G576 查看數據表（PDF） - Global Mixed-mode Technology Inc
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G576 Datasheet PDF : 12 Pages
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Global Mixed-mode Technology Inc.
G576
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, Global
Positioning Satellite (GPS) systems, multimedia, and
hard-disk versions were soon available. As the num-
ber 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 (Personal Computer Memory Card Inter-
national Association) 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, i.e. cards and
hosts from different vendors should be compatible.
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
connectors. 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.
Designing for Voltage Regulation
The current PCMCIA specification for output voltage
regulation of the 5V output is 5% (250mV). In a typical
PC power-system design, the power supply will have an
output voltage regulation (VPS(reg)) of 2% (100mV). Also,
a voltage drop from the power supply to the PC Card
will result from resistive losses (VPCB) in the PCB traces
and the PCMCIA connector. A typical design would limit
the total of these resistive losses to less than 1% (50mV)
of the output voltage. Therefore, the allowable voltage
drop (VDS) for the G576 would be the PCMCIA voltage
regulation less the power supply regula-tion and less
the PCB and connector resistive drops:
VDS = VO(reg)-VPS(reg)-VPCB
Typically, this would leave 100mV for the allowable
voltage drop across the G576. The voltage drop is the
output current multiplied by the switch resistance of
the G576. Therefore, the maximum output current that
can be delivered to the PC Card in regulation is the
allowable voltage drop across the G576 divided by the
output switch resistance.
IOmax = VDS / RDS(on)
temperature range. Using the same equations, the
PCMCIA specification for output voltage regulation of
the 3.3V output is 300mV. Using the voltage drop per-
centages for power supply regulation (2%) and PCB
resistive loss (1%), the allowable voltage drop for the
3.3V switch is 200mV. The 12V outputs AVPP/BVPP
of the G576 can deliver 150mA continuously.
Overcurrent and overtemperature protection
PC Cards are inherently subuect to damage from mis-
handling. 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 G576 uses sense FETs to check for overcurrent
conditions in each of the AVCC/BVCC and AVPP/
BVPP outputs.Unlike sense resistors or polyfuses,
these FETs do not add to the series resistance of the
switch; therefore voltage and power losses are re-
duced. 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
AOC / BOC indicator, normally a ligic high, are a logic
low when an overcurrent condition is detected provid-
ing for initiation of system diagnostics and/or sending
a warning message to the user.
During power up, the G576 controls the rise time of
the AVCC/BVCC and AVPP/BVPP 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 10A to 15A may
flow into the short before the current limiting of the
G576 engages. If the AVCC/BVCC or AVPP/BVPP
outputs are driven below ground, the G576 may latch
nondestructively in an off state, Cycling power will re-
establish normal operation.
Overcurrent limiting for the AVCC/BVCC outputs is
designed to activate if powered up into a short in the
range of 0.8A to 2.2A, typically at about 1.5A. The
AVPP/BVPP outputs limit from 120mA to 400mA, typi-
cally around 200mA. 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 rating are
exceeded. Thermal limiting disables power output until
the device has cooled.
The AVCC/BVCC outputs deliver 1A continuous at
3.3V and 5.5V within regulation over the operating
Ver: 1.0
Jan 23, 2003
TEL: 886-3-5788833
http://www.gmt.com.tw
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