CS8191 datasheet(8/12 Pages) ONSEMI

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CS8191

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COSINE

SINE

Air Core

Gauge

Speedometer

VCC

F/VOUT

VREG

CP+

CP–

GND

COS+

SINE+

SQOUT

BIAS

GND

COS–

SINE–

FREQIN

Figure 9. Speedometer or Tachometer Application

Notes:

1. The product of C4 and RT have a direct effect on gain and therefore directly

affect temperature compensation.

2. C4 Range; 20 pF to 0.2

µF.

3. R4 Range; 100 k

Ω to 500 kΩ.

4. The IC must be protected from transients above 60 V and reverse battery conditions.

5. Additional filtering on the FREQIN lead may be required.

6. Gauge coil connections to the IC must be kept as short as possible (

≤ 3.0 inch)

for best pointer stability.

Battery

GND

Typical Speedometer

Input

0.1

µF

3.9,

500 mW

50 V,

500 mW Zener

1.0 A,

600 PIV

10 k

Ω

0.1

µF

0.47

µF

1.0 k

Ω

CCP

0.0033

µF,

+/–30 PPM/

°C

3.0 k

Ω

Trim Resistor,

+/–20 PPM/

°C

Design Example

Maximum meter Deflection = 270

Maximum Input Frequency = 350 Hz

1. Select RT and CCP

Q + 970

FREQ

CCP

Let CCP = 0.0033 µF, find RT

RT +

270

970

350 Hz

0.0033

RT + 243 kW

RT should be a 250 k

Ω 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

Ω

The charge current for CCP is

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

+ 285ms

Choose R4 = 1.0 k

Ω.

Discharge time: tDCHG= R3 × CCP = 3.3 kΩ × 0.0033 µF

= 10.9

µs

Charge time: tCHG = (R3 + R4)CCP = 4.3 kΩ. × 0.0033 µF

= 14.2

µs

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

µF, the F/V ripple voltage is 44 mV.

Figure 10 shows how the CS8191 and the CS8441 are

used to produce a Speedometer and Odometer circuit.

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