CS8190 datasheet(8/12 Pages) ONSEMI

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CS8190

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GND

COSINE

SINE

CCP

Speedo Input

Battery

Air Core

Gauge

200

CP+

CP−

SQOUT

F/VOUT

VREG

GND

SINE+

SINE−

BIAS

FREQIN

GND

COS+

COS−

VCC

Speedometer

Trim Resistor

± 20 PPM/°C

0.1

1.0 A

600 PIV

Figure 9. Speedometer or Tachometer Application

3.9,

500 mW

10 k

3.0 k

1.0 k

0.0033

0.47

0.1

50 V,

500 mW

Zener

± 30 PPM/°C

2000

Notes:

1. C2 (> 2000

mF) is needed if return to zero function is required.

2. The product of CCP and RT have a direct effect on the transfer function (f to V conversion) and therefore directly affect

temperature compensation.

3. CCP 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

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

The maximum charge current for CCP is worst case

estimated at:

VREG * 0.7 V

3.3 k

+ 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.

+ 10%

350 Hz

+ 285 ms

Choose R4 = 1.0 k

Discharge time: tDCHG = R4

× CCP = 3.3 kW × 0.0033 mF

= 3.3

Charge time: tCHG = (R3 + R4)CCP = 4.3 k

W. × 0.0033 mF

= 14.2

3. Determine C4

C4 is selected to satisfy both the maximum allowable

ripple voltage and response time of the meter movement.

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.

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