CS1124

Dual Variable-Reluctance
Sensor Interface IC
The CS1124 is a monolithic integrated circuit designed primarily to
condition signals used to monitor rotating parts.
The CS1124 is a dual channel device. Each channel interfaces to a
Variable Reluctance Sensor, and monitors the signal produced when a http://onsemi.com
metal object is moved past that sensor. An output is generated that is a
comparison of the input voltage and the voltage produced at the IN Adj 8
lead. The resulting square–wave is available at the OUT pin. 1
When the DIAG pin is high, the reference voltage at INAdj is SO–8
increased. This then requires a larger signal at the input to trip the D SUFFIX
comparator, and provides for a procedure to test for an open sensor. CASE 751

Features PIN CONNECTIONS AND

• Dual Channel Capability MARKING DIAGRAM
• Built–In Test Mode 1 8
• On–Chip Input Voltage Clamping
INAdj VCC
IN1 OUT1

ALYW
•

1124
Works from 5.0 V Supply
IN2 OUT2
• Accurate Built–In Hysteresis GND DIAG

VCC A = Assembly Location

WL, L = Wafer Lot
YY, Y = Year
VCC VCC VCC VCC WW, W = Work Week
INP1
OUT1
DIAG INAdj To µP ORDERING INFORMATION
R1 IN1 Device Package Shipping
+
– CS1124YD8 SO–8 95 Units/Rail
C1 Active
RRS COMP1
Clamp CS1124YDR8 SO–8 2500 Tape & Reel

VRS
Variable
Reluctance VCC VCC
Sensor
INP2 OUT2
To µP
R2 IN2
+
–
C2 Active
RRS COMP2
Clamp

VRS
Variable GND
Reluctance
RAdj
Sensor

Figure 1. Block Diagram

 Semiconductor Components Industries, LLC, 2001 1 Publication Order Number:

April, 2001 – Rev. 6 CS1124/D
 CS1124

MAXIMUM RATINGS*
Rating Value Unit

Storage Temperature Range –65 to 150 °C

Ambient Operating Temperature –40 to 125 °C

Supply Voltage Range (continuous) –0.3 to 7.0 V

Input Voltage Range (at any input, R1 = R2 = 22 k) –250 to 250 V

Maximum Junction Temperature 150 °C

ESD Susceptibility (Human Body Model) 2.0 kV

Lead Temperature Soldering: Reflow: (SMD styles only) (Note 1) 230 peak °C
1. 60 second maximum above 183°C.
*The maximum package power dissipation must be observed.

ELECTRICAL CHARACTERISTICS (4.5 V < VCC < 5.5 V, –40°C < TA < 125°C, VDIAG = 0; unless otherwise specified.)
Characteristic Test Conditions Min Typ Max Unit

VCC SUPPLY
Operating Current Supply VCC = 5.0 V – – 5.0 mA

Sensor Inputs
Input Threshold – Positive VDIAG = Low 135 160 185 mV
VDIAG = High 135 160 185 mV

Input Threshold – Negative VDIAG = Low –185 –160 –135 mV

VDIAG = High 135 160 185 mV

Input Bias Current (INP1, INP2) VIN = 0.336 V –16 –11 –6.0 µA

Input Bias Current (DIAG) VDIAG = 0 V – – 1.0 µA

Input Bias Current Factor (KI) VIN = 0.336 V, VDIAG = Low – 100 – %INP
(INAdj = INP × KI) VIN = 0.336 V, VDIAG = High 152 155 157 %INP

Bias Current Matching INP1 or INP2 to INAdj, VIN = 0.336 V –1.0 0 1.0 µA

Input Clamp – Negative IIN = –50 µA –0.5 –0.25 0 V

IIN = –12 mA –0.5 –0.30 0 V

Input Clamp – Positive IIN = +12 mA 5.0 7.0 9.0 V

Output Low Voltage IOUT = 1.6 mA – 0.2 0.4 V

Output High Voltage IOUT = –1.6 mA VCC – 0.5 VCC – 0.2 – V

Mode Change Time Delay – 0 – 20 µs

Input to Output Delay IOUT = 1.0 mA – 1.0 20 µs

Output Rise Time CLOAD = 30 pF – 0.5 2.0 µs

Output Fall Time CLOAD = 30 pF – 0.05 2.0 µs

Open–Sensor Positive Threshold VDIAG = High, RIN(Adj) = 40 k. Note 2 29.4 54 86.9 kΩ

