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CS8190
http://onsemi.com
8
R3
R4
R2
C3
C1
D2
R1
D1
GND
COSINE
SINE
C4
CCP
RT
+
Speedo Input
Battery
Air Core
Gauge
200 W
CP+
CP
SQOUT
F/VOUT
VREG
GND
SINE+
SINE
BIAS
FREQIN
GND
COS+
COS
VCC
1
Speedometer
CS8190
Trim Resistor
± 20 PPM/°C
0.1 mF
1.0 A
600 PIV
Figure 9. Speedometer or Tachometer Application
3.9,
500 mW
10 kW
3.0 kW
1.0 kW
0.0033 mF
0.47 mF
0.1 mF
50 V,
500 mW
Zener
± 30 PPM/°C
C2
2000 mF
Notes:
1. C2 (> 2000 mF) is needed if return to zero function is required.
2. The product of C4 and RT have a direct effect on gain and therefore directly affect temperature compensation.
3. C4 Range; 20 pF to 0.2 mF.
4. RT Range; 100 kW to 500 kW.
5. The IC must be protected from transients above 60 V and reverse battery conditions.
6. Additional filtering on the FREQIN lead may be required.
7. Gauge coil connections to the IC must be kept as short as possible (≤ 3.0 inch) for best pointer stability.
Design Example
Maximum meter Deflection = 270
°
Maximum Input Frequency = 350 Hz
1. Select RT and CCP
q + 970
FREQ
CCP
RT + 270°
Let CCP = 0.0033 mF, find RT
RT +
270°
970
350 Hz
0.0033 mF
RT + 243 kW
RT should be a 250 k
W potentiometer to trim out any
inaccuracies due to IC tolerances or meter movement
pointer placement.
2. Select R3 and R4
Resistor R3 sets the output current from the voltage
regulator. The maximum output current from the voltage
regulator is 10 mA. R3 must ensure that the current does not
exceed this limit.
Choose R3 = 3.3 k
W
The charge current for CCP is
VREG * 0.7 V
3.3 kW
+ 1.90 mA
CCP must charge and discharge fully during each cycle of
the input signal. Time for one cycle at maximum frequency
is 2.85 ms. To ensure that CCP is charged, assume that the
(R3 + R4) CCP time constant is less than 10% of the
minimum input period.
T + 10%
1
350 Hz +
285 ms
Choose R4 = 1.0 k
W.
Discharge time: tDCHG = R3 × CCP = 3.3 kW × 0.0033 mF
= 10.9
ms
Charge time: tCHG = (R3 + R4)CCP = 4.3 kW. × 0.0033 mF
= 14.2
ms
3. Determine C4
C4 is selected to satisfy both the maximum allowable
ripple voltage and response time of the meter movement.
C4 +
CCP(VREG * 0.7 V)
DVMAX
With C4 = 0.47
mF, the F/V ripple voltage is 44 mV.
The last component to be selected is the return to zero
capacitor C2. This is selected by increasing the input signal
frequency to its maximum so the pointer is at its maximum
deflection, then removing the power from the circuit. C2
should be large enough to ensure that the pointer always
returns to the 0
° position rather than 360° under all operating
conditions.
Figure
10 shows how the CS8190 and the CS8441 are
used to produce a Speedometer and Odometer circuit.