOLTAGE-TO-FREQUENCY/
FREQUENCY-TO-VOLTAGECONVERTERS
3
TC9400
TC9401
TC9402
+5V
14
+
5V
V
R
10kΩ
L
DD
f
THRESHOLD
DETECT
OUT 8
11
3µsec
DELAY
+
5V
THRESHOLD
DETECTOR
R
L
10kΩ
f
/2
OUT
10
9
SELF-
START
÷2
OUTPUT
COMMON
–3V
12 AMP OUT
V
OUT
REF
5
20kΩ
C
INT
C
REF
820pF
12pF
180pF
TC9400
TC9401
TC9402
R
1MΩ
IN
INPUT
60pF
I
IN
3
V
–
IN
+5V
OpAmp
+
ZERO
ADJUST
0V –10V
50kΩ
510kΩ
2
V
V
7
I
GND
6
SS
REF
BIAS
–5V
1
4
OFFSET
ADJUST
10kΩ
R
BIAS
100kΩ
REFERENCE
VOLTAGE
(TYPICALLY –5V)
–5V
Figure 1. 10 Hz to 10 kHz V/F Converter
VOLTAGE-TO-FREQUENCY (V/F)
CIRCUIT DESCRIPTION
At the end of the charging period, CREF is shorted out.
This dissipates the charge stored on the reference capaci-
tor, so that when the output again crosses zero the system
is ready to recycle. In this manner, the continued discharg-
ing of the integrating capacitor by the input is balanced out
by fixed charges from the reference voltage. As the input
voltage is increased, the number of reference pulses re-
quired to maintain balance increases, which causes the
output frequency to also increase. Since each charge in-
crement is fixed, the increase in frequency with voltage is
linear. In addition, the accuracy of the output pulse width
does not directly affect the linearity of the V/F. The pulse
must simply be long enough for full charge transfer to take
place.
The TC9400 V/F converter operates on the principal
of charge balancing. The operation of the TC9400 is easily
understood by referring to Figure 1. The input voltage (VIN)
is converted to a current (IIN) by the input resistor. This
current is then converted to a charge on the integrating
capacitor and shows up as a linearly decreasing voltage at
the output of the op amp. The lower limit of the output
swing is set by the threshold detector, which causes the
reference voltage to be applied to the reference capacitor
for a time period long enough to charge the capacitor to
the reference voltage. This action reduces the charge on
the integrating capacitor by a fixed amount (q = CREF
×
VREF), causing the op amp output to step up a finite
amount.
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3-291
VOLTAGE-TO-FREQUENCY/
FREQUENCY-TO-VOLTAGECONVERTERS
TC9400
TC9401
TC9402
3 µsec
TYP
f
OUT
1/f
f
/2
OUT
C
REF
INT
V
REF
C
0V
AMP
OUT
NOTES: 1. To adjust f
, set V = 10mV and adjust the 50kΩ offset for 10Hz output.
MIN
IN
2. To adjust f
3. To increase f
, set V = 10V and adjust R or V
for 10 kHz output.
MAX
IN
IN
REF
to 2pF and C
MAX to 100kHz, change C
to 75pF.
OUT
REF
INT
4. For high-performance applications, use high-stability components for R , C
resistors and glass capacitors). Also, separate output ground (pin 9) from input ground (pin 6).
, V
(metal film
IN REF REF
Figure 2 . Output Waveforms
The TC9400 contains a "self-start" circuit to ensure the
V/F converter always operates properly when power is first
applied. In the event that, during power-on, the Op Amp
output is below the threshold and CREF is already charged,
apositivevoltagestepwillnotoccur. Theop-ampoutputwill
continue to decrease until it crosses the –3.0V threshold of
the "self-start" comparator. When this happens, an internal
resistor is connected to the op-amp input, which forces the
output to go positive until the TC9400 is in its normal
operating mode.
PIN FUNCTIONS
Threshold Detector Input
In the V/F mode, this input is connected to the amplifier
output (pin 12) and triggers a 3 µsec pulse when the input
voltage passes through its threshold. In the F/V mode, the
input frequency is applied to this input.
The nominal threshold of the detector is halfway be-
tween the power supplies, or (VDD + VSS)/2 ±400mV. The
TC9400's charge balancing V/F technique is not dependent
on a precision comparator threshold, because the threshold
only sets the lower limit of the op-amp output. The op-amp's
peak-to-peakoutputswing,whichdeterminesthefrequency,
The TC9400 utilizes low power CMOS processing for
low input bias and offset currents with very low power
dissipation. Theopen-drainN-channeloutputFETsprovide
high voltage and high current sink capability.
is only influenced by external capacitors and by VREF
.
