1
Features
SINE-
SINE+
Gnd
V
REG
F/V
OUT
SINE
Output
COS
Output
V
REG
7.0V
V
CC
COS-
COS+
Gnd
Gnd
FREQ
IN
SQ
OUT
CP+
Input
Comp.
+
Gnd
CP-
Voltage
Regulator
High Voltage
Protection
BIAS
Charge Pump
Func.
Gen.
+
+
+
+
+
s
Direct Sensor Input
s
High Torque Output
s
Low Pointer Flutter
s
High Input Impedance
s
Overvoltage Protection
s
Accurate to 8V
Functional to 6.5V (typ)
Package Options
16 Lead PDIP
(internally fused leads)
20 Lead SOIC
(internally fused leads)
CS4121
Low Voltage Precision Air-Core
Tach/Speedo Driver
1
CP+
2
3
4
5
6
7
8
SQ
OUT
FREQ
IN
Gnd
Gnd
COS+
COS-
V
CC
16
15
14
13
12
11
10
9
CP-
F/V
OUT
V
REG
Gnd
Gnd
SINE+
SINE-
BIAS
1
CP+
2
3
4
5
6
7
8
SQ
OUT
FREQ
IN
Gnd
Gnd
Gnd
Gnd
COS+
16
15
14
13
12
11
10
CP-
F/V
OUT
V
REG
Gnd
Gnd
Gnd
Gnd
SIN+
9
COS-
SIN-
17
18
V
CC
BIAS
19
20
CS4121
Description
The CS4121 is specifically designed
for use with air-core meter move-
ments. The IC provides all the func-
tions necessary for an analog
tachometer or speedometer. The
CS4121 takes a speed sensor input
and generates sine and cosine relat-
ed output signals to differentially
drive an air-core meter.
Many enhancements have been
added over industry standard
tachometer drivers such as the
CS289 or LM1819. The output uti-
lizes differential drivers which elim-
inates the need for a zener reference
and offers more torque. The device
withstands 60V transients which
decreases the protection circuitry
required. The device is also more
precise than existing devices allow-
ing for fewer trims and for use in a
speedometer.
The CS4121 is compatible with the
CS8190, and provides higher accu-
racy at a lower supply voltage (8.0V
min. as opposed to 8.5V). It is func-
tionally operational to 6.5V.
Block Diagram
Absolute Maximum Ratings
Supply Voltage (<100ms pulse transient)..........................................V
CC
= 60V
(continuous) ..............................................................V
CC
= 24V
Operating Temperature .............................................................40C to +105C
Storage Temperature..................................................................40C to +165C
Junction Temperature .................................................................40C to+150C
ESD (Human Body Model) .............................................................................4kV
Lead Temperature Soldering
Wave Solder (through hole styles only)............10 sec. max, 260C peak
Reflow (SMD styles only).............60 sec. max above 183C, 230C peak
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
A Company
Rev 12/4/96
2
Electrical Characteristics: -40C T
A
85C, 8.0V V
CC
16V unless otherwise specified.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
CS4121
s Supply Voltage Section
I
CC
Supply Current
V
CC
= 16V, -40C, No Load
50
125
mA
V
CC
Normal Operation Range
8.0
13.1
16.0
V
s Input Comparator Section
Positive Input Threshold
1.0
2.0
3.0
V
Input Hysteresis
200
500
mV
Input Bias Current *
0V V
IN
8V -10
-80
A
Input Frequency Range
0
20
kHz
Input Voltage Range
in series with 1k
-1
V
CC
V
Output V
SAT
I
CC
= 10mA
0.15
0.40
V
Output Leakage
V
CC
= 7V
10
A
Logic 0 Input Voltage
1
V
*Note: Input is clamped by an internal 12V Zener.
