OM9373 データシートの表示（PDF） - International Rectifier

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OM9373

FULL-FEATURED POWER MODULE FOR DIRECT DRIVE OF 3-PHASE BRUSHLESS DC MOTOR

International Rectifier 

OM9373

QUAD SELECT INPUT (Pin 14) -- This input is used

to set the OM9373 in a half control or full control

chopping regime. When driven with a logic low level,

the OM9373 is in the half control mode, whereby only

the three lower (pull-down) power switches associated

with the Phase Outputs are allowed to chop. Alternately,

when driven with a logic high level, the OM9373 is

in the full control mode, where all six power switches

(pull-up and pull-down) associated with the Phase

Outputs are chopped by the PWM. During motor braking,

changing the logic state of the Quad Select Input

has no effect on the operation of the OM9373.

TACHOMETER OUTPUT (Pin 15) -- This output

provides a fixed width 5V pulse when any Hall-

effect Input (1, 2 or 3) changes state. The pulse width

of the Tachometer Output is set internally in the

OM9373 to 113µs (nominal). The average value of

the output voltage on pin 15 is directly proportional

to the motor's speed, so this output may be used

(with an external averaging filter) as a true tachometer

output, and fed back to the Speed Input (pin 23) to

sense the actual motor speed.

Note: Whenever pin 15 is high, the internal Hall-effect

position latches are inhibited (i.e. "latched"), to reject

noise during the chopping portion of the commutation

cycle, and this makes additional com mutations

impossible. This means that in order to prevent false

commutation at a speed less than the desired maximum

speed, the highest speed as observed at the Tachometer

Output should be set above the expected maximum

value.

BRAKE / TACH TIMING INPUT (Pin 16) -- The

Brake/Tach Timing Input is a dual-purpose input.

Internal to the OM9373 are timing components tied

from pin 16 to Ground (a 51kΩ resistor and a 3300pF

capacitor) These components set the minimum pulse

width of the Tachometer Output to 113µs, and this

time may be adjusted using external components,

according to the equation:

( ) T(tach) = 0.67 x (Ct + 3300pf) x Rt x 51kΩ (µs)

Rt + 51kΩ

The recommended range of external resistance (to

Ground) is 15kΩ to ∞, and the range of external

capacitance (to Ground) is 0pF to 0.01uF. With each

Tachometer Output pulse, the capacitor tied to pin

16 is discharged from approximately 3.33V to

approximately 1.67V by an internal timing resistor.

The Brake / Tach Timing Input has another function.

If this pin is pulled below the brake threshold

voltage, the OM9373 will enter the brake mode. The

brake mode is defined as the disabling of all three

high-side (pull-up) drivers associated with the Phase

Outputs, and the enabling of all three low-side (pull-

down) drivers.

OVERVOLTAGE / COAST INPUT (Pin 17) -- This

input may be used as a shutdown or an enable/

disable input to the OM9373. Also, since the switching

inhibit threshold is so tightly defined, this input can

be directly interfaced with a resistive divider which

senses the voltage of the motor supply, Vm, for

overvoltage conditions. A high level (greater than the

inhibit threshold) on pin 17 causes the coast condition

to occur, whereby all Phase Outputs revert to a Hi-Z

state and any motor current which flowed prior to the

Overvoltage/ Coast command and is commutated via the

power "catch" rectifiers associated with each Phase

Output.

SOFT-START INPUT (Pin 18) -- The Soft-Start input

is internally connected to a 10µA (nominal) current

source, the collector of an NPN clamp/discharge

transistor, and a voltage comparator whose soft-

start/restart threshold is 0.2Vdc (nominal). An

external capacitor is connected from this pin to

Ground (pin 19). Whenever the Vcc supply input

drops below the turn-on threshold, approximately

9Vdc, or the sensed current exceeds the over-

current threshold, approximately 0.3V at the current

sense amplifier, the soft-start latch is set. This drives

the NPN clamp transistor which discharges the

external soft-start capacitor. When the capacitor

voltage drops below the soft-start/restart threshold

and a fault condition does not exist, the soft-start

latch is cleared; the soft-start capacitor charges via

the internal current source.

In addition to discharging the soft-start capacitor, the

clamp transistor also clamps the output of the error

amplifier internal to the controller IC, not allowing

the voltage at the output of the error amplifier to

exceed the voltage at pin 18, regardless of the

inputs to the amplifier. This action provides for an

orderly motor start-up either at start-up or when

recovering from a fault condition.

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