www.ti.com.................................................................................................................................................. SLVS536J – JULY 2004 – REVISED SEPTEMBER 2009
DETAILED PIN DESCRIPTIONS
A logic low level on this input indicates that the card present supports PCI Express functions. CPPE connects to
the AUXIN input through an internal pullup. When a card is inserted, CPPE is physically connected to ground if
the card supports PCI Express functions.
A logic low level on this input indicates that the card present supports USB functions. CPUSB connects to the
AUXIN input through an internal pullup. When a card is inserted, CPUSB is physically connected to ground if the
card supports USB functions.
When asserted (logic low), this input instructs the power switch to turn off all voltage outputs and the discharge
FETs are activated. SHDN has an internal pullup connected to AUXIN.
When asserted (logic low) after the card is inserted, this input places the power switch in standby mode by
turning off the 3.3-V and 1.5-V power switches and keeping the AUX switch on. If asserted prior to the card being
present, STBY places the power switch in OFF Mode by turning off the AUX, 3.3-V, and 1.5-V power switches.
STBY has an internal pullup connected to AUXIN.
This pin serves as both an input and an output. On power up, a discharge FET keeps this signal at a low state as
long as any of the output power rails are out of their tolerance range. Once all output power rails are within
tolerance, the switch releases RCLKEN allowing it to transition to a high state (internally pulled up to AUXIN).
The transition of RCLKEN from a low to a high state starts an internal timer for the purpose of deasserting
PERST. As an input, RCLKEN can be kept low to delay the start of the PERST internal timer.
Because RCLKEN is internally connected to a discharge FET, this pin can only be driven low and should never
be driven high as a logic input. When an external circuit drives this pin low, RCLKEN becomes an input;
otherwise, this pin is an output.
RCLKEN can be used by the host system to enable a clock driver.
On power up, this output remains asserted (logic level low) until all power rails are within tolerance. Once all
power rails are within tolerance and RCLKEN has been released (logic high), PERST is deasserted (logic high)
after a time delay as shown in the parametric table. On power down, this output is asserted whenever any of the
power rails drop below their voltage tolerance.
The PERST signal is an output from the host system and an input to the ExpressCard module. This signal is only
used by PCI Express-based modules and its function is to place the ExpressCard module in a reset state.
During power up, power down, or whenever power to the ExpressCard module is not stable or not within voltage
tolerance limits, the ExpressCard standard requires that PERST be asserted. As a result, this signal also serves
as a power-good indicator to the ExpressCard module, and the relationship between the power rails and PERST
are explicitly defined in the ExpressCard standard.
The host can also place the ExpressCard module in a reset state by asserting a system reset SYSRST. This
system reset generates a PERST to the ExpressCard module without disrupting the voltage rails. This is what is
normally called a warm reset. However, in a cold start situation, the system reset can also be used to extend the