SCPA033
3 Power Switch Implementation
The following figure shows the serial interface between the PCI1520 and the TPS2226A power switch:
VCCB | VCCA |
PCI1520
CLOCK
DATA
TPS2226A
LATCH
Pulldown if using internal clock
VPPA
VCCA | Socket A |
| |
VPPB |
|
VCCB | Socket B |
Figure 2. Power Switch Implementation
A power switch is necessary in order to control power to the PC Card sockets. When the PCI1520 receives a socket power request, it sends the appropriate data across the P2C interface (CLOCK, DATA, and LATCH). In turn, the power switch turns on the appropriate levels for VCC and VPP for that socket. A 2.7kΩ pulldown on LATCH is used to indicate to the PCI1520 that an EEPROM is being used to program the PCI1520. CLOCK can be provided either internally or externally depending on bit 27 in System Control register in the PCI configuration space at offset 80h. If an external clock is used, the frequency should be between 32kHz and 100kHz. If the internal clock is used, a 43k pulldown resistor is necessary.
PCI1520 Implementation Guide | 5 |