s Voltage Regulator Section
Output Voltage
6.25
7.00
7.50
V
Output Load Current
10
mA
Output Load Regulation
0 to 10 mA
10
50
mV
Output Line Regulation
8.0V V
CC
16V
20
150
mV
Power Supply Rejection
V
CC
= 13.1V, 1V
P
/
P
1kHz
34
46
dB
s Charge Pump Section
Inverting Input Voltage
1.5
2.0
2.5
V
Input Bias Current
40
150
nA
Vbias Input Voltage
1.5
2.0
2.5
V
Non Invert. Input Voltage
I
IN
= 1mA
0.7
1.1
V
Linearity*
@ 0, 87.5, 175, 262.5, + 350Hz
-0.10
0.28
+0.70
%
F/V
OUT
Gain
@ 350Hz, C
T
= 0.0033F, R
T
= 243k
7
10
13
mV/Hz
Norton Gain, Positive
I
IN
= 15A
0.9
1.0
1.1
I/I
Norton Gain, Negative
I
IN
= 15A
0.9
1.0
1.1
I/I
*Note: Applies to % of full scale (270).
s Function Generator Section: -40C T
A
85C, V
CC
= 13.1V unless otherwise noted.
Differential Drive Voltage
8.0V V
CC
16V
5.5
6.5
7.5
V
(V
COS
+ - V
COS
-)
Q = 0
Differential Drive Voltage
8.0V V
CC
16V
5.5
6.5
7.5
V
(V
SIN
+ - V
SIN
-)
Q = 90
Differential Drive Voltage
8.0V V
CC
16V
-7.5
-6.5
-5.5
V
(V
COS
+ - V
COS
-)
Q = 180
Differential Drive Voltage
8.0V V
CC
16V
-7.5
-6.5
-5.5
V
(V
SIN
+ - V
SIN
-)
Q = 270
Differential Drive Current
8.0V V
CC
16V, T
A
=25C
33
42
mA
Zero Hertz Output Angle
-1.5
0.0
1.5
deg
Function Generator Error *
V
CC
= 13.1V, T
A
=25C
-2
0
+2
deg
Reference Figures 1,2,3,4
Q = 0 to 305
*Note: Deviation from nominal per Table 1 after calibration at 0 and 270.
3
PACKAGE LEAD #
LEAD SYMBOL
FUNCTION
CS4121
Electrical Characteristics: continued
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
Package Lead Description
Typical Performance Characteristics
0
45
90
135
180
225
270
315
Output V
oltage (V)
Degrees of Deflection (
)
7
6
5
4
3
2
1
0
-1
-2
-3
-4
-5
-6
-7
COS
SIN
0
45
90
135
180
225
270
315
F/V Output (V)
Frequency/Output Angle (
)
7
6
5
4
3
2
1
0
Figure 2: Charge Pump Output Voltage vs Output Angle
Figure 1: Function Generator Output Voltage
vs Degrees of Deflection
F/V
OUT
= 2.0V + 2 FREQ
C
T
R
T
(V
REG
- 0.7)
s Function Generator Section: continued
Function Generator Error
13.1V V
CC
16V, T
A
=25C
-2.5
0
+2.5
deg
Function Generator Error
13.1V V
CC
11V, T
A
=25C
-1
0
+1
deg
Function Generator Error
13.1V V
CC
8V, T
A
=25C
-3
0
+3
deg
Function Generator Error
25C T
A
85C
-3
0
+3
deg
Function Generator Error
25C T
A
105C
-5.5
0
+5.5
deg
Function Generator Error
40C T
A
25C
-3
0
+3
deg
Function Generator Gain
T
A
= 25C
Q vs F/V
OUT
60
77
95
/V
16L PDIP*
20L SO*
1
1
CP+
Positive input to charge pump.
2
2
SQ
OUT
Buffered square wave output signal.
3
3
FREQ
IN
Speed or rpm input signal.
4, 5, 12, 13
4-7, 14-17
Gnd
Ground Connections.
6
8
COS+
Positive cosine output signal.
7
9
COS-
Negative cosine output signal.
8
10
V
CC
Ignition or battery supply voltage.
