MIC2561 Micrel
MIC2561 6 January 2005
Applications Information
PCMCIA V
CC
and V
PP
control is easily accomplished using
the MIC2561 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 MIC2561 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 avail-
able, the MIC2561 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 de-
termine the output voltage and device mode.
Supply Bypassing
External capacitors are not required for operation. The
MIC2561 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 func-
tions 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 Personal Computer Memory Card International Associa-
tion (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 PCM-
CIA specifications requires a MIC2561, a MIC2557 PCMCIA
V
PP
Switching Matrix, and a controller. Figure 3 shows this
full configuration, supporting both 5.0V and 3.3V V
CC
opera-
tion.
Figure 3. MIC2561 Typical PCMCIA memory card application with dual V
CC
(5.0V or 3.3V) and separate V
PP1
and V
PP2.
System
Power
Supply
PCMCIA
Card Slot
Controller
MIC2561
PCMCIA
Card Slot
5V
3.3V
12V
EN0
EN1
V
PP1
V
CC
V
PP
IN V
CC5
INV
CC3
IN
V
CC5_EN
V
CC3_EN
V
PP2
MIC2557
EN0
EN1
V
PP IN
V
DD
V
PP
OUT
V
CC
