G570 datasheet(8/14 Pages) GMT

8 / 14 page

Ver 1.0

Nov 09, 2000

TEL: 886-3-5788833

http://www.gmt.com.tw

G570

Global Mixed-mode Technology Inc.

Application Information

Overview

PC Cards were initially introduced as a means to add

EEPROM (flash memory) to portable computers with

limited on-board memory. The idea of add-in cards

quickly took hold; modems, wireless LANs, Global

Positioning Satellite (GPS), 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. To this end, the

PCMCIA was established, comprised of members

from leading computer, software, PC Card, and

semiconductor manufactures. One key goal was to

realize the “plug-and play” concept. Cards and hosts

from different vendors should be compatible—able to

communicate with one another transparently.

PC Card Power Specification

System compatibility also means power compatibility.

The most current set of specifications (PC Card Stan-

dard) set forth by the PCMCIA committee states that

power is to be transferred between the host and the

card through eight of the 68 terminals of the PC Card

connector. This power interface consists of two VCC,

two VPP, and four ground terminals. Multiple VCC and

ground terminals minimize connector-terminal and line

resistance. The two VPP terminals were originally

specified as separate signals but are commonly tied

together in the host to form a single node to minimize

voltage losses. Card primary power is supplied

through the VCC terminals; flash-memory programming

and erase voltage is supplied through the VPP termi-

nals.

Overcurrent and Over-Temperature Protection

PC Cards are inherently subject to damage that can

result from mishandling. Host systems require protec-

tion against short-circuited cards that could lead to

power supply or PCB-trace damage. Even systems

robust enough 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. Most hosts include fuses for

protection. However, the reliability of fused systems is

poor, as blown fuses require troubleshooting and re-

pair, usually by the manufacturer.

The G570 takes a two-pronged approach to overcur-

rent protection. First, instead of fuses, sense FETs

monitor each of the power outputs. Excessive current

generates an error signal that linearly limits the output

current, preventing host damage or failure. Sense

FETs, unlike sense resistors or polyfuses, have an

added advantage in that they do not add to the series

resistance of the switch and thus produce no addi-

tional voltage losses. Second, when an overcurrent

condition is detected, the G570 asserts a signal at

OC that can be monitored by the microprocessor to

initiate diagnostics and/or send the user a warning

message. In the event that an overcurrent condition

persists, causing the IC to exceed its maximum

junction

temperature,

thermal-protection

circuitry

activates, shutting down all power outputs until the

device cools to within a safe operating region.

12V Supply Not Required

Most PC Card switches use the externally supplied

12V VPP power for switch-gate drive and other chip

functions, which requires that power be present at all

times. The G570 offers considerable power savings by

using an internal charge pump to generate the re-

quired higher voltages from 5V or 3.3V input; therefore,

the external 12V supply can be disable except when

needed for flash-memory functions, thereby extending

battery lifetime. Do not ground the 12V input if the 12V

input is not used. Additional power savings are real-

ized by the G570 during a software shutdown in which

quiescent current drops to a typical of 2µA.

3.3V Low Voltage Mode

The G570 operates in 3.3V low voltage mode when

3.3V is the only available input voltage (VI(5V)=0).This

allows host and PC Cards to be operated in low power

3.3V only modes such as sleep modes or pager

modes. Note that in this operation mode, the G570

derives its bias current from the 3.3V input pin and

only 3.3V can be delivered to the Card. The 3.3V

switch resistance increases, but the added switch re-

sistance should not be critical, because only a small

amount of current is delivered in this mode.

Voltage Transitioning Requirement

PC Cards, like portables, are migrating from 5V to

3.3V to minimize power consumption, optimize board

space, and increase logic speeds. The G570 is de-

signed to meet all combinations of power delivery as

currently defined in the PCMCIA standard. The latest

protocol accommodates mixed 3.3V/5V systems by

first powering the card with 5V, then polling it to de-

termine its 3.3V compatibility. The PCMCIA specifica-

tion requires that the capacitors on 3.3V compatible

cards be discharged to below 0.8 V before applying

3.3V power. This ensures that sensitive 3.3V circuitry

is not subjected to any residual 5V charge and func-

tions as a power reset. The G570 offer a selectable

VCC and VPP ground state, in accordance with PCMCIA

3.3V/5V switching specifications, to fully discharge the

card capacitors while switching between VCC voltage.

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