Micrel MIC2593-2BTQ Dual-slot pci hot plug controller Datasheet

MIC2593
Dual-Slot PCI Hot Plug Controller
General Description
Features
The MIC2593 is a power controller supporting power
distribution requirements for Peripheral Component
Interconnect hot plug systems compliant to PCI v2.3 and
PCI-X 1.0b. TheMIC2593 provides complete power control
support for two PCI slots, including the 3.3VAUX defined by
the PCI v2.3 specification. Support for +5V, +3.3V, +12V,
and –12V supplies is provided and includes programmable
current limit, voltage supervision, fault reporting, and circuit
breaker functions which provide fault isolation. The
MIC2593 also incorporates an SMBus interface that
provides complete status and control of power within each
slot.
Data sheets and support documentation can be found on
Micrel’s web site at: www.micrel.com.
• Supports two completely independent PCI slots:
– Compliant to PCI v2.3 and PCI-X 1.0b power
control requirements
– Provides all major power control functions for two
independent PCI-X 2.0 slots
• Five voltage supplies supported: +12V, -12V,
+5V,+3.3V, and +3.3VAUX
– Integrated gate driver circuits, current sense, and
power MOSFETs for 3.3VAUX, +12V, and –12V
– High-side +5V and +3.3V gate driver circuits for
external N-Channel MOSFETs
• Overcurrent protection with adjustable timeout
eliminates false tripping of circuit breakers
• Dual-level, dual-speed overcurrent detection circuitry
for quick fault response without nuisance tripping
• Slot power control with “Power-is-Good” and Fault
status reporting
– Via software over an SMBus interface or
– Via dedicated hardware input/output lines: Hot
Plug Interface (HPI)
• Complete thermal isolation between circuitry for Slot A
and Slot B
• One General Purpose Input (GPI) pin per slot for
mechanical switch or plug-in card retention/removal
input
Applications
• PCI hot plug power distribution
Ideal Applications:
• Mid- and High-end Server Applications compliant to PCI
v2.3, PCI-X 1.0b, and PCI-X 2.0
___________________________________________________________________________________________________________
Ordering Information
Part Number
5V & 3V Fast-trip
Threshold
+12V & –12V Fast-trip
Threshold
Operating
Temp. Range
Package
Lead Finish
MIC2593-2BTQ
100mV
1.5A/0.4A
0° to +70°C
48-Pin TQFP
Standard
MIC2593-2YTQ
100mV
1.5A/0.4A
0° to +70°C
48-Pin TQFP
Pb-Free
Note:
Contact factory for availability of the MIC2593-5YTQ option that disables the 100mV fast-trip threshold.
LITTLE FOOT is a registered trademark of Siliconix Incorporated.
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
September 2008
M9999-092208
Micrel, Inc.
MIC2593
Typical Application
Power
Supply
+12V
12V
+5.0V
+3.3V
0.1µF
0.1µF
0.1µF
PCI Connector
VSTBY
5
0.1µF
17
12VINA 12VINB
11
0.1µF
32
26
18
12MVINA 12MVINB
VAUXA
VSTBYA
5VINA
VSTBYB
PCI Bus
15
0.1µF
6
5VSENSEA
7
5VGATEA
8
5VOUTA
9
RSENSE
3.3VAUXA
375mA
*R12VGATEA
**C3
3
12VSLEWA
34
12VSLEWB
0.01µF
**C4
3VINA
VSTBY
100k
**C1
2
CFILTERA
35
CFILTERB
100k
4
GPIA
38
GPIB
VSTBY
GPIA
MIC2593
45
AUXENA
AUXENB
ONA
42
44
43
ONB
VSTBY
Hot Plug
Controller
0.1µF
13
3VGATEA
14
3VOUTA
12VOUTA
12MVOUTA
16
5VINB
31
5VSENSEB
30
5VGATEB
29
GPIB
10k × 4
12
3VSENSEA
**C2
*R3VGATEA
Si4420DY
3.3V, 7.6A
12V, 0.5A
–12V, 0.1A
10
19
CGATE
0.01µF
0.1µF
RSENSE
Si4420DY
0.01µF
ONB
5VOUTB
28
5V, 5A
0.1µF
3VINB
1
/FAULTA
36
/FAULTB
41
SMBus
Base
Address
40
39
VSTBY
/FAULTA
3VSENSEB
/FAULTB
3VGATEB
A0
A1
A2
RSENSE
25
24
*R3VGATEB
Si4420DY
23
3VOUTB
21
3.3V, 7.6A
12VOUTB
27
12V, 0.5A
12MVOUTB
20
–12V, 0.1A
22
3.3VAUXB
37
/INT
47
SCL
VAUXB
GND
48
SDA
GND
33
CGATE
46
0.01µF
PCI Bus
10k × 3
*
RSENSE
*R12VGATEB
AUXENA
AUXENB
ONA
10k × 2
SMBus I/O
Si4420DY
SDA
SDA
SCL
SCL
/INT
/INT
PCI Connector
Management
Controller
Values for R5VGATE[A/B] and R3VGATE[A/B] may vary depending upon the CGS of the external MOSFETs.
** Values determined by design requirements. See “Functional Description” section for detailed information.
# MBRS140T3 or equivalent is recommended.
Bold lines indicate high current paths
September 2008
2
M9999-092208
Micrel, Inc.
MIC2593
Pin Configuration
SDA
SCL
GND
AUXENA
ONA
ONB
AUXENB
A0
A1
A2
GPIB
/INT
Hot-Plug
Control
Interface
/FAULTB
CFILTERB
12VSLEWB
GND
12VINB
5VINB
5VSENSEB
5VGATEB
5VOUTB
12VOUTB
VSTBYB
3VINB
Slot A
Interface
3VSENSEA
3VGATEA
VAUXA
3VOUTA
12MVINA
12MVINB
12MVOUTA
12MVOUTB
3VOUTB
VAUXB
3VGATEB
3VSENSEB
/FAULTA
CFILTERA
12VSLEW
GPI
12VINA
5VINA
5VSENSEA
5VGATEA
5VOUTA
12VOUTA
VSTBYA
3VINA
Slot B
Interface
48-Pin TQFP (TQ)
Pin Description
Pin Number
Pin Name
5, 32
12VINA, 12VINB
10, 27
12VOUTA, 12VOUTB
+12V Output [A/B]: Pin 10 is connected to the source terminal of the internal
MOSFET switch for +12V Slot A and pin 27 is connected similarly for Slot B.
17, 18
12MVINA, 12MVINB
–12V Supply Power [A/B]: Pin 17 is the input to the drain side of the internal
MOSFET switch for +12V Slot A. Pin 18 is the input to the drain side of the
internal MOSFET switch for –12V Slot B. These two pins must ultimately
connect to each other within 10cm of the MIC2593. An undervoltage lockout
circuit (UVLO) prevents the switches from turning on while this input is less than
its lockout threshold.
19, 20
12MVOUTA, 12MVOUTB
–12V Output [A/B]: Pin 19 is connected to the source terminal of the internal
MOSFET switch for –12V Slot A and pin 20 is connected similarly for Slot B.
3, 34
12VSLEWA, 12VSLEWB
12V Slew Rate Control [A/B]: Connect capacitors between these pins and
ground to set the output slew rates of the +12V and –12V supplies. See the
“Functional Description” section for more details.
September 2008
Pin Function
+12V Supply Power [A/B]: Pin 5 is the input to the drain side of the internal
MOSFET switch for +12V Slot A. Pin 32 is the input to the drain side of the
internal MOSFET switch for +12V Slot B. These two pins must ultimately
connect to each other within 10cm of the MIC2593. An undervoltage lockout
circuit (UVLO) prevents the switches from turning on while this input is less than
its lockout threshold.
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M9999-092208
Micrel, Inc.
MIC2593
Pin Number
Pin Name
Pin Function
6, 31
5VINA, 5VINB
7, 30
5VSENSEA, 5VSENSEB
5V Circuit Breaker Sense Input [A/B]: The current limit thresholds are set by
connecting sense resistors between these pins and 5VIN[A/B]. When the
current limit threshold of IR = 50mV is reached, the 5VGATE[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
tFLT (see CFILTER[A/B] pin description), the circuit breaker is tripped and the
GATE pin for the affected supply’s external MOSFET is immediately pulled low.
9, 28
5VOUTA, 5VOUTB
5V Power-Good Sense Inputs: Connect to 5V[A/B] outputs. Used to monitor the
5V output voltages for Power-is-Good status.
8, 29
5VGATEA, 5VGATEB
5V Supply Power and Sense Input [A/B]: Pin 6 is the (+) Kelvin-sense
connection to the supply side of the sense resistor for 5V Slot A. Pin 31 is the
(+) Kelvin sense connection to the supply side of the sense resistor for 5V Slot
B. These two pins must ultimately connect to each other within10cm of the
MIC2593. An undervoltage lockout circuit (UVLO) prevents the switches from
turning on while this input is less than its lockout threshold.
5V Gate Drive Output [A/B]: Each pin connects to the gate of an external NChannel MOSFET. During power-up, the CGATE and the CGS of the MOSFETs
are charged by 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 the pin is adjusted to maintain constant
current through the switch for a period of tFLT. 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.
12, 25
3VINA, 3VINB
3.3V Supply Power and Sense Input [A/B]: Pin 12 is the (+) Kelvin-sense
connection to the supply side of the sense resistor for 3.3V Slot A. Pin 25 is the
(+) Kelvin-sense connection to the supply side of the sense resistor for 3.3V Slot
B. These two pins must ultimately connect to each other within 10cm of the
MIC2593. An undervoltage lockout circuit (UVLO) prevents the switches from
turning on while this input is less than its lockout threshold.
