PCI1225 Datasheet, PDF (22/131 Pages) Texas Instruments – PC CARD CONTROLLERS

PCI1225 GHK/PDV
PC CARD CONTROLLERS
SCPS035B – MAY 1998 – REVISED – MAY 2000
power supply sequencing
The PCI1225 contains 3.3-V I/O buffers with 5-V tolerance requiring a core power supply and clamp power
supplies. The core power supply is always 3.3 V. The clamp power supplies can be either 3.3 V or 5 V, depending
on the interface. The following power-up and power-down sequences are recommended.
The power-up sequence is:
1. Apply 3.3-V power to the core.
2. Assert PRST to the device to disable the outputs during power up. Output drivers must be powered up in
the high-impedance state to prevent high current levels through the clamp diodes to the 5-V supply.
3. Apply the clamp power.
The power-down sequence is:
1. Use PRST to switch outputs to a high-impedance state.
2. Remove the clamp power.
3. Remove the 3.3-V power from the core.
I/O characteristics
Figure 1 shows a 3-state bidirectional buffer. The recommended operating conditions table, on page 120,
provides the electrical characteristics of the inputs and outputs.
NOTE:
The PCI1225 meets the ac specifications of the 1997 PC Card Standard and PCI Local Bus
Specification Rev. 2.2.
Tied for Open Drain
OE
VCCP
Pad
Figure 1. 3-State Bidirectional Buffer
NOTE:
Unused pins (input or I/O) must be held high or low to prevent them from floating.
clamping rail voltages
The clamping rail voltages are set to match whatever external environment the PCI1225 will be working with:
3.3 V or 5 V. The I/O sites can be pulled through a clamping diode to a power rail that protects the core from
external signals. The core power supply is always 3.3 V and is independent of the clamping rail voltages. For
example, PCI signaling can be either 3.3 V or 5 V, and the PCI1225 must reliably accommodate both voltage
levels. This is accomplished by using a 3.3-V I/O buffer that is 5-V tolerant, with the applicable clamping rail
voltage applied. If a system designer desires a 5-V PCI bus, V_CCP can be connected to a 5-V power supply.
The PCI1225 requires four separate clamping rails because it supports a wide range of features. The four rails
are listed and defined in the recommended operating conditions, on page 120.
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