LM5163-Q1: Support for Sleep Mode Condition

Hi Nishanth,

When the load current is lower than half of peak-to-peak inductor ripple current, the minimum value of inductor current falls to zero, the device enters into DEM mode. In the DEM state, the load current is lower than half of the peak-to-peak inductor current ripple and the switching frequency decreases when the load is further decreased as the device operates in a pulse skipping mode.

When load is decreased further, the frequency of operation decreases and VFB remains above 1.2 V (VREF) with the output capacitor sourcing the load current for greater than 15 µs, the converter enters an ultra-low IQ sleep mode to prevent draining the input power supply.

For calculating peak to peak inductor current, please use the excel tool LM5163-LM5164DESIGN-CALC Calculation tool | TI.com or refer to Equation 18, Datasheet (section 7.2.2.3)

Regards

Arpita

Hi Nishant,

Do you have any other query?

Hi Arpita Nath,

Thank you for the quick support.

As per the Calculation tool, I have calculated the peak-to-peak ripple current, and I have got 84mA as the output. So, does the device enters the sleep mode once the output current goes below 42mA??

Is my understanding correct?

Is your peak-to-peak current ripple 84mA?

• When the load current is lower than half of peak-to-peak inductor ripple current, i.e iout<=42mA for your case, the device enters into DEM mode.
• If Iout is decreased further, the device enters into pulse skipping mode and frequency decreases.
• If Iout is decreased even further, at a point, frequency decreases as well as VFB remains above 1.2 V (VREF) with the output capacitor sourcing the load current for greater than 15 µs then the converter enters an ultra-low IQ sleep mode to prevent draining the input power supply.

Regards

Arpita

Ok understood. Yes, the calculated peak-to-peak ripple current is 84mA, I've attached the image for your reference.

Is there any peak-to-peak ripple current percentage range or something like that for all these step-by-step processes when all these enable. Since to enter DEM mode, the load current should be below 50% of the peak-to-peak ripple current. Same way you have mentioned in next point as, "If Iout is decreased further, the device enters into pulse skipping mode", is there any particular range (i.e. below 40%) to get into this condition for all these step-by-step processes.

Hi Nishant,

Sorry for delay in response. It is very difficult to calculate directly load current threshold for entering into low power modes as it depends on the circuit parameters. During pulse-skipping mode, after an on time of programmed TON, the switching pulse is kept off until VFB drops below 1.2V, thus reducing the switching frequency, (as it takes longer for VFB to drop below 1.2V during light load conditions, the switching frequency reduces). A switching pulse is set when VFB drops below 1.2 V. According to datasheet, if iout is decreased even further, at a point, frequency decreases as well as VFB remains above 1.2 V (VREF) with the output capacitor sourcing the load current for greater than 15 µs., the device enters into sleep mode. You can have an estimation from the above discussion.

Regards

Arpita