CS289 Datasheet, PDF (4/8 Pages) Cherry Semiconductor Corporation – 20mA Air-Core Tachometer Drive Circuit

Circuit Description
Charge Pump
The input frequency is buffered through a transistor, then
applied to the charge pump for frequency-to-voltage con-
version (Figure 1). The charge pump output voltage, E∅,
will range from 2.1V with no input (∅= 0°) to 7.1V at ∅ =
270°. The charge that appears on C_T is reflected to C_OUT
through a Norton amplifier. The frequency applied at
S_QIN charges and discharges C_T through R₁ and R₂. C_OUT
reflects the charge as a voltage across resistor R_T.
Function Generator/Sine and Cosine Amplifiers
The output waveforms of the sine and cosine amplifiers
are derived by On-Chip Amplifier/Comparator circuitry.
The various trip points for the circuit (i.e. 90°, 180°, 270°)
are determined by an internal resistor divider connected
to the voltage regulator. The voltage E∅ is compared to
the divider network by the function generator circuitry.
Use of an external zener reference at V_Z allows both sine
and cosine amplifiers to swing positive and negative with
respect to this reference. The output magnitudes and
directions have the relationship as shown in Typical
Characteristics diagrams.
Note: Pin connections referenced are for the 14L DIP.
Function Generator Output (∅): V_CC=13.1V, T_A=25°C
∅=ArcTan ^Vsine (Measured angle after calibration at 180°C)
V cos
For ∅_A=45°, 90°, 135°, 180°, 225°, 270°, (Desired angle)
(∅_A-∅_M)≤4.0°
Temperature Sensitivity: V_CC=13.1V
∆∅_MT=∅_M (T=25°C) -∅M (-20°C≤T≤+85°C)
(∆∅_MT)≤3.5°C, -20°C≤T≤+85°C
15
B+
18V
Voltage Sensitivity: T_A=25°C
∆∅_MV=∅_M (V_CC=13.1V) -∅_M (11.3V≤V_CC≤15V)
(∆∅_MV)≤2°, 11.3V≤V_CC≤15V
B+
100Ω
ZENER
5.4V
80mH
225
SINE
80mH
225
Figure 1. Functional Diagram of CS289 Circuit.
1kΩ
2kΩ
TACH INPUT
R2
2kΩ
E_Θ
CS289
C_OUT
1µF
±10%
R_T
180kΩ
*
R1
C_T
1kΩ
0.01µF
* ADJUST FOR TRIMMING
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