TPS2211 Datasheet, PDF (15/22 Pages) Texas Instruments – SINGLE-SLOT PC CARD POWER INTERFACE SWITCH FOR PARALLEL PCMCIA CONTROLLERS

TPS2211
SINGLE-SLOT PC CARD POWER INTERFACE SWITCH
FOR PARALLEL PCMCIA CONTROLLERS
SLVS156E – JULY 1997 – REVISED JANUARY 2001
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
PC power-system design, the power supply will have an output voltage regulation (V_PS(reg)) of 2% (100 mV).
Also, a voltage drop from the power supply to the PC Card will result from resistive losses (V_PCB) in the PCB
traces and the PCMCIA connector. A typical design would limit the total of these resistive losses to less than
1% (50 mV) of the output voltage. Therefore, the allowable voltage drop (V_DS) for the TPS2211 is the PCMCIA
voltage regulation less the power supply regulation and less the PCB and connector resistive drops:
+ V_DS V_OǒregǓ – V_{PSǒregǓ} – V_PCB
Typically, this would leave 100 mV for the allowable voltage drop across the TPS2211. 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 TPS2211 divided by the
output switch resistance.
+ I_Omax
V_DS
r_DSǒonǓ
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 TPS2211 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 TPS2211 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 TPS2211 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 TPS2211 engages. If the AVCC
or AVPP outputs are driven below ground, the TPS2211 may latch nondestructively in an off state. Cycling
power will reestablish 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 2.2 A, typically at about 1.6 A. The AVPP outputs limit from 120 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.
• POST OFFICE BOX 655303 DALLAS, TEXAS 75265
15