OM9369CM Просмотр технического описания (PDF) - Omnirel Corp => IRF

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OM9369CM

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

Omnirel Corp => IRF 

OM9369CM

TACHOMETER OUTPUT (Pin 16) -- 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 OM9369CM

to 113µs (nominal). The average value of the output

voltage on pin 16 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 24) to sense the actual

motor speed.

Note: Whenever pin 16 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 commutations

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 17) -- The

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

Internal to the OM9369CM are timing components tied

from pin 17 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 17

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

OM9369CM 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 18) -- This

input may be used as a shutdown or an enable/disable

input to the OM9369CM. 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 18 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

SOFT-START INPUT (Pin 19) -- 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 20). 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 19, 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.

GROUND (Pin 20) -- The voltages that control the

OM9369CM 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 pin

20 for proper circuit operation. Additionally, pin 20 must

be connected as close as physically possible to the Motor

Return, pin A.

HALL-EFFECT INPUTS (H1, Pin 23; H2, Pin 22; H3, Pin

21) -- Each input has an internal pull-up resistor to the

+5V Reference. Each input also has an internal 180pF

noise filter capacitor to Ground. In order to minimize the

noise which may be coupled from the motor commutation

action to these inputs, it is strongly recommended that

additional external filter capacitors, whose value is in the

range of 2200pF, be connected from each Hall-Effect

Input pin to Ground. Whatever capacitor value is used,

the rise/fall times of each input must be guaranteed to be

less than 20us for proper tachometer action to occur.

Motors with 60 degree position sensing may be used if

one or two of the Hall-effect sensor signals is inverted

prior to connection to the Hall-Effect Inputs.

SPEED INPUT (Pin 24) - This pin is connected to the “+”

input of a voltage comparator, whose threshold is

0.25Vdc. As long as the Speed Input is less than 0.25V,

the direction latch is transparent. When the Speed Input

is greater than 0.25V, then the direction latch inhibits all

changes in direction. It is recommended, especially while

operating in the half control mode, that the Tachometer

Output is connected to the Speed Input via a low-pass

filter, such that the direction latch is transparent only

when the motor is spinning very slowly. In this case,

the motor has too little stored energy to damage the

power devices during direction reversal.

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