LMQ66430: Switchng frequency reduction

shinichi miyano

Part Number: LMQ66430

Tool/software:

Hello

During operating Auto-Mode, how much does the frequency of the device decrease relative to the set value?　
For example, set switching freqency 1MHz with resister.
How much does the switching frequency drop during rising Vout toward the set voltage?

Best Regard
Miyano Shinichi

2 months ago

0 Ridge Lahti 2 months ago

TI__Genius 13495 points

Hello,

When the device enters its light load operating mode, the specific switching frequency is difficult to determine. Since Diode Emulation mode (see Section 8.4.3.2.1 of the datasheet) utilizes the Ipeakmin specification, the frequency in light load operation depends on the output voltage, output current, and the inductor value. If knowing the exact frequency is important for your application, then FPWM mode is recommended but comes at the cost of the improved light load efficiency in auto mode.

Best regards,

Ridge

0 shinichi miyano 2 months ago in reply to Ridge Lahti

Prodigy 230 points

Hello Ridge

Thank you for your reply.

What I'd like to know is following:
Is it reasonable that the device is switches lower frequency than set value, from starting Switchng to reach Vout to set voltage?

It is not working in Diode-Emulation mode in above situation. In the steady state, where the load is lower, it is running Diode-Emulation mode.

Best Regard

Miyano Shinichi

+1 Ridge Lahti 2 months ago in reply to shinichi miyano

TI__Genius 13495 points

Hello Shinichi,

Thank you for clarifying. Yes, it is reasonable to see such behavior. During startup, the device is not able to enter FPWM mode until after the soft start time of 3.5ms. (Section 8.3.1 of device datasheet)

After soft start, the device will begin switching at the set frequency.