SNVSCM3 June 2024 LM5171
PRODUCTION DATA
Each channel of the LM5171 has the independent current setting pin, ISET1 and ISET2, for independent channel operation. For multiphase in parallel operation, connect all ISET pins together to achieve balanced power sharing among multiphases.
Each ISET pin accepts an analog voltage to program the channel dc current, as shown in Figure 6-3. The ISET pin signal feeds directly to one of the two non-inverting inputs of the gm amplifier. The other non-inverting pin is controlled by the soft-start. The current sense signal internally has an 1V dc offset voltage before it feeds to the inverting input of the gm amplifier. The channel DC current that flows through the current sense resistor is determined by Equation 1 in the closed loop operation.
Or by Equation 2,
Or by Equation 3,
Where
If a PWM signal is provided to control the channel current but no DAC is available, it is recommend to use a two-stage RC filter to convert it to the analog voltage at the ISET, as shown in Figure 6-4. The corner frequency of the filter must be set to at least 1 decade below the PWM frequency in order to attenuate the ripple voltage to less than 1% at the ISET pin, namely, the RC selection satisfies Equation 4, and the PWM to analog voltage conversion is given by Equation 5.
Where
Note that the internal pulldown resistor RPD has some tolerances. If RISET << RPD, the effects of the tolerance on VISET accuracy can be greatly reduced.