General Description
The MAX5946 dual hot-plug controller is designed for
PCI Express™ applications. The device provides hot-
plug control for 12V, 3.3V, and 3.3V auxiliary supplies of
two PCI express slots. The MAX5946’s logic inputs/out-
puts allow interfacing directly with the system hot-plug
management controller or through an SMBus™ with an
external I/O expander. An integrated debounced atten-
tion switch and present-detect signals are included to
simplify system design.
The MAX5946 drives four external n-channel MOSFETs
to control the 12V and 3.3V main outputs. The 3.3V aux-
iliary outputs are controlled through internal 0.3Ω
n-channel MOSFETs. Internal charge pumps provide
gate drive for the 12V outputs while the gate drive of
the 3.3V output is driven by the 12V input supply. The
3.3V auxiliary outputs are completely independent from
the main outputs with their own charge pumps.
At power-up, the MAX5946 keeps all of the external
MOSFETs off until the supplies rise above their respec-
tive undervoltage lockout (UVLO) thresholds. The
device keeps the internal MOSFETs off only until the
auxiliary input supply rises above its UVLO threshold.
Upon a turn-on command, the MAX5946 enhances the
external and internal MOSFETs slowly with a constant
gate current to limit the power-supply inrush current.
The MAX5946 actively limits the current of all outputs at
all times and shuts down if an overcurrent condition
persists for longer than a programmable overcurrent
timeout. Thermal-protection circuitry also shuts down all
outputs if the die temperature exceeds +150°C. After an
overcurrent or overtemperature fault condition, the
MAX5946L latches off while the MAX5946A automatical-
ly restarts after a restart time delay. The device is avail-
able in a 36-pin (6mm ×6mm) thin QFN package and
operates over the -40°C to +85°C temperature range.
Applications
Servers
Desktop Mobile Server Platforms
Workstations
Embedded Devices
Features
♦PCI Express Compliant
♦Hot Swaps 12V, 3.3V, and 3.3V Auxiliary for 2
PCI-E Slots
♦Integrated Power MOSFET for Auxiliary Supply
Rails
♦Controls dI/dt and dV/dt
♦Active Current Limiting Protects Against
Overcurrent/Short-Circuit Conditions
♦Programmable Current-Limit Timeout
♦PWRGD Signal Outputs with Programmable
Power-On Reset (POR) (160ms Default)
♦Latched FAULT Signal Output after Overcurrent
or Overtemperature Fault
♦Attention Switch Inputs/Outputs with 4ms
Debounce
♦Present-Detect Inputs
♦Forced-On Inputs Facilitates Testing
♦Thermal Shutdown
♦Allows Control through SMBus with an I/O
Expander
MAX5946
Dual PCI Express, Hot-Plug
Controller
________________________________________________________________ Maxim Integrated Products 1
19-3483; Rev 0; 11/04
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
EVALUATION KIT
AVAILABLE
ONB
AUXONB
12SB+
12GB
3.3SB+
3.3SB-
PRES-DETB
1
2
3
4
5
6
7
8
9
27
26
25
24
23
22
21
20
19
3.3VAUXIN
3.3VAUXOB
PWRGDB
3.3GB
3.3VAUXOA
PWRGDA
FAULTA
3.3GA
PGND
GND
12VIN
INPUT1
OUTPUT1
OUTPUT2
INPUT2
TIM
PORADJ
THIN QFN
MAX5946
TOP VIEW
12SB-
FAULTB
FONB
ONA
AUXONA
12SA+
12GA
3.3SA+
3.3SA-
PRES-DETA
12SA-
FONA
36 35 34 33 32 31 30 29 28
10 11 12 13 14 15 16 17 18
Pin Configuration
Ordering Information
PART TEMP RANGE PIN-PACKAGE
MAX5946AETX
-40°C to +85°C 36 Thin QFN
MAX5946LETX
-40°C to +85°C 36 Thin QFN
Typical Application Circuit appears at end of data sheet.
SMBus is a trademark of Intel Corp.
PCI Express is a trademark of PCI-SIG Corp.