VOLTAGE-TO-TIME MEASUREMENTS
Pulse Freq Out
The TC9400 output can be measured in the time do-
main as well as the frequency domain. Some microcom-
puters, for example, have extensive timing capability but
limited counter capability. Also, the response time of a time
domain measurement is only the period between two out-
put pulses, while the frequency measurement must accu-
mulate pulses during the entire counter timebase period.
Time measurements can be made from either the
TC9400's Pulse Freq Out output or from the Freq/2 output.
The Freq/2 output changes state on the rising edge of
Pulse Freq Out, so Freq/2 is a symmetrical square wave at
one half the pulse output frequency. Timing measurements
can therefore be made between successive Pulse Freq
Out pulses, or while Freq/2 is high (or low).
This output is an open-drain N-channel FET which
provides a pulse waveform whose frequency is proportional
to the input voltage. This output requires a pull-up resistor
and interfaces directly with MOS, CMOS, and TTL logic.
Freq/2 Out
This output is an open-drain N-channel FET which
provides a square wave one-half the frequency of the pulse
frequencyoutput. TheFreq/2outputwillchangestateonthe
rising edge of Pulse Freq Out. This output requires a pull-
up resistor and interfaces directly with MOS, CMOS, and
TTL logic.
3-292
TELCOM SEMICONDUCTOR, INC.
VOLTAGE-TO-FREQUENCY/
FREQUENCY-TO-VOLTAGECONVERTERS
3
TC9400
TC9401
TC9402
Output Common
VREF Out
The sources of both the Freq/2 out and the Pulse Freq
Out are connected to this pin. An output level swing from the
drainvoltagetogroundortotheVSS supplymaybeobtained
by connecting this pin to the appropriate point.
The charging current for CREF is supplied through this
pin. When the op amp output reaches the threshold level,
this pin is internally connected to the reference voltage and
a charge, equal to VREF x CREF, is removed from the
integrator capacitor. After about 3 µsec, this pin is internally
connected to the summing junction of the op amp to dis-
charge CREF. Break-before-make switching ensures that
the reference voltage is not directly applied to the summing
junction.
RBIAS
An external resistor, connected to VSS, sets the bias
point for the TC9400. Specifications for the TC9400 are
based on RBIAS = 100kΩ ±10%, unless otherwise noted.
Increasing the maximum frequency of the TC9400
beyond 100kHz is limited by the pulse width of the Pulse
Output (typically 3µsec). Reducing RBIAS will decrease the
pulsewidthandincreasethemaximumoperatingfrequency,
but linearity errors will also increase. RBIAS can be reduced
to 20kΩ, which will typically produce a maximum full scale
frequency of 500kHz.
V/F CONVERTER DESIGN INFORMATION
Input/Output Relationships
Theoutputfrequency(fOUT)isrelatedtotheanaloginput
voltage (VIN) by the transfer equation:
VIN
RIN
1
Frequency out =
×
(VREF) (CREF
)
Amplifier Out
External Component Selection
The output stage of the operational amplifier. During
V/F operation, a negative-going ramp signal is available at
this pin. In the F/V mode, a voltage proportional to the
frequency input is generated.
RIN
The value of this component is chosen to give a full-
scale input current of approximately 10µA:
Zero Adjust
VIN Full Scale
RIN
.
10µA
10V
This pin is the noninverting input of the operational
amplifier. The low-frequency set point is determined by
adjusting the voltage at this pin.
Example:
RIN
= 1MΩ.
10µA
Note that the value is an approximation and the exact
relationship is defined by the transfer equation. In practice,
the value of RIN typically would be trimmed to obtain full-
scale frequency at VIN full scale (see "Adjustment Proce-
dure"). Metal film resistors with 1% tolerance or better are
recommended for high-accuracy applications because of
their thermal stability and low-noise generation.
IIN
The inverting input of the operational amplifier and the
summing junction when connected in the V/F mode. An
input current of 10µA is specified, but an overrange current
up to 50µA can be used without detrimental effect to the
circuit operation. IIN connects the summing junction of an
operational amplifier. Voltage sources cannot be attached
directly, but must be buffered by external resistors.
