M63155FP

Rev.1.0, Sep.16.2003, page 21 of 40

12. Braking Mode Selection (BRS)

1) In the normal mode (FLT output is “H”)

The braking mode whether coast (free-run) or brake (short-brake) is selected by the BRS terminal. In the coast

(free-run) mode, all of the output terminals are floating. On the other side, in the brake (short-brake) mode, all of

the top side MOS FETs are turned off and all of the bottom side MOS FETs are turned on. This Braking Mode

provides a braking torque which depends on the motor speed.

2) In the fault mode (FLT output is “L”)

In this case, the braking mode whether coast or brake is selected by the PWM signal irrelevant to the BRK

signal and the Current Control (RSS, CTL, TCL) function. The BRS state is latched by the FLT “L” signal. In

the BRS “L” state the coast mode is selected, while in the BRS “H” state the PWM signal determines the brake

mode.

And at this time, the positive power supply for the gate of the bottom side MOS FETs is provided by the charge-

pump external capacitor (Cgb; cf. Application circuit).

If gate drive to the bottom side MOS FETs is chopped via external control of the PWM pin, the minimum value

for Cgb is given in the following formula.

Coarse Cgb calculation

Cgb(min)= t x f x 3q(gate) / [Vcgb(initial) - Vcgb(final)]

for C in farads:

t = soft braking time (sec)

f = a chop frequency for PWM pin (Hz)

q(gate) = a electric charge stored in MOS FET gate (C)

q(gate) : refer to the data sheet of selected MOS FET

* In brake mode, the three bottom side MOS FETs(UB,VB,WB) turns on simultaneously. So, it is needed

by 3q(gate).

Vcgb = delta V from initial to final (volts)

Table 3. gives the BRS selection truth table.

TABLE 3.

BRS Selection Truth Table

normal mode (FLT;H)

fault mode (FLT;L)

BRS

BRK; H

BRK; L

PWM; H

PWM; L

High

Normal

Brake

Brake

Coast

Low

Normal

Coast

Coast

13. Reset input (RST)

This input used to enable the device. The “H” input allows the gate drive output to follow “Motor I/O truth table”.

The “L” input forces all gate drive output to 0V, coast(free-run) mode, and overrides the BRK state. And this “L”

input also resets the BRS state latched by the FLT “L” signal.

Table 4. gives the RST selection truth table.

TABLE 4.

RST Selection Truth Table

RST

Function Mode

High

Enable the device

Low

Disable the device (Reset the BRS and FLT state)