CS209A

CS209A
Proximity Detector
Description Features
The CS209A is a bipolar monolithic feedback circuit provides drive to main- ■ Separate Current
integrated circuit for use in metal detec- tain oscillation. The peak demodulator Regulator for Oscillator
tion/proximity sensing applications. senses the negative portion of the oscil-
The IC (see block diagram) contains two lator envelop and provides a demodu- ■ Negative Transient
on-chip current regulators, oscillator lated waveform as input to the com- Suppression
and low-level feedback circuitry, peak parator. The comparator sets the states
detection/demodulation circuit, a com- of the complementary outputs by com-
■ Variable Low-Level
parator and two complementary output paring the input from the demodulator Feedback
stages. to an internal reference. External loads ■ Improved Performance
The oscillator, along with an external are required for the output pins. over Temperature
LC network, provides controlled oscilla- A transient suppression circuit is
■ 6mA Supply Current
tions where amplitude is highly depen- included to absorb negative transients
dent on the Q of the LC tank. During at the tank circuit terminal.
Consumption at
low Q conditions, a variable low-level VCC = 12V
■ Output Current Sink
Absolute Maximum Ratings Capability
20mA at 4VCC
Supply Voltage ................................................................................................24V 100mA at 24VCC
Power Dissipation (TA = 125¡C).............................................................200mW
Storage Temperature Range ....................................................Ð55¡C to +165¡C
Junction Temperature...............................................................Ð40¡C to +150¡C Package Options
Electrostatic Discharge (except TANK pin) ................................................2kV
Lead Temperature Soldering 14L SO
Wave Solder(through hole styles only) ...........10 sec. max, 260¡C peak
Reflow (SMD styles only) ...........60 sec. max above 183¡C, 230¡C peak OSC 1 14 N.C.

TANK 2 13 RF

Gnd 3 12 VCC
Block Diagram
OUT1 4 11 N.C.

N.C. 5 10 DEMOD

OUT2 6 9 N.C.
DVBE/R Current
Regulator
VBE/R Current VCC N.C. 7 8 N.C.
300mA Regulator

Oscillator
OSC
4.8kW 23.6kW
OSC
8L PDIP & SO
Feedback OUT1
RF
VCC OSC 1 8 RF
Neg Transient
Suppression TANK 2 7 VCC
+ OUT2
COMP Gnd 3 6 DEMOD
DEMOD -
OUT1 4 5 OUT2

TANK GND DEMOD

Cherry Semiconductor Corporation

2000 South County Trail, East Greenwich, RI 02818
Tel: (401)885-3600 Fax: (401)885-5786
Email: info@cherry-semi.com
Web Site: www.cherry-semi.com
Rev. 3/11/99 1 A ¨ Company
CS209A Electrical Characteristics: -40¡C ² TA ² 125¡C unless otherwise specified

PARAMETER TEST CONDITIONS MIN TYP MAX UNIT

Supply Current ICC VCC = 4V 3.5 6.0 mA

VCC = 12V 6.0 11.6 mA
VCC = 24V 11.0 20.0 mA
Tank Current VCC = 20V -550 -300 -100 µA
Demodulator Charge Current VCC = 20V -60 -30 -10 µA
Output Leakage Current VCC = 24V 0.01 10.00 µA
Output VSAT VCC = 4V, IS =20mA 60 200 mV
VCC = 24V, IS =100mA 200 500 mv
Oscillator Bias VCC = 20V 1.1 1.9 2.5 V
Feedback Bias VCC = 20V 1.1 1.9 2.5 V
Osc - Rf Bias VCC = 20V -250 100 550 mV
Protect Voltage ITANK = -10mA -10.0 -8.9 -7.0 V
Detect Threshold 720 1440 1950 mV
Release Threshold 550 1200 1700 mV

Package Pin Description

PACKAGE PIN# PIN SYMBOL FUNCTION

8L PDIP & SO 14L SO

1 1 OSC Adjustable feedback resistor connected between OSC and
RF sets detection range.
2 2 TANK Connects to parallel tank circuit.
3 3 Gnd Ground connection.
4 4 OUT1 Complementary open collector output; When OUT1 =
LOW, metal is present.
5 6 OUT2 Complementary open collector output; When OUT2 =
HIGH, metal is present.
6 10 DEMOD Input to comparator controlling OUT1 and OUT 2.
7 12 VCC Supply voltage.
8 13 RF Adjustable feedback resistor connected between OSC and
RF set detection range.
5,7,8,9,11,14 NC No Connection.

