The LMG365xR035 allows users to adjust the drive strength of the device and obtain a desired slew rate, which provides flexibility when optimizing switching losses and minimizing EMI. The typical value of turn-on slew rate and the maximum value of turn-off slew rate can be independently controlled by connecting the resistors and capacitor as shown in the Figure 8-1. The resistance and capacitance on FLT/RDRV pin is sensed once at power-up. To do so, the device forces a step-function from 0V to 1.2V on the external R1-R2-C2 network and measures the resulting current waveform. The DC measurement determines the turn-on slew rate setting, which is programmed by the resistance R1. The AC measurement dependent on R1-R2-C2 determines the turn-off slew rate setting, which is dependent on the magnitude of the drain-to-source current charging the output capacitance but can be limited to a maximum value programmed by the resistance R2 and capacitance C2, connected in parallel to R1. Table 8-1 shows the recommended typical resistances and capacitance programming values at each slew rate setting.

The slew rate settings are determined one time at power up, then the FLT/RDRV pin is used as a push-pull 5V digital output for fault monitoring, as described in Fault Reporting. If R2 and C2 are not used, the device turns-off at full-speed and the turn-off slew rate is strictly determined by the Coss and the load current. If R1 is not used, the device defaults to the 100V/ns slew rate setting. Using slower turn-on settings results in higher Eon losses, and slower turn-off settings results in higher Eoff losses.

Figure 8-1 Drive Strength Adjustment Circuit

For example, setting R1 = 53.6kΩ, R2 = 4.64kΩ and C2 = 270pF results in turn-on slew rate of 60V/ns and turn-off slew rate is limited to a maximum of 20V/ns.