MIC2561 Micrel
January 2005 7 MIC2561
However, many cost sensitive designs (especially notebook/
palmtop computers) connect V
PP1
to V
PP2
and the MIC2557
is 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 compatible with and desires a different V
CC
level, the controller commands this change by disabling V
CC
,
waiting at least 100ms, and then re-enabling the other V
CC
voltage.
If no card is inserted or the system is in sleep mode, the
controller outputs a (V
CC3
IN, V
CC5
IN) = (0,0) to the
MIC2561, which shuts down V
CC
. This also places the switch
into a high impedance output shutdown (sleep) mode, where
current consumption drops to nearly zero, with only tiny
CMOS leakage currents flowing.
During Flash memory programming with standard (+12V)
Flash memories, the PCMCIA controller outputs a (1,0) to the
EN0, EN1 control pins of the MIC2561, which connects
V
PP
IN to V
PP OUT
. The low ON resistance of the MIC2561
switches allow using small bypass capacitors (in some cases,
none at all) on the V
CC OUT
and V
PP OUT
pins, with the main
filtering action performed by a large filter capacitor on the
input supply voltage to V
PP
IN (usually the main power
supply filter capacitor is sufficient). The V
PP OUT
transition
from V
CC
to 12.0V typically takes 15µs. After programming is
completed, the controller outputs a (EN1, EN0) = (0,1) to the
MIC2561, which then reduces V
PP OUT
to the V
CC
level for
read verification. Break-before-make switching action re-
duces switching transients and lowers maximum current
spikes through the switch from the output capacitor. The flag
comparator prevents having high voltage on the V
PP
OUT
capacitor from contaminating the V
CC
inputs, by disabling the
low voltage V
PP
switches until V
PP
OUT
drops below the V
CC
level selected. The lockout delay time varies with the load
current and the capacitor on V
PP OUT
. With a 0.1µF capacitor
and nominal I
PP OUT
, the delay is approximately 250µs.
Internal drive and bias voltage is derived from V
PP
IN. Internal
device control logic is powered from V
CC3
IN. Input logic
threshold voltages are compatible with common PCMCIA
controllers using either 3.3V or 5V supplies. No pull-up
resistors are required at the control inputs of the MIC2561.
Output Current and Protection
MIC2561 output switches are capable of more current than
needed in PCMCIA applications and meet or exceed all
PCMCIA specifications. For system and card protection,
output currents are internally limited. For full system protec-
tion, long term (millisecond or longer) output short circuits
invoke overtemperature shutdown, protecting the MIC2561,
the system power supplies, the card socket pins, and the
memory card. The MIC2561 overtemperature shutdown oc-
curs at a die temperature of 110°C.
Suspend Mode
An additional feature in the MIC2561 is a pseudo power-down
mode, Suspend Mode, which allows operation without a V
PP
IN supply. In Suspend Mode, the MIC2561 supplies 3.3V to
V
CC
OUT whenever a V
CC
output of 3.3V is enabled by the
PCMCIA controller. This mode allows the system designer
the ability to turn OFF the V
PP
supply generator to save
power when it is not specifically required. The PCMCIA card
receives V
CC
at reduced capacity during Suspend Mode, as
the switch resistance rises to approximately 4.5Ω.
High Current V
CC
Operation Without a
+12V Supply
Figure 5 shows the MIC2561 with V
CC
switch bias provided
by a simple charge pump. This enables the system designer
to achieve full V
CC
performance without a +12V supply,
which is often helpful in battery powered systems that only
provide +12V when it is needed. These on-demand +12V
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
IN
V
CC3
IN
V
CC5_EN
V
CC3_EN
V
PP2
Figure 4. MIC2561 Typical PCMCIA memory card application with dual V
CC
(5.0V or 3.3V). Note that V
PP1
and V
PP2
are
driven together.
