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I cannot se how the device is a buck charger when charging and a boost on the output. Am I stupid or is the datasheet wrong?

"5A Single Cell Li-Ion Switching Battery Charger with Direct Charge, Power Path Management and USB OTG Boost Mode " https://www.richtek.com/assets/product_file/RT9468/DS9468-01.pdf

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2 Answers 2

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Buck Regulator for Charging Battery.
= Stepdown from 5V to Battery (CC then 4.2V then cutoff)

Boost Regulator as OTG (on-the-go USB power)
= Step-Up from Battery to USB or 3~4V to 5V

It is consistent and correct.

I have redrawn the switches to show more clearly the topology used.

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  • \$\begingroup\$ so the input("vbus") is the output in Boost OTG mode? \$\endgroup\$
    – user103776
    Commented Mar 27, 2019 at 16:32
  • \$\begingroup\$ Yes Vbus is the output in Boost mode. Thus the design needs a Full bridge to change Vbat current direction and a bridge to swap PWM from series (Buck) to shunt mode.(Boost) \$\endgroup\$
    – Tony Stewart EE75
    Commented Mar 27, 2019 at 17:04
  • \$\begingroup\$ They don't really want you to understand how they designed it, just to use it. \$\endgroup\$
    – Tony Stewart EE75
    Commented Mar 27, 2019 at 18:27
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A synchronous buck converter, operating in continuous mode, will work just fine in reverse. In a lossless circuit, the PWM ratio plus the continuous conduction in the inductor enforces a voltage ratio from input to output, but lets current go either way. It's just a matter of how you arrange your control circuit.

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    \$\begingroup\$ So the input (Vbus) will be the output in boost mod? \$\endgroup\$
    – user103776
    Commented Mar 27, 2019 at 16:35
  • \$\begingroup\$ I assume so -- it'd pretty much have to be, and it would fit with the notion of having a box that either takes 5V in and charges a battery, or puts 5V out. The datasheet is a bit light on that sort of detail. \$\endgroup\$
    – TimWescott
    Commented Mar 27, 2019 at 18:25

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