9
11
BIAS
Test point or zero adjustment.
10
12
SIN-
Negative sine output signal.
11
13
SIN+
Positive sine output signal.
14
18
V
REG
Voltage regulator output.
15
19
F/V
OUT
Output voltage proportional to input signal frequency.
16
20
CP-
Negative input to charge pump.
*Internally Fused Leads
4
0
0
1
1.09
2
2.19
3
3.29
4
4.38
5
5.47
6
6.56
7
7.64
8
8.72
9
9.78
10
10.84
11
11.90
12
12.94
13
13.97
14
14.99
15
16.00
16
17.00
17
17.98
18
18.96
19
19.92
20
20.86
21
21.79
22
22.71
23
23.61
24
24.50
25
25.37
26
26.23
27
27.07
28
27.79
29
28.73
30
29.56
31
30.39
32
31.24
33
32.12
34
33.04
35
34.00
36
35.00
37
36.04
38
37.11
39
38.21
40
39.32
41
40.45
42
41.59
43
42.73
44
43.88
45
45.00
50
50.68
55
56.00
60
60.44
65
64.63
70
69.14
75
74.00
80
79.16
85
84.53
90
90.00
95
95.47
100
100.84
105
106.00
110
110.86
115
115.37
120
119.56
125
124.00
130
129.32
135
135.00
140
140.68
145
146.00
150
150.44
155
154.63
160
159.14
165
164.00
170
169.16
175
174.33
180
180.00
185
185.47
190
190.84
195
196.00
200
200.86
205
205.37
210
209.56
215
214.00
220
219.32
225
225.00
230
230.58
235
236.00
240
240.44
245
244.63
250
249.14
255
254.00
260
259.16
265
264.53
270
270.00
275
275.47
280
280.84
285
286.00
290
290.86
295
295.37
300
299.21
305
303.02
Ideal
Q
Nominal
Ideal
Q
Nominal
Ideal
Q
Nominal
Ideal
Q
Nominal
Ideal
Q
Nominal
Ideal
Q
Nominal
Degrees
Q Degrees
Degrees
Q Degrees
Degrees
Q Degrees
Degrees
Q Degrees
Degrees
Q Degrees
Degrees
Q Degrees
Typical Performance Characteristics: continued
CS4121
Nominal Angle vs. Ideal Angle (After calibrating at 180)
+7V
7V
(V
COS+
) - (V
COS-
)
7V
Angle
-7V
Q
(V
SINE+
) - (V
SINE-
)
]
V
SIN+
V
SIN-
V
COS+
V
COS-
Q = ARCTAN
[
-1.50
Deviation (
)
0
45
90
135
180
225
270
315
-1.25
-1.00
-0.75
-0.50
-0.25
0.00
0.25
0.50
0.75
1.00
1.25
1.50
Theoretical Angle (
)
Figure 4: Nominal Output Deviation
Figure 3: Output Angle in Polar Form
Ideal Angle
(Degrees)
Nominal Angle (Degrees)
0
5
10
15
20
25
30
35
40
45
1
5
9
13
17
21
25
29
33
37
41
45
Ideal Degrees
Nominal Degrees
Table 1:
Function Generator Output Nominal Angle vs. Ideal Angle (After calibrating at 270)
Note:
Temperature, voltage and nonlinearity not included.
Note:
Temperature, voltage and nonlinearity not included.
5
CS4121
The CS4121 is specifically designed for use with air-core
meter movements. It includes an input comparator for
sensing an input signal from an ignition pulse or speed
sensor, a charge pump for frequency to voltage conver-
sion, a bandgap voltage regulator for stable operation,
and a function generator with sine and cosine amplifiers
to differentially drive the motor coils.
