MIC2557 查看數據表（PDF） - Micrel
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MIC2557 Datasheet PDF : 8 Pages
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MIC2557
3.3V
System
Power
Supply
3.3V to 12V
DC–DC
Converter
VCC
Switch
EN0
EN1
VPP IN VCC VDD
MIC2557
VPP1
PCMCIA
Card Slot
PCMCIA
Card Slot
Controller
VPP2
Figure 4. MIC2557 Palmtop application. Note that the
VPP1 and VPP2 pins are combined. Although this does
not fully satisfy PCMCIA specifications, it simplifies the
circuitry and is acceptable in certain applications.
VPP OUT. The low ON resistance of the MIC2557 switch
requires only a small bypass capacitor on VPP OUT, with the
main filtering action performed by a large filter capacitor on
VPP IN. The VPP OUT transition from VCC to 12.0V typically
takes 25µS. After programming is completed, the controller
outputs a (0,1) to the MIC2557, which then reduces VPP OUT
to the VCC level. Break-before-make switching action re-
duces switching transients and lowers maximum current
spikes through the switch from the output capacitor.
Micrel
If no card is inserted, or the system is in sleep mode, the
controller outputs either a (0,0) or a (1,1) to the MIC2557.
Either input places the switch into its shutdown mode, where
only a small leakage current flows.
The HiZ/Low input controls the optional logic low output
clamp. With HiZ/Low in the high state and ENO = EN1 = 0,
VPP OUT enters a high impedance (open) state. With HiZ/
Low in the low state and EN0 = EN1 = 0, VPP OUT is clamped
to ground, providing a logic low signal. The clamp does not
require DC bias current for operation.
MOSFET drive and bias voltage is derived from VPP IN.
Internal device control logic is powered from VDD, which
should be connected to the same supply voltage as the
PCMCIA controller (normally either 3.3V or 5V).
Output Current
MIC2557 output switches are capable of far more current
than usually needed in PCMCIA applications. PCMCIA VPP
output current is limited primarily by switch resistance voltage
drop (I x R) and the requirement that VPP OUT cannot drop
more than 5% below nominal. VPP OUT will survive output
short circuits to ground if VPP IN and VCC are current limited
by the regulator that supplies these voltages.
MIC2557
6
1997
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