To set the driving currents of MP3398 the spec sheet recommend to use the “setting the LED current”. Is it possible to reduce the drive currents of the MP3398 via the OSC (“Progammable switching freq”, “The clock frequency is proportional to the current sourced from this pin.”, R5 in the data sheet") as opposed to the PWM. If it is possible how to determine the R5 for the desired value?. My design is now used R5= 191K and I want the driving current to reduce ~ 30%. what is the value of R5.?. Thanks.
Hi LLe:
Welcome to our MPS community !!
The MP3398 uses the current in the resistor R5 to set the switching frequency based on the formula on page 14 for Fsw (KHz) = 67320/R5 (KOhms) . So if R5 =191K you are operating at 352.4 Khz switching frequency. The current in the LED can be set using the resistor R3 connected to the ISET (pin6) pin. The LED current ILED (mA) = (810 * 1.22) / R3. For example, if R3= 8.2k then LED current calculates to 120mA using this formula as given on page 14 of the datasheet.