MIC2591B
Micrel
Pin Name
12VINA
12VINB
Pin Function
12V Supply Power and Sense Inputs: Two pins are provided for Kelvin
connection (one for each slot). Pin 5 is the (+) Kelvin-sense connection to
the supply side of the sense resistor for 12V Slot A. Pin 32 is the (+) Kelvin-
sense connection to the supply side of the sense resistor for 12V Slot B.
These two pins must ultimately connect to each other as close as possible
at the MIC2591B controller in order to eliminate any IR drop between these
pins. An undervoltage lockout circuit (UVLO) prevents the switches from
turning on while this input is less than its lockout threshold.
3.3V Supply Power and Sense Inputs: Two pins are provided for
connection (one for each slot). Pin 12 is the (+) Kelvin-sense connection to
the supply side of the sense resistor for 3V Slot A. Pin 25 is the (+) Kelvin-
sense connection to the supply side of the sense resistor for 3V Slot B.
These two pins must ultimately connect to each other as close as possible
at the MIC2591B controller in order to eliminate any IR drop between these
pins. An undervoltage lockout circuit (UVLO) prevents the switches from
turning on while this input is less than its lockout threshold.
3.3V Power-Good Sense Inputs: Connect to 3.3V[A/B] outputs (i.e., the
source terminal of the external power MOSFET). Used to monitor the 3.3V
output voltages for Power-is-Good status.
12V Power-Good Sense Inputs: Connect to 12V[A/B] outputs (i.e., the drain
terminal of the external power MOSFET). Used to monitor the12V output
voltages for Power-is-Good status.
12V Circuit Breaker Sense Inputs: The current limit thresholds are set
by connecting sense resistors between these pins and 12VIN[A/B]. When
the current limit threshold of IR = 50mV is reached, the 12VGATE[A/B] pin
is modulated to maintain a constant voltage across the sense resistor and
therefore a constant current into the load. If the 50mV threshold is exceeded
for t
FLT
, the circuit breaker is tripped and the GATE pin for the affected 12V
supply’s external MOSFET is immediately pulled high.
3V Circuit Breaker Sense Inputs: The current limit thresholds are set by
connecting sense resistors between these pins and 3VIN[A/B]. When the
current limit threshold of IR = 50mV is reached, the 3VGATE[A/B] pin is
modulated to maintain a constant voltage across the sense resistor and
therefore a constant current into the load. If the 50mV threshold is exceeded
for t
FLT
, the circuit breaker is tripped and the GATE pin for the affected 3V
supply’s external MOSFET is immediately pulled low.
12V Gate Drive Outputs: Each pin connects to the gate of an external
P-Channel MOSFET. During power-up, the C
GATE
and the C
GS
of the
MOSFETs are connected to a 25µA current sink. This controls the value of
dv/dt seen at the source of the MOSFETs.
During current limit events, the voltage at this pin is adjusted to maintain
constant current through the switch for a period of t
FLT
. Whenever an
overcurrent, thermal shutdown, or input undervoltage fault condition occurs,
the GATE pin for the affected slot is immediately brought high. These pins
are charged by an internal current source during power-down. Also, the 3V
supply for the affected slot is shut-down.
th
3V Gate Drive Outputs: Each pin connects to the gate of an external
N-Channel MOSFET. During power-up, the C
GATE
and the C
GS
of the
MOSFETs are connected to a 25µA current source. This controls the value
of dv/dt seen at the source of the MOSFETs, and hence the current flowing
into the load capacitance.
During current limit events, the voltage at this pin is adjusted to maintain
constant current through the switch for a period of t
FLT
. Whenever an
overcurrent, thermal shutdown, or input undervoltage fault condition occurs,
the GATE pin for the affected slot is immediately brought low. During power-
down, these pins are discharged by an internal current source. Also, the 12V
supply for the affected slot is shut down.
Pin Description
Pin Number
5
32
12
25
3VINA
3VINB
16
21
10
27
8
29
3VOUTA
3VOUTB
12VOUTA
12VOUTB
12VSENSEA
12VSENSEB
13
24
3VSENSEA
3VSENSEB
3
34
12VGATEA
12VGATEB
14
23
3VGATEA
3VGATEB
March 2005
4
M9999-033105
MICREL [ MICREL SEMICONDUCTOR ]
