OM9375 Просмотр технического описания (PDF) - Omnirel Corp => IRF

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OM9375

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

Omnirel Corp => IRF 

OM9375

TACHOMETER OUTPUT (Pin 15) -- This output SOFT-START INPUT (Pin 18) -- The Soft-Start input is

provides a fixed width 5V pulse when any Hall-effect internally connected to a 10µA (nominal) current source,

Input (1, 2 or 3) changes state. The pulse width of the the collector of an NPN clamp/discharge transistor, and

Tachometer Output is set internally in the OM9375 to a voltage comparator whose soft-start/restart threshold

113µs (nominal). The average value of the output is 0.2Vdc (nominal). An external capacitor is connected

voltage on pin 15 is directly proportional to the motor's from this pin to Ground (pin 19). Whenever the Vcc

speed, so this output may be used (with an external supply input drops below the turn-on threshold,

averaging filter) as a true tachometer output, and fed approximately 9Vdc, or the sensed current exceeds the

back to the Speed Input (pin 23) to sense the actual over-current threshold, approximately 0.3V at the current

motor speed.

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

Note: Whenever pin 15 is high, the internal Hall-effect NPN clamp transistor which discharges the external soft-

position latches are inhibited (i.e. "latched"), to reject start capacitor. When the capacitor voltage drops below

noise during the chopping portion of the commutation the soft-start/restart threshold and a fault condition does

cycle, and this makes additional commutations not exist, the soft-start latch is cleared; the soft-start

impossible. This means that in order to prevent false capacitor charges via the internal current source.

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.

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

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

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

Internal to the OM9375 are timing components tied

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.

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:

GROUND (Pin 19) -- The voltages that control the

OM9375 are referenced with respect to this pin. All

bypass capacitors, timing resistors and capacitors, loop

compensation components, and the Hall-effect filter

capacitors must be referenced as close as possible to

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

Rt + 51kΩ

The recommended range of external resistance (to

pin 19 for proper circuit operation. Additionally, pin 19

must be connected as close as physically possible to the

Motor Return, pins 27 and 28.

Ground) is 15kΩ to ∞, and the range of external HALL-EFFECT INPUTS (H1, Pin 22; H2, Pin 21; H3,

capacitance (to Ground) is 0pF to 0.01uF. With each Pin 20) -- Each input has an internal pull-up resistor to

Tachometer Output pulse, the capacitor tied to pin 16 the +5V Reference. Each input also has an internal

is discharged from approximately 3.33V to 180pF noise filter capacitor to Ground. In order to

approximately 1.67V by an internal timing resistor. minimize the noise which may be coupled from the motor

The Brake / Tach Timing Input has another function. If commutation action to these inputs, it is strongly

this pin is pulled below the brake threshold voltage, recommended that additional external filter capacitors,

the OM9375 will enter the brake mode. The brake whose value is in the range of 2200pF, be connected

mode is defined as the disabling of all three high-side from each Hall-Effect Input pin to Ground. Whatever

(pull-up) drivers associated with the Phase Outputs, capacitor value is used, the rise/fall times of each input

and the enabling of all three low-side (pull-down) must be guaranteed to be less than 20us for proper

drivers.

tachometer action to occur. Motors with 60 degree

position sensing may be used if one or two of the Hall-

OVERVOLTAGE / COAST INPUT (Pin 17) -- This effect sensor signals is inverted prior to connection to the

input may be used as a shutdown or an Hall-Effect Inputs.

enable/disable input to the OM9375. 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 is commutated via the

power "catch" rectifiers associated with each Phase

Output.

2.1 - 7

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