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CS8190EDWFR20

Precision Air−Core Tach/Speedo Driver with Return to Zero

ON Semiconductor 

CS8190

R3

Speedo Input

3.0 kW

CCP

0.0033 mF

± 30 PPM/°C

R2

R4

1.0 kW

10 kW C3 0.1 mF

1 CP+

CP−

SQOUT F/VOUT

FREQIN VREG

GND

GND

C4

+

0.47 mF

RT

Trim

± 20

Resistor

PPM/°C

GND

GND

COS+ SINE+

Battery

R1

COS− SINE−

D1

3.9,

1.0 A 500 mW

C1

600 PIV

0.1 mF

C2

VCC

BIAS

2000 mF

COSINE

SINE

GND

D2

50 V,

Notes:

500 mW

Zener

Air Core

Gauge

200 W

Speedometer

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. R4 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.

Figure 9. Speedometer or Tachometer Application

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 + 970

270°

350 Hz 0.0033 mF

RT + 243 kW

RT should be a 250 kW 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 kW

The charge current for CCP is

VREG * 0.7

3.3 kW

V

+

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 kW.

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 *

DVMAX

0.7

V)

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.

http://onsemi.com

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