參數(shù)資料
型號: TPS2202AIDFR
廠商: TEXAS INSTRUMENTS INC
元件分類: 電源管理
英文描述: 2-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO30
封裝: PLASTIC, SSOP-30
文件頁數(shù): 6/28頁
文件大?。?/td> 605K
代理商: TPS2202AIDFR
TPS2202AI
DUAL-SLOT PC CARD POWER-INTERFACE SWITCH
WITH RESET FOR SERIAL PCMCIA CONTROLLER
SLVS123B – SEPTEMBER 1995 – REVISED JANUARY 2001
14
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
APPLICATION INFORMATION
designing around 1-A delivery (continued)
Calculating the rDS(on) necessary to support a 100 mV or 198 mV switch loss, using R = E/I and setting I = 1 A,
the 5-V and 3.3-V switches would need to be 100 m
and 198 m respectively. One solution would be to pay
for a more expensive switch with lower rDS(on). A second, less expensive approach is to increase the headroom
of the power supply—for example, to increase the 5 V supply 1.5% or to 5.075
±2%. Working through the
numbers once more, the 2% for the regulator plus 1 % for etch and terminal losses leaves 97% or 4.923 V. The
allowable voltage loss across the power distribution switch is now 4.923 V minus 4.750 V or 173 mV. Therefore,
a switch with 173 m
or less could deliver 1 A or greater. Setting the power supply high is a common practice
for delivering voltages to allow for system switch connector and etch losses. This practice has a minimal effect
on overall battery life. In the example above, setting the power supply 1.5% high would only decrease a 3-hour
battery life by approximately 2.7 minutes, trivial when compared with the decrease in battery life when running
a 5-W PC Card.
heat dissipation
A greater concern in delivering 1 A or 5 W is the ability of the host to dissipate the heat generated by the PC
Card. For desktop computers the solution is simpler: locate the PC Card cage such that it receives convection
cooling from the forced air of the fan. Notebooks and other handheld equipment will not be able to rely on
convection, but on conduction of heat away from the PC Card through the rails into the card cage. This is difficult
because PC Card/card cage heat transfer is very poor. A typical design scenario would require the PC Card
to be held at 60
°C maximum with the host platform operating as high as 50°C. Preliminary testing reveals that
a PC Card can have a 20
°C rise, exceeding the 10°C differential in the example, when dissipating less than 2 W
of continuous power. Sixty degrees centigrade was chosen because it is the maximum operating temperature
allowable by PC Card specification. Power handling requirements and temperature rises are topics of concern
and are currently being addressed by the PCMCIA committee.
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 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 the rather sudden and unacceptable loss of system power. Most hosts include fuses for protection.
The reliability of fused systems is poor though, as blown fuses require troubleshooting and repair, usually by
the manufacturer.
The TPS2202AI takes a two-pronged approach to overcurrent 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 additional voltage
losses. Second, when an overcurrent condition is detected, the TPS2202AI 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.
相關(guān)PDF資料
PDF描述
TPS2202AIDBRG4 2-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO30
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