13, 24
3VSENSEA, 3VSENSEB
3V Circuit Breaker Sense Input [A/B]: 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
tFLT (see CFILTER[A/B] pin description), the circuit breaker is tripped and the
GATE pin for the affected supply’s external MOSFET is immediately pulled low.
16, 21
3VOUTA, 3VOUTB
3.3V Power-Good Sense Inputs: Connect to 3.3V[A/B] outputs. Used to monitor
the 3.3V output voltages for Power-is-Good status.
14, 23
3VGATEA, 3VGATEB
3V Gate Drive Output [A/B]: Each pin connects to the gate of an external Nchannel MOSFET. During power-up, the CGATE and the CGS 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 tFLT. 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.
11, 26
September 2008
VSTBYA, VSTBYB
.3V Standby Input Voltage: Required to support PCI VAUX output. Additionally,
the SMBus logic and internal registers run off of VSTBY[A/B] to ensure that the
MIC2593 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 connected together externally at the IC.
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M9999-092208
Micrel, Inc.
MIC2593
Pin Number
Pin Name
Pin Function
15, 22
VAUXA, VAUXB
44, 43
ONA, ONB
Enable Inputs: Rising-edge triggered. Used to enable or disable the MAINA and
MAINB (5V, 3.3V, +12V and –12V) outputs. Taking ON[A/B] low after a fault
resets the 5V, 3.3V, +12V and/or –12V fault latches for the affected slot. Tie
these pins to GND if using SMI power control. Also, see pin description for
/FAULTA and /FAULTB.
45, 42
AUXENA, AUXENB
Enable Inputs: Rising-edge triggered. Used to enable or disable VAUXA and
VAUXB outputs. 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.
2, 35
CFILTERA, CFILTERB
Overcurrent Timer (Filter) Capacitor [A/B]: Capacitors connected between these
pins and GND set the duration of tFLT. tFLT is the amount of time for which a slot
remains in current limit before its circuit breaker is tripped.
1, 36
/FAULTA, /FAULTB
3.3VAUX[A/B] Output to PCI Card Slot: These outputs connect the 3.3AUX pin
of the PCI connectors to VSTBY[A/B] via internal 400mΩ MOSFETs. These
outputs are current limited and protected against short-circuit faults.
/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 VSTBY.
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 outputs (5V,
3.3V, +12V, or –12V).
/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[A/B] outputs of the same slot,
then both ON[A/B] and AUXEN[A/B] must be brought low to de-assert the
/FAULT[A/B] output.
4, 38
GPIA, GPIB
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.
40, 41
A1, A0
SMBus Address Select Pins: Connect to ground or leave open in order to 41 A0
program device SMBus base address. These inputs have internal pull-up
resistors to VSTBY[A/B].
48
SDA
SMBus Data: Bidirectional SMBus data line.
47
SCL
SMBus Clock: Input.
37
/INT
Interrupt Output: Open-drain, active-low. Asserted whenever a power fault is
detected if the INTMSK bit (CS Register Bit D[3]) is a logical "0". This output is
de-asserted by performing an "echo reset" to the appropriate fault bit(s) in the
STAT[A/B] and/or CS registers. This pin requires an external pull-up resistor to
VSTBY.
33, 46
GND
IC Ground Connections: Tie directly to the system’s analog ground plane
directly at the device.
September 2008
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M9999-092208
Micrel, Inc.
MIC2593
Absolute Maximum Ratings(1)
Operating Ratings(2)
Supply Voltage
(12VIN) ..........................................................................+14V
(12MVIN) .......................................................................–14V
(5VIN) ..............................................................................+7V
(3VIN), (VSTBY) .................................................................+7V
Any Logic Pin ....................................................–0.5 to 3.6V
Output Current (FAILT[A/B], /INT, SDA). ....................10mA
Lead Temperature
IR Reflow, Peak Temperature........................ 240 0°C/–5°C
Storage Temperature (Ts) .........................–65°C to +150°C
ESD Rating(3)
Human Body Model........................................................ 2kV
Machine Model .............................................................200V
Supply Voltage
(12VIN) .................................................... +11.65V to +12.6V
(12MVIN) ................................................... –11.0V to –13.2V
(5VIN) .......................................................... +4.85V to 5.25V
(3VIN) ............................................................ +3.1V to +3.6V
(VSTBY) .......................................................... +3.15V to 3.6V
Ambient Temperature (TA) .............................. 0°C to +70°C
Junction Temperature (TJ) ......................................... 125°C
Thermal Resistance
TQFP (θJA) ......................................................56.5°C/W
Electrical Characteristics(4)
12VIN[A/B] = 12V; 12MVIN[A/B] = –12V; 5VIN[A/B] = 5V; 3VIN[A/B] = 3.3V; VSTBY[A/B] = 3.3V; TA = 25°C; unless otherwise noted.
Bold indicates specification applies over the full operating rating temperature range from 0°C to 70°C.
Symbol
Parameter
ICC12V
Supply Current
Condition
Min
Typ
Max
Units
0.6
2.0
mA
ICC5V
1.2
2.0
mA
ICC3.3V
0.5
0.7
mA
ICC12MV
–1.0
–2.0
mA
ICCVSBY
2.5
5.0
mA
Under Voltage Lockout Thresholds
VUVLO(12V)
12VIN[A/B]
12VIN increasing
8
9
10
V
VUVLO(3V)
3VIN[A/B]
3VIN increasing
2.2
2.5
2.75
V
VUVLO(5V)
5VIN[A/B]
5VIN increasing
3.7
4.0
4.3
V
VUVLO(12MV)
12MVIN[A/B]
12MVIN increasing
–10
–9
–8
V
VUVLO(STBY)
VSTBY[A/B]
VSTBY increasing
2.8
2.9
3.0
V
VHYSUV
Under Voltage Lockout Hysteresis 12VIN, 12MVIN, 5VIN, 3VIN
180
mV
VHYSSTBY
Under-voltage Lockout Hysteresis VSTBY
50
mV
Power Good Under-Voltage Thresholds
VUVTH(12V)
12VOUT[A/B]
12VOUT[A/B] decreasing
10.2
10.5
10.8
V
VUVTH(12MV)
12MVOUT [A/B]
12MVOUT[A/B] decreasing
–10.8
–10.6
–10.2
V
VUVTH(3V)
3VOUT [A/B]
3VOUT[A/B] decreasing
2.7
2.8
2.9
V
VUVTH(5V)
5VOUT [A/B]
5VOUT[A/B] decreasing
4.4
4.5
4.7
V
VUVTH(VAUX)
VAUX[A/B]
VAUX[A/B] decreasing
2.7
2.8
2.9
V
VHYSPG
Power-Good Detect Hysteresis
30
VGATE
5VGATE/3VGATE Voltage
IGATE(SOURCE)
5VGATE/3VGATE Charge Current
start cycle
IGATE(SINK)
5VGATE/3VGATE Sink Current (Fault Off)
any fault condition, VGATE = 5V
September 2008
12VIN–15
6
15
25
70
mV
12VIN
V
35
µA
mA
M9999-092208
Micrel, Inc.
MIC2593
Symbol
Parameter
VFILTER
CFILTER Threshold Voltage
IFILTER
CFILTER [A/B] Charge Current
ISLEW
12VSLEW[A/B] Charge Current
VTHILIMIT
VTHFAST
Min
Typ
Max
Units
1.20
1.25
1.30
V
1.80
2.5
5.0
µA
During turn-on only
13
22
35
µA
5V[A/B] Supplies
V5VIN[A/B] – V5VSENSE[A/B]
35
50
65
mV
3.3V[A/B] Supplies
V3VIN[A/B] – V3VSENSE[A/B]
35
50
65
mV
90
113
135
mV
V5VIN[A/B] – V5SENSE[A/B] > VTHILIMIT
and/or
V3VIN[A/B] – V3SENSE[A/B] > VTHILIMIT
Current Limit Threshold Voltages
Fast-Trip Current Limit Thresholds
5V[A/B] and 3V[A/B]
I5VSENSE[A/B]
Condition
5VSENSE[A/B] Input Current
I3VSENSE[A/B]
3VSENSE[A/B] Input Current
VIL
LOW-Level Input Voltage
MIC2593-2xTQ
V5VIN[A/B] – V5VSENSE[A/B] = 50mV
(5)
0.5
V3VIN[A/B] – V3VSENSE[A/B] = 50mV
(5)
0.5
µA
µA
0.8
V
0.4
V
ON[A/B], AUXEN[A/B], GPI[A/B], SCL,
SDA, A[0-2]
VOL
Output LOW Voltage
IOL = 3mA
/FAULT[A/B], /INT, SDA
VIH
HIGH-Level Input Voltage
V
2.1
ON[A/B], AUXEN[A/B], GPI[A/B], SCL,
SDA, A[0-2]
RPULL-UP
Internal Pullups from A[0-2] to VSTBY
ILKG,OFF(12VIN[A/B])
12VIN[A/B] Input Leakage Current
VSTBY[A/B] = +3.3V
12VIN[A/B] = OFF
ILKG,OFF(12MVIN[A/B])
12MVIN[A/B] Input Leakage Current
5VIN[A/B] Input Leakage Current
kΩ
1
µA
60
µA
200
µA
1
µA
(5)
VSTBY[A/B] = +3.3V
12MVIN[A/B] = OFF
ILKG,OFF(5VIN[A/B])
40
(5)
VSTBY[A/B] = +3.3V
5VIN[A/B] = OFF(5)
ILKG,OFF(3VIN[A/B])
3VIN[A/B] Input Leakage Current
VSTBY[A/B] = +3.3V
3VIN[A/B] = OFF
IIL
(5)
Input Leakage Current
±5
µA
±5
µA
SCL, ON[A/B], AUXEN[A/B], GP[A/B])
ILKG(OFF)
Off-State Leakage Current
SDA, /FAULT[A/B], /INT
TOV
Overtemperature Shutdown & Reset
Thresholds, with overcurrent on slot
Overtemperature Shutdown & Reset
Thresholds, all other conditions (all
outputs will latch OFF)
TJ Increasing, each slot
(6)
140
°C
TJ Decreasing, each slot (6)
130
°C
TJ Increasing, both slots (6)
160
°C
150
°C
TJ Decreasing, both slots
(6)
Output MOSFET Resistance
ROUT(12V)
+12V MOSFET
IDS = 500mA, TJ = 125°C
500
mΩ
ROUT(12MV)
–12V MOSFET
IDS = 100mA, TJ = 125°C
2
Ω
ROUT(AUX)
VAUX MOSFET
IDS = 375mA, TJ = 125°C
400
mΩ
September 2008
7
M9999-092208
Micrel, Inc.