MAX5946
Dual PCI Express, Hot-Plug
Controller
2_______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
(All voltages referenced to GND, unless otherwise noted.)
12VIN......................................................................-0.3V to +14V
12GA, 12GB ..............................................-0.3V to (V12VIN + 6V)
12SA+, 12SA-, 12SB+, 12SB-,
3.3GA, 3.3GB .....................................-0.3V to (V12VIN + 0.3V)
3.3VAUXIN, ONA, ONB, FAULTA, FAULTB ............-0.3V to +6V
PWRGDA, PWRGDB ................................................-0.3V to +6V
PGND ....................................................................-0.3V to +0.3V
All Other Pins to GND......................-0.3V to (V3.3VAUXIN + 0.3V)
Continuous Power Dissipation (TA= +70°C)
36-Pin Thin QFN (derate 26.3mW/°C above +70°C).....2.105W
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
ELECTRICAL CHARACTERISTICS
(V12VIN = V12S_- = V12S_+ = 12V, V3.3S_+ = V3.3S_- = V3.3VAUXIN = VON_ = VAUXON_ = VFON__= 3.3V, PWRGD_ = FAULT_ = PORADJ
= TIM = OUTPUT_ = 12G_ = 3.3G_ = OPEN, INPUT_ = PRES_DET_ = PGND = GND, TA= -40°C to +85°C, unless otherwise noted.
Typical values are at TA= +25°C.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN TYP MAX
UNITS
12V SUPPLY
12V Supply Voltage Range V12VIN
10.8 12 13.2
V
V12VIN rising 9.5 10 10.5
12VIN Undervoltage Lockout
V12UVLO Hysteresis
0.1
V
12VIN Supply Current I12VIN V12VIN = 13.2V
0.5
1mA
12VIN CONTROL
12VIN Current-Limit
Threshold (V12S_+ - V12S_-)V12ILIM
49 54 59
mV
12G_ Gate Charge Current
I12G_CHG
V12G_ = GND 4 5 6 µA
Normal turn-off, ON_ = GND, V12G_ = 2V
50 150 250
µA
12G_ Gate Discharge Current
I12G_DIS O utp ut shor t- ci r cui t cond i ti on, str ong g ate p ul l d ow n
to r eg ul ati on, V
1 2V IN
- V
1 2S _ ≥ 1V , V
1 2G_= 5V
50 120 180
mA
12G_ Gate High Voltage
(V12G_ - V12VIN)V12G_H I12G_ = 1µA
4.8 5.3 5.8
V
12G_ Threshold Voltage For
PWRGD_ Assertion (Note 2) VPGTH12 Referred to V12VIN, I12G_ = 1µA
-3.0
-4
-4.8
V
12S_- Input Bias Current 1µA
12S_+ Input Bias Current
20 60
µA
3.3V SUPPLY
3.3V Supply Voltage Range V3.3SA+,
V3.3SB+
3.0 3.3 3.6
V
3.3SA+ rising
2.52 2.65 2.78
V
Undervoltage Lockout
(Note 3) Hysteresis
30
mV
MAX5946
Dual PCI Express, Hot-Plug
Controller
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(V12VIN = V12S_- = V12S_+ = 12V, V3.3S_+ = V3.3S_- = V3.3VAUXIN = VON_ = VAUXON_ = VFON__= 3.3V, PWRGD_ = FAULT_ = PORADJ
= TIM = OUTPUT_ = 12G_ = 3.3G_ = OPEN, INPUT_ = PRES_DET_ = PGND = GND, TA= -40°C to +85°C, unless otherwise noted.