From the simplified block diagram of Figure 5A, the
input signal is applied to the FREQ
IN
lead, this is the
input to a high impedance comparator with a typical pos-
itive input threshold of 2.0V and typical hysteresis of
0.5V. The output of the comparator, SQ
OUT
, is applied to
the charge pump input CP+ through an external capacitor
C
T
. When the input signal changes state, CT is charged
or discharged through R3 and R4. The charge accumulat-
ed on C
T
is mirrored to C4 by the Norton Amplifier cir-
cuit comprising of Q1, Q2 and Q3. The charge pump out-
put voltage, F/V
OUT
, ranges from 2V to 6.3V depending
on the input signal frequency and the gain of the charge
pump according to the formula:
F/V
OUT
= 2.0V + 2
FREQ C
T
R
T
(V
REG
0.7V)
R
T
is a potentiometer used to adjust the gain of the F/V
output stage and give the correct meter deflection. The
F/V output voltage is applied to the function generator
which generates the sine and cosine output voltages. The
output voltage of the sine and cosine amplifiers are
derived from the on-chip amplifier and function genera-
tor circuitry. The various trip points for the circuit (i.e., 0,
90, 180, 270) are determined by an internal resistor
divider and the bandgap voltage reference. The coils are
differentially driven, allowing bidirectional current flow
in the outputs, thus providing up to 305 range of meter
deflection. Driving the coils differentially offers faster
response time, higher current capability, higher output
voltage swings, and reduced external component count.
The key advantage is a higher torque output for the
pointer.
The output angle,
Q, is equal to the F/V gain multiplied
by the function generator gain:
Q = A
F/V
A
FG
,
where:
A
FG
= 77/V (typ)
The relationship between input frequency and output
angle is:
Q = A
FG
2 FREQ C
T
R
T
(V
REG
0.7V)
or,
Q = 970 FREQ C
T
R
T
The ripple voltage at the F/V converters output is deter-
mined by the ratio of C
T
and C4 in the formula:
V =
Ripple voltage on the F/V output causes pointer or nee-
dle flutter especially at low input frequencies.
The response time of the F/V is determined by the time
constant formed by R
T
and C4. Increasing the value of C4
will reduce the ripple on the F/V output but will also
increase the response time. An increase in response time
causes a very slow meter movement and may be unac-
ceptable for many applications.
Design Example
Maximum meter Deflection = 270
Maximum Input Frequency = 350Hz
1. Select R
T
and C
T
Q = A
GEN
F/V
F/V
= 2
FREQ C
T
R
T
(V
REG
0.7V)
Q = 970 FREQ C
T
R
T
Let C
T
= 0.0033F, Find R
T
R
T
=
R
T
= 243k
R
T
should be a 250k potentiometer to trim out any inac-
curacies due to IC tolerances or meter movement pointer
placement.
2. Select R3 and R4
Resistor R3 sets the output current from the voltage regu-
lator. The maximum output current from the voltage reg-
ulator is 10mA R3 must ensure that the current does not
exceed this limit.
Choose R3 = 3.3k
The charge current for C
T
is
= 1.90mA
C1 must charge and discharge fully during each cycle of
the input signal. Time for one cycle at maximum frequen-
cy is 2.85ms. To ensure that C
T
is discharged, assume that
the (R3 + R4) C
T
time constant is less than 10% of the
minimum input frequency pulse width.
T = 285s
Choose R4 = 1k.
Charge time:
T = R3
C
T
= 3.3k
0.0033F = 10.9s
Discharge time:T = (R3 + R4)C
T
= 4.3k
0.0033F = 14.2s
3. Determine C4
C4 is selected to satisfy both the maximum allowable rip-
ple voltage and response time of the meter movement.
C4 =
With C4 = 0.47F, the F/V ripple voltage is 44mV.
Figure 7 shows how the CS4121 and the CS-8441 are used
to produce a Speedometer and Odometer circuit.
C
T
(V
REG
0.7V)
V
RIPPLE(MAX)
V
REG
0.7V
3.3k
270
970
350Hz 0.0033F
C
T
(V
REG
0.7V)
C4
Circuit Description and Application Notes
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