TPS2221 datasheet(16/23 Pages) TI

16 / 23 page

TPS2228

TPS2221

SLVS419A – MAY 2002 REVISED SEPTEMBER 2002

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APPLICATION INFORMATION

OVERVIEW

PC cards were initially introduced as a means to add

EEPROM (flash memory) to portable computers with

limited onboard memory. The idea of add-in cards quickly

took hold; modems, wireless LANs, GPS systems,

multimedia, and hard-disk versions were soon available.

As the number of PC card applications grew, the

engineering community quickly recognized the need for a

standard to ensure compatibility across platforms. As a

result, the PCMCIA (Personal Computer Memory Card

International Association) was established, comprised of

members from leading computer, software, PC card, and

semiconductor manufacturers. One key goal was to

realize the plug-and-play concept, so that cards and hosts

from different vendors could communicate with one

another transparently.

PC CARD POWER SPECIFICATION

The current PC card standard set forth by the PCMCIA

committee states that power is to be transferred between

the host and the card through eight of the PC card

connector’s 68 terminals. This power interface consists of

two VCC, two VPP/VCORE, and four ground terminals.

Multiple

power

and

ground

terminals

minimize

connector-terminal and line resistance. The two Vpp/

Vcore terminals were originally specified as separate

signals, but the host is no longer required to provide

separate programmable voltages on each pin. Primary

power for the card is supplied through the VCC terminals;

flash- memory programming and erase voltage is supplied

through the VPP/VCORE terminals. The VPP/VCORE

terminals are also intended to be used as a supplemental

source of power, such as a core voltage for integrated

circuits.

OVERCURRENT AND OVER TEMPERATURE

PROTECTION

PC cards are inherently subject to damage caused by

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 the

rather sudden and unacceptable loss of system power.

The TPS2228/2221 power interface switch is designed to

respond quickly to an overcurrent condition to protect the

system. During an overcurrent event, the current limit

circuit of the TPS2228/2221 generates an internal error

signal that linearly limits the output current of the affected

output. The propogation delay associated with activating

the current-limit circuit has an effect on the amount of

current initially delivered to the output. During this time, the

input voltage to the switch may droop a small amount. The

amount of voltage droop is system dependent. Power

supply bulk capacitors play an important role in minimizing

this voltage droop.

Overcurrent sensing is applied to each output separately.

As a result, only the affected output is current-limited

during an overcurrent event. The TPS2228/2221 also has

an overcurrent status output (OC) that is asserted low to

provide feedback that an overcurrent condition has

occurred.

The TPS2228/2221 has two thermal shutdown circuits.

The higher thermal shutdown circuit protects the device

from a high junction temperature condition. In the event

that the junction temperature exceeds a minimum of

155

°C, the higher thermal shutdown circuit turns off all

switches to protect the device. Normal switch operation

resumes when the junction temperature cools down

approximately 10

°C.

In the event of an overcurrent condition, the lower thermal

shutdown circuit activates when the junction temperature

exceeds a minimum of 120

°C. On the TPS2221, this lower

thermal shutdown circuit disables both the VCC and the

VPP/VCORE switches once the junction temperature

exceeds the lower thermal trip point. On the TPS2228,

only the channel in overcurrent (either AVCC and

AVPP/VCORE, or BVCC and BVPP/VCORE) is disabled. For

both the TPS2221 and the TPS2228, normal operation of

the switches resumes once the junction temperature cools

down approximately 10

°C. This cycle continues until the

overcurrent condition is removed.

VOLTAGE TRANSISTIONING REQUIREMENT

PC cards, like portables, are migrating from 5 V to 3.3 V

and even 1.8 V to minimize power consumption, optimize

board

space,

and

increase

logic

speeds.

The

TPS2228/2221 power interface switch is designed to meet

all combinations of power delivery as currently defined in

the PC card 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 if it is compatible with 3.3-V

power. The PC card standard 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 PC card standard

requires that VCC be discharged 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. The TPS2228/2221 power interface switch

includes discharge transistors on all VCC and VPP/VCORE

outputs to meet the specification requirement.

TPS2221 Datasheet(PDF) 16 Page - Texas Instruments

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