Logic Inputs
DIAG Input Low Threshold – – – 0.2 × VCC V

DIAG Input High Threshold – 0.7 × VCC – – V

DIAG Input Resistance VIN = 0.3 × VCC , VCC = 5.0 V 8.0 22 70 kΩ

VIN = VCC, VCC = 5.0 V 8.0 22 70 kΩ
2. This parameter is guaranteed by design, but not parametrically tested in production.

http://onsemi.com
2
 CS1124

PACKAGE PIN DESCRIPTION*

PACKAGE PIN #
SO–8 PIN SYMBOL FUNCTION
1 INAdj External resistor to ground that sets the trip levels of both channels.
Functions for both diagnostic and normal mode.

2 IN1 Input to channel 1.

3 IN2 Input to channel 2.

4 GND Ground.

5 DIAG Diagnostic mode switch. Normal mode is low.

6 OUT2 Output of channel 2.

7 OUT1 Output of channel 1.

8 VCC Positive 5.0 volt supply input.

VCC

VCC VCC VCC VCC

INP1
OUT1
DIAG
INAdj To µP
R1 IN1
+
–
C1 Active
RRS COMP1
Clamp

VRS Variable
Reluctance
Sensor

GND

RAdj

Figure 2. Application Diagram

THEORY OF OPERATION

NORMAL OPERATION INP1/INAdj – Internal current sources that determine trip

points via R1/RAdj.
Figure 2 shows one channel of the CS1124 along with the
COMP1 – Internal comparator with built–in hysteresis
necessary external components. Both channels share the
set at 160 mV.
INAdj pin as the negative input to a comparator. A brief
OUT1 – Output 0 V – 5.0 V square wave with the same
description of the components is as follows:
frequency as VRS.
VRS – Ideal sinusoidal, ground referenced, sensor output
By inspection, the voltage at the (+) and (–) terminals of
– amplitude usually increases with frequency, depending on
COMP1 with VRS = 0V are:
loading.
RRS – Source impedance of sensor. V+  INP1(R1  RRS) (1)
R1/RAdj – External resistors for current limiting and
biasing.

http://onsemi.com
3
 CS1124

V–  INAdj
RAdj (2) OPEN SENSOR PROTECTION

As VRS begins to rise and fall, it will be superimposed on The CS1124 has a DIAG pin that when pulled high (5.0 V),
the DC biased voltage at V+. will increase the INAdj current source by roughly 50%.
Equation (7) shows that a larger VRS(+TRP) voltage will be
V+  INP1(R1  RRS)  VRS (3) needed to trip comparator COMP1. However, if no VRS
To get comparator COMP1 to trip, the following signal is present, then we can use equations 1, 2, and 4
condition is needed when crossing in the positive direction, (equation 5 does not apply in this mode) to get:

V+  V–  VHYS (4) INP1(R1  RRS)  INP1
KI
RAdj  VHYS (12)

(VHYS is the built–in hysteresis set to 160 mV), or when Since RRS is the only unknown variable we can solve for
crossing in the negative direction, RRS,
V+  V–  VHYS (5) INP1
KI
RAdj  VHYS
RRS   R1 (13)
INP1
Combining equations 2, 3, and 4, we get:
Equation (13) shows that if the output switches states
INP1(R1  RRS)  VRS  INAdj
RAdj  VHYS (6) when entering the diag mode with VRS = 0, the sensor
impedance must be greater than the above calculated value.
therefore, This can be very useful in diagnosing intermittent sensor.
VRS(+TRP)  INAdj
RAdj  INP1(R1  RRS)  VHYS
(7) INPUT PROTECTION
It should be evident that tripping on the negative side is: As shown in Figure 2, an active clamp is provided on each
input to limit the voltage on the input pin and prevent
VRS(–TRP)  INAdj
RAdj  INP1(R1  RRS)  VHYS
substrate current injection. The clamp is specified to handle
(8)
±12 mA. This puts an upper limit on the amplitude of the
In normal mode, sensor output. For example, if R1 = 20 k, then
INP1  INAdj (9) VRS(MAX)  20 k
12 mA  240 V