Typical Performance Characteristics

Output Switching Delay vs. Output Load Output Switching Delay vs. Temperature

6.5

8 (VCC = 12V, Rload = 1kW)

(T = 22°C, VCC= 12V)
5.5
Switching Delay (ms)
Switching Delay (ms)

6
4.5

4
3.5

2 2.5
12 16 20 -40 -20 0 20 40 60 80 100 120
100 4 8
Output Load (kW) Temperature (°C)

2
 CS209A
Typical Performance Characteristics: continued

Demodulator Voltage vs. Distance for Different RF

Object (T = 21°C, VCC = 12V)

Detected
1.75

1.5

DEMOD (V)
2.5kW 5kW 7.5kW 12.5kW 15kW 17.5kW

1.25 Object Not

Detected,
L Unloaded.

1.0

0.75
0.0 0.100 0.200 0.300 0.400
Distance To Object (in.)

Principle of Operation

The CS209A is a metal detector circuit which operates on is well outside the trip point. Higher values of feedback
the principle of detecting a reduction in Q of an inductor resistance for the same inductor Q will therefore eventu-
when it is brought into close proximity of metal. The ally result in a latched-ON condition because the residual
CS209A contains an oscillator set up by an external parallel voltage will be higher than the comparatorÕs thresholds.
resonant tank and a feedback resistor connected between As an example of how to set the detection range, place the
OSC and RF. (See Test and Applications Diagram) The metal object at the maximum distance from the inductor
impedance of a parallel resonant tank is highest when the the circuit is required to detect, assuming of course the Q
frequency of the source driving it is equal to the tankÕs res- of the tank is high enough to allow the object to be within
onant frequency. In the CS209A the internal oscillator the ICÕs detection range. Then adjust the potentiometer to
operates close to the resonant frequency of the tank circuit obtain a lower resistance while observing one of the
selected. As a metal object is brought close to the inductor, CS209A outputs return to its normal state (see Test and
the amplitude of the voltage across the tank gradually Applications Diagram). Readjust the potentiometer slow-
begins to drop. When the envelope of the oscillation reach- ly toward a higher resistance until the outputs have
es a certain level, the IC causes the output stages to switch switched to their tripped condition. Remove the metal
states. and confirm that the outputs switch back to their normal
The detection is performed as follows: A capacitor con- state. Typically the maximum distance range the circuit is
nected to DEMOD is charged via an internal 30µA current capable of detecting is around 0.3 inch. The higher the Q,
source. This current, however, is diverted away from the the higher the detection distance.
capacitor in proportion to the negative bias generated by For this application it is recommended to use a core
the tank at TANK. Charge is therefore removed from the which concentrates the magnetic field in only one direc-
capacitor tied to DEMOD on every negative half cycle of tion. This is accomplished very well with a pot core half.
the resonant voltage. (See Figure 1) The voltage on the The next step is to select a core material with low loss fac-
capacitor at DEMOD, a DC voltage with ripple, is then tor (inverse of Q). The loss factor can be represented by a
directly compared to an internal 1.44V reference. When the resistance in series with the inductor which arises from
internal comparator trips it turns on a transistor which core losses and is a function of frequency.
places a 23.6k½ resistor in parallel to the 4.8k½. The result-
The final step in obtaining a high Q inductor is the selec-
ing reference then becomes approximately 1.2V. This hys-
tion of wire size. The higher the frequency the faster the
teresis is necessary for preventing false triggering.
decrease in current density towards the center of the wire.
The feedback potentiometer connected between OSC and Thus most of the current flow is concentrated on the sur-
RF is adjusted to achieve a certain detection distance face of the wire resulting in a high AC resistance. LITZ
range. The larger the resistance the greater the trip-point wire is recommended for this application. Considering
distance (See graph Demodulator Voltage vs Distance for the many factors involved, it is also recommended to
Different RF). Note that this is a plot representative of one operate at a resonant frequency between 200 and 700kHz.
particular set-up since detection distance is dependent on The formula commonly used to determine the Q for par-
the Q of the tank. Note also from the graph that the capaci- allel resonant circuits is:
tor voltage corresponding to the greatest detection dis- R
tance has a higher residual voltage when the metal object QP @
2¹fRL

