TPS2211A

SINGLE-SLOT PC CARD POWER INTERFACE SWITCH

FOR PARALLEL PCMCIA CONTROLLERS

SLVS282A – SEPTEMBER 2000 – REVISED NOVEMBER 2002

13

POST OFFICE BOX 655303

APPLICATION INFORMATION

designing for voltage regulation

The current PCMCIA specification for output voltage regulation of the 5-V output is 5% (250 mV). In a typical

the PCMCIA connector. A typical design limits the total of these resistive losses to less than 1% (50 mV) of the

less the power supply regulation and less the PCB and connector resistive drops:

V

V

O reg

– V

PS reg

– V

PCB

Typically, this leaves 100 mV for the allowable voltage drop across the TPS2211A. The voltage drop is the output

current multiplied by the switch resistance of the TPS2211. Therefore, the maximum output current that can be

delivered to the PC Card in regulation is the allowable voltage drop across the TPS2211A divided by the output

switch resistance.

I

O

max

+

V

DS

r

DS on

The AVCC outputs deliver 1 A continuous at 5 V and 3.3 V within regulation over the operating temperature

range. Using the same equations, the PCMCIA specification for output voltage regulation of the 3.3 V output

is 300 mV. Using the voltage drop percentages for power supply regulation (2%) and PCB resistive loss (1%),

the allowable voltage drop for the 3.3 V switch is 200 mV. The 12-V outputs (AVPP) of the TPS2211A can deliver

150 mA continuously.

overcurrent and overtemperature protection

PC Cards are inherently subject to damage from mishandling. Host systems require protection against

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

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

a sudden loss of system power. Most hosts include fuses for protection. The reliability of fused systems is poor

and requires troubleshooting and repair, usually by the manufacturer, when fuses are blown.

The TPS2211A uses sense FETs to check for overcurrent conditions in each of the AVCC and AVPP 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. When an

overcurrent condition is detected, only the power output affected is limited; all other power outputs continue to

function normally. The OC indicator, normally a logic high, is a logic low when an overcurrent condition is

detected providing for initiation of system diagnostics and/or sending a warning message to the user.

During power up, the TPS2211A controls the rise time of the AVCC and AVPP outputs and limits the current

into a faulty card or connector. If a short circuit is applied after power is established (e.g., hot insertion of a bad

card), current is initially limited only by the impedance between the short and the power supply. In extreme

cases, as much as 10 A to 15 A may flow into the short before the current limiting of the TPS2211A engages.

If the AVCC or AVPP outputs are driven below ground, the TPS2211A may latch nondestructively in an off state.

Cycling power reestablishes normal operation.

Overcurrent limiting for the AVCC outputs is designed to activate if powered up into a short in the range of

1 A to 2.5 A, typically at about 1.6 A. The AVPP outputs limit from 180 mA to 400 mA, typically around 280 mA.

The protection circuitry acts by linearly limiting the current passing through the switch rather than initiating a full

shutdown of the supply. Shutdown occurs only during thermal limiting.

Thermal limiting prevents destruction of the IC from overheating if the package power dissipation ratings are

exceeded. Thermal limiting disables power output until the device has cooled.