TPS2214A, TPS2216A

LOW-COST DUAL-SLOT PC CARD POWER SWITCH

FOR SERIAL PCMCIA CONTROLLERS

SLVS267 – DECEMBER 1999

19

POST OFFICE BOX 655303

APPLICATION INFORMATION

designing for voltage regulation (continued)

overcurrent and overtemperature protection

PC Cards are inherently subject to damage that can result from mishandling. Host systems require protection

against short-circuited cards that could lead to power-supply or PCB trace damage. Even systems robust

enough to withstand a short circuit would still undergo rapid battery discharge into the damaged PC Card,

resulting in the rather sudden and unacceptable loss of system power. Most hosts include fuses for protection.

However, the reliability of fused systems is poor, as blown fuses require troubleshooting and repair, usually by

the manufacturer.

The TPS2214A and TPS2216A take a two-pronged approach to overcurrent protection, which is designed to

activate if an output is shorted or when an overcurrent condition is present when switches are powered up. First,

instead of fuses, sense FETs monitor each of the xVCC and xVPP power outputs. Unlike sense resistors or

polyfuses, these FETs do not add to the series resistance of the switch; therefore voltage and power losses are

reduced. Overcurrent sensing is applied to each output separately. Excessive current generates an error signal

that limits the output current of only the affected output, preventing damage to the host. Each xVCC output

overcurrent limits from 1 A to 2.2 A, typically around 1.6 A; the xVPP outputs limit from 250 mA to 500 mA,

typically around 375 mA.

Second, when an overcurrent condition is detected, these devices assert an active low OC signal that can be

monitored by the microprocessor or controller to initiate diagnostics and/or send the user a warning message.

In the event that an overcurrent condition persists, causing the IC to exceed its maximum junction temperature,

thermal-protection circuitry activates. This shuts down all power outputs until the device cools to within a safe

operating region, which is ensured by a thermal shutdown hysteresis.

12-V supply not required

Many PC Card switches use the externally supplied 12 V to power gate drive and other chip functions; this

requires that power be present at all times. The TPS2214A and TPS2216A offer considerable power savings

by using an internal charge pump to generate the required higher gate drive voltages from the 5-V or 3.3-V

power supplies. Therefore, the external 12-V supply can be disabled except when needed for flash-memory

functions, thereby extending battery lifetime. Additional power savings are realized by the IC during shutdown

mode, in which quiescent current drops to a maximum of 1

µA.

3.3-V low-voltage mode

The TPS2214A and TPS2216A will operate in 3.3-V low-voltage mode when 3.3 V is the only available input

modes such as sleep modes. Note that in this operation mode, the IC will derive its bias current from the 3.3-V

input pin and can only provide 3.3 V to the outputs.

voltage transitioning requirement

PC Cards are migrating from 5 V to 3.3 V to minimize power consumption, optimize board space, and increase

logic speeds. The TPS2214A and TPS2216A meet all combinations of power delivery as currently defined in

the PCMCIA standard. The latest protocol accommodates mixed 3.3-V/5-V systems by first powering the card

with 5 V, then polling it to determine its 3.3-V compatibility. The PCMCIA specification requires that the

capacitors on 3.3-V-compatible cards be discharged to below 0.8 V before applying 3.3-V power. This action

ensures that sensitive 3.3-V circuitry is not subjected to any residual 5-V charge and functions as a power reset.

to provide a discharge path for voltages stored on PC Card capacitance because of possible high-impedance

isolation by power-management schemes. The TPS2214A and TPS2216A include discharge transistors on all

xVCC and xVPP outputs to meet the specification requirement.