G574 データシートの表示（PDF） - Global Mixed-mode Technology Inc
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G574 Datasheet PDF : 16 Pages
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Global Mixed-mode Technology Inc.
G574
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 semi-
conductor manufactures. One key goal was to realize
the “plug-and play” concept. Cards and hosts from
different vendors should be compatible—able to com-
municate 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 G574 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 G574 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 junc-
tion 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 G574 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 G574 during a software shutdown in which
quiescent current drops to a typical of 2µA.
3.3V Low Voltage Mode
The G574 operates in 3.3V low voltage mode when
3.3V is the only available input voltage (VI(5V)=0,
VI(12V)=0).This allows host and PC Cards to be oper-
ated in low power 3.3V only modes such as sleep
modes or pager modes. Note that in this operation
mode, the G574 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 resistance 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 G574 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 G574 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.
Ver: 1.2
Jul 28, 2006
TEL: 886-3-5788833
http://www.gmt.com.tw
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