TPS2202AI

DUAL-SLOT PC CARD POWER-INTERFACE SWITCH

WITH RESET FOR SERIAL PCMCIA CONTROLLER

SLVS123A – SEPTEMBER 1995 – REVISED JUNE 1998

15

POST OFFICE BOX 655303

POST OFFICE BOX 1443

APPLICATION INFORMATION

voltage transitioning requirement

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

and increase logic speeds. The TPS2202AI is designed to 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 ensures

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

output ground switches

Several PCMCIA power-distribution switches on the market do not have an active-grounding FET switch. These

can not be relied on to provide a discharge path for voltages stored on PC Card capacitance because of possible

high-impedance isolation by power-management schemes. A method commonly shown to alleviate this

problem is to add to the switch output an external 100 k

Ω resistor in parallel with the PC Card. Considering that

this is the only discharge path to ground, a timing analysis will reveal that the RC time constant delays the

required discharge time to more than 2 seconds. The only way to ensure timing compatibility with PC Card

standards is to use a power-distribution switch that has an internal ground switch, like that of the TPS22xx family,

or add an external ground FET to each of the output lines with the control logic necessary to select it.

In summary, the TPS2202AI is a complete single-chip dual-slot PC Card power interface. It meets all currently

defined PCMCIA specifications for power delivery in 5-V, 3.3-V, and mixed systems, and offers a serial controller

interface. The TPS2202AI offers functionality, power savings, overcurrent and thermal protection, and fault

reporting in one 30-pin SSOP surface-mount package for maximum value added to new portable designs.

power supply considerations

outputs. Any individual pin can conduct the rated input or output current. Unless all pins are connected in

parallel, the series resistance is significantly higher than that specified, resulting in increased voltage drops and

leads.

Although the TPS2202AI is fairly immune to power input fluctuations and noise, it is generally considered good

design practice to bypass power supplies typically with a 1-

µF electrolytic or tantalum capacitor paralleled by

a 0.047-

bypassed with a 0.1-

µF or larger capacitor; doing so improves the immunity of the TPS2202AI to electrostatic

discharge (ESD). Care should be taken to minimize the inductance of PCB traces between the TPS2202AI and

the load. High switching currents can produce large negative-voltage transients, which forward biases substrate

diodes, resulting in unpredictable performance.

The TPS2202AI, unlike other PC Card power-interface switches, does not use the 12-V power supply for

Careful system design using this feature reduces power consumption and extends battery lifetime.

The 3.3-V power input should not be taken higher than the 5-V input. Though doing so is nondestructive, this

results in high current flow into the device and could result in abnormal operation. In any case, this occurrence

indicates a malfunction of one input voltage or both which should be investigated.

Similarly, no pin should be taken below – 0.3 V; forward biasing the parasitic-substrate diode results in substrate

currents and unpredictable performance.