G571SZ 查看數據表（PDF） - Global Mixed-mode Technology Inc
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G571SZ Datasheet PDF : 11 Pages
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Global Mixed-mode Technology Inc.
G571
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 G571 would be the
PCMCIA voltage regulation less the power supply
regula-tion and less the PCB and connector resistive
drops:
IOmax = VDS / RDS(on)
The AVCC outputs deliver 1A continuous at 3.3V and
5.5V within regulation over the operating temperature
range. Using the same equations, the PCMCIA
specification for output voltage regulation of the 3.3V
output is 300mV. Using the voltage drop percentages
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) of the G571
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 ro-
bust 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 G571 uses sense FETs to check for overcurrent
conditions in each of the AVCC and AVPP out-
puts.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 sepa-
rately. When an overcurrent condition is detected, only
the power output affected is limited; all other power
outputs continue to function normally. The OC indi-
cator, normally a ligic high, is a logic low when an
overcurrent condition is detected providing for initiation
of system diagnostics and/or sending a warning mes-
sage to the user.
During power up, the G571 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 ap-
plied after power is established (e.g., hot insertion of a
bad card ),current is initially limited only by the im-
pedance 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 G571 en-
gages. If the AVCC or AVPP outputs are driven below
ground, the G571 may latch nondestructively in an off
state, Cycling power will reestablish normal operation.
VDS = VO(reg)-VPS(reg)-VPCB
Typically, this would leave 100mV for the allowable
voltage drop across the G571. The voltage drop is the
output current multiplied by the switch resistance of
the G571. Therefore, the maximum output current that
can be delivered to the PC Card in regulation is the
allowable voltage drop across the G571 divided by the
output switch resistance.
Overcurrent limiting for the AVCC 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 out-
puts limit from 120mA to 400mA, typically around
200mA. The protection circuitry acts by linearly limiting
the current passing through the switch rather than ini-
tiating a full shutdown of the supply. Shutdown occurs
only during thermal limiting.
Ver 1.1
Jan 08, 2001
TEL: 886-3-5788833
http://www.gmt.com.tw
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