Symbol
MIC2593
Parameter
Condition
Min
Typ
Max
Units
50
mV
Off-State Output Offset Voltage
VOFF(+12V)
12VOUT[A/B]
12VOUT[A/B] = Off, TJ = 125°C
VOFF(12MV)
12MVOUT[A/B]
12MVOUT[A/B] = Off, TJ = 125°C
VOFF(AUX)
VAUX[A/B]
VAUX[A/B] = Off, TJ = 125°C
mV
–50
50
mV
Current Limit Slow-Trip Threshold
ILIM(12V)
+12V MOSFET
12VOUT[A/B] = 0V
0.52
1.0
1.5
A
ILIM(12MV)
–12V MOSFET
12MVOUT[A/B] = 0V
–0.11
–0.2
–0.3
A
Current Limit Fast-Trip Thresholds
MIC2593-2BTQ
1.0
2.15
3.0
A
–0.20
–0.45
–0.6
A
IFASTLIM(12V)
+12V MOSFET
12VOUT[A/B]
IFASTLIM(12MV)
–12V MOSFET
12MVOUT[A/B]
IAUX(THRESH)
Auxiliary Output Current Limit Threshold
Figure 4
Current which must be drawn
from VAUX to register as a fault
0.84
A
ISC(TRAN)
Maximum Transient Short Circuit
Current
VAUX Enabled, then Grounded
IMAX = VSTBY / RDS(AUX)
A
ILIM(AUX)
Regulated Current after Transient
From end of ISC(TRAN) to CFILTER
Time Out
0.7
A
RDISCH
Output Discharge Resistance
RDISCH(12V)
12VOUT[A/B]
12VOUT[A/B] = 6.0V
1600
Ω
RDISCH(12MV)
12MVOUT[A/B]
12MVOUT[A/B] = –6.0V
600
Ω
RDISCH(3V)
3VOUT[A/B]
3VOUT[A/B] = 1.65V
150
Ω
RDISCH(5V)
5VOUT[A/B]
5MVOUT[A/B] = 2.5V
150
Ω
RDISCH(VAUX)
VAUX[A/B]
5VOUT[A/B] = 1.65V
430
Ω
tOFF(3V)
Current Limit Response Time for 3.3V
and 5V Outputs, Figure 2
MIC2593-2
1
µs
33
µs
tOFF(5V)
0.375
1.35
CGATE = 10nF
VIN – VSENSE = 200mV
TSC(TRAN)
VAUX Current Limiter Response Time,
Figure 5
(6)
VAUX[A/B] = 0V
tOFF(12V)
12V Current Limit Response Time,
Figure 3
12VOUT[A/B] = 0V (6)
1
µs
tOFF(12MV)
–12V Current Limit Response Time,
Figure 3
12MVOUT[A/B] = 0V (6)
1
µs
tPROP(3VFAULT)
Delay from 3V[A/B] overcurrent-limit to
FAULT Output
MIC2593-2
1
µs
1
µs
VSENSE – VTHLIMIT = 200mV
CFILTER = open
tPROP(5VFAULT)
Delay from 5V[A/B] overcurrent-limit to
FAULT Output
MIC2593-2
VSENSE – VTHLIMIT = 200mV
CFILTER = open
tW
ON[A/B], AUXEN[A/B] Pulse Width
Note 5
100
ns
tPOR
MIC2593 Power-On Reset Time after
VSTBY becomes valid
Note 5
500
µs
SMBus Timing, Note 5
t1
SCL (Clock) Period
Figure 1
2.5
µs
t2
Data In Set-Up Time to SCL HIGH
Figure 1
100
ns
September 2008
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M9999-092208
Micrel, Inc.
MIC2593
Symbol
Parameter
Condition
Min
Typ
Max
Units
t3
Data Out Stable after SCL LOW
Figure 1
300
ns
t4
Data LOW Set-Up Time to SCL LOW
Start Condition, Figure 1
100
ns
t5
Data HIGH Hold Time after SCL HIGH
Start Condition, Figure 1
100
ns
Notes:
1. Exceeding the absolute maximum rating may damage the device.
2. The device is not guaranteed to function outside its operating rating.
3. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5kΩ in series with 100pF.
4. Specification for packaged product only.
5. Schottky diode clamp used for –12VIN[A/B] power bus. See the typical applications circuit.
6. Parameters guaranteed by design. Not 100% production tested.
September 2008
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M9999-092208
Micrel, Inc.
MIC2593
Test Circuit
t1
SCL
t4
t5
t2
SDA
Data In
t3
SDA
Data Out
Figure 1. SMBus Timing
VTHFAST
VTHFAST
VTHILIMIT
VTHLIMIT
3VGATE
6V
12VGATE
tOFF(12V)
1V
tOFF3
Figure 2. 12V Current Limit Response Timing
Figure 3. 3V Current Limit Response Timing
IAUX(THRESH) Must Trip
ISC(TRAN)
May Not Trip
ILIM(AUX)
IOUT(AUX)
ILIM(AUX)
IOUT(AUX)
IOUT(AUX)
tSC(TRAN)
0 Amps
0 Amps
Figure 4. VAUX Current Limit Threshold
September 2008
Figure 5. VAUX Current Limit Response Timing
10
M9999-092208
Micrel, Inc.
MIC2593
When using the System Management Interface for power
control, do not use the Hot Plug Interface. Conversely,
when using the Hot Plug Interface for power control, do
not execute power control commands over the System
Management Interface bus (all other register accesses via
the SMI bus remain permissible while in the HPI control
mode). When utilizing the SMI exclusively, the HPI input
pins ON[A/B] and AUXEN[A/B] should be tied to ground
as shown below in Figure 6 (Disabling HPI when SMI
control is used). This configuration safeguards the power
slots in the event that the SMBus communication link is
disconnected for any reason.
Additionally, when utilizing the HPI exclusively, the
SMBus (or SMI) will be inactive if the input pins (SDA,
SCL, A0, A1, and A2) are configured as shown in Figure 6
below (disabling SMI when HPI Control is used).
Functional Description
Hot Swap Insertion
When circuit boards are inserted into systems carrying
live supply voltages (“hot-plugged”), high inrush currents
often result due to the charging of bulk capacitance that
resides across the circuit board’s supply pins. This
transient inrush current can cause the system’s supply
voltages to temporarily go out of regulation, causing data
loss or system lock-up. In more extreme cases, the
transients occurring during a hot plug event may cause
permanent damage to connectors or on-board
components.
The MIC2593 addresses these issues by limiting the
inrush currents to the load (PCI Board), and thereby
controlling the rate at which the load’s circuits turn-on. In
addition to this inrush current control, the MIC2593 offers
input and output voltage supervisory functions and current
limiting to provide robust protection for both the system
and circuit board.
Power-On Reset and Power Cycling
The MIC2593 utilizes VSTBY[A/B] as the main supply
input source. VTSBY[A/B] is required for proper operation
of the MIC2593 SMBus interface and registers and must
be applied at all times. A Power-On Reset (POR) cycle is
initiated after VSTBY[A/B] rises above its UVLO threshold
and remains valid at that voltage for 500µs. All internal
registers are cleared after POR. If VSTBY[A/B] is
recycled, the MIC2593 enters a new power-on reset
cycle. VSTBY[A/B] must be the first supply input applied
followed by the MAIN supply inputs of 12VIN, 12MVIN,
5VIN, and 3VIN. The MAIN supply inputs may be applied in
any order. The SMBus is ready for access at the end of
the POR interval (500µs after VSTBY[A/B] is valid). All
outputs remain off during tPOR.
System Interfaces
The MIC2593 employs two system interfaces: the
hardware Hot Plug Interface (HPI) and the System
Management Interface (SMI). The HPI includes ON[A/B],
AUXEN[A/B], as well as /FAULT[A/B]; the SMI consists of
SDA, SCL, and /INT, whose signals conform to the levels
and timing of the SMBus specification. The MIC2593 can
be operated exclusively from the SMI, or can employ the
HPl for power control while continuing to use the SMI for
access to all but the power control registers.
