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HA16121FP Datasheet(PDF) 8 Page - Hitachi Semiconductor |
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HA16121FP Datasheet(HTML) 8 Page - Hitachi Semiconductor |
8 / 34 page HA16116FP/FPJ, HA16121FP/FPJ 8 The triangle wave is a voltage waveform used as a reference in creating a PWM pulse. This block operates according to the following principles. A constant current I O, determined by an external timing resistor RT, is made to flow continuously to external timing capacitor C T. When the C T pin voltage exceeds the comparator threshold voltage V H, the comparator output causes a switch to operate, discharging a current IO from C T. Next, when the C T pin voltage drops below threshold voltage VL, the comparator output again causes the switch to operate, stopping the I O discharge. The triangle wave is generated by this repeated operation. Note that I O = 1.1 V/RT. Since the IO current mirror circuit has a very limited current producing ability, RT should be set to ≥ 5 kΩ (I O ≥ 220 µA). With this IC series, V H and VL of the triangle wave are fixed internally at about 1.6 V and 1.0 V by the internal resistors R A, RB, and RC. The oscillator frequency can be calculated as follows. 1 t1 + t2 + t3 fOSC = t1 = CT ⋅ (VH − VL) 1.1 V/RT CT RT ⋅ (VH − VL) 1.1 V = t2 = CT ⋅ (VH − VL) (2 − 1) × 1.1 V/R T CT RT ⋅ (VH − VL) 1.1 V == t1 VH − VL = 0.6 V 1 2t1 + t3 fOSC ≈ ≈ 1 1.1 CT RT + 0.8 µs [Hz] t1 = t2 = CT RT 0.6 1.1 t3 ≈ 0.8 µs (comparator delay time in the oscillator) Accordingly, Here, Note that the value of f OSC may differ slightly from the above calculation depending on the amount of delay in the comparator circuit. Also, at high frequencies this comparator delay can cause triangle wave overshoot or undershoot, skewing the dead band threshold. Confirm the actual value in implementation and adjust the constants accordingly. |
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