MIC2557_11 Datasheet, PDF (5/8 Pages) Micrel Semiconductor – PCMCIA Card Socket VPP Switching Matrix Final Information

MIC2557
Applications Information
PCMCIA V_PP control is easily accomplished using the
MIC2557 voltage selector/switch IC. Two control bits deter-
mine output voltage and standby/operate mode condition.
Output voltages of 0V (defined as less than 0.4V), V_CC (3.3V
or 5V), V_PP, or a high impedance state, are available. When
either the high impedance or low voltage conditions are
selected, the device switches into "sleep" mode, and draws
only nanoamperes of leakage current.
The MIC2557 is a low-resistance power MOSFET switching
matrix that operates from the computer system main power
supply. Device power is obtained from V_DD, which may be
either 3.3V or 5V, and FET drive is obtained from V_{PP IN}
(usually +12V). Internal break-before-make switches deter-
mine the output voltage and device mode.
Supply Bypassing
For best results, bypass V_CC and V_{PP IN} at their inputs with
1µF capacitors. V_{PP OUT} should have a 0.01µF to 0.1µF
capacitor for noise reduction and electrostatic discharge
(ESD) damage prevention. Larger values of output capacitor
will create large current spikes during transitions, requiring
larger bypass capacitors on the V_CC and V_{PP IN} pins.
5V
System
Power
Supply
12V
Micrel
VCC Switch
VCC
EN0
EN1
VPP _IN
VCC
MIC2557
VPP1
PCMCIA
Card Slot
A
EN0
EN1
VPP _IN
VCC
MIC2557
VPP2
PCMCIA
Card Slot
Controller
VCC
EN0
EN1
VPP _IN
VCC
MIC2557
VPP1
PCMCIA
Card Slot
B
5V
System
Power 3.3V
Supply
12V
VCC Select and
Switch
VCC
EN0
EN1
VPP _IN
VCC
MIC2557
VPP2
EN0
EN1
VPP _IN
VCC
MIC2557
VPP1
PCMCIA
Card Slot
A
Figure 3. MIC2557 Typical two slot PCMCIA applica-
tion with single 5.0V V_CC.
PCMCIA Implementation
PCMCIA
Card Slot
Controller
EN0
EN1
VPP _IN
VCC
MIC2557
VPP2
VCC Select and
Switch
VCC
EN0
EN1
VPP _IN
VCC
MIC2557
VPP1
PCMCIA
Card Slot
B
EN0
EN1
VPP _IN
VCC
MIC2557
VPP2
The Personal Computer Memory Card International Asso-
ciation (PCMCIA) specification requires two V_PP supply pins
per PCMCIA slot. V_PP is primarily used for programming
Flash (EEPROM) memory cards. The two V_PP supply pins
may be programmed to different voltages. Fully implement-
ing PCMCIA specifications requires two MIC2557, and a
controller. Figure 2 shows this full configuration, supporting
both 5.0V and 3.3V V_CC operation. Figure 3 is a simplified
design with fixed V_CC = 5V. Palmtop computers, where size
and battery life are tantamount, can sometimes use a com-
promise implementation, with V_PP1 tied to V_PP2 (see Figure
4).
When a memory card is initially inserted, it should receive
V_CC, usually 5.0V ±5%. The card sends a handshaking data
stream to the controller, which then determines whether or
not this card requires V_PP and if the card is designed for 5.0V
or 3.3V V_CC. If the card uses 3.3V V_CC, the controller
commands this change, which is reflected on the V_CC pins of
both the PCMCIA slot and the MIC2557.
Figure 2. MIC2557 Typical two slot PCMCIA applica-
tion with dual V_CC (5.0V or 3.3V).
During Flash memory programming, the PCMCIA controller
outputs a (1,0) to the MIC2557, which connects V_{PP IN} to
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MIC2557