TPS2201, TPS2201Y

DUAL-SLOT PC CARD POWER-INTERFACE SWITCHES

FOR PARALLEL PCMCIA CONTROLLERS

SLVS094B – AUGUST 1994 – REVISED AUGUST 1995

6–16

POST OFFICE BOX 655303

APPLICATION INFORMATION

voltage transitioning requirement (continued)

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 over 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 TPS2201 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 TPS2201 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 terminal can conduct the rated input or output current. Unless all terminals are connected

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

5V input leads.

Although the TPS2201 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 TPS2201 to electrostatic

discharge (ESD). Care should be taken to minimize the inductance of PCB traces between the TPS2201 and

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

diodes, resulting in unpredictable performance.

The TPS2201, unlike other PC Card power-interface switches, does not use the 12-V power supply for switching

system design making use of 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. Doing so, though nondestructive, 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 terminal should be taken below – 0.3 V; forward biasing the parasitic-substrate diode results in

substrate currents and unpredictable performance.