Page 7

3932

THREE-PHASE POWER MOSFET CONTROLLER

APPLICATION INFORMATION

consumption in the external MOSFETs, the 3932 control

logic will turn on the appropriate driver during the load

current recirculation, PWM “off” cycle. The intrinsic body

diode of the power MOSFET will only conduct during the

dead time required at each PWM transition.

current for the gate drive circuit. As the gates are driven high

they will require current from an external decoupling

capacitor to support the transients. This capacitor should be

placed as close as possible to the VREG pin. The value of

the capacitor should be at least 20 times larger than the

bootstrap capacitor. Additionally, a 1nF ceramic monolithic

capacitor should be connected between LCAP and AGND as

close to the device pins as possible.

external MOSFETs by turning off all MOSFETs if any of the

following fault conditions are detected.

1)

Gate Source Monitor (high side only). The

voltage on GHx pins must stay within 3.3V of the

bootstrap capacitor voltage during an ON cycle. If this

voltage droops below this threshold the high side turns

off, and the low side gate will turn on in an attempt to

recharge the bootstrap capacitor. When the bootstrap

capacitor has been properly charged, the high side is

turned back on. The circuit will allow three faults of this

type within one commutation cycle before signaling a

fault and coast the motor.

2)

Bootstrap Monitor. The bootstrap capacitor is

charged whenever a sink side FET is on, Sx output goes

low, and load current recirculates. This happens

constantly during normal operation. A 170µs timer is

started at the beginning of this cycle and the capacitor is

charged with typically 100 mA. If the charge current

remains higher than 13mA or the Sx node remains

higher than 2V for longer than the 170µs a fault will be

signaled and the motor will coast.

3)

Undervoltage. VREG supplies the low side gate

driver and the bootstrap charge current. It is critical to

ensure that the voltages are at a proper level before

enabling any of the outputs. The undervoltage circuit is

active during power up and will force a motor coast

condition until VREG is greater than approximately

10V.

4)

Hall Invalid. Illegal codes for the hall inputs (000/111)

will force a fault and coast the motor.

5)

Thermal Shutdown. Junction temperature greater

6)

Motor Lead. The 3932 will signal a fault if the motor

lead is shorted to ground or supply. The status is

checked after any high side has turned on.

Faults are cleared at the beginning of each commutation. If a

stalled motor results from a fault, the fault can only be

cleared by toggling the RESET pin or by a power up

sequence.