Typical values are at TA= +25°C.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
UNITS
3.3V CONTROL
3.3V Current-Limit Threshold
(V3.3S_+ - V3.3S_-)V3.3ILIM
17 20 23
mV
3.3G_ Gate Charge Current
I3.3G_CHG
V3.3G_ = GND 4 5 6 µA
ON_ = GND, V3.3G_ = 2V
50 150 250
µA
3.3G_ Gate Discharge
Current I3.3G_DIS O utp ut shor t- ci r cui t cond i ti on, str ong g ate p ul l d ow n
to r eg ul ati on, V
3 .3 S _ +
- V
3 .3 S _
≥ 1V , V
3 .3 G_ = 5V
100 150 220
mA
3.3G_ Gate High Voltage
(V3.3G_ - V3.3S_+)V3.3G_H Sourcing 1µA
4.5 5.5 6.8
V
3.3G_ Threshold Voltage For
PWRGD_ Assertion (Note 2) VPGTH3.3 Referred to V3.3VAUXIN, I3.3G_ = 1µA
-3.0
-4
-4.5
V
3.3S_- Input Bias Current 1µA
3.3S_+ Input Bias Current
20 60
µA
3.3V AUXILIARY SUPPLY
3.3VAUXIN Supply Voltage
Range
V3.3VAUXIN 3.0 3.3 3.6
V
3.3VAUXIN rising
2.52 2.65 2.78
V
3.3VAUXIN Undervoltage
Lockout
V
3 .3 V A U X U V L O
Hysteresis
30
mV
3.3VAUXIN Supply Current V3.3VAUXIN = 3.6V
1.5
3mA
3.3VAUXIN to 3.3VAUXO_
Maximum Dropout I3.3VAUXO_ = 375mA
225
mV
3.3VAUXO_ Current-Limit
Threshold 3.3VAUXO_ shorted to GND
376 470 564
mA
3.3VAUXO_ Threshold For
PWRGD_ Assertion
(V3.3VAUXIN - V3.3VAUXO_)
(Note 3)
VPGTH3.3AUX 400
mV
LOGIC SIGNALS
Rising edge
1.0 2.0
V
Input-Logic Threshold
(ON_, FON_, AUXON_,
PRES-DET_, INPUT_) Hysteresis
25
mV
Input Bias Current
(ON_, AUXON_, INPUT_) 1µA
FON_, PRES-DET_ Internal
Pullup
25 50 75
kΩ
ON_, AUXON_ High-to-Low
Deglitch Time 4µs
MAX5946
Dual PCI Express, Hot-Plug
Controller
4_______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS (continued)
(V12VIN = V12S_- = V12S_+ = 12V, V3.3S_+ = V3.3S_- = V3.3VAUXIN = VON_ = VAUXON_ = VFON__= 3.3V, PWRGD_ = FAULT_ = PORADJ
= TIM = OUTPUT_ = 12G_ = 3.3G_ = OPEN, INPUT_ = PRES_DET_ = PGND = GND, TA= -40°C to +85°C, unless otherwise noted.
Typical values are at TA= +25°C.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN TYP MAX
UNITS
PRES-DET_ High-to-Low
Deglitch Time tDEG 357ms
PORADJ = open
90 160 250
RPORADJ = 20kΩ
35 55 75
RPORADJ = 100kΩ
145 265 380
PWRGD_ Power-On Reset
Time (Note 2) tPOR_HL
RPORADJ = 200kΩ
570
ms
PWRGD_ Low-to-High
Deglitch Time tPOR_LH 4µs
Sinking 2mA
0.1
PWRGD_, FAULT_ Output
Low Voltage Sinking 30mA
0.7
V
PWRGD_, FAULT_ Output-
High Leakage Current VPWRGD_ = VFAULT_ = 5.5V 1 µA
TIM = open
5.5 11 17.0
RTIM = 15kΩ
1.4 2.6 3.8
RTIM = 120kΩ
12 22 32
FAULT_ Timeout tFAULT
RTIM = 300kΩ
59
ms
FAULT_ Timeout During
Startup tSU 2 x tFAULT ms
Autorestart Delay Time tRESTART
64 x tFAULT
ms
Fault Reset Minimum Pulse
Width (Note 4) tRESET
100
µs
Thermal-Shutdown Threshold
TSD TJ rising
+150
°C
Thermal-Shutdown Threshold
Hysteresis
20
°C
OUTPUT_ Debounce Time tDBC
2.6 4.4 6.2