CINT
The exact value is not critical but is related to CREF by
the relationship:
VREF
Areferencevoltagefromeitheraprecisionsourceorthe
VSS supply is applied to this pin. Accuracy of the TC9400 is
dependent on the voltage regulation and temperature char-
acteristics of the reference circuitry.
Since the TC9400 is a charge balancing V/F converter,
the reference current will be equal to the input current. For
this reason, the DC impedance of the reference voltage
source must be kept low enough to prevent linearity errors.
For linearity of 0.01%, a reference impedance of 200Ω or
less is recommended. A 0.1µF bypass capacitor should be
connected from VREF to ground.
3CREF ≤ CINT ≤ 10 CREF
.
Improved stability and linearity are obtained when
CINT ≤ 4CREF. Low-leakage types are recommended,
although mica and ceramic devices can be used in applica-
tions where their temperature limits are not exceeded.
Locate as close as possible to pins 12 and 13.
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3-293
VOLTAGE-TO-FREQUENCY/
FREQUENCY-TO-VOLTAGECONVERTERS
TC9400
TC9401
TC9402
CREF
Improved Single Supply V/F Converter
Operation
Theexactvalueisnotcriticalandmaybeusedtotrimthe
full-scalefrequency(see"Input/OutputRelationships").Glass
film or air trimmer capacitors are recommended because of
their stability and low leakage. Locate as close as possible
to pins 5 and 3.
A TC9400 which operates from a single 12 to 15V
variablepowersourceisshowninFigure5. Thiscircuituses
twoZenerdiodestosetstablebiasinglevelsfortheTC9400.
The Zener diodes also provide the reference voltage, so the
outputimpedanceandtemperaturecoefficientoftheZeners
will directly affect power supply rejection and temperature
performance.
Full scale adjustment is accomplished by trimming the
input current. Trimming the reference voltage is not recom-
mended for high accuracy applications unless an op amp is
used as a buffer, because the TC9400 requires a low
impedance reference (see the VREF pin description section
for more information).
VDD, VSS
Power supplies of ±5V are recommended. For high-
accuracy requirements, 0.05% line and load regulation and
0.1µF disc decoupling capacitors located near the pins are
recommended.
Adjustment Procedure
Figure 1 shows a circuit for trimming the zero location.
The circuit of Figure 5 will directly interface with CMOS
logic operating at 12V to 15V. TTL or 5V CMOS logic can be
accommodated by connecting the output pullup resistors to
the +5V supply. An optoisolator can also be used if an
isolated output is required.
Full scale may be trimmed by adjusting RIN, VREF, or CREF
Recommended procedure for a 10kHz full-scale frequency
is as follows:
.
(1) Set VIN to 10 mV and trim the zero adjust circuit to
obtain a 10Hz output frequency.
(2) Set VIN to 10V and trim either RIN, VREF, or CREF to
obtain a 10kHz output frequency.
If adjustments are performed in this order, there should be
no interaction and they should not have to be repeated.
500
V
V
R
V
= +5V
= – 5V
= 1MΩ
= +10V
DD
SS
IN
400
300
200
100
IN
T
= +25°C
A
1 kHz
100kHz
–2
–3
–4
–5
–6
–7
0
–1
V
(V)
REF
Figure 3. Recommended CREF vs VREF
3-294
TELCOM SEMICONDUCTOR, INC.
VOLTAGE-TO-FREQUENCY/
FREQUENCY-TO-VOLTAGECONVERTERS
3
TC9400
TC9401
TC9402
+
V
= 8V TO 15V (FIXED)
R
2
14
10kΩ
V
2
0.9
2
6
5V
R
1
8
f
OUT
0.01
µF
8.2
kΩ
GAIN
ADJUST
10kΩ
7
10
f
/2
V
2
kΩ
OUT
REF
11
0.01
µF
OFFSET
ADJUST
0.2
TC9400
12
5
R
1
R
820
pF
IN
180
pF
1MΩ
3
I
V
IN
IN
0V–10V
I
1
4
9
IN
100 kΩ
+
1
R
R
2
V
1
f
= I
×
OUT IN
–
10V
12V 1.4 MΩ 14kΩ
15V 2 MΩ 20kΩ
1 MΩ 10kΩ
(V V ) (C
)
2
7
REF
+
(V –V )
IN
(V –V )
2
2
+
=
I
IN
R
(0.9 R +0.2 R )
1 1
IN
Figure 4 . Fixed Voltage — Single Supply Operation
+12 to +15V
1.2k*
14
V
DD
1µF
11 THRESHOLD
DETECT
R1
910k
R4
100k
C
INT
12
10k
10k
AMP OUT
D2
5.1VZ
C
5
C
REF
REF
R3
GAIN
TC9400
3
2
6
I
8
IN
ZERO
f
OUT
ADJUST
100k
10
9
OUTPUT
FREQUENCY
GND
f
/2
OUT
R2
910k
R5
91k
D1
5.1VZ
0.1µ
OUTPUT
COMMON
7
1
V
I
REF
Rp
OFFSET
20k
INPUT
VOLTAGE
(0 to 10V)
BIAS
100k
V
SS
4
DIGITAL
GROUND
ANALOG GROUND
COMPONENT SELECTION
F/S FREQ.
