CS209A

http://onsemi.com

5

Figure 5. Test and Application Diagram

RL

1.0 kΩ

NORMALLY

HI

RL

1.0 kΩ

NORMALLY

LO

L: Core: Siemens B65531−D−R−33

52 Turns, 6 × 44 AWG, Litz Unserved

Single Polyurethane

DEMOD

2200 pF

GND

TANK

4300 pF

L

20 kΩ

CS209A

OSC

RF

Figure 6. Capacitor Ripple

Figure 7. Output Pulse for an 8 Tooth Gear

The feedback potentiometer connected between OSC and

RF is adjusted to achieve a certain detection distance range.

The larger the resistance the greater the trip−point distance.

(See Figure 4.) Note that this is a plot representative of one

particular set−up since detection distance is dependent on

the Q of the tank. Note also from the graph that the capacitor

voltage corresponding to the greatest detection distance has

a higher residual voltage when the metal object is well

outside the trip point. Higher values of feedback resistance

for the same inductor Q will therefore eventually result in a

latched−ON condition because the residual voltage will be

higher than the comparator’s thresholds.

As an example of how to set the detection range, place the

metal object at the maximum distance from the inductor the

circuit is required to detect, assuming of course the Q of the

tank is high enough to allow the object to be within the IC’s

detection range. Then adjust the potentiometer to obtain a

lower resistance while observing one of the CS209A outputs

return to its normal state. (See Figure 5.) Readjust the

potentiometer slowly toward a higher resistance until the

outputs have switched to their tripped condition. Remove

the metal and confirm that the outputs switch back to their

normal state. Typically the maximum distance range the

circuit is capable of detecting is around 0.3 inch. The higher

the Q, the higher the detection distance.