Using switcher (boost) to supply 3.3Vdc to VBAT3

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apogostin
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Using switcher (boost) to supply 3.3Vdc to VBAT3

How do you recommend attaching a boost mode switcher to VBAT3V? Concerned about output ripples and load transients effecting your chip's performance. Can't find in your docs anything about these maximum input limits to VBAT3V. Voltage regulation examples I've found in your reference designs utilize LDOs - no switchers. My current design contains a switcher - adding an LDO would be costly. The design uses a PAN1740, so forced to use VBAT3V. Thanks for your help.

JE_Dialog
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Hello Apogostin,  page 149 of

Hello Apogostin,  page 149 of the datasheet has the on board dc-dc characteristics of the DA14580 which is the chip inside the PAN1740.  Internally we have LDO's from the dc-dc output feeding into the RF stages. Page 144 describes the max limits on Vbat 3V.

BR JE_Dialog

apogostin
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Thanks JE_Dialog for your

Thanks JE_Dialog for your help. I reviewed those specs before I posted my original question. I can't see how those specs answer my question - no mention of maximum allowable input ripple. Let me detail my concerns again. The DA14580 expects a battery supply input at VBAT3V and a battery would normally present 0Vdc voltage ripple to VBAT3. So I'm concerned that connecting a switcher which produces a voltage ripple of between 7mv to 10mv at 1Mhz might be an issue (~3.3Vdc offset). Was hoping to get some maximum allowable input ripple voltage for VBAT3. If I need to use an additional capacitor at the VBAT3 input - I want to make sure I use the smallest possible value.

Thanks again.

AJP

MH_Dialog (not verified)
Hello AJP,

Hello AJP,

8mV ripple should be acceptable because DA14580 internal boost converter also generate this number. We recommend that VBAT voltage should be below than 3.3V.

BR, Morris