DIO74557S

Version 1.1, May 2024

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© 2024 DIOO MICROCIRCUITS CO., LTD.

8

8. Application Information

Important notice: Validation and testing are the most reliable ways to confirm system functionality.

The application information is not part of the specification and is for reference purposes only.

Figure 3. Application circuit interfacing with typical SIM card

8.1. Embedded enable

The embedded enable feature is available for the QFN1.8*1.4-10 package when the enable pin of the QFN

package is tied to VCCA. The DIO74557S includes an automatic enable function that activates the level shifter

function when the voltage of VCCB exceeds VCCB_EN. Conversely, the SIM card side drivers and level shifter

function are deactivated as soon as VCCB falls below VCCB_DIS. Additionally, the I/O pin on the host side is set up

as an input with a 5 kΩ resistor that is pulled up to VCCA.

When VCCB falls below VCCB_DIS but remains above the MOS threshold voltage (VTH), the pull-down NMOS in the

one-directional and bidirectional drivers will be turned off, while the NMOS controlled by CTL will be turned on.

As a result, the CLK/RST/IO pins on the card side will be pulled low by the 450 Ω resistor. Furthermore, both the

host and card side CLK/RST pins have a 100 kΩ pull-down resistor. The 450 Ω resistor is used for discharge

during VCCB power off (when VTH < VCCB < VCCB_EN), while the 100 kΩ resistor is used to keep

RST_SIM/CLK_SIM low when VCCB is below VTH.