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Moteur de recherche de fiches techniques de composants électroniques |
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Moteur de recherche de fiches techniques de composants électroniques |
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CS4121 Fiches technique(PDF) 5 Page - Cherry Semiconductor Corporation |
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CS4121 Fiches technique(HTML) 5 Page - Cherry Semiconductor Corporation |
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5 / 8 page  5 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 FREQIN 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, SQOUT, is applied to the charge pump input CP+ through an external capacitor CT. When the input signal changes state, CT is charged or discharged through R3 and R4. The charge accumulat- ed on CT is mirrored to C4 by the Norton Amplifier cir- cuit comprising of Q1, Q2 and Q3. The charge pump out- put voltage, F/VOUT, ranges from 2V to 6.3V depending on the input signal frequency and the gain of the charge pump according to the formula: F/VOUT = 2.0V + 2 ´ FREQ ´ CT ´ RT ´ (VREG Ð 0.7V) RT 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 = AF/V ´ AFG, where: AFG = 77¡/V (typ) The relationship between input frequency and output angle is: Q = AFG ´ 2 ´ FREQ ´ CT ´ RT ´ (VREG Ð 0.7V) or, Q = 970 ´ FREQ ´ CT ´ RT The ripple voltage at the F/V converterÕs output is deter- mined by the ratio of CT and C4 in the formula: ÆV = 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 RT 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 RT and CT Q = AGEN ´ ÆF/V ÆF/V = 2 ´ FREQ ´ CT ´ RT ´ (VREG Ð 0.7V) Q = 970 ´ FREQ ´ CT ´ RT Let CT = 0.0033µF, Find RT RT = RT = 243k½ RT should be a 250k½ 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 = 3.3k½ The charge current for CT 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 CT is discharged, assume that the (R3 + R4) CT time constant is less than 10% of the minimum input frequency pulse width. T = 285µs Choose R4 = 1k½. Charge time: T = R3 ´ CT = 3.3k½ ´ 0.0033µF = 10.9µs Discharge time:T = (R3 + R4)CT = 4.3k½ ´ 0.0033µF = 14.2µs 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 = 0.47µF, 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. CT(VREG Ð 0.7V) VRIPPLE(MAX) VREG Ð 0.7V 3.3k½ 270¡ 970 ´ 350Hz ´ 0.0033µF CT(VREG Ð 0.7V) C4 Circuit Description and Application Notes |
Numéro de pièce similaire - CS4121 |
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Description similaire - CS4121 |
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