CS4121EDWFR20 ON Semiconductor, CS4121EDWFR20 Datasheet - Page 7

• Manufacturer Part Number: CS4121EDWFR20
• Description: IC TACH/SPEEDO DRIVER 20-SOIC
• Manufacturer: ON Semiconductor
• Type: Sensor Interfacer

Specifications of CS4121EDWFR20

• Input Type: Voltage
• Output Type: Differential
• Current - Supply: 125mA
• Mounting Type: Surface Mount
• Package / Case: 20-SOIC (7.5mm Width)
• Operating Supply Voltage: 13.1 V
• Supply Current: 125 mA
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Interface: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

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 conversion,
a bandgap voltage regulator for stable operation, and a
function generator with sine and cosine amplifiers to
differentially drive the meter coils.
applied to the FREQ
impedance comparator with a typical positive input
threshold of 2.0 V and typical hysteresis of 0.5 V. The output
of the comparator, SQ
input CP+ through an external capacitor C
input signal changes state, C
through R3 and R4. The charge accumulated on C
mirrored to C4 by the Norton Amplifier circuit comprising
of Q1, Q2 and Q3. The charge pump output voltage, F/V
ranges from 2.0 V to 6.3 V depending on the input signal
frequency and the gain of the charge pump according to the
formula:
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 generator 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 function generator gain:
where:
angle is:
determined by the ratio of C
F V OUT + 2.0 V ) 2.0
q + A FG
q + 970
The CS4121 is specifically designed for use with air−core
From the partial schematic of Figure 7, the input signal is
R
The output angle, q, is equal to the F/V gain multiplied by
The relationship between input frequency and output
The ripple voltage at the F/V converter’s output is
T
is a potentiometer used to adjust the gain of the F/V
FREQ
2.0
DV +
FREQ
q + A F V
A FG + 77° V(typ)
C CP
IN
OUT
C CP (V REG * 0.7 V)
FREQ
lead, this is the input to a high
or,
, is applied to the charge pump
C CP
CP
R T
CP
and C4 in the formula:
CIRCUIT DESCRIPTION and APPLICATION NOTES
C CP
C4
A FG ,
is charged or discharged
R T
R T
(V REG * 0.7 V)
(V REG * 0.7 V)
CP
. When the
http://onsemi.com
CP
OUT
is
CS4121
,
7
flutter especially at low input frequencies.
constant formed by R
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 unacceptable for
many applications.
Design Example
inaccuracies due to IC tolerances or meter movement
pointer placement.
regulator. The maximum output current from the voltage
regulator is 10 mA. R3 must ensure that the current does not
exceed this limit.
the input signal. Time for one cycle at maximum frequency
is 2.85 ms. To ensure that C
(R3 + R4) C
minimum input period.
ripple voltage and response time of the meter movement.
Charge time: t
Ripple voltage on the F/V output causes pointer or needle
The response time of the F/V is determined by the time
Maximum meter Deflection = 270
Maximum Input Frequency = 350 Hz
Let C
R
Resistor R3 sets the output current from the voltage
Choose R3 = 3.3 kW
The charge current for C
C
Choose R4 = 1.0 kW.
Discharge time: t
C4 is selected to satisfy both the maximum allowable
With C4 = 0.47 mF, the F/V ripple voltage is 44 mV.
1. Select R
2. Select R3 and R4
3. Determine C4
T
CP
should be a 250 kW potentiometer to trim out any
must charge and discharge fully during each cycle of
T
q + 970
= 0.0033 mF, find R
R T +
CP
T + 10%
T
V REG * 0.7 V
CHG
C4 +
and C
time constant is less than 10% of the
970
DCHG
3.3 kW
= (R3 + R4)C
FREQ
T
= 14.2 ms
R T + 243 kW
C CP (V REG * 0.7 V)
CP
and C4. Increasing the value of C4
= 10.9 ms
= R3 C
350 Hz
350 Hz
CP
CP
T
DV MAX
1
is
270°
C CP
+ 1.90 mA
is charged, assume that the
CP
CP
+ 285 ms
0.0033 mF
= 4.3 kW. 0.0033 mF
= 3.3 kW 0.0033 mF
R T + 270°