AS3956 datasheet(77/107 Pages) AMSCO

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Page 77

[v1-11] 2018-Nov-14

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AS3956 − Detailed Description

I²C Electrical Connection

The I²C bus can operate from a minimum of 100kHz up to 1MHz

SCL clock speed. The I²C bus needs pull-up resistors on SDA and

SCL lines in order to operate properly. AS3956 has internal

pull-up resistors that can be used instead of external pull-ups.

The intention of internal pull-up resistors is to simplify the

design of the PCB and to decrease the number of necessary

components on a PCB.

The configuration of the internal pull-up resistors is stored in

configuration word 1 (FAB_CFG2, bit 5) in EEPROM. This setting

can be set only during the production. If this bit is not set, the

internal pull-up resistors are disabled.

Note the SPI pull-down configuration bit miso_pd1 in

FAB_CFG2 must also be set to 0.

Figure 81:

I²C Interface with Built-In Pull-Up Resistors

Internal pull-up resistors are enabled only if proper

configuration is written in the internal EEPROM configuration

word. The configuration is read during the initialization of the

chip when the interface and other configurations are set.

Note the pull-up resistors are applied to the SDA and SCL lines

during chip initialization until the /SS line is taken low. After /SS

is taken low, bit b5 of FAB_CFG2 determines whether the

pull-up resistor are connected or not.

RP=3kΩ

VP_IO

SDA

SCL

AS3956

VSS

Pull-up

enable

Data out

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