IXMS150PSI View Datasheet(PDF) - IXYS CORPORATION

Part Name

Description

Manufacturer

IXMS150PSI

High Performance Dual PWM Microstepping Controller

IXYS CORPORATION 

IXMS 150

mode, either SW1 and SW4 are on (Vm

= VHV) or SW2 + SW3 are on (Vm = -

VHV). By appropriately controlling the

duty cycle of SW1//4 vs. SW2/3, the

average motor voltage can be controlled

such that:

Vm(avg) = 2 • VHV (0.5-DUTY)

Note: DUTY is defined as the duty

cycle of VOUTA.

The IXMS150 can now regulate the

motor coil current by commanding the

voltage level and polarity required.

enhance the MOSFETs, with the top two

transistors (Q2, Q4) being destroyed

due to excessive power dissipation.

Therefore one has to limit the duty

cycle excursions. The solution selected

by IXYS limits the minimum output

pulse-width to 0.5 ms, which translates

to a duty cycle range of 5 % to 95 %

when operating at 100 kHz, or wider at

lower frequencies. There is a penalty of

slightly limiting the maximum slew rate

to (1-2 • Min Duty) of the unrestricted

case, which translates to 90 % of the

ration with a particular motor. The basic

elements involved in the current loop

are illustrated in Fig. 11a. Referring to

Fig. 11b, the loop gain for this system

(the product of the forward and feed-

back gain terms) can be expressed as:

Gloop(s) = Ge/a(s) • Kpwm • Gm(s) • Gi(s) (14)

where

Ge/a(s) = error amplifier gain

Kpwm = cascade of pwm and output H-

bridge gain

SW1

SW3

D1 D2

SW2

Vm

D3 D4

SW4

Fig. 8 Simplified H-Bridge Diagram

The Power Stage:

An AC Coupled H-Bridge

Fig. 9 shows the power driver selected

for this application. Two of these are

required to drive the two phase step

motor. This circuit uses two N-channel

and two P-channel power MOSFETs as

opposed to an all N-channel architec-

ture. The drawback of using P-channel

transistors is that they are larger and

therefore more expensive than similarly

rated N-channel devices. But the

advantages are much simplified drive

and level shifting circuitry. This results

in a lower component count and

therefore higher reliability. It also lends

itself easily to hybridization. Other

advantages of this topology are: a) the

high efficiency associated with level

shifting by AC coupling since no power

is dissipated in the capacitors, and b)

the same circuit can be used for motor

applications ranging from 12 V to several

hundred volts, the only modification

being appropriately rated power tran-

sistors and coupling capacitors.

A limitation of this circuit is that it cannot

be used at duty cycle extremes. This

would require one input to be continu-

ously low while the other is continu-

ously high. Eventually the coupling

capacitors (C1, C2) would charge up to

a voltage that would no longer fully

I - 42

Fig. 9 AC Coupled H-Bridge Diagram

unrestricted maximum slew rate for

100 kHz operation.

Loop Compensation Information

When used with the appropriate power

stage, each channel of the IXMS150

acts as a closed loop transconductance

amplifier. As such, it must be properly

compensated to guarantee stable ope-

Gm(s) = cascade of motor winding

impedance and H-bridge parasitic

resistance

Gi(s) = current sense resistor and

sampling amplifier gain

The value of each of these terms can

be determined from the Laplace

transform diagram in Fig. 11b:

Fig. 10a Simplified Microstepping System

© 1998 IXYS All rights reserved

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