Micrel, Inc. MIC2560
September 2006 6
M9999-092106
Application Information
PCMCIA V
CC
and V
PP
control is easily accomplished
using the MIC2560 voltage selector/switch IC. Four
control bits determine V
CC OUT
and V
PP OUT
voltage and
standby/operate mode condition. V
PP OUT
output voltages
of V
CC
(3.3V or 5V), V
PP
, or a high impedance state are
available. When the V
CC
high impedance condition is
selected, the device switches into “sleep” mode and
draws only nano-amperes of leakage current. An error
flag falls low if the output is improper, because of
overtemperature or overcurrent faults. Full protection
from hot switching is provided which prevents feedback
from the V
PP OUT
to the V
CC
inputs (from 12V to 5V, for
example) by locking out the low voltage switch until
V
PP OUT
drops below V
CC
. The V
CC
output is similarly
protected against 5V to 3.3V shoot through.
The MIC2560 is a low-resistance power MOSFET
switching matrix that operates from the computer system
main power supply. Device logic power is obtained from
V
CC3
and internal MOSFET drive is obtained from the
V
PP IN
pin (usually +12V) during normal operation. If
+12V is not available, the MIC2560 automatically
switches into “suspend” mode, where V
CC OUT
can be
switched to 3.3V, but at higher switch resistance.
Internal break-before-make switches determine the
output voltage and device mode.
Supply Bypassing
External capacitors are not required for operation. The
MIC2560 is a switch and has no stability problems. For
best results however, bypass V
CC3 IN
, V
CC5 IN
, and V
PP IN
inputs with filter capacitors to improve output ripple. As
all internal device logic and voltage/current comparison
functions are powered from the V
CC3 IN
line, supply
bypass of this line is the most critical, and may be
necessary in some cases. In the most stubborn layouts,
up to 0.47µF may be necessary. Both V
CC OUT
and
V
PP OUT
pins may have 0.01µF to 0.1µF capacitors for
noise reduction and electrostatic discharge (ESD)
damage prevention. Larger values of output capacitor
might create current spikes during transitions, requiring
larger bypass capacitors on the V
CC3 IN
, V
CC5 IN
, and V
PP IN
pins.
PCMCIA Implementation
The MIC2560 is designed for compatibility with the
Personal Computer Memory Card International
Association’s (PCMCIA) Specification, revision 2.1 as
well as the PC Card Specification, (March 1995),
including the CardBus option.
The Personal Computer Memory Card International
Association (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 implementing PCMCIA specifications
requires a MIC2560, a MIC2557 PCMCIA V
PP
Switching
Matrix, and a controller. Figure 3 shows this full config-
uration, supporting both 5.0V and 3.3V V
CC
operation.
Figure 3. MIC2560 Typical PCMCIA Memory Card
Application with Dual V
CC
(5.0V or 3.3V)
and separate V
PP1
and V
PP2
.
Figure 4. MIC2560 Typical PCMCIA Memory Card
Application with Dual V
CC
(5.0V or 3.3V).
Note that V
PP1
and V
PP2
are Driven Together.
However, many cost sensitive designs (especially
notebook/palmtop computers) connect V
PP1
to V
PP2
and
the MIC2557is not required. This circuit is shown in
Figure 4.
When a memory card is initially inserted, it should
receive V
CC
— either 3.3V ± 0.3V or 5.0V ±5%. The
initial voltage is determined by a combination of
mechanical socket “keys” and voltage sense pins. 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 dual V
CC
. If the card is
