MIC2580A-1.0BTS Micrel Inc, MIC2580A-1.0BTS Datasheet - Page 18

• Manufacturer Part Number: MIC2580A-1.0BTS
• Description: IC CTRLR HOTSWAP PCI PWR 24TSSOP
• Manufacturer: Micrel Inc
• Type: Hot-Swap Controllerr

Specifications of MIC2580A-1.0BTS

• Applications: General Purpose, CompactPCI™
• Internal Switch(s): No
• Voltage - Supply: 3.3V, 5V, ±12V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-TSSOP
• Peak Reflow Compatible (260 C): No
• Supply Voltage: 12.6V
• Hot Swap Controller Type: PCI
• Fault Output: Active Low
• Supply Voltage Max: 12.6V
• Number Of Controlled Voltages: 4
• Leaded Process Compatible: No
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

MIC2580A
Functional Description
Start-Up Sequence
The start-up sequence iniates after all four supplies are
connected to the inputs and then /ON is asserted by
transistioning from high to low. During the start-up sequence,
all four gates ramp up at a rate determined by C
this time /PWRGD is deasserted until all four supplies are
within specified levels. When /PWRGD is asserted the power-
on-reset signal /POR timer begins. The time period is defined
by C
during the start-up sequence.
During the start-up sequence, a current source charges
C
reached. This period of time defines an interval during which
overcurrent events are ignored. This prevents high inrush
currents that normally occur when charging capacitance
erroneously asserting /FAULT. The magnitude of the start-
up time, t
The MIC2580A employs foldback current limiting that en-
sures the device starts up in current limit. This minimizes high
inrush currents due to ramping a voltage into capacitance
regardless of the size of the load capacitance.
Overcurrent Detection
The MIC2580A senses overcurrent via the use of external
sense resistors for the 5V and 3.3V supply rails. When the
sense voltage across these resistors is greater than or equal
to 50mV an overcurrent condition is detected. Therefore the
overcurrent set point is determined by I
For the +12V and –12V supply rails overcurrent detection is
set internally at 1.3A and –0.5A respectively.
When an overcurrent condition is detected /FAULT is as-
serted only if the overcurrent condition lasts for a minimum
time period of 10µs. This delay prevents spurious noise from
the system erroneously tripping the circuit breaker and as-
serting /FAULT. Upon /FAULT being asserted an internal
latch is set that immediately turns off all four supplies to
prevent further damage to the system. Toggling /ON will reset
the latch and initiate another start-up sequence. Figures 2
and 3 depict the timing for two fault conditions.
MIC2580A
START
RST
. Refer to Figure 1 for a timing diagram of the signals
at a constant rate until a threshold voltage of 2.4V is
START
is defined by C
START
.
LIMIT
= 50mV/R
SLEW
. During
SENSE
.
18
Thermal Shutdown
The +12V and –12V internal MOSFET switches are protected
by current limit and overtemperature shutdown circuitry.
When the die temperature exceeds 160°C, /FAULT is as-
serted and all supplies are shut off. The power dissipated in
the MIC2580A is primarily due to the sum of current flowing
through the internal MOSFET switches and, to a lesser
extent, power dissipated due to the supply current. To com-
pute the total power dissipation of the MIC2580A the follow-
ing equation is used:
P
where:
To relate this to operating junction temperature:
where:
Precharge Voltage
For CompactPCI applications, the MIC2580A-1.0BSM/BTS
integrates a 1V ±20% voltage source that satisfies
CompactPCI precharge requirements. The voltage source
can provide up to 10mA. For higher current, the MIC2580A-
1.6BSM/BTS integrates a 1.6V ±20% voltage source to bias
a NPN transistor.
Turnoff
Deasserting /ON will turn off all four supplies. Alternatively
driving /FAULT low will turn off all supplies but will not latch
the supplies off. Releasing /FAULT will initiate a new start
sequence.
D(total)
P
P
T
T
θ
JA
J
A
D(switches)
D(supplies)
= P
= P
= ambient temperature
= package thermal resistance
D(+12V switch)
D
× θ
Figure 5. Voltage Source
JA
MIC2580A-1.6
= V
= R
VPCHG
+ T
SUPPLY
DS(on)
A
+ P
× I
D(–12V switch)
× I
OUT
SUPPLY
DATA
BUS
+5V
2
R
I > 10mA
+ P
D(supplies)
February 2005
Micrel, Inc.