M63155FP datasheet(19/41 Pages) RENESAS

19 / 41 page

M63155FP

Rev.1.0, Sep.16.2003, page 19 of 40

9. Current Decay Method (DS)

The current decay method is determined by the input into the DS terminal. In slow-decay mode, only the high side

MOS FET is switched open during a PWM OFF (Low) cycle. The fast-decay mode switches both the high and low

side MOS FETs.

Table 1. gives the DS selection truth table.

TABLE 1.

DS Selection Truth Table

Function Mode

High

Slow-Decay

Low

Fast-Decay

The output MOS FETs are controlled by PWM signal as follows.

(1)Condition: Q1 is ON and Q4 is ON.

(PWM ON period)

The motor current I1 goes to RS through the

transistors Q1 and Q4.

(2)Condition: Q4 is ON and Q2, Q1 are OFF.

(PWM ON -> OFF switching period)

The discharge current I2 goes through the

diode D2. This diode is a parasitic diode of the

output power FET.

(3)Condition: Q4 is ON and Q2, Q1 are OFF.

(PWM OFF period)

The discharge current I2 keeps going through

the diode D2. Q2 keeps being OFF.

(4)Condition: Q4 is ON and Q2, Q1 are OFF.

(PWM OFF -> ON switching period)

Likewise state (3), the discharge current I2

keeps going through the diode D2. Q2 keeps

being OFF.

a) Slow-Decay Function

b) Fast-Decay Function

(1)Condition: Q1 is ON and Q4 is ON

(PWM ON period)

The motor current I1 goes to RS through the

transistors Q1 and Q4.

(2)Condition: Q1, Q4, Q2 and Q3 are OFF.

(PWM ON -> OFF switching period)

The discharge current I2 goes through the

diode D2 and D3. This diode is a parasitic diode of

the output power FET.

(3)Condition: Q1, Q4, Q2 and Q3 are OFF.

(PWM OFF period)

The discharge current I2 keeps going through

the diode D2 and D3.

(4)Condition: Q1, Q4, Q2 and Q3 are OFF.

(PWM OFF -> ON switching period)

Likewise state (2), the discharge current I2 goes

through the diode D2 and D3.

* When all the output power FETs are OFF, for example as

the phase change, the discharge current goes to VM through

these parasitic diodes.

Fig. 9 Current Decay Method at the MOS FETs Control with PWM Signal

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