AM2168 datasheet(5/10 Pages) AMTEK

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AM2168

Motor Driver ICs

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Application Information

•PWM Current control

The AM2168 dual bridge is designed to drive both windings of a bipolar stepper motor or to control bidirectionally

two DC motors. The output current of each part is sensed and controlled independently in each bridge by external

sense resistors (RS), internal comparator, and monostable multivibrator.

When the bridge is turned ON, current increases in the motor winding and it is sensed by the external sense resistor

until the sense voltage (VCOMPIN) reaches the level set at the comparator’s input:

ITRIP = VREF / 10RS

The comparator then triggers the monostabel that turns OFF the source driver of the bridge. The actual load current

peak will be slightly higher than the trip point (especially for low-inductance loads) because of the internal logic and

switching delays. This delay (td) is typically 2 µs. After turn-off, the motor current decays, circulating through the

ground-clamp diode and sink transistor. The source driver’s OFF time (and therefore the magnitude of the current

decrease) is determined by the monostable’s external RC timing components, where toff = RTCT within the range of

20kΩ to 100kΩ and 100pF to 1000pF.

When the source driver is re-enabled, the winding current (the sense voltage) is again allowed to rise to the

comparator’s threshold. This cycle repeats itself, maintaining the average motor winding current at the desired level.

Loads with highly distributed capacitances may result in high turn-ON current peaks. This peak (appearing across

RS) will attempt to trip the comparator, resulting in erroneous current control or high-frequency oscillations. An

external RCCC time delay should be used to further delay the action of the comparator. Depending on load type,

many applications will not require these external components (SENSE connected to COMP IN).

Load Current Paths

VBB

BRIDGE ON

SOURCE OFF

ALL OFF

PWM Output Current Wave Form

VPHASE

I TRIP

t off

t d

I OUT

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