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3.4. PWM interface

The interface module is fitted with a dual MOSFET switch. This provides two outputs that can be configured as Pulse Width Modulated (PWM) outputs or used as DC switches to switch external loads.

The MOSFET can switch loads at up to 30V. Although the MOSFET is rated for 3A, because of the power dissipation of the package the maximum load current is 2.5A if only one PWM output is used or 1.75A if both outputs are used.

Warning

The device U21, fitted to the underside of the PCB, and the surrounding area of the board becomes very hot when high load currents are used.

As a PWM output, the interfaces can be driven by the DC-DC PrimeCell (PL160). The DC-DC PrimeCell has feedback inputs that negate the drive outputs when LOW. These inputs can be used to implement a current limit with external circuitry.

Table 3.4 shows the assignment of the PWM interface signals to the logic module signals on the EXPIM connector.

PWM interface signals
SignalEXPIM connectorDescription
PWM1_DRIVEIM_BBANK37PWM1 switch control signal
PWM2_DRIVEIM_BBANK38PWM2 switch control signal
PWM1_FBIM_BBANK39PWM1 feedback
PWM2_FBIM_BBANK40PWM2 feedback

Figure 3.4 shows the pin numbering of the PWM connectors.

Figure 3.4. PWM interface connector (J10/J14)

PWM interface connector (J10/J14)

Table 3.5 shows the signal assignment.

PWM connector signals
PinJ14J10Description
1PWM1_+VPWM2_+VPWM supply voltage
2PWM1_SWITCHPWM2_SWITCHPWM switched load connection
3PWM1_FBPWM2_FBPWM feedback signal
4PWM_GNDPWM_GNDPWM ground
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