AN2014 datasheet(25/65 Pages) STMICROELECTRONICS

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AN2014

Hardware considerations

Figure 17. Serial Data input/output SDA

On the Master side, the SDA output must be an open drain output. The Master SDA output

must not be a push-pull buffer as this would lead to a conflict when the Master drives high

SDA line and when the EEPROM drives low the SDA line (this induces a high current

between the power supply of the Master and the ground of the EEPROM device). This event

occurs each time when the I2C device acknowledges an instruction from the Master (see

Figure 18).

Figure 18. SDA bus conflict with push-pull buffers (NOT RECOMMENDED)

1. RS > VCC/IO with IO = min(Master IOH, EEPROM IOL). Without the RS resistor the current is limited by the

Master buffer and transistor T2 producing overstress at both Master and EEPROM side.

4.1.3

Serial clock (SCL)

The M24xxx serial clock (SCL) input is a CMOS Schmitt trigger. In applications with a

multiple master configuration, the master must have an open drain output with an external

pull-up resistor. In applications using a single master configuration, the SCL line can be

Ai11088

SDA pad

ESD/EOS Protection

RC Filter

Schmitt trigger

Open-drain Resistor

INPUT

OUTPUT

AN2014 数据表(PDF) 25 Page - STMicroelectronics