We can now re–write equation (7) as: Therefore, the VRS(pk–pk) voltage can be as high as 480 V.
The CS1124 will typically run at a frequency up to 1.8 MHz
VRS(+TR)  INP1(RAdj  R1  RRS)  VHYS (10)
if the input signal does not activate the positive or negative
By making input clamps. Frequency performance will be lower when
the positive or negative clamps are active. Typical
RAdj  R1  RRS (11) performance will be up to a frequency of 680 kHz with the
clamps active.
you can detect signals with as little amplitude as VHYS.
A design example is given in the applications section.

http://onsemi.com
4
 CS1124

CIRCUIT DESCRIPTION

Figure 3 shows the part operating near the minimum input

thresholds. As the sin wave input threshold is increased, the OUT1, 2.0 V/div IN1, 5.0 V/div

low side clamps become active (Figure 4). Increasing the

amplitude further (Figure 5), the high–side clamp becomes
active. These internal clamps allow for voltages up to –250 V
and 250 V on the sensor side of the setup (with R1 = R2 =
22 k) (reference the diagram page 1).
Figure 6 shows the effect using the diagnostic (DIAG)
function has on the circuit. The input threshold (negative) is
switched from a threshold of –160 mV to +160 mV when
DIAG goes from a low to a high. There is no hysteresis when
DIAG is high.
20 ms/div

IN1, 200 mV/div

Figure 5. Low– and High–Side Clamps

DIAG
5.0 V/div

OUT1, 2.0 V/div

IN1
1.0 V/div

OUT1
20 ms/div
5.0 V/div
Figure 3. Minimum Threshold Operation

20 ms/div

Figure 6. Diagnostic Operation

OUT1, 2.0 V/div IN1, 5.0 V/div

20 ms/div

Figure 4. Low–Side Clamp

http://onsemi.com
5
 CS1124

APPLICATION INFORMATION

Referring to Figure 2, the following will be a design 5. Calculate C1 for low pass filtering
example given these system requirements: Since the sensor guarantees 40 Vpk–pk @ 10 kHz, a low
pass filter using R1 and C1 can be used to eliminate high
RRS  1.5 k
( 12 k
is considered open)
frequency noise without affecting system performance.
VRS(MAX)  120 Vpk Gain Reduction  0.29 V  0.0145  36.7 dB
20 V
VRS(MIN)  250 mVpk Therefore, a cut–off frequency, fC, of 145 Hz could be
used.
FVRS  10 kHz @ VRS(MIN)  40 Vpk–pk 1
C1   0.07 F
2fCR1
1. Determine tradeoff between R1 value and power Set C1 = 0.047 µF.
rating. (use 1/2 watt package)

 
6. Calculate the minimum RRS that will be indicated as
120 2 an open circuit. (DIAG = 5.0 V)
2
Rearranging equation (7) gives
PD   12 W

R1
VHYS  [INP1
KI
RAdj]
Set R1 = 15 k. (The clamp current will then be 120/15 k
 VRS(+TRP)
= 8.0 mA, which is less than the 12 mA limit.)
RRS   R1
INP1
2. Determine RAdj
Set RAdj as close to R1 + RRS as possible. But, VRS = 0 during this test, so it drops out.
Therefore, RAdj = 17 k. Using the following as worst case Low and High:

3. Determine VRS(+TRP) using equation (7). Worst Case Low (RRS) Worst Case High (RRS)
INAdj 23.6 µA = 15 µA × 1.57 10.7 µA = 7.0 µA × 1.53
VRS(+TRP)  11A
17k  11A(15k  1.5k)  160 mV
RAdj 16.15 k 17.85 k

