MIC2557 Datasheet, PDF (6/6 Pages) Micrel Semiconductor – PCMCIA Card Socket VPP Switching Matrix

MIC2557
Micrel
3.3V
System
Power
Supply
3.3V to 12V
DC–DC
Converter
VCC
Switch
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.
EN0
EN1
VPP _IN VCC VDD
MIC2557
VPP1
PCMCIA
Card Slot
The HiZ/Low input controls the optional logic low output
clamp. With HiZ/Low in the high state and ENO = EN1 = 0,
V_{PP OUT} enters a high impedance (open) state. With HiZ/
Low in the low state and EN0 = EN1 = 0, V_{PP OUT} is clamped
to ground, providing a logic low signal. The clamp does not
PCMCIA
Card Slot
Controller
require DC bias current for operation.
VPP2
MOSFET drive and bias voltage is derived from V_{PP IN}.
Internal device control logic is powered from V_DD, which
should be connected to the same supply voltage as the
Figure 4. MIC2557 Palmtop application. Note that the ^{PCMCIA controller (normally either 3.3V or 5V).}
V_PP1 and V_PP2 pins are combined. Although this does
not fully satisfy PCMCIA specifications, it simplifies the
circuitry and is acceptable in certain applications.
Output Current
V_{PP OUT}. The low ON resistance of the MIC2557 switch MIC2557 output switches are capable of far more current
2
requires only a small bypass capacitor on V_{PP OUT}, with the than usually needed in PCMCIA applications. PCMCIA V_PP
main filtering action performed by a large filter capacitor on output current is limited primarily by switch resistance voltage
V_{PP IN}. The V_{PP OUT} transition from V_CC to 12.0V typically
takes 25µS. After programming is completed, the controller
outputs a (0,1) to the MIC2557, which then reduces V_{PP OUT}
to the V_CC level. Break-before-make switching action re-
duces switching transients and lowers maximum current
drop (I x R) and the requirement that V_{PP OUT} cannot drop
more than 5% below nominal. V_{PP OUT} will survive output
short circuits to ground if V_{PP IN} and V_CC are current limited
by the regulator that supplies these voltages.
spikes through the switch from the output capacitor.
1997
2-9