In addition to the basic power control features of the
MIC2593 accessible by the HPI, the SMI also gives the
host access to the following information from the part:
1. Fault conditions occurring on each supply.
2. GPI[A/B] pin status.
VSTBY
100k
100k
MIC2593
100k
47
48
/INT
37
39
40
41
MIC2593
SCL
SDA
/INT
A2
A1
A0
45
42
44
43
Disabling SMI when
HPI Control is used
AUXENA
AUXENB
ONA
ONB
Disabling HPI when
SMI Control is used
Figure 6. Input Pin Configuration for
Disabling HPI/SMI Control
September 2008
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M9999-092208
Micrel, Inc.
MIC2593
dv/dt (at load) =
Power-Up Cycle
When a slot is off, the 5VGATE and 3VGATE pins are
held low with an internal pull-down current source. When
a slot’s MAIN outputs are enabled by applying a risingedge signal at the ON[A/B] control input and all input
voltages are above their respective undervoltage lockout
thresholds, all four main supplies will then execute a
controlled turn on. The 5VGATE and 3VGATE pins are
each connected to a constant current source of 25µA,
nominal. Both the 5V and 3.3V outputs act as source
followers, where:
[
VSOURCE = VGATE − VTH(ON)
ISLEW = 22µA
]
ISLEW = 25µA
25000V/s
0.01µF
2500V/s
0.1µF
250V/s
1µF
25V/s
Table 1. 3.3V/5V Output Slew Rate Selection
For the +12V and –12V supplies, the output slew rate is
controlled by capacitors connected to the 12VSLEWA and
12VSLEWB pins. To determine the minimum value of the
slew rate capacitor, (CSLEW), and to ensure the device
does not enter into current limit during start-up, the
following equation is used:
C SLEW (min) =
ISLEW
ILIM[12V/12MV]
0.01µF
2.2V/ms
0.1µF
0.22V/ms
1µF
0.022V/ms
Circuit Breaker Functions
The MIC2593 provides an electronic circuit breaker
function that protects against excessive loads, such as
short circuits, at each supply. When the current from one
or more of a slot’s MAIN outputs exceeds the current limit
threshold (50mV/RSENSE for 3.3V and 5V, 1.0A for +12V,
and/or 0.2A for –12V) for a duration greater than the
overcurrent timer, tFLT, the circuit breaker is tripped and all
MAIN supplies (all outputs except VAUX[A/B]) are shut
off. Should the load current exceed ITHFAST (+12V and –
12V), or cause a MAIN output’s VSENSE to exceed VTHFAST
(+3.3V and +5V), the outputs are shut off with no delay.
Undervoltage conditions on the MAIN supply inputs also
× C LOAD
where CLOAD is the load capacitance connected to the
+12V and –12V outputs, ILIM[12V/12MV] are the current limit
slow-trip thresholds and ISLEW is the slew rate charge
current found in the “Electrical Characteristics” table. The
slew rate dv/dt is computed by:
September 2008
22V/ms
Standby Mode
Standby mode is entered when any (one or more)
enabled MAIN supply input (12VIN, 12MVIN, 5VIN and/or
3VIN) drops below its respective UVLO threshold. The
MIC2593 supplies two 3.3V auxiliary outputs, VAUX[A/B],
satisfying PCI 2.x specifications. These outputs are fed
via the VSTBY[A/B] input and controlled by the
AUXEN[A/B] inputs or via their SMI bus Control Registers.
These outputs are independent of the MAIN outputs:
should one or more of the MAIN supply inputs move
below its UVLO thresholds, VAUX[A/B] will still function as
long as VSTBY[A/B] is present. Prior to entering standby
mode, ONA and ONB (or the MAINA and MAINB bits in
the Control Registers) inputs should be de-asserted. If this
is not done, the MIC2593 will assert /FAULT and also
/INT if interrupts are enabled, when the MIC2593 detects
an undervoltage condition on a supply input.
Table 1 provides a reference list of the expected GATE
output slew rate for the 3.3V and 5V supplies using
several (decade-scale) standard capacitors.
0.001µF
dv/dt (load)
Power Down Cycle
When a slot is turned off, internal switches are connected
to each of the outputs to discharge the PCI board's
bypass capacitors to ground.
IGATE(SOURCE)
dv/dt (load)
CGATE
0.001µF
Table 2. ±12V Output Slew Rate Selection
(C GATE × VDRAIN )
CGATE
C SLEW × 10 6
By appropriately selecting the value of CSLEW, the
magnitude of the inrush current will not exceed the current
limit for a given load capacitance. Since one capacitor
fixes the slew rate for both +12V and –12V, the capacitor
value should be chosen to provide the slower slew rate of
the two. Table 2 depicts the ±12V output slew rate for
various values of CSLEW.
until the associated output is equal to its input. The
voltages on the gates of the external MOSFETs for the 5V
and 3.3V MAIN supplies will continue to rise to
approximately 11.5V, ensuring minimum RDS(ON) of the
MOSFET. Note that a delay exists between the ON
command to a slot and the appearance of voltage at the
slot’s 3.3V or 5V MAIN output. This delay is the time
required to charge the 3V or 5V GATE output up to the
threshold voltage of the external MOSFET (typically about
4V). For the 5V and 3.3V MAIN supplies, the source
(output) side of the external MOSFET will reach the drain
(input) voltage in a time given by:
t DELAY =
ISLEW
12
M9999-092208
Micrel, Inc.
MIC2593
where tFLT[A/B] is the selected overcurrent response time
and IFILTER and VFILTER are specified in the “Electrical
Characteristics” table.
trip the circuit breaker, but only when the MAIN outputs
are enabled (to signal a supply input brown-out condition).
The VAUX[A/B] outputs have their own separate circuit
breaker functions. VAUX[A/B] do not incorporate a fasttrip threshold, but instead regulate the output current into
a fault to avoid exceeding their operating current limit. The
circuit breaker will trip due to overcurrents on VAUX[A/B]
when the overcurrent fault timer (tFLT) expires. This use of
the overcurrent timer prevents the circuit breaker from
tripping prematurely due to brief current transients.
Following a fault condition, the outputs can be turned on
again via the ON inputs (if the fault occurred on one of the
MAIN outputs), via the AUXEN inputs (if the fault occurred
on the AUX outputs), or by cycling both ON and AUXEN
(if faults occurred on both the MAIN and AUX outputs). A
fault condition can alternatively be cleared under SMI
control of the ENABLE bits in the CNTRL[A/B] registers
(See Register Bits D[1:0]). When the circuit breaker trips,
/FAULT[A/B] will be asserted if the outputs were enabled
through the Hot Plug Interface inputs. At the same time,
/INT will be asserted (unless interrupts are masked). Note
that /INT is de-asserted by writing a Logic 1 back into the
respective fault bit position(s) in the STAT[A/B] register or
the Common Status Register. The response time (tFLT) of
the MIC2593’s primary overcurrent detector is set by
external capacitors at the CFILTER[A/B] pins to GND. For
Slot A, CFILTER[A] is located at Pin 2; for Slot B,
CFILTER[B] is located at Pin 35. For a given response
time, the value for CFILTER[A/B] is given by.
CFILTER[A/B]( μF) =
Thermal Shutdown
The internal +12V, –12V, and VAUX MOSFETs are
protected against damage not only by current limiting, but
by dual-mode overtemperature protection as well. Each
slot controller on the MIC2593 is thermally isolated from
the other. Should an overcurrent condition raise the
junction temperature of one slot’s controller and internal
pass elements to 140°C, all of the outputs for that slot
(including VAUX) will be shut off, and the slot’s /FAULT
output will be asserted. The other slot’s operation will
remain unaffected. However, should the MIC2593’s
overall die temperature exceed 160°C, both slots (all
outputs, including VAUXA and VAUXB) will be shut off,
whether or not a current limit condition exists. A 160°C
overtemperature
condition
additionally
sets
the
overtemperature bit (OT_INT) in the Common Status
Register.
Output Power-Good Status
For the MIC2593, “Power-is-Good” is valid on a slot when
the outputs of the four MAIN supplies (12V, –12V, 5V, and
3.3V) and the auxiliary supply output are all above their
respective power-good thresholds specified in the
“Electrical Characteristics” table. The power-good status
of either slot is verified by polling the CNTRL[A/B]
Register Bits D[7:6]. CNTRL[A/B] Register Bits D[7] and
D[6] indicate output power-good status for the AUX supply
and MAIN supplies, respectively. Figure7 below illustrates
an equivalent logic circuit that determines the output
power-good status for the MAIN and AUX supplies.
t FLT[A/B] (ms) × IFILTER ( μA)
VFILTER (V) × 10 3
VSTBY[A/B]
3VAUX_UV[A/B](1)
AUX[A/B]PG(2)
VSTBY[A/B]
12VOUT_UV[A/B](1)
MAIN[A/B]PG(3)
(1)
3VOUT_UV[A/B]
Notes:
1. Internal flag
2. CNTRL[A/B] Register Bit D[7]
3. CNTRL[A/B] Register Bit D[6]
Figure 7. Power-Good Status Logic Diagram
September 2008
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M9999-092208
Micrel, Inc.
MIC2593
•
General Purpose Input (GPI) Pins
Two pins on the MIC2593 are available for use as GPI
pins. The logic state of each of these pins can be
determined by polling Bits [4:5] of Common Status
Register. Both of these inputs are compliant to 3.3V. If
unused, connect the GPI[A/B] pins to GND.
•
The MIC2593’s global die temperature exceeds
160°C
To clear any one or all STAT[A/B] Register Bits D[4:0]
and/or CS Register Bits D[2:1] once asserted, a software
subroutine can perform an “echo reset” where a Logical
“1” is written back to those register bit locations that have
indicated a fault.