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CS209A Principle of Operation: continued
where R is the effective resistance of the tank. The resis- Note that the above is only a comparison among different
tance component of the inductor consists primarily of core metals and no attempt was made to achieve the greatest
losses and Òskin effectÓ or AC resistance. detection distance.
The resonant capacitor should be selected to resonate with A different type of application involves, for example,
the inductor within the frequency range recommended in detecting the teeth of a rotating gear. For these applica-
order to yield the highest Q. The capacitor type should be tions the capacitor on DEMOD should not be selected too
selected to have low ESR: multilayer ceramic for example. small (not below 1000pF) where the ripple becomes too
Detection distances vary for different metals. Following large and not too large (not greater than 0.01µF) that the
are different detection distances for some selected metals response time is too slow. Figure 1 for example shows the
and metal objects relative to one particular circuit set-up: capacitor ripple only and Figure 2 shows the entire capaci-
tor voltage and the output pulses for an 8-tooth gear rotat-
Commonly encountered metals:
ing at about 2400 rpm using a 2200pF capacitor on the
¥ Stainless steel 0.101" DEMOD pin.
¥ Carbon steel 0.125"
Because the output stages go into hard saturation, a time
¥ Copper 0.044"
interval is required to remove the stored base charge
¥ Aluminum 0.053"
resulting in both outputs being low for approximately 3µs
¥ Brass 0.052"
(see Output Switching Delay vs. Temperature graph). If
Coins: more information is required about output switching
¥ US Quarter 0.055" characteristics please consult the factory.
¥ Canadian Quarter 0.113"
¥ 1 German Mark 0.090"
¥ 1 Pound Sterling 0.080"
¥ 100 Japanese Yen 0.093"
¥ 100 Italian Lira 0.133"
12 oz. soda can: 0.087"

VOUT1

VTANK

VDEMOD

VDEMOD

Figure 1. Capacitor ripple. Figure 2. Output pulse for an 8 tooth gear.

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 CS209A
Test and Application Diagram

VCC

RL RL
1kW 1kW
OSC
20kW
CS209A OUT1
NORMALLY
HI
RF

OUT2
NORMALLY
LO

TANK Gnd DEMOD

L: Core: Siemens B65531-D-R-33

52 Turns, 6x44 AWG, Litz Unserved
4300pF CDEMOD Single Polyurethane
2200 pF

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CS209A Package Specification

PACKAGE DIMENSIONS IN mm (INCHES) PACKAGE THERMAL DATA

D Thermal Data 8L PDIP 8L SO 14L SO

Lead Count Metric English RQJC typ 52 45 30 ¡C/W
Max Min Max Min RQJA typ 100 165 125 ¡C/W
8L PDIP 10.16 9.02 .400 .355
8L SO 5.00 4.80 .197 .189
14L SO 8.75 8.55 .344 .337

Plastic DIP (N); 300 mil wide

7.11 (.280)
6.10 (.240)

8.26 (.325) 1.77 (.070)

2.54 (.100) BSC
7.62 (.300) 1.14 (.045)

3.68 (.145)
2.92 (.115)

.356 (.014) 0.39 (.015)

MIN.
.203 (.008)
.558 (.022) Some 8 and 16 lead
.356 (.014) packages may have
1/2 lead at the end
REF: JEDEC MS-001 D of the package.
All specs are the same.

Surface Mount Narrow Body (D); 150 mil wide

4.00 (.157) 6.20 (.244)

3.80 (.150) 5.80 (.228)

0.51 (.020)
1.27 (.050) BSC
0.33 (.013)

1.75 (.069) MAX

1.57 (.062)
1.37 (.054)

1.27 (.050) 0.25 (.010)

0.40 (.016) 0.19 (.008) 0.25 (0.10)
0.10 (.004)
D
REF: JEDEC MS-012

Ordering Information

Part Number Description

CS209AYN8 8 L PDIP
CS209AYD8 8L SO Narrow
CS209AYDR8 8L SO Narrow (tape & reel) Cherry Semiconductor Corporation reserves the
right to make changes to the specifications without
CS209AYD14 14L SO Narrow notice. Please contact Cherry Semiconductor
CS209AYDR14 14L SO Narrow (tape & reel) Corporation for the latest available information.
Rev. 3/11/99 © 1999 Cherry Semiconductor Corporation
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