CS8191

http://onsemi.com

8

COSINE

SINE

Air Core

Gauge

Speedometer

CP+

CP–

GND

GND

COS+

SINE+

BIAS

GND

GND

COS–

SINE–

1

Figure 9. Speedometer or Tachometer Application

Notes:

affect temperature compensation.

µF.

Ω to 500 kΩ.

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

R2

C3

C1

D2

R1

D1

0.1

µF

3.9,

500 mW

50 V,

500 mW Zener

1.0 A,

600 PIV

10 k

Ω

0.1

µF

C4

0.47

µF

R4

1.0 k

Ω

0.0033

µF,

+/–30 PPM/

°C

R3

3.0 k

Ω

Trim Resistor,

+/–20 PPM/

°C

+

Design Example

Maximum meter Deflection = 270

°

Maximum Input Frequency = 350 Hz

Q + 970

FREQ

CCP

RT

RT +

270

°

970

350 Hz

0.0033

mF

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

VREG * 0.7 V

3.3 k

W

+ 1.90 mA

the input signal. Time for one cycle at maximum frequency

minimum input period.

T

+ 10%

1

350 Hz

+ 285ms

Choose R4 = 1.0 k

Ω.

= 10.9

µs

= 14.2

µs

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

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.