1 kHz
CREF
2200pF 4700pF
CINT
10 kHz
100 kHz
180pF
27pF
470pF
75pF
Figure 5. Voltage to Frequency
TELCOM SEMICONDUCTOR, INC.
3-295
VOLTAGE-TO-FREQUENCY/
FREQUENCY-TO-VOLTAGE CONVERTERS
TC9400
TC9401
TC9402
Input Voltage Levels
FREQUENCY-TO-VOLTAGE (F/V)
CIRCUIT DESCRIPTION
TheinputfrequencyisappliedtotheThresholdDetector
input (Pin 11). As discussed in the V/F circuit section of this
data sheet, the threshold of pin 11 is approximately (VDD
VSS) /2 ±400mV. Pin 11's input voltage range extends from
VDD to about 2.5 V below the threshold. If the voltage on pin
11 goes more than 2.5 volts below the threshold, the V/F
mode startup comparator will turn on and corrupt the output
voltage. The Threshold Detector input has about 200 mV of
hysteresis.
When used as an F/V converter, the TC9400 generates
anoutputvoltagelinearlyproportionaltotheinputfrequency
waveform.
Each zero crossing at the threshold detector's input
causes a precise amount of charge (q = CREF × VREF) to be
dispensed into the op amp's summing junction. This charge
in turn flows through the feedback resistor, generating
+
voltagepulsesattheoutputoftheopamp.Acapacitor(CINT
)
In ±5 V applications, the input voltage levels for the
TC9400 are ±400mV, minimum. If the frequency source
being measured is unipolar, such as TTL or CMOS operat-
ing from a +5V source, then an AC coupled level shifter
should be used. One such circuit is shown in Figure 6a.
ThelevelshiftercircuitinFigure6bcanbeusedinsingle
supply F/V applications. The resistor divider ensures that
the input threshold will track the supply voltages. The diode
clamp prevents the input from going far enough in the
negative direction to turn on the startup comparator. The
diode's forward voltage decreases by 2.1 mV/°C, so for high
ambient temperature operation two diodes in series are
recommended.
across RINT averages these pulses into a DC voltage which
is linearly proportional to the input frequency.
F/V CONVERTER DESIGN INFORMATION
Input/Output Relationships
The output voltage is related to the input frequency (fIN)
by the transfer equation:
VOUT = [VREF CREF RINT] fIN.
The response time to a change in fIN is equal to (RINT
CINT). TheamountofrippleonVOUT isinverselyproportional
to CINT and the input frequency.
CINT can be increased to lower the ripple. Values of 1µF
to 100µF are perfectly acceptable for low frequencies.
When the TC9400 is used in the single-supply mode,
VREF is defined as the voltage difference between pin 7 and
pin 2.
+8V to +5V
14
+5V
14
V
V
DD
DD
10k
TC9400
TC9400
0.01µF
0.01µF
Frequency
Input
33k
33k
Frequency
Input
11
11
DET
DET
IN914
+5V
0V
IN914 1.0M
+5V
0V
1.0M
GND
6
V
SS
4
V
SS
10k
0.1µF
4
–5V
(B) Single Supply
(A) ±5V Supply
Figure 6. Frequency Input Level Shifter
3-296
TELCOM SEMICONDUCTOR, INC.
