MIC2592B
Micrel
Pin Name
VSTBYA
VSTBYB
Pin Function
3.3V Standby Input Voltage: Required to support PCI Express VAUX output.
Additionally, the SMBus logic and internal registers run off of VSTBY[A/B]
to ensure that the chip is accessible during standby modes. A UVLO circuit
prevents turn-on of this supply until VSTBY[A/B] rises above its UVLO
threshold. Both pins must be externally connected together at the MIC2592B
controller.
3.3VAUX[A/B] Outputs to PCI Express Card Slots: These outputs connect
the 3.3AUX pin of the PCI Express connectors to VSTBY[A/B] via internal
400mΩ MOSFETs. These outputs are current limited and protected against
short-circuit faults.
Enable Inputs: Rising-edge triggered. Used to enable or disable the MAINA
and MAINB (+3.3V and +12V) outputs. The outputs can be switched on by
these controls only after the V
STBY
input supply is valid and stabe (i.e., t
POR
elapses - See the Electrical Characteristics Table). Taking ON[A/B] low after
a fault resets the +12V and/or +3.3V fault latches for the affected slot. Tie
these pins to GND if using SMI power control. Also, see pin description for
/FAULTA and /FAULTB.
Enable Inputs: Rising-edge triggered. Used to enable or disable the
VAUX[A/B] outputs. The outputs can be switched on by these controls only
after the V
STBY
input supply is valid and stabe (i.e., t
POR
elapses - See the
Electrical Characteristics Table). Taking AUXEN[A/B] low after a fault resets
the respective slot’s Aux Output Fault Latch. Tie these pins to GND if using
SMI power control. Also, see pin description for /FAULTA and /FAULTB.
Overcurrent Timers: Capacitors connected between these
pins and GND set the duration of t
FLT
for each slot. The overcurrent filter
delay (t
FLT
) is the amount of time for which a slot remains in current limit
before its circuit breaker is tripped.
/PWRGD[A/B] Outputs: Open-drain, active-low. Asserted when a slot has
been commanded to turn on and has successfully begun delivering power to
its respective +12V, +3.3V, and VAUX outputs. Each pin requires an external
extern
pull-up resistor to V
STBY
.
/FAULT[A/B] Outputs: Open-drain, active-low. Asserted whenever the
circuit breaker trips due to a fault condition (overcurrent, input undervoltage,
overtemperature). Each pin requires an external pull-up resistor to V
STBY
.
Bringing the slot’s ON[A/B] pin low resets /FAULT[A/B] if /FAULT[A/B]
was asserted in response to a fault condition on one of the slot’s MAIN out-
puts (+12V or +3.3V).
/FAULT[A/B] is reset by bringing the slot’s AUXEN[A/B] pin low if
/FAULT[A/B] was asserted in response to a fault condition on the slot’s
VAUX output. If a fault condition occurred on both the MAIN and VAUX
outputs of the same slot, then both ON[A/B] and AUXEN[A/B] must be
brought low to deassert the /FAULT[A/B] output.
Enable Inputs: Active-low, level-sensitive. Asserting a /FORCE_ON[A/B]
input will turn on all three of the respective slot’s outputs (+12V, +3.3V, and
VAUX), while specifically defeating all protections on those supplies. This
explcitly includes all overcurrent and short circuit protections, and on-chip
thermal protection for the VAUX[A/B] supplies. Additionally included are the
UVLO protections for the +3.3V and +12V main supplies. The
/FORCE_ON[A/B] pins do not disable UVLO protection for the VAUX[A/B]
supplies. These input pins are intended for diagnostic purposes only.
Asserting /FORCE_ON[A/B] will cause the respective slot’s /PWRGD[A/B]
and /FAULT[A/B] pins to enter their open-drain state. Note that the SMBus
register set will continue to reflect the actual state of each slot’s supplies.
There is a pair of register bits, accessible via the SMBus, which can be set
to disable (unconditionally deassert) either or both of the /FORCE_ON[A/B]
pins -- See CNTRL[A/B] Register Bit D[2].
General Purpose Inputs: The states of these two inputs are available by
reading the Common Status Register, Bits [4:5]. If not used, connect each
pin to GND.
Pin Description (continued)
Pin Number
11
26
15
22
VAUXA
VAUXB
44
43
ONA
ONB
45
42
AUXENA
AUXENB
2
35
CFILTERA
CFILTERB
6
31
/PWRGDA
/PWRGDB
1
36
/FAULTA
/FAULTB
9
28
/FORCE_ONA
/FORCE_ONB
4
38
GPI_A0
GPI_B0
March 2005
5
M9999-033105
MICREL [ MICREL SEMICONDUCTOR ]
