AS3668 datasheet(19/60 Pages) AMSCO

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AS3668

Data Sheet - D e t a i l e d D e s c r i p t i o n

8.3 Power - On Reset

The AS3668 provides an power - on reset feature that is controlled by two different sources:

VBAT supply voltage

Serial interface state (SCL only)

If the internal VBAT supply voltage reset is forced, when the supply voltage VBAT of AS3668 drops below a predefined voltage, the device enters

shutdown mode. This predefined voltage is 2V (typ.) and is defined as VPOR_VBAT. Besides this hard wired voltage level where an internal reset

is forced to shut down the device, AS3668 supports an additional VBAT monitoring feature. This means that the designer can select according to

its application requirements a reset level which is appropriate for mobile Li-Ion battery powered applications. The use case for this second VBAT

monitoring is to make sure that if a mobile device switches off suddenly, at a dedicated voltage, to make sure that also AS3668 enters power

down mode. Otherwise unwanted LED effects could occur even if the digital system is not running any more. AS3668 allows the designer now to

set the VBAT monitoring level to the same voltage level the whole system is powering down. There’s no need any more for the CPU to reset or

power down AS3668 in a low battery case any more. The device can handle this use case automatically.

In addition to the VBAT voltage monitoring the device supports also a shut down function forced by the serial interface. If the voltage on the serial

interface pin SCL is below 1V (typ.) and GPIO/AUDIO_IN pin is low, the device forces a reset. To prevent the system against wrong resets

caused by electromagnetically influences there is also a debounce timer integrated with a typical debounce time of 100ms. This debounce time

is used for VBAT monitoring as well. If the serial interface monitoring is not supposed to be used in an application it is also possible to disable the

feature using the corresponding register bit.

Table 15. Current Control Register CURR4

0x05 Current Control Register

Bit

Bit Name

Default

Access

Bit Description

7:0

curr4_current

R/W

0000 0000: 0mA current output from source CURR4

0000 0001: 0.1mA current output from source CURR4

0000 0010: 0.2mA current output from source CURR4

0000 0011: 0.3mA current output from source CURR4

...

1111 1111: 25.5mA current output from source CURR4

Table 16. CURRx Low Voltage Status Register

0x2b Current Source Low Voltage Status Register

Bit

Bit Name

Default

Access

Bit Description

curr4_low_v

This is a read only register and returns 0 if the voltage on current source

CURR4 is ok. If the voltage drops below 200mV across the current source

the bit is set to 1.

0: CURR4 voltage is OK

1: CURR4 voltage is too low

curr3_low_v

This is a read only register and returns 0 if the voltage on current source

CURR3 is ok. If the voltage drops below 200mV across the current source

the bit is set to 1.

0: CURR3 voltage is OK

1: CURR3 voltage is too low

curr2_low_v

This is a read only register and returns 0 if the voltage on current source

CURR2 is ok. If the voltage drops below 200mV across the current source

the bit is set to 1.

0: CURR2 voltage is OK

1: CURR2 voltage is too low

curr1_low_v

This is a read only register and returns 0 if the voltage on current source

CURR1 is ok. If the voltage drops below 200mV across the current source

the bit is set to 1.

0: CURR1 voltage is OK

1: CURR1 voltage is too low

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