TPS2202AI Datasheet, PDF (15/23 Pages) Texas Instruments – DUAL-SLOT PC CARD POWER-INTERFACE SWITCH WITH RESET FOR SERIAL PCMCIA CONTROLLER

TPS2202AI
DUAL-SLOT PC CARD POWER-INTERFACE SWITCH
WITH RESET FOR SERIAL PCMCIA CONTROLLER
SLVS123A – SEPTEMBER 1995 – REVISED JUNE 1998
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
TPS2202AI offers a selectable V_CC and V_pp ground state, in accordance with PCMCIA 3.3-V/5-V switching
specifications, to fully discharge the card capacitors while switching between V_CC voltages.
output ground switches
Several PCMCIA power-distribution switches on the market do not have an active-grounding FET switch. These
devices do not meet the PC Card specification requiring a discharge of V_CC within 100 ms. PC Card resistance
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 kΩ 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
The TPS2202AI has multiple pins for each of its 3.3-V, 5-V, and 12-V power inputs and for the switched V_CC
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
lost power. Both 12-V inputs must be connected for proper V_pp switching; it is recommended that all input and
output power pins be paralleled for optimum operation. The V_DD input lead must be connected to the 5-V input
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-µF to 0.1-µF ceramic capacitor. It is strongly recommended that the switched V_CC and V_pp outputs be
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
switching or other chip functions. Instead, an internal charge pump generates the necessary voltage from V_DD,
allowing the 12-V input supply to be shut down except when the V_pp programming or erase voltage is needed.
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.
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