The open-drain, active-LOW /INT output signal is
activated after power-on-reset when the INTMSK bit (CS
Register Bit D[3]) has been reset to Logical “0”. Once
activated, the /INT output is asserted by any one of the
fault conditions listed above and de-asserted when one or
all STAT[A/B] Register Bits D[4:0] and/or CS Register Bits
D[2:1] are reset upon the execution of an SMBus “echo
reset” WRITE_BYTE cycle.
Fault Reporting and /INT Interrupt Generation
SMI-only Control Applications
In applications where the MIC2593 is controlled only by
the SMI, the ON[A/B] and AUXEN[A/B] should be
connected to GND as shown in Figure 6. In this case, the
MIC2593’s /FAULT[A/B] outputs and STAT[A/B] Register
Bit D[7] (FAULT[A/B]) are not activated, as fault status is
determined by polling STAT[A/B] Register Bits D[4:0] and
CS (Common Status) Register Bits D[2:1]. Individual fault
bits in STAT[A/B] and CS are asserted after power-onreset when
Either or both CNTRL[A/B] Register Bits D[1:0] are
asserted,
AND
•
12VIN[A/B], 12MVIN[A/B], 5VIN[A/B], 3VIN[A/B],
or VSTBY[A/B] input voltage is lower than its
respective ULVO threshold, OR
•
The fast OC circuit breaker[A/B] has tripped, OR
•
The slow OC circuit breaker[A/B] has tripped
AND its filter timeout has expired, OR
The slow OC circuit breaker[A/B] has tripped
AND Slot[A/B] die temperature exceeds 140°C,
OR
HPI-only Control Applications
In applications where the MIC2593 is controlled only by
the HPI, SMBus signals SCL, SDA, and /INT signals are
connected to VSTBY as shown in Figure 6. In this
configuration, the MIC2593’s /FAULT[A/B] outputs are
activated after power-on-reset and become asserted
when:
+3.3V
UVLO
VSTBY
AUXEN[A/B]
VIH
VIH
VIL
0
tPOR
AUX_OUT[A/B]
0
ILIM(AUX)
IAUX_OUT[A/B]
tFLT
ISTEADY-STATE
0
VIH
ON[A/B]
VIH
VIL
0
MAIN_OUT[A/B]
0
ILIM(MAIN)
IMAIN_OUT[A/B]
/FAULT_[A/B]
tFLT
ISTEADY-STATE
0
0
*
/INT*
*
0
* /INT de-asserted by software
Figure 8. Hot Plug Interface Mode Operation
September 2008
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M9999-092208
Micrel, Inc.
MIC2593
Either or both external ON[A/B] and AUXEN[A/B] input
signals are asserted, AND
•
12VIN[A/B], 12MVIN[A/B], 5VIN[A/B], 3VIN[A/B],
or VSTBY[A/B] input voltage is lower than its
respective ULVO threshold, OR
•
The fast OC circuit breaker[A/B] has tripped, OR
•
The slow OC circuit breaker[A/B] has tripped
AND its filter timeout[A/B] has expired, OR
•
The slow OC circuit breaker[A/B] has tripped
AND Slot[A/B] die temperature exceeds 140°C,
OR
Serial Port Operation
The MIC2593 uses standard SMBus Write_Byte and
Read_Byte operations for communication with its host.
The SMBus Write_Byte operation involves sending the
device’s slave address, with the R/W bit (LSB) set to the
low (write) state, followed by a command byte and a
data byte. The SMBus Read_Byte operation is similar,
but is a composite write and read operation: the host first
sends the device’s slave address followed by the
command byte, as in a write operation. A new “Start” bit
must then be sent to the MIC2593, followed by a repeat
of the slave address with the R/W bit set to the high
(read) state. The data to be read from the part may then
be clocked out. There is one exception to this rule: If the
location latched in the pointer register from the last write
operation is known to be correct (i.e., points to the
desired register within the MIC2593), then the
“Receive_Byte” procedure may be used. To perform a
Receive_Byte operation, the host sends an address byte
to select the slave MIC2593, with the R/W bit set to the
high (read) state, and then retrieves the data byte.
Figures 9 through 11 show the formats for these data
read and data write procedures.
The Command Register is eight bits (one byte) wide.
This byte carries the address of the MIC2593’s register
to be operated upon. The command byte values
corresponding to the various MIC2593 register
addresses are shown in Table 4. Command byte values
other than 0000 0XXXb = 00h - 07hare reserved and
should not be used.
•
The MIC2593’s global die temperature
exceeds160°C
In order to clear /FAULT[A/B] outputs once asserted,
ON[A/B] and/or AUXEN[A/B] input signals must be deasserted. Please see the /FAULT[A/B] pin description for
additional information.
Hot Plug Interface (HPI) Operation
Once the input supplies are above their respective UVLO
thresholds, the Hot Plug Interface can be utilized for
power control by enabling the control input pins
(AUXEN[A/B] and ON[A/B]) for each slot. In order for the
MIC2593 to switch on the VAUX supply for either slot, the
AUXEN[A/B] control must be enabled after the power-onreset delay, tPOR (typically 500µs), has elapsed. The MAIN
output supplies can also be enabled after tPOR. The timing
response diagram of Figure 8 illustrates a Hot Plug
Interface operation where an overcurrent fault is detected
by the MIC2593 controller after initiating a power-up
sequence. The figure illustrates the output response of
/FAULT, /INT, VAUX[A/B] supplies, and an external
MOSFET control MAIN[A/B] output supply, either 3.3V or
5V.
Inputs
MIC2593 SMBus Address Configuration
The MIC2593 responds to its own unique address which
is assigned using A2, A1, and A0. These represent the 3
LSBs of its 7-bit address, as shown in Table 3. These
address bits are assigned only during power up of the
VSTBY[A/B] supply input. These three bits allow up to
eight MIC2593 devices in a single system. These pins
are either grounded or left unconnected to specify a
logical 0 or 1, respectively. A pin designated as a logical
1 may also be pulled up to VSTBY.
September 2008
MIC2593 Slave Addresses
A2
A1
A0
Binary
Hex
0
0
0
1000 000b
80h
0
0
1
1000 001b
82h
0
1
0
1000 010b
84h
0
1
1
1000 011b
86h
1
0
0
1000 100b
88h
1
0
1
1000 101b
8Ah
1
1
0
1000 110b
8Ch
1
1
1
1000 111b
8Eh
Table 3. MIC2593 SMBus Addressing
15
M9999-092208
Micrel, Inc.
MIC2593
Register Set and Programmer’s Model
Power-On
Default
Common
Byte Value
Target Register
Label
Description
Read
Write
RESERVED
Do not Use
00h
n/a
n/a
RESERVED
Do not Use
01h
n/a
n/a
CNTRLA
Control Register Slot A
02h
02h
00h
CNTRLB
Control Register Slot B
03h
03h
00h
STATA
Slot A Status
04h
04h
00h
STATB
Slot B Status
05h
05h
00h
CS
Common Status Register
06h
06h
Xxxx 0000b
RESERVED
Reserved / Do not Use
07h 0FFh
07h 0FFh
Undifined
Table 4. MIC2593 Register Addresses
MIC2593 Slave Address
DATA
S 1 0 0 1
Command Byte to MIC2593
0 A 0 0 0 0 0 0 X X A
R/W = WRITE
START
Data Byte to MIC2593
ACKNOWLEDGE
A P
ACKNOWLEDGE
ACKNOWLEDGE
STOP
CLK
Master to slave transfer,
i.e., DATA driven by master.
Slave to master transfer,
i.e., DATA driven by slave.
Figure 9.WRITE_BYTE Protocol
MIC2593 Slave Address
DATA
Command Byte to MIC2593
MIC2593 Slave Address
Data Read From MIC2593
S 1 0 0 1 A2 A1 A0 0 A 0 0 0 0 0 0 X X A S 1 0 0 1 A2 A1 A0 1 A
START
R/W = WRITE
ACKNOWLEDGE
ACKNOWLEDGE
R/W = READ
START
/A P
ACKNOWLEDGE NOT ACKNOWLEDGE
STOP
CLK
Master to slave transfer,
i.e., DATA driven by master.
Slave to master transfer,
i.e., DATA driven by slave.
Figure 10.READ_BYTE Protocol
Byte Read from MIC2593
MIC2593 Slave Address
DATA
S 1 0 0 1
START
1 A
R/W = READ
/A P
ACKNOWLEDGE NOT ACKNOWLEDGE
STOP
CLK
Master to slave transfer,
i.e., DATA driven by master.
Slave to master transfer,
i.e., DATA driven by slave.
Figure 11.RECEIVE_BYTE Protocol
September 2008
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M9999-092208
Micrel, Inc.
MIC2593
Detailed Register Descriptions below:
Control Register, Slot A (CNTRLA)
8-Bits, Read/Write
Control Register, Slot A (CNTRLA)
D[7]
D[6]
D[5]
D[4]
D[3]
D[2]
D[1]
D[0]
read-only
read-only
read-only
read-only
read-only
read-only
read/write
read/write
AUXAPG
MAINAPG
Reserved
Reserved
Reserved
Reserved
MAINA
AUXA
Bit(s)
Function
Operation
AUXAPG
AUX output power-good status, Slot A
1 = Power-is-Good
(VAUXA Output is above its UVLO threshold)
MAINAPG
MAIN output power-good status, Slot A
1 = Power-is-Good
(MAINA Outputs are above their UVLO thresholds)
D[5]
Reserved
Always read as zero
D[4]
Reserved
Always read as zero
D[3]
Reserved
Always read as zero
D[2]
Reserved
Always read as zero
MAINA
MAIN enable control, Slot A
0 = Off, 1 = On
AUXA
VAUX enable control, Slot A
0 = Off, 1 = On
Power-Up Default Value:
0000 0000b = 00h
Read Command_Byte Value (R/W):
0000 0010b = 02h
The power-up default value is 00h. Slot is disabled upon power-up, i.e., all supply outputs are off.
