Function description and application information

SPMD150STP

12/23

Doc ID 17160 Rev 1

Figure 8.

Logic inputs internal structure

Figure 9.

EN pin open collector driving

4.3

PWM current controller

The control block is composed by a constant Off-time PWM current controller for both two

bridges. The current control circuit senses the bridge current, by sensing the voltage drop

across a sense resistor connected between the source of the two lower power MOSFETs

and ground. As the current in the motor buildup, the voltage across the sense resistor

increases proportionally. When the voltage on the sense resistor becomes greater than the

voltage at the reference inputs VREFA (pin6) or VREFB (pin11), the sense comparator

triggers a mono-stable circuit, switching the bridge off.

The bridge MOSFETs remain off for the time set by pin RCA (pin7) or RCB (pin12);

during this Off-time (see Figure 11, toff versus Roff and Coff), the motor phase current re-

circulates as defined by the selected decay mode, described in the next section. When the

used to prevent cross conduction in the bridge, delays the turn on of the power MOSFETs,

relative to Bridge A, it is necessary to connect a proper resistor Ra and/or a proper capacitor

Ca in parallel between pin RCA and GND1, see Figure 10 and Figure 11; To set the toff

relative to Bridge B, it is necessary to connect a proper resistor Rb and/or a proper capacitor

Cb in parallel between pin RCB and GND1, see Figure 10 and Figure 11; A 56 k

Ω resistor

and a 470 pF capacitor are already present between pin RCA/B and GND1 inside the