M54679SP 查看數據表（PDF） - Renesas Electronics

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产品描述 (功能)

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M54679SP

2-Phase Stepper Motor Driver

Renesas Electronics 

M54679SP

(3) Equivalent circuit of Vref terminal.

The equivalent circuit of Vref terminal is shown in bellow circuit. As Vref terminal needs typical 500 µA input

current, consider this value when Vref voltage is set.

Vref

18K

3.5K 0.68K

2K

I0

I1

(4) Current sensing comparators.

The current sensing comparators compare the voltage (VRS) of current sensing resistor and threshold voltage (VCH) of

this comparators, then if VRS > VCH, the comparators output change and shut off the output.

(5) Oscillation circuit.

External capacitor (390 pF typ) is charged and discharged by the constant current and a triangular waveform (VTH (Fref

terminal high voltage) = 2.5 V, VTL (Fref terminal low voltage) = 0.5 V) appears to Fref terminal.

This triangular waveform is a carrier frequency of PWM circuit. The carrier frequency changes if this external

capacitor value is changed.

M54679SP is designed that the oscillation frequency is 30 kHz if the external capacitor value is 390 pF.

The oscillation frequency is in inverse proportion to the value of an external capacitor.

(6) Spike current cancellation.

Output power transistors go to ON, then the spike current appears on the RS (current sensing) in a short time and this is

caused by the internal delay time. M54679SP has the cancellation circuit of the spike current as the current sensing

comparators do not cause error functions.

So, the function of current sensing comparators is shut off during 2 µs since the output power transistors go to ON.

(7) Ph signal delay circuit.

M54679SP has a delay time of 3.0 µs until output H-bridge power stage go to ON since Ph signal change Low to high.

This delay time is enough short time for the frequency (plus rate) of Ph signal and there is no problem in the normal

function.

(8) Rs and S1 or S2 terminal.

If S1 or S2 terminal (non-inverted input of the current sensing comparators) is connected the nearest position of current

sensing resistor, the error of the current sensing by means of wire resistance on the board will be decreased.

(9) Voltage stabilizer.

M54679SP has a voltage stabilizer of 3.5 V. The reference voltage (Vref) can connect the output (Regout) of voltage

stabilizer directly. In this case, the current capability of the output of voltage stabilizer is 1.0 mA (source current), 0.1

mA (sink current).

Rev.1.0, Sep.17.2003, page 6 of 11

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