Control Register, Slot A (CNTRLB)
8-Bits, Read/Write
Control Register, Slot B (CNTRLB)
D[7]
D[6]
D[5]
D[4]
D[3]
D[2]
D[1]
D[0]
read-only
read-only
read-only
read-only
read-only
read-only
read/write
read/write
AUXBPG
MAINBPG
Reserved
Reserved
Reserved
Reserved
MAINB
AUXB
Bit(s)
Function
Operation
AUXBPG
AUX output power-good status, Slot B
1 = Power-is-Good
(VAUXB Output is above its UVLO threshold)
MAINBPG
MAIN output power-good status, Slot B
1 = Power-is-Good
(MAINB Outputs are above their UVLO thresholds)
D[5]
Reserved
Always read as zero
D[4]
Reserved
Always read as zero
D[3]
Reserved
Always read as zero
D[2]
Reserved
Always read as zero
MAINB
MAIN enable control, Slot B
0 = Off, 1 = On
AUXB
VAUX enable control, Slot B
0 = Off, 1 = On
Power-Up Default Value:
0000 0000b = 00h
Command_Byte Value (R/W): 0000 0011b = 03h
The power-up default value is 00h. Slot is disabled upon power-up, i.e., all supply outputs are off.
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MIC2593
Status Register, Slot A (STATA)
8-Bits, Read-Only
Status Register, Slot A (STATA)
D[7]
D[6]
D[5]
D[4]
D[3]
D[2]
D[1]
D[0]
read-only
read-only
read-only
read/write
read/write
read/write
read/write
read/write
FAULTA
MAINA
VAUXA
VAUXAF
12MVAF
12VAF
5VAF
3VAF
Bit(s)
FAULTA
Function
Operation
1 = /FAULTA pin asserted
(/FAULTA pin is LOW)
FAULT Status, Slot A
0 = /FAULTA pin de-asserted
(/FAULTA pin is HIGH)
See Notes 1 and 2
MAINA
Represents the actual state (on/off) of the four Main
Power outputs for Slot A (+12V, –12V, +5V and +3.3V)
MAIN Enable Status, Slot A
1 = Main Power ON
0 = Main Power OFF
VAUXA
Represents the actual state (on/off) of the Auxiliary
Power output for Slot A
VAUX Enable Status, Slot A
1 = AUX Power ON
0 = Main Power OFF
VAUXAF
Overcurrent Fault: VAUXA supply A
1 = Fault, 0 = No fault
12MVAF
Overcurrent Fault: –12V supply A
1 = Fault, 0 = No fault
12VAF
Overcurrent Fault: +12V supply A
1 = Fault, 0 = No fault
5VAF
Overcurrent Fault: 5V supply A
1 = Fault, 0 = No fault
3VAF
Overcurrent Fault: 3V supply A
1 = Fault, 0 = No fault
Power-Up Default Value:
0000 0000b = 00h
Command_Byte Value (R/W): 0000 0100b = 04h
The power-up default value is 00h. Both slots are disabled upon power-up, i.e., all supply outputs are off. In response to
anovercurrent fault condition, writing a logical 1 back into the active (or set) bit position will clear the bit and de-assert /INT.
Thestatus of the /FAULTA pin is not affected by reading the Status Register or by clearing active status bits.
Note 1.
If FAULTA has been set by an overcurrent condition on one or more of the MAIN outputs, the ONA input must go LOW to reset FAULTA.
If FAULTA has been set by a VAUXA overcurrent event, the AUXENA input must go LOW to reset FAULTA.
If an overcurrent has occurred on both a MAIN output and the VAUX output of slot A, both ONA and AUXENA of the slot must go low to
reset FAULTA.
Note 2.
Neither the FAULTA bit nor the /FAULTA pin is active when the MIC2593 power paths are controlled by the System Management
Interface. When using SMI power path control, AUXENA and ONA pins for that slot must be tied to GND.
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Micrel, Inc.
MIC2593
Status Register, Slot B (STATB)
8-Bits, Read-Only
Status Register, Slot B (STATB)
D[7]
D[6]
D[5]
D[4]
D[3]
D[2]
D[1]
D[0]
read-only
read-only
read-only
read/write
read/write
read/write
read/write
read/write
FAULTB
MAINB
VAUXB
VAUXBF
12MVBF
12VBF
5VBF
3VBF
Bit(s)
FAULTB
Function
Operation
1 = /FAULTB pin asserted
(/FAULTB pin is LOW)
FAULT Status, Slot B
0 = /FAULTB pin de-asserted
(/FAULTB pin is HIGH)
See Notes 1 and 2
MAINB
Represents the actual state (on/off) of the four Main
Power outputs for Slot B (+12V, –12V, +5V and +3.3V)
MAIN Enable Status, Slot B
1 = Main Power ON
0 = Main Power OFF
VAUXB
Represents the actual state (on/off) of the Auxiliary
Power output for Slot B
VAUX Enable Status, Slot B
1 = AUX Power ON
0 = Main Power OFF
VAUXBF
Overcurrent Fault: VAUXB supply B
1 = Fault, 0 = No fault
12MVBF
Overcurrent Fault: –12V supply B
1 = Fault, 0 = No fault
12VBF
Overcurrent Fault: +12V supply B
1 = Fault, 0 = No fault
5VBF
Overcurrent Fault: 5V supply B
1 = Fault, 0 = No fault
3VBF
Overcurrent Fault: 3V supply B
1 = Fault, 0 = No fault
Power-Up Default Value:
0000 0000b = 00h
Command_Byte Value (R/W): 0000 0101b = 05h
The power-up default value is 00h. Both slots are disabled upon power-up, i.e., all supply outputs are off. In response to an
overcurrent fault condition, writing a logical 1 back into the active (or set) bit position will clear the bit and de-assert /INT. The
status of the /FAULTB pin is not affected by reading the Status Register or by clearing active status bits.
Note 1.
If FAULTB has been set by an overcurrent condition on one or more of the MAIN outputs, the ONB input must go LOW to reset FAULTB.
If FAULTB has been set by a VAUXB overcurrent event, the AUXENB input must go LOW to reset FAULTB.
If an overcurrent has occurred on both a MAIN output and the VAUX output of slot B, both ONB and AUXENB of the slot must go low to
reset FAULTB.
Note 2.
Neither the FAULTB bit nor the /FAULTB pin is active when the MIC2593 power paths are controlled by the System Management
Interface. When using SMI power path control, AUXENB and ONB pins for that slot must be tied to GND.
September 2008
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Micrel, Inc.
MIC2593
Common Status Register (CS)
8-Bits, Read/Write
Common Status Register (CS)
D[7]
D[6]
D[5]
D[4]
D[3]
D[2]
D[1]
read/write
read/write
read-only
read-only
read/write
read/write
read/write
read-only
Reserved
Reserved
GPI_B
GPI_A
INTMSK
UV_INT
OV_INT
Reserved
Bit(s)
Function
Operation
D[7]
Reserved
Always read as zero
D[6]
Reserved
Always read as zero
GPI_B
General Purpose Input 0, Slot B
State of GPIB pin
GPI_A
General Purpose Input 0, Slot A
State of GPIA pin
Interrupt Mask
0 = /INT generation is enabled
INTMSK
D[0]
1 = /INT generation is disabled
The MIC2593 does not participate in the SMBus Alert
Response Address (ARA) protocol.
UV_INT
Undervoltage Interrupt
0 = No UVLO fault
1 = UVLO fault
Set whenever a circuit breaker fault condition occurs as
a result of an undervoltage lockout condition on one of
the main supply inputs. This bit is only set if a UVLO
condition occurs while the ON[A/B] pin is asserted or
the MAIN[A/B] control bits are set.
OV_INT
Overtemperature Interrupt
0 = Die Temp < 160°C
1 = Fault: Die Temp > 160°C
Set if a fault occurs as a result of theMIC2593’s die
temperature exceeding160°C.
D[0]
Reserved
Undefined
Power-Up Default Value:
0000 0000b = 00h
Command_Byte Value (R/W): 0000 0110b = 06h
To reset the OT_INT and UV_INT fault bits, a logical 1 must be written back to these bits.
September 2008
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M9999-092208
Micrel, Inc.
MIC2593
Application Information
A 1W sense resistor would work well in this application.
Current Sensing
For the three power supplies switched with internal MOSFETs (+12V, –12V, and VAUX), the MIC2593 provides all
necessary current sensing functions to protect the IC, the
load, and the power supply. For the remaining four
supplies which the part is designed to control, the high
currents at which these supplies typically operate make
sensing the current inside the MIC2593 impractical.
Therefore, each of these supplies, 3V[A/B] and 5V[A/B],
requires an external current sensing resistor. The VIN
connection to the IC from each supply (e.g., 5VINA) is
connected to the positive terminal of the slot’s current
sense amplifier, and the corresponding SENSE input (in
this case, 5VSENSEA) is connected to the negative
terminal of the current sense amplifier.
Kelvin Sensing
Because of the low values of the sense resistors, special
attention to the layout must be used in order for the
MIC2593's circuit breaker function to operate properly.