VOLTAGE-TO-FREQUENCY/
FREQUENCY-TO-VOLTAGECONVERTERS
3
TC9400
TC9401
TC9402
+5V
14
+
+
V
V
V
DD
*
f
OUT/2
10
9
TC9400A
TC9401A
TC9402A
Ϭ2
OUTPUT
COMMON
*
THRESHOLD
DETECT
*
f
SEE
FIGURE
6
8
11
3 µsec
DELAY
OUT
f
IN
* OPTIONAL
IF BUFFER
IS NEEDED
THRESHOLD
DETECTOR
V
REF
OUT
5
3
SEE
EQUATION,
PAGE 12
C
56 pF
REF
12pF
I
IN
OFFSET
ADJUST
R
1 MΩ
C
INT
INT
60pF
+
+5V
1000pF
AMP
OUT 12
–
OP
V
100kΩ
O
AMP
ZERO ADJUST
2
+
2 kΩ
2.2kΩ
I
V
V
7
BIAS
SS
REF
GND
6
1
4
10 kΩ
V
REF
(TYPICALLY –5V)
–5V
Figure 7. DC — 10 kHz F/V Converter
Input Buffer
5.0µsec
MIN
0.5µsec
fOUT and fOUT/2 are not used in the F/V mode. However,
these outputs may be useful for some applications, such as
a buffer to feed additional circuitry. Then, fOUT will follow the
input frequency waveform, except that fOUT will go high
3µsec after fIN goes high; fOUT/2 will be squarewave with a
MIN
INPUT
frequency of one-half fOUT
If these outputs are not used, pins 8, 9 and 10 should be
connected to ground.
.
f
OUT
DELAY = 3µsec
f
/2
OUT
Figure 8 . F/V Digital Outputs
TELCOM SEMICONDUCTOR, INC.
3-297
VOLTAGE-TO-FREQUENCY/
FREQUENCY-TO-VOLTAGECONVERTERS
TC9400
TC9401
TC9402
+
V
= 10V to 15V
14
10k
VDD
6
GND
.01µF
6.2V
10k
TC9400
5
3
V
REFOUT
500k
ZERO
ADJUST
2
47pF
100k
+
V
IIN
Offset
Adjust
.001µF
1M
12
6
AMP OUT
GND
1.0k
0.01µF
33k
Frequency
Input
11
VOUT
DET
IN914
IBIAS
1.0M
VREF
VSS
4
7
0.1µF
1.0k
100k
Note: The output is referenced to pin 6, which is at 6.2V (Vz). For frequency meter applications,
a 1 mA meter with a series-scaling resistor can be placed across pins 6 and 12.
Figure 9. F/V Single Supply F/V Converter
Output Filtering
The output of the TC9400 has a sawtooth ripple super-
imposed on a DC level. The ripple will be rejected if the
TC9400 output is converted to a digital value by an integrat-
ing analog to digital converter, such as the TC7107 or
TC7109. The ripple can also be reduced by increasing the
value of the integrating capacitor, although this will reduce
the response time of the F/V converter.
5
3
V
REFOUT
47pF
IIN
TC9400
.001µF
200
1M
12
AMP OUT
The sawtooth ripple on the output of an F/V can be
eliminated without affecting the F/V's response time by
using the circuit in Figure 10. The circuit is a capacitance
multiplier, where the output coupling capacitor is multiplied
by the AC gain of the op amp. A moderately fast op amp,
such as the TL071, should be used.
0.1µF
1M
.01µF
GND
6
+5
VOUT
7
4
2
3
–
+
6
TL071
1M
–5
Figure 10. Ripple Filter
3-298
TELCOM SEMICONDUCTOR, INC.
VOLTAGE-TO-FREQUENCY/
FREQUENCY-TO-VOLTAGECONVERTERS
3
TC9400
TC9401
TC9402
In some cases, however, the TC9400 output must be
zero at power-on without a frequency input. In such cases,
a capacitor connected from pin 11 to VDD will usually be
sufficient to pulse the TC9400 and provide a power-on reset
(see Figure 11A). Where predictable power-on operation is
critical, a more complicated circuit, such as Figure 11B, may
be required.
F/V POWER-ON RESET
In F/V mode, the TC9400 output voltage will occasion-
allybeatitsmaximumvaluewhenpowerisfirstapplied.This
conditionremainsuntilthefirstpulseisappliedtofIN. Inmost
frequency-measurement applications this is not a problem,
because proper operation begins as soon as the frequency
input is applied.
V
DD
14
1000pF
1kΩ
THRESHOLD
DETECTOR
11
f
IN
(A)
TC9400
V
DD
(B)
16
5
2
1
V
B
R
C
CC
3
4
CLRA
100kΩ
1µF
CD4538
6
Q
To TC 9400
A
V
SS
f
IN
8
Figure 11. Power-On Operation/Reset
TELCOM SEMICONDUCTOR, INC.
3-299
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