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參數(shù)資料
| 型號： | G574 |
| 英文描述： | Dual slot PCMCIA power switch. compatible with TPS2216.|PCMCIA Power Switch Series |
| 中文描述： | 雙插槽的PCMCIA電源開關(guān)。兼容TPS2216。|的PCMCIA電源開關(guān)系列 |
| 文件頁數(shù)： | 12/16頁 |
| 文件大?。?/td> | 368K |
| 代理商： | G574 |
Ver: 1.1
Mar 07, 2003
TEL: 886-3-5788833
http://www.gmt.com.tw
12
G574
Global Mixed-mode Technology Inc.
Shutdown Mode
In the shutdown mode, which can be controlled by bit
D8 of the input serial DATA word, each of he xVCC
and xVPP outputs is forced to a high-inpedance state.
In this mode, the chip quiescent current is limited to
2μA or less to conserve battery power.
Standby Mode
The G574 can be put in standby mode by pulling
STBY
low to conserve power during low-power opera-
tion. In this mode, all of the power outputs (xVCC and
xVPP) will have a nominal current limit of 50mA.
STBY
has an internal 150 k
pullup resistor. The out-
put-switch status of the device must be set, allowing
the output capacitors to charge, prior to enabling the
standby mode. Changing the setting of the output
switches with the device in standby mode may cause
an overcurrent response to be generated.
Mode
The mode pin programs the switches in either G574 or
G570 mode. An internal 150 k
pulldown resistor is
connected to the pin. Floating or pulling the mode pin
low sets the switches in G570 mode; pulling the mode
pin high sets the switches in G574 mode. In
G570mode, xVPP outputs are dependent on xVCC
outputs. In G574 mode, xVPP is programmed inde-
pendent of xVCC. Refer to G574 control-logic tables
for more information.
Output Ground Switches
Several PCMCIA power distribution switches on the
market do not have an active grounding FET switch.
These devices do not meet the PC Card specification
requiring a discharge of V
CC
within 100ms. PC Card
resistance can not be relied on to provide a discharge
path for voltages stored on PC Card capacitance be-
cause of possible high impedance isolation by power
management schemes. A method commonly shown to
alleviate this problem is to add to the switch output an
external 100k
Ω
resistor in parallel with the PC Card.
Considering that this is the only discharge path to
ground, a timing analysis show that the RC time con-
stant delays the required discharge time to more than
2 seconds. The only way to ensure timing compatibility
with PC Card standards is to use a power-distribution
switch that has an internal ground switch, like that of
the G574, or add an external ground FET to each of
the output lines with the control logic necessary to se-
lect it.
In summary, the G574 is a complete single-chip
dual-slot PC Card power interface. It meets all cur-
rently defined PCMCIA specifications for power deliv-
ery in 5V, 3.3V, and mixed systems, and offers a serial
control interface. The G574 offers functionality, power
savings, overcurrent and thermal protection, and fault
reporting in one 30 pin SSOP surface-mount package
for maximum value added to new portable designs.
Power Supply Considerations
The G574 has multiple pins for each of its 3.3V, 5V,
and 12V power inputs and for switched V
CC
outputs.
Any individual pin can conduct the rated input or out-
put current. Unless all pins are connected in parallel,
the series resistance is significantly higher than that
specified, resulting in increased voltage drops and lost
power. Both 12V inputs must be connected for proper
V
PP
switching; it is recommended that all input and
output power pins be paralleled for optimum operation.
Although the G574 is fairly immune to power input
fluctuations and noise, it is generally considered good
design practice to bypass power supplies typically with
a 1μF electrolytic or tantalum capacitor paralleled by a
0.047μF to 0.1μF ceramic capacitor. It is strongly re-
commended that the switched V
CC
and V
PP
outputs be
bypassed with a 0.1μF or larger capacitor; doing so
improves the immunity of the G574 to electrostatic
discharge (ESD). Care should be taken to minimize
the inductance of PCB traces between the G574 and
the load. High switching currents can produce large
negative-voltage transients, which forward biases
substrate diodes, resulting in unpredictable perform-
ance. Similarly, no pin should be taken below –0.3V.
RESET or RESET Inputs
To ensure that cards are in a known state after power
brownouts or system initialization, the PC Cards
should be reset at the same time as the host by ap-
plying a low impedance to the xV
CC
and xV
PP
terminals
to ground. A low impedance output state allows dis-
charging of residual voltage remaining on PC Card
filter capacitance, permitting the system (host and PC
Cards) to be powered up concurrently. The RESET or
RESET input will closes internal switches S1, S4, S7,
and S11 with all other switches left open (see G574
control logic table). The G574 remains in the low im-
pedance output state until the signal is deasserted and
further data is clocked in and latched. RESET or
RESET are provided for direct compatibility with sys-
tems that use either an active-low or active-high reset
voltage supervisor. The unused pin is internally pulled
up or down and should be left unconnected.
Overcurrent and Thermal Protection
The G574 uses sense FETs to check for overcurrent
conditions in each of the V
CC
and V
PP
outputs. 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 separately. When an overcur-
rent condition is detected, only the power output af-
fected is limited; all other power outputs continue to
function normally. The OC indicator, normally a logic
high, is a logic low when any overcurrent condition is
detected, providing for initiation of system diagnostics
and/or sending a warning message to the user.
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