LMZ34002: EXT SYNC on CLK Pin with frequency not between 400-600 or 700-900

Lucy Gong

Part Number: LMZ34002

Hello,

I am thinking of using the LMZ34002 to produce a -9V output at roughly 0.5A. The board it would be included on has many other DCDC Converters all of which have a SYNC or CLK pin connected to a 625kHz external clock. While this value is not one included in the options mentioned in the datasheet (400-600 or 700-900 kHz), it is between these 2 ranges and relatively close to 600 kHz. Would it still be possible to sync the LMZ34002 to this 625kHz clock? If so, which frequency range should it be programmed to (400-600 or 700-900)? If not, how would the out-of-range frequency affect the performance of the converter?

Thank you,

over 7 years ago

0 J Arrigo over 7 years ago

TI__Mastermind 28020 points

It should be fine to synchronize to 625kHz for your application. Let me look into the limitations and reply back. What is the input voltage for this application?

0 Lucy Gong over 7 years ago in reply to J Arrigo

Prodigy 80 points

Hi J,

The input voltage is 5 to 19 V.

Thank you for the reply,

0 J Arrigo over 7 years ago in reply to Lucy Gong

TI__Mastermind 28020 points

625kHz should be fine for your operating conditions.

0 Lucy Gong over 7 years ago in reply to J Arrigo

Prodigy 80 points

Hello Katelyn,

Thank you for the clarification - it was confusing since the datasheet also showed this example for external clock sync:

The datasheet also showed that the RT pin should be connected to A_VOUT either by a 93.1k resistor (400-600kHz) or shorting it (700-900kHz). If I would like to sync LMZ34002 to the 625kHz which option should I implement?

Thank you,

0 Lucy Gong over 7 years ago in reply to Lucy Gong

Prodigy 80 points

Hello J,

Sorry for the confusing post. I had a question about another device and ended up combining both posts together...

Thank you for the clarification. The datasheet also showed that the RT pin should be connected to A_VOUT either by a 93.1k resistor (400-600kHz) or shorting it (700-900kHz). If I would like to sync LMZ34002 to the 625kHz which option should I implement? The screenshot I meant to show was this one:

Apologies for the inconvenience,

0 J Arrigo over 7 years ago in reply to Lucy Gong

TI__Mastermind 28020 points

For this case, I would recommend placing a 43.2kΩ resistor between RT pin and A_VOUT. This value will set the switching frequency to 625kHz when no sync signal is present.

0 Lucy Gong over 7 years ago in reply to J Arrigo

Prodigy 80 points

I see, thank you! Is there either a graph or a formula that was used to get the 43.2k resistor value?

Power management

Power management forum

LMZ34002: EXT SYNC on CLK Pin with frequency not between 400-600 or 700-900