MCIMX253CJM4 View Datasheet(PDF) - Freescale Semiconductor

Part Name

Description

Manufacturer

MCIMX253CJM4

i.MX25 Applications Processor for Consumer and Industrial Products

Freescale Semiconductor 

Table 4. Signal Considerations (continued)

Signal

Description

MESH_C, MESH_D Wire-mesh tamper detect pins that can be routed at the PCB board to detect attempted tampering of a

protected wire. When security measures are implemented, MESH_C should be pulled-up or connected to

NVCC_DRYICE and triggers a tamper event when floating or when connected to MESH_D. MESH_D

should be pulled-down or connected to GND and triggers an event when floating or connected to

MESH_C. These pins can be left unconnected if the DryIce security features are not being used.

NVCC_DRYICE

This is the DryIce power supply output. The supply source is QVDD when the i.MX25 is in run mode.

When i.MX25 is in reduced power mode, the DryIce supply source is the BATT_VDD supply. This pin can

be used to power external DryIce components (external tamper detect, wire-mesh tamper detect). In

order to guarantee the power-loss protection feature which guarantees that RTC and/or secure keys be

maintained after power-off an external capacitor no less than 4 µF must be connected to this supply output

pin. A 4.7 µF capacitor is recommended.

OSC_BYP

The 32 kHz oscillator bypass-control pin. If this signal is pulled down, then OSC32K_EXTAL and

OSC32K_XTAL analog pins should be tied to the external 32.768 kHz crystal circuit. If on the other hand

the signal is pulled up, then the external 32 kHz oscillator output clock must be connected to

OSC32K_EXTAL analog pin, and OSC32K_XTAL can be no connect (NC).

OSC32K_EXTAL These analog pins are connected to an external 32 kHz CLK circuit depending on the state of OSC_BYP

OSC32K_XTAL pin (see the description of OSC_BYP under the preceding bullet). The 32 kHz reference CLK is required

for normal operation.

POWER_FAIL

An interrupt from PMIC, which should be connected to a low-battery detection circuit. This signal is

internally connected to an on-chip 100 kΩ pull-down device. If there is no low-battery detection, then users

can tie this pin to GND through a pull-down resistor, or leave the signal as NC. This pin can also be

configured to work as a normal GPIO.

REF

External ADC reference voltage. REF may be tied to GND if the user plans to only use the internally

generated 2.5 V reference supply.

SJC_MOD

Must be externally connected to GND for normal operation. Termination to GND through an external

pull-down resistor (such as 1 kΩ) is allowed, but the value should be much smaller than the on-chip 100

kΩ pull-up.

TAMPER_A,

TAMPER _B

DryIce external tamper detect pins, active high. If TAMPER_A or TAMPER_B is connected to

NVCC_DRYICE, then external tampering is detected. These pins can be left unconnected if the DryIce

security features are not being used.

TEST_MODE

For Freescale factory use only. This signal is internally connected to an on-chip pull-down device. Users

must either float this signal or tie it to GND.

UPLL_BYPCLK

Primarily for Freescale factory use. There is no internal on-chip pull-up/down on this pin, so it must be

externally connected to GND or VDD. Aside from factory use, this pin can also be configured (through

muxing) to work as a normal GPIO.

USBPHY1_RREF Determines the reference current for the USB PHY1 bandgap reference. An external 10 kΩ 1% resistor to

GND is required.

USBPHY2_DM The output impedance of these signals is expected at 10 Ω. It is recommended to also have on-board 33 Ω

USBPHY2_DP series resistors (close to the pins).

i.MX25 Applications Processor for Consumer and Industrial Products, Rev. 9

10

Freescale Semiconductor

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