Specifically, the use of a 4-wire Kelvin connection to
measure the voltage across RSENSE is highly
recommended. Kelvin sensing is simply a means of
making sure that any voltage drops in the power traces
connecting to the resistors does not get picked up by the
traces themselves. The Kelvin connections should be
isolated from all other signal traces to avoid introducing
noise onto these sensitive nodes. Additionally, a highfrequency noise filter across the sense inputs is highly
recommended to avoid nuisance tripping of the
(overcurrent) circuit breaker on the opposite slot to the
slot that incurred an overcurrent event. Due to the
variation of each system's susceptibility to noise, the
exact value of this filter is experimentally determined. A
value between 10pF to 100pF is a good starting point.
Figure 12 illustrates how Kelvin sensing is performed. All
the high current in the circuit (from the 5V supply through
RSENSE and then to the drain of the 5V (Slot A) output
MOSFET) flows directly through the power PCB traces
and RSENSE. The voltage drop resulting across RSENSE is
sampled in such away that the high currents through the
power traces will not introduce any extraneous IR drops.
R SENSE =
Power Trace
From 5VIN
35mV
34mV
=
(1.03 ) ILOAD(CONT) ILOAD(CONT)
(
)
65mV
(0.97 )(R SENSE(NOM) )
=
5VINA
Power Trace
To MOSFET Drain
Signal Trace
to MIC2593 VSENSE
MIC2593
67mV
R SENSE(NOM)
Figure 12. Kelvin Sensing Connections for RSENSE
(Applicable to 5V[A/B] and 3V[A/B])
As an example, if an output must carry a continuous 4.5A
without nuisance trips occurring, RSENSE for that output
should be 34mΩ/4.5A = 7.55mΩ. The nearest standard
value is 7.5mΩ, so a 7.5mΩ ±1% resistor would be a
good choice. At the other set of tolerance extremes for the
output in question, ILOAD(CONT,max) = 67mV/7.5mΩ = 8.93A.
Knowing this final datum, we can determine the
necessary wattage of the sense resistor, using P = I2R,
where I is ILOAD(CONT, MAX), and R is (0.97)(RSENSE(NOM)).
These numbers yield the following:
PMAX = (8.93A)2 (7.28mΩ) = 0.581W
September 2008
22pF
Signal Trace
to MIC2593 VIN
Once the value of RSENSE has been chosen in this
manner, it is good practice to check the maximum
ILOAD(CONT) which the circuit may let through in the case of
tolerance build-up in the opposite direction. Here, the
worst-case maximum current is found using a 65mV trip
voltage and a sense resistor which is 3% low in value.
The resulting current is:
ILOAD(CONT, MAX) =
RSENSE
5VSENSEA
Sense Resistor Selection
The MIC2593 uses low-value sense resistors to measure
the current flowing through the MOSFET switches to the
loads. These sense resistors are nominally valued at
50mV/ILOAD(CONT). To accommodate worst-case tolerances
for the sense resistor (allow ±3% over time and
temperature for a resistor with ±1% initial tolerance) and
still supply the maximum required steady-state load
current, a slightly more detailed calculation must be used.
The current limit threshold voltage (i.e., the “trip point”) for
the MIC2593 may be as low as 35mV, which would
equate to a sense resistor value of 35mV/ILOAD(CONT).
Carrying the numbers through for the case where the
value of the sense resistor is 3% high yields this:
MOSFET Selection
Selecting the proper MOSFET for use as a current pass
and switching element for each of the 3V and 5V slots of
the MIC2593 primarily involves three straightforward
tasks:
1. Choice of a MOSFET which meets the minimum
voltage requirements.
2. Selection of a device to handle the maximum
continuous current (steady-state thermal issues).
3. Verification that the selected part can withstand
any current peaks (transient thermal issues).
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MIC2593
value is 0.5% increase in RON per °C rise in junction
temperature above the point at which RON was initially
specified by the manufacturer. For instance, if the
selected MOSFET has a calculated RON of 10mΩ at TJ =
25°C and the actual junction temperature ends up at
110°C, a good first cut at the operating value for RON
would be:
MOSFET Voltage Requirements
The first voltage requirement for each MOSFET is easily
stated: the drain-source breakdown voltage of the
MOSFET must be greater than VIN(MAX) for the slot in
question. For instance, the 5V input may reasonably be
expected to see high-frequency transients as high as
6.5V. Therefore, the drain-source breakdown voltage of
the MOSFET must be at least 7V.
The second breakdown voltage criteria which must be
met is a bit subtler than simple drain-source breakdown
voltage, but is not hard to meet. Low-voltage MOSFETs
generally have low breakdown voltage ratings from gate
to source as well. In MIC2593 applications, the gates of
the external MOSFETs are driven from the +12V input to
the MIC2593 controller. That supply may well be at 12V +
(5% x 12V) = 12.6V. At the same time, if the output of the
MOSFET (its source) is suddenly shorted to ground, the
gate-source voltage will go to (12.6V – 0V) = 12.6V. This
means that the external MOSFETs must be chosen to
have a gate-source breakdown voltage in excess of 13V;
after 12V absolute maximum, the next commonly
available voltage class has a 20V maximum gate-source
voltage. At the present time, most power MOSFETs with a
20V gate-source voltage rating have a 30V drain-source
breakdown rating or higher. As a general tip, look to
surface mount devices with a drain-source rating of 30V
as a starting point.
R ON ≅ 10mΩ[1 + (110 − 25)(0.05)] ≅ 14.3mΩ
Next, approximate the steady-state power dissipation
(I2R) using ILOAD(CONT,max) and the approximated RON.
[
The final step is to make sure that the heat sinking
available to the MOSFET is capable of dissipating at least
as much power (rated in °C/W) as that with which the
MOSFET’s performance was specified by the
manufacturer. Here are a few practical tips:
1. The heat from a surface-mount device such as an
SO-8 MOSFET flows almost entirely out of the
drain leads. If the drain leads can be soldered
down to one square inch or more, the copper
trace will act as the heat sink for the part. This
copper trace must be on the same layer of the
board as the MOSFET drain.
2. Airflow works. Even a few LFM (linear feet per
minute) of air will cool a MOSFET down
substantially. If you can, position the MOSFET(s)
near the inlet of a power supply’s fan, or the outlet
of a processor’s cooling fan.
3. The best test of a surface-mount MOSFET for an
application (assuming the above tips show it to be
a likely fit) is an empirical one. Check the
MOSFET's temperature in the actual layout of the
expected final circuit, at full operating current. The
use of a thermocouple on the drain leads, or
infrared pyrometer on the package, will then give
a reasonable idea of the device’s junction
temperature.
MOSFET Steady-State Thermal Issues
The selection of a MOSFET to meet the maximum
continuous current is a fairly straightforward exercise.
First, arm yourself with the following data:
•
The value of ILOAD(CONT, MAX) for the output in
question (see Sense Resistor Selection).
•
The manufacturer’s data sheet for the candidate
MOSFET.
•
The maximum ambient temperature in which the
device will be required to operate.
•
Any knowledge you can get about the heat
sinking available to the device (e.g., Can heat be
dissipated into the ground plane or power plane,
if using a surface mount part? Is any airflow
available?).
The data sheet will almost always give a value of on
resistance given for the MOSFET at a gate-source
voltage of 4.5V, and another value at a gate-source
voltage of 10V. As a first approximation, add the two
values together and divide by two to get the on-resistance
of the part with 7V to 8V of enhancement (11.5V nominal
VGATE minus the 3.5V to 4.5V gate threshold of the
MOSFET). Call this value RON. Since a heavily enhanced
MOSFET acts as an ohmic (resistive) device, almost all
that’s required to determine steady-state power
dissipation is to calculate I2R. The one addendum to this
is that MOSFETs have a slight increase in RON with
increasing die temperature. A good approximation for this
September 2008
]
RON ≅ ILOAD(CONT,MAX) 2 × RON ≅ (8.93A)2 × 14.3mΩ ≅ 1.14W
MOSFET Transient Thermal Issues
Having chosen a MOSFET that will, a) withstand both the
applied voltage stresses, and b) handle the worst-case
continuous I2R power dissipation that it will endure;
verifying the MOSFET’s ability to handle short-term
overload power dissipation without overheating is the lone
item to be determined. A MOSFET can handle a much
higher pulsed power without damage than its continuous
dissipation ratings would imply. The reason for this is that
thermal devices (silicon die, lead frames, etc.) have
thermal inertia.
In terms related directly to the specification and use of
power MOSFETs, this is known as “transient thermal
impedance. ”Almost all power MOSFET data sheets give
a Transient Thermal Impedance Curve. For example, take
the case where tFLT for the 5V supply has been set to
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M9999-092208
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MIC2593
50ms, ILOAD(CONT, MAX) is 5.0A, the slow-trip threshold is
50Mv nominal, and the fast-trip threshold is 100mV. If the
output is connected to a 0.60Ω load, the output current
from the MOSFET for the slot in question will be regulated
to 5.0A for 50ms before the MIC2593 circuit breaker trips.
During that time, the dissipation in the MOSFET is given
by:
temperature, and find the operating junction temperature
increase (∆TJ) from that point. Then, as shown next, the
final junction temperature is found by adding TA(MAX) and
∆TJ. Since this is not a closed-form equation, getting a
close approximation may take one or two iterations, but
it’s not a hard calculation to perform and tends to
converge quickly.
Then the starting (steady-state) TJ is:
P = E × I E MOSFET = [5V − 5A(0.6ΩA] = 2V
PMOSFET = (2V × 5A ) = 10W for 50ms
TJ ≅ TA(MAX) + ΔTJ
[
]
≅ TA(MAX) + R ON + (TA(MAX) − TA )(0.005°C)(R ON )
At first glance, it would appear that a really hefty MOSFET
is required to withstand this sort of fault condition. This is
where the transient thermal impedance curves become
very useful. Figure 13 shows the curve for the Vishay
(Siliconix) Si4430DY, a commonly used SO-8 power
MOSFET.
