LM5170-Q1: oscillator frequency lower than the recommended conditions

John Chou62

Intellectual 1950 points

Part Number: LM5170-Q1
Other Parts Discussed in Thread: LM5170, LM5176

hi Team,

my customer is using the LM5170-Q1 to design charge stations

in the datasheet, the recommended MIN Oscillator Frequency is 50kHz.

they would like to try the low Frequency to 30kHz to get the max duty about 99% for 250W Buck Converter.

we'd like to check whether there might be any concerns or side effects with lowing the oscillator frequency to 30kHz

Thanks

over 2 years ago

0 Yinsong Cai1 over 2 years ago

TI__Expert 7450 points

Hi John,

Thank you for reaching out.

In general, we do not recommend any situation that goes beyond the DS specifications. In this case, may I know their operating conditions (input/output voltages)?

A 99% duty cycle may already violate the min/max LV/HV port voltage rating of LM5170.

Thanks,

Yinsong

0 John Chou62 over 2 years ago in reply to Yinsong Cai1

TI__Intellectual 1950 points

hi YinSong

Thanks very much for the feedback

The worst case of bidirectional DCDC HV 48.5V(min) to LV 48V(max).

Does TI have any other suggestion about this bidirectional DCDC?

appreciate the support

0 Yinsong Cai1 over 2 years ago in reply to John Chou62

TI__Expert 7450 points

Hi John,

Thank you for the information. I'll check with our engineers about the frequency and let you know.

Thanks,

Yinsong

0 John Chou62 over 2 years ago in reply to Yinsong Cai1

TI__Intellectual 1950 points

Thanks Yinsong

0 Yinsong Cai1 over 2 years ago in reply to John Chou62

TI__Expert 7450 points

Hi John,

1. For the frequency, we can only guarantee 50kHz minimum to the customer. They can still try 30kHz and it may work but it's up to their decision and we cannot guarantee the performance.

2. Depending on their max voltage, they can also consider the buck-boost controller LM5176.

3. Another get-around would be to use two stages that first boost/buck the 48.5V to some intermediate voltage and then buck/boost back to 48V so that the duty cycle can be kept in a reasonable range.

Thanks,

Yinsong

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LM5170-Q1: oscillator frequency lower than the recommended conditions