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TPS2220A Datasheet

  • TPS2220A

  • 具有串行接口的 1A 单槽 PC 卡电源开关

  • 735.73KB

  • 31页

  • TI

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TPS2220A, TPS2223A
TPS2224A, TPS2226A
SLVS428B 鈥?MAY 2002 鈥?REVISED SEPTEMBER 2004
APPLICATION INFORMATION
OVERVIEW
PC Cards were initially introduced as a means to add flash memory to portable computers. The idea of add-in
cards quickly took hold, and modems, wireless LANs, global positioning satellite system (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. Therefore, the
PCMCIA (Personal Computer Memory Card International Association) was established, comprising 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 would be transparently compatible.
PC CARD POWER SPECIFICATION
System compatibility also means power compatibility. The most current set of specifications (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 68 terminals of the PC Card connector. This power interface consists of two V
CC
, two V
pp
, and four
ground terminals. Multiple V
CC
and ground terminals minimize connector-terminal and line resistance. The two
V
pp
terminals were originally specified as separate signals, but are normally tied together in the host to form a
single node to minimize voltage losses. Card primary power is supplied through the V
CC
terminals; flash-memory
programming and erase voltage is supplied through the V
pp
terminals. Cardbus cards of today typically do not
use 12 V, which is now more of an optional requirement in the host.
DESIGNING FOR VOLTAGE REGULATION
The current PCMCIA specification for output voltage regulation, V
O(reg)
, of the 5-V output is 5% (250 mV). In a
typical PC power-system design, the power supply has an output-voltage regulation, V
PS(reg)
, of 2% (100 mV).
Also, a voltage drop from the power supply to the PC Card results from resistive losses, V
PCB
, in the PCB traces
and the PCMCIA connector. A typical design would limit the total of these resistive losses to less than 1% (50
mV) of the output voltage. Therefore, the allowable voltage drop, V
DS
, for the TPS2220A, TPS2223A, TPS2224A,
and TPS2226A would be the PCMCIA voltage regulation less the power supply regulation and less the PCB and
connector resistive drops:
V
+
V
鈥揤
鈥揤
DS
O(reg) PS(reg) PCB
Typically, this would leave 100 mV for the allowable voltage drop across the 5-V switch. The specification for
output voltage regulation of the 3.3-V output is 300 mV; therefore, using the same equation by deducting the
voltage drop percentages (2%) for power-supply regulation and PCB resistive loss (1%), the allowable voltage
drop for the 3.3-V switch is 200 mV. The voltage drop is the output current multiplied by the switch resistance of
the device. Therefore, the maximum output current, I
O
max, that can be delivered to the PC Card in regulation is
the allowable voltage drop across the IC, divided by the output-switch resistance.
V
I max
+
r DS
O
DS(on)
The xVCC outputs have been designed to deliver the peak and average currents defined by the PC Card
specification within regulation over the operating temperature range. The xVPP outputs of the device have been
designed to deliver 100 mA continuously.
OVERCURRENT AND OVERTEMPERATURE PROTECTION
PC Cards are inherently subject to damage that can result from mishandling. Host systems require protection
against short-circuited cards that can lead to power-supply or PCB trace damage. Even extremely robust
systems can undergo rapid battery discharge into a damaged PC Card, resulting in the sudden and unacceptable
loss of system power. In comparison, the reliability of fused systems is poor because blown fuses require
troubleshooting and repair, usually by the manufacturer.
The TPS2220A, TPS2223A, TPS2224A, and TPS2226A take a two-pronged approach to overcurrent protection,
which is designed to activate if an output is shorted or when an overcurrent condition is present when switches
are powered up. First, instead of fuses, sense FETs monitor each of the xVCC and xVPP power outputs. Unlike
21

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