DIO74557

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© 2024 Dioo Microcircuits Co.,Ltd. Jiangsu

DIO74557• Rev. 1.5

- 9 -

EN Shutdown Mode

To properly turn off the SIM card and save power, the SIM card signals should be shut down in accordance with

the specification specified in the ISO-7816-3 standard. The proper shutdown of these signals also helps prevent

any inappropriate writing and data corruption during the hot swap.

To properly initiate the shutdown sequence, it's crucial to ensure that the EN pin is pulled LOW before the VCCA

and VCCB supplies go LOW. When the EN pin is asserted LOW, the RST_SIM channel is powered down, which

then triggers the sequential power down of CLK_SIM and IO_SIM channels one by one. The SIM pins are pulled

LOW by their respective internal pull-down resistors. The entire shutdown sequence is completed within a few

microseconds.

Figure 7. Shutdown sequence

Input/output Capacitor Selections

Place a 100 nF capacitor with low Equivalent Series Resistance (ESR) in close proximity to the VCCA and VCCB

input terminals each. The preferred capacitor types are X5R or X7R multi-layer ceramic capacitors (MLCC) due

to their consistent value and ESR performance across temperature variations. The maximum ESR should be

under 500 mΩ (with a typical value being 50 mΩ).

Level Shifter Stage

The device eliminates the need for an additional input signal to control the direction of data flow between the host

and SIM. The control logic enables a change in driving direction only when both sides are in a HIGH state. The

first falling edge is recognized by the control logic, granting it control over the other signal side. In the event of a

rising edge signal, a one-shot circuit is employed to drive the non-driving output and accelerate the rising edge.

The internal logic of the device safeguards against communication errors or unforeseen incidents that may drive

both connected sides to be drivers simultaneously, thereby preventing a stuck-at situation. Once released from

being driven LOW, both I/Os will return to a HIGH level automatically.

The RST and CLK channels just contain single direction drivers without the holding mechanism of the I/O

channel, as these are just driven from the host to the SIM card side.

EMI Filter

EMI filters at the input/output driver stages reduce interference to sensitive mobile communications.

ESD Protection

The DIO74557 has strong ESD protections on all SIM card pins as well as on the VCCB pin. The feature prevents

any stress for the host: the voltage converter releases any stress to the supply floor.