MIC2561_05 Datasheet, PDF (6/12 Pages) Micrel Semiconductor – PCMCIA Card Socket VCC and VPP Switching Matrix

MIC2561
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.
Micrel
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.
5V
System
Power 3.3V
Supply
12V
PCMCIA
Card Slot
Controller
VPPIN VCC3IN VCC5IN
EN0
EN1
MIC2561
VCC5_EN
VCC3_EN
VPP1
PCMCIA
Card Slot
VPP2
VCC
VPP _IN VDD VCC
EN0
VPP OUT
EN1 _MIC2557
Figure 3. MIC2561 Typical PCMCIA memory card application with dual V_CC (5.0V or 3.3V) and separate V_PP1 and V_PP2.
MIC2561
6
January 2005