MTS2916A datasheet(9/20 Pages) MICROCHIP

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DS22259C-page 9

MTS2916A

3.2

PWM Current Control

The current level in each motor winding is controlled by

a PWM circuit with a fixed TOFF time. The load current

flowing in the winding is sensed through an external

sensing resistor RS connected between the power

bridge's source pin SENSE (sources of transistors Na

and Nb) and GND.

FIGURE 3-2:

PWM Current Control Circuit Principle (Channel 1 Shown).

The voltage across RS is compared to a fraction of the

reference voltage VREF, chosen with the logic input bits

I0 and I1 (Table 3-3). The power bridge, and thus the

load current, can also be switched off completely when

both logic inputs are high. Note that any logic input left

unconnected will be treated as a high level (pull-up

resistor).

The maximum trip current for regulation, given for

I0 I1 = 0 is calculated in Equation 3-1.

EQUATION 3-1:

VLOAD

SENSE

VREF

COMPIN

÷10

One-Shot

Source

Disable

Power

Bridge

OUTA

OUTB

MAX

REF



------------------

TABLE 3-3:

CURRENT LEVEL CONTROL TRUTH TABLE

Comp. Trip Voltage

Output Current

VTRIP = 1/10 x VREF

IMAX = VREF/10RS

VTRIP = 1/15 x VREF

2/3 x IMAX = VREF/15RS

VTRIP = 1/30 x VREF

1/3 x IMAX = VREF/30RS

0 (no current)

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