tc9400 Microchip Technology Inc., tc9400 Datasheet - Page 14

• Manufacturer Part Number: tc9400
• Description: Voltage-to-frequency / Frequency-to-voltage Converters
• Manufacturer: Microchip Technology Inc.

TC9400/9401/9402
6.0
6.1
The output voltage is related to the input frequency
(F
EQUATION 6-1:
The response time to a change in F
C
proportional to C
C
1 µF to 100 µF are perfectly acceptable for low frequen-
cies.
When the TC9400 is used in the Single Supply mode,
V
and Pin 2.
FIGURE 6-1:
DS21483D-page 14
Frequency
REF
INT
INT
IN
Input
) by the transfer equation:
). The amount of ripple on V
can be increased to lower the ripple. Values of
is defined as the voltage difference between Pin 7
+5V
0V
F/V CONVERTER DESIGN
INFORMATION
Input/Output Relationships
V
OUT
33 kΩ
INT
= [V
and the input frequency.
REF
0.01 µF
Frequency Input Level Shifter.
(a) ±5V Supply
C
REF
IN914
R
INT
] F
IN
1.0
MΩ
OUT
IN
is equal to (R
11
GND
DET
is inversely
TC9400
6
+5V
V
-5V
DD
V
14
4
SS
INT
Frequency
Input
6.2
The input frequency is applied to the Threshold
Detector input (Pin 11). As discussed in the V/F circuit
section of this data sheet, the threshold of Pin 11 is
approximately (V
voltage range extends from V
the threshold. If the voltage on Pin 11 goes more than
2.5 volts below the threshold, the V/F mode start-up
comparator will turn on and corrupt the output voltage.
The Threshold Detector input has about 200 mV of
hysteresis.
In ±5V applications, the input voltage levels for the
TC9400 are ±400 mV, minimum. If the frequency
source being measured is unipolar, such as TTL or
CMOS operating from a +5V source, then an AC
coupled level shifter should be used. One such circuit
is shown in
The level shifter circuit in
single 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
start-up comparator. The diode’s forward voltage
decreases by 2.1 mV/°C, so for high ambient
temperature operation, two diodes in series are
recommended.
+5V
0V
Input Voltage Levels
33 kΩ
Figure
0.01 µF
DD
6-1(a).
+ V
0.1 µF 10 kΩ
IN914
© 2007 Microchip Technology Inc.
SS
Figure
)/2 ±400 mV. Pin 11’s input
(b) Single Supply
10 kΩ
DD
1.0
MΩ
6-1(b) can be used in
to about 2.5V below
11
DET
TC9400
+8V to +15V
V
DD
V
14
4
SS