Pulse-width modulators (PWMs) used many purposes. Analog signals often

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Pulse-width modulators (PWMs) used many purposes. Analog signals often

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Pulse Width Modulator Using ispPAC®20
Pulse-width modulators (PWMs) used many purposes. Analog signals often pulse-width modulated transmission along fiber-optic links across isolation barriers. most common PWMs, however, controlling power electronics. rapidly switching power transistor specific duty cycle, possible make that transistor appear proportionally from standpoint load. There several advantages duty cycling transistor on-off digital operating mode opposed operating device linear mode. first that more system's power delivered load wasted heat transistor. losses well designed power driver order magnitude lower than those comparable linear-mode power driver. example this shown Figure power transistor linear driver resistive heater element (Figure will dissipate much power heater when operated power. transistor driver either 100% power time, however, same amount average power delivered load, transistor dissipates much less power. Additionally, case certain kinds reactive loads, such motors, pulse-width modulated driver circuit switching power supply, converting high-voltage, average-current input into low-voltage high average current output available drive load. Figure Resistive Heater Driven with Linear Driver Driver
100% 100%
Power 100% duty cycle
100% Power duty cycle
RLOAD
RLOAD
Figure shows ispPAC20 device used develop digital output, where duty cycle value loaded into DAC. output signal produced CP2OUT pin. This circuit operates following way. input amplifier output amplifier used form fixedrate integrator, driven from on-chip 1.5V reference. IA4's polarity control determines direction down) which integration occurs. tying output back negative CPIN (and tying positive VREFout) Comparator configured Schmidt trigger with hysteresis. combining this Schmidt trigger with integrator, obtains fixed-frequency triangle-wave oscillator. waveforms developed this oscillator shown Figure frequency this oscillator controlled value OA2's feedback capacitor. value shown (61.59pF), operating frequency approximately 10kHz. reducing value capacitor, this frequency increased approximately 200kHz with tradeoff reduced linearity duty-cycle input voltage.
www.latticesemi.com
cs1012_01
Lattice Semiconductor
Figure Pulse-width Modulator Using ispPAC20
Pulse Width Modulator Using ispPAC20
ispPAC20
VREF 2.5V 61.59pF
VREFout
CPIN
CP1OUT
1.5V
Polarity Control: CP1OUT Internal Signal Path
CP2OUT
OUTPUT
Figure Voltage Waveforms
CP1OUT
+2.5V
INPUT
-2.5V +2.5V
OUTPUT
-2.5V
CP2OUT
Lattice Semiconductor
Pulse Width Modulator Using ispPAC20
Comparator used compare value triangle waveform appearing output OA2. duty cycle CP2's output proportional time which triangle wave (after being inverted) greater than voltage. this way, value sets duty cycle output signal. Because signal inversion CP2's input, scale inverted, with voltage -2.5V (code 15h) providing 100% duty cycle, voltage 2.5V (code providing duty cycle. also possible control duty cycle external input voltage. external signal brought through input routed directly CP2's negative input, leaving PACblock free used other functions. Voltage controlled PWMs especially useful feedback control systems motors, solenoids temperature controllers.
Technical Support Assistance
Hotline: 1-800-LATTICE (Domestic) 1-408-826-6002 (International) e-mail: ispPACs@latticesemi.com

Pulse-width modulators (PWMs) used many purposes. Analog signals often

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