MIC2558 Datasheet, PDF (5/6 Pages) Micrel Semiconductor – PCMCIA Dual Card Socket VPP Switching Matrix

MIC2558
Applications Information
PCMCIA V_PP1 and V_PP2 control is easily accomplished
using the MIC2558 voltage selector/switch IC. Two control
bits per V_{PP OUT} pin determine 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 MIC2558 is a dual 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 determine the output voltage and device mode.
V_PP1 and V_PP2 are completely indepenent from each other.
Supply Bypassing
For best results, bypass V_CC and V_{PP IN} inputs with 1µF
capacitors. Both V_{PP OUT} pins should have a 0.01µF to
0.1µF capacitor for noise reduction and electrostatic dis-
charge (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
EN01
VPP _IN
VCC
EN11
MIC2558
EN02
EN12
VPP1
PCMCIA
Card Slot
A
VPP2
PCMCIA
Card Slot
Controller
VCC
EN01
VPP _IN
VCC
EN11
MIC2558
VPP1
PCMCIA
Card Slot
B
5V
System
Power 3.3V
Supply
12V
VCC Select and
Switch
VCC
EN02
EN12
VPP2
EN01
VPP _IN
VCC
EN11
MIC2558
VPP1
PCMCIA
Card Slot
A
Figure 3. MIC2558 Typical two slot PCMCIA applica-
tion with single 5.0V V_CC.
PCMCIA Implementation
PCMCIA
Card Slot
Controller
EN02
EN12
VPP2
VCC Select and
Switch
VCC
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 a MIC2558 and a con-
troller. 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.
EN01
VPP _IN
VCC
EN11
MIC2558
EN02
EN12
VPP1
PCMCIA
Card Slot
B
VPP2
Figure 2. MIC2558 Typical two slot PCMCIA applica-
tion with dual V_CC (5.0V or 3.3V).
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 MIC2558.
During Flash memory programming, the PCMCIA controller
outputs a (1,0) to one or both halves of the MIC2558, which
connects V_{PP IN} to V_{PP OUT1} and/or V_{PP OUT2}. The low ON
resistance of the MIC2558 switch requires only a small
bypass capacitor on the V_{PP OUT} pins, with the main filtering
2-14
1997