RT9758 datasheet(46/61 Pages) RICHTEK

46 / 61 page

RT9758

is a registered trademark of Richtek Technology Corporation.

www.richtek.com

DS9758-03

May 2023

Auto Transition Function Feature (AT_Function)

For more flexible mode change application between bypass mode and DIV2 mode, the auto transition function

(AT_Function) is established in the RT9758 to make converter mode change automatically by adjusting VBUS

voltage. In register map, the AT_FUNCTION_EN bit is used to enable this function and the AT_FUNCTION bit is

used to set the threshold of mode transition. When the AT_Function is active in bypass mode, if VBUS is higher than

AT_Function threshold in tAT_FUNCTION_DEG time, the device will stop charging, set OPERATION_MODE_

SELECTION bit to 1 and then start DIV2 charging process if the start-up conditions are met. In another case, if VBUS

is lower than AT_Function threshold when the device operates in DIV2 mode, it will stop charging, set

OPERATION_MODE_ SELECTION bit to 0 and then start bypass charging process if the start-up conditions are met.

The Figure 8 is recommended operation flow for using auto transition function, user should follow step 1-4 to use

auto transition function. Especially, if user desires device be transited from bypass mode to DIV mode by using

AT_Function, be sure to enable VOUT_PD bit to 1 before increase VBUS voltage.

1. Set AT_FUNCTION threshold level

2. Set AT_FUNCTION_EN = 1 to enable

AT_Function

Set VOUT_PD = 1 to enable VOUT pull down

resistor

3. Increase VBUS higher than AT_Function

threshold and over 10msec deglitch time

Device stop charging &

set OPERATION_MODE_SELECTION = 1 automatically

Start DIV2 charging process when VBUS_INSERT = 1 &

VBUS_LOW_ERR = 0

Device operates in DIV2 mode

Device operates in bypass mode

1. Set AT_FUNCTION threshold level

2. Set AT_FUNCTION_EN = 1 to enable

AT_Function

3. Decrease VBUS lower than AT_Function

threshold and over 10msec deglitch time

Device stop charging &

set OPERATION_MODE_SELECTION = 0 automatically

Start bypass charging process when VBUS_INSERT = 1 &

VBUS_LOW_ERR = 0

Device operates in DIV2 mode

Device operates in bypass mode

4. Set AT_FUNCTION_EN = 0 to disable

AT_Function

4. Set AT_FUNCTION_EN = 0 to disable

AT_Function

Figure 8. Operation Flow for Using Auto Transition Function

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