Taking the simplest case first, we’ll assume that once a
fault event such as the one in question occurs, it will be a
long time, several seconds, before the fault is isolated and
the channel is reset. In such a case, we can approximate
this as a “single pulse” event, that is to say, there’s no
significant duty cycle. Then, reading up from the X-axis at
the point where “Square Wave Pulse Duration” is equal to
0.1sec (=100msec), we see that the Zθ(JA) of this MOSFET
to a highly infrequent event of this duration is only 7% of
its continuous Rθ(JA).
This particular part is specified as having an Rθ(JA) of
35°C/W for intervals of 10 seconds or less. Thus:
Assume TA = 55°C maximum, 1 square inch of copper at
the drain leads, no airflow.
Recalling from our previous approximation hint, the part
has an RON of (0.014/2) = 7mΩ at 25°C.
Assume it has been carrying just about 5A for some time.
When performing this calculation, be sure to use the
highest anticipated ambient temperature (TA(MAX)) in which
the MOSFET will be operating as the starting
× I 2 × R θ(JA)
]
TJ ≅ 55°C + [7mΩ + (55°C − 25°C)(0.005)(7mΩm
× (5A) 2 × (35°C/W)
TJ ≅ 55°C + (0.20125W) (35°C)
≅ 62.0°C
Iterate the calculation once to see if this value is within a
few percent of the expected final value. For this iteration
we will start with TJ equal to the already calculated value
of 62.0°C:
]
TJ ≅ TA + [7mΩ + (62.0°C − 25°C)(0.005)(7mΩm
× (5A) 2 × (35°C/W)
TJ ≅ 55°C + (0.20125W) (35°C) ≅ 62.35°C
So our original approximation of 62.0°C was very close to
the correct value. We will use TJ = 62°C.
Finally, add (10W)(35°C/W)(0.07) = 24.5°C to the steadystate TJ to get TJ(TRANSIENT MAX.) = 86.5°C. This is an
acceptable maximum junction temperature for this part.
Normalized Thermal Transient Imperance, Juction-to-Ambient
Normalized Effective Transient
Thermal Impedance
2
1
Duty Cycle = 0.5
0.2
Notes:
0.1
PDM
0.1
t1
0.05
1.
2.
3.
4.
0.02
Single Pulse
t2
t
Duty Cycle, D = 1
t2
Per Unit Base = RqJA = 67°C/W
TJM – TA = PDMZqJA(t)
Surface Mounted
0.01
10-4
10-3
10-2
10-1
1
10
100
600
Square Wave Pulse Duration (sec)
Figure 13. Si4430DY MOSFET Transient Thermal Impedance Curve
September 2008
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Micrel, Inc.
MIC2593
is both small and inexpensive. An LC filter made of a
ferrite bead between the noisy power supply input and the
MIC2593, followed by a "composite capacitor" from the
affected MIC2593 input pin to ground, will suffice for
almost any situation. A good composite capacitor for this
purpose is the parallel combination of a 47µF tantalum
bulk decoupling capacitor, and one 1µF and one 0.01µF
ceramic capacitor for high-frequency bypass. A suggested
ferrite bead for such use is Fair-Rite Products Corporation
part number 2743019447 (this is a surface-mountable
part). Similar parts from other vendors or a 0.27µH aircore coil can also be used.
MOSFET and Sense Resistor Selection Guide
Listed in Table 5 below, by Manufacturer and Type
Number, are some of the more popular MOSFET and
resistor types used in PCI hot plug applications.
Although far from comprehensive, this information will
constitute a good starting point for most designs.
Power Supply Decoupling
In general, prudent system design requires that power
supplies used for logic functions should have less than
100mV of noise at frequencies of 100kHz and above. In
particular, the –12V supply should have less than 100mV
of peak-to-peak noise at frequencies of 1MHz or higher.
This is because the –12V supply is the most negative
potential applied to the IC, and is therefore connected to
the device's substrate. All of the subcircuits integrated
onto the silicon chip are hence subjected by capacitive
coupling to any HF noise on the –12V supply. While
individual capacitances are quite low, the amount of
injected energy required to cause a "glitch" can also be
quite low at the internal nodes of high speed logic circuits.
Less obviously, but equally important, is the fact that the
internal charge pump for the 3.3VAUX supplies is
somewhat susceptible to noise on the +12V input when
that input is at or near zero volts. The +12V supply should
not carry HF noise in excess of 200mV peak-to-peak with
respect to chip ground when it is in the "off" state.
If either the –12V input, the +12V input, of both supplies
do carry significant HF noise (as can happen when they
are locally derived by a switching converter), the solution
MOSFET Vendors
Vishay (Siliconix)
Noisy VIN
To MIC2593
SMT Ferrite Bead
Fair-Rite Products
Type 2743019447
47µF
Tanalum
10nF
Ceramic
1µF
Ceramic
Figure 14. Filter Circuit for Noisy Supplies
(+3.3V and/or –12V)
It is theoretically possible that high-amplitude, HF noise
reflected back into one or both of the MIC2593’s –12V
outputs could interfere with proper device operation,
although such noisy loads are unlikely to occur in the real
world. If this becomes an application-specific concern, a
pair of filters similar to that in Figure 14 will provide the
required HF bypassing. The capacitors would be
connected to the MIC2593’s –12V output pins, and the
ferrite beads would be placed between the –12V output
pins and the loads.
Key MOSFET Type(s)
®
Si4430DY (“LittleFoot ” Series)
Web Address
www.siliconix.com
Si4420DY (“LittleFoot®” Series)
International Rectifier
IRF7413A (SO-8 package part)
www.irf.com
Si4420DY (second source to Vishay)
Fairchild Semiconductor
FDS6644 (SO-8 package part)
www.fairchildsemi.com
FDS6670A (SO-8 package part)
FDS6688 (SO-8 package part)
Resistor Vendors
Sense Resistors
Vishay (Dale)
WSL Series
IRC
Web Address
WSL 3637 Series
www.vishay.com/docs/wsl_30100.pdf
OARS Series
irctt.com/pdf_files/OARS.pdf
LR Series
irctt.com/pdf_files/LRC.pdf
(second source to WSL)
September 2008
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MIC2593
–12V Input Clamp Diode
The –12V input to the MIC2593 is the most negative
potential on the part and is therefore connected to the
chip’s substrate (as described in “Power Supply
Decoupling,” above). Although no particular sequencing of
the –12V supply relative to the other MIC2593 supplies is
required for normal operation, this substrate connection
does mean that the –12V input must never exceed the
voltage on the GROUND pin of the IC by more than 0.3
volts. Small amounts of internal leakage current can
cause this to happen when the VSTBY pins are energized
and the 12MVIN pins are not energized. In addition,
power supply output ringing or L(di/dt) effects in the wiring
and on the PCB itself will cause brief transient voltages in
excess of +0.3V to appear at the –12V input. For this
reason, it is required to clamp the –12V input to ground
with a Schottky diode. A diode rated at 1 amp and 20V to
40V as shown in our application schematic diagram is
suggested. The diode’s anode should be physically
placed directly at the –12V input to the MIC2593, and its
cathode should have as short a path as possible back to
the part’s ground. A good SMT part for this application is a
type MBRS140T3 (1A, 40V).
Gate Resistor Guidelines
The MIC2593 controls four external power MOSFETs,
that handle the high currents for each of the two 3.3V and
5V outputs. A capacitor is connected in the application
circuit from each GATE pin of the MIC2593 to ground.
However, an external capacitor, CGATE, is not required for
operation of the MIC2593. Each CGATE controls the rampup rate of its respective power output (e.g., 5VOUTB).
These capacitors, which are typically in the 10nF range,
cause the GATE outputs of the MIC2593 to have very low
AC impedances to ground at any significant frequency. It
is therefore necessary to place a modest value of gate
damping resistance (RGATE) between each CGATE and the
gate of its associated MOSFET as shown in Figure 15.
These resistances prevent high-frequency MOSFET
source-follower oscillations from occurring. The exact
value of the resistors used is not critical; 10Ω to 33Ω is
usually a sufficient choice. Each RGATE should be
physically located directly adjacent to the MOSFET gate
lead to which it connects.
MIC2593
RGATE
GATE
External
MOSFET
CGATE
10nF
Figure 15. CGATE and RGATE Connection
September 2008
25
M9999-092208
Micrel, Inc.
MIC2593
Package Information
NOTES:
1 . D IM E N S I O N D O E S N O T IN C L U D E M O L D F L A S H O R P R O T R U S I O N S ,
E ITHE R OF WHIC H SH ALL NOT EX CEED 0.254MM .
2 . L E A D D I M E N S I O N D O E S N O T IN C L U D E D A M B A R P R O T R U S I O N .
3 . P A C K A G E T O P M O LD D I M E N S IO N S A R E S M A LL E R T H A N B O T T O M
4 . M O L D D I M E N S I O N S A N D T OP O F P A C K A G E W I L L N O T O V E R H A N G
B O T T O M OF PAC K A G E .
48-Pin TQFP (TQ)
MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http://www.micrel.com
The information furnished by Micrel in this data sheet is believed to be accurate and reliable. However, no responsibility is assumed by Micrel for its
use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer.
Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product
can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant
into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A
Purchaser’s use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and Purchaser agrees to fully
indemnify Micrel for any damages resulting from such use or sale.
© 2002 Micrel, Incorporated.
September 2008
26
M9999-092208
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