VRS(+TRP)  166 mV typical VHYS 135 mV 185 mV

(easily meets 250 mV minimum) INP1 16 µA 6.0 µA
R1 15.75 k 14.25 k
KI 1.57 1.53
4. Calculate worst case VRS(+TRP)
Examination of equation (7) and the spec reveals the worst
case trip voltage will occur when: 135 mV  23.6 A
16.15 k
RRS   15.75 k
VHYS = 180 mV 16 A
INAdj = 16 µA  16.5 k
INP1 = 15 µA
R1 = 14.25 k (5% low) Therefore,
RAdj = 17.85 k (5% High) RRS(MIN)  16.5 k (meets 12 k system spec)
VRS(+)MAX  16 A(17.85 k)
 15A(14.25 k  1.5 k)  180 mV
and,
 229 mV 185 mV  10.7 A
17.85 k
RRS(MAX)   14.25 k
6.0A
which is still less than the 250 mV minimum amplitude of  48.4 k
the input.

http://onsemi.com
6
 CS1124

PACKAGE DIMENSIONS

SO–8
D SUFFIX
CASE 751–07
ISSUE V
–X–
NOTES:
A 1. DIMENSIONING AND TOLERANCING PER ANSI
Y14.5M, 1982.
2. CONTROLLING DIMENSION: MILLIMETER.
8 5 3. DIMENSION A AND B DO NOT INCLUDE MOLD
PROTRUSION.
4. MAXIMUM MOLD PROTRUSION 0.15 (0.006) PER
B S 0.25 (0.010) M Y M SIDE.
1 5. DIMENSION D DOES NOT INCLUDE DAMBAR
PROTRUSION. ALLOWABLE DAMBAR
4
K PROTRUSION SHALL BE 0.127 (0.005) TOTAL IN
–Y– EXCESS OF THE D DIMENSION AT MAXIMUM
MATERIAL CONDITION.

C N X 45

SEATING
PLANE
–Z–
0.10 (0.004)
H M J
D

0.25 (0.010) M Z Y S X S

PACKAGE THERMAL DATA

Parameter SO–8 Unit
RΘJC Typical 45 °C/W
RΘJA Typical 165 °C/W

http://onsemi.com
7
 CS1124

ON Semiconductor and are trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC reserves the right to make changes
without further notice to any products herein. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any particular
purpose, nor does SCILLC assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability,
including without limitation special, consequential or incidental damages. “Typical” parameters which may be provided in SCILLC data sheets and/or
specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including “Typicals” must be
validated for each customer application by customer’s technical experts. SCILLC does not convey any license under its patent rights nor the rights of others.
SCILLC products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications
intended to support or sustain life, or for any other application in which the failure of the SCILLC product could create a situation where personal injury or
death may occur. Should Buyer purchase or use SCILLC products for any such unintended or unauthorized application, Buyer shall indemnify and hold
SCILLC and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable
attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim
alleges that SCILLC was negligent regarding the design or manufacture of the part. SCILLC is an Equal Opportunity/Affirmative Action Employer.

PUBLICATION ORDERING INFORMATION

Literature Fulfillment: JAPAN: ON Semiconductor, Japan Customer Focus Center
Literature Distribution Center for ON Semiconductor 4–32–1 Nishi–Gotanda, Shinagawa–ku, Tokyo, Japan 141–0031
P.O. Box 5163, Denver, Colorado 80217 USA Phone: 81–3–5740–2700
Phone: 303–675–2175 or 800–344–3860 Toll Free USA/Canada Email: r14525@onsemi.com
Fax: 303–675–2176 or 800–344–3867 Toll Free USA/Canada
ON Semiconductor Website: http://onsemi.com
Email: ONlit@hibbertco.com
For additional information, please contact your local
N. American Technical Support: 800–282–9855 Toll Free USA/Canada
Sales Representative.

http://onsemi.com CS1124/D
8