Use LT3010 to power LTC4020 INT_Vcc

Question

hello 
 
 I see in the datasheet that the LT3010 is used to power INT_vcc. May I ask whether the GND of LT3010 is connected to SGND or PGND

BI1IZF

ARad · Accepted Answer

The LTC4020 datasheet says the INTVCC capacitor connects to PGND, so that is where I would ground the LT3010.)

ADIApproved · Answer

I am glad you asked this question because the use of the INTVcc preregulator in datasheet figure 9, figure 10 and the application circuit on p. 39. will not work. Please use the following circuit instead. Note that I have connected the ground pin of the LT3012 to PGND. 
 I used the LT3012 which can supply 250mA; the LT3010 can supply 50mA.

ADIApproved · Answer

You may leave FBG open for this application, since the voltage divider is connected to ground. (Note, divider should be returned to SGND, not PGND.) 
 LT3010 may be used if your gate-drive-current requirement is 50mA or less. You must calculate your gate-drive current based on information in datasheet p.25-26, External Power for BST1 and BST2 Supplies . 
 It important to connect and lay out the design with careful attention to PGND, SGND connections. I recommend reviewing the PGND, SGND connections in the DC2044A schematic https://www.analog.com/media/en/technical-documentation/eval-board-schematic/DC2044A-2-SCH.PDF , because the use of SGND and PGND in your schematic is not correct. Also, see the layout in https://www.analog.com/media/en/reference-design-documentation/design-integration-files/DC2044A.zip which shows good placement of SGND, PGND planes. 
 
 Following is more explanation on FBG and DC2044A schematic. 
 For CC/CV mode a powerpath FET is used to disconnect the battery after timeout. The voltage divider connected from the battery is returned to FBG. After timeout FBG is disconnected from ground (internal to LTC4020), so the voltage divider does not drain current from the battery. This is why the DC2044A uses the FBG connection instead of SGND for the voltage divider. 
 For Lead-Acid mode no powerpath FET is necessary because the charger operates continuously (trickle charge). It is OK to use SGND for the voltage divider return, because the charger operates continuously.

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Use LT3010 to power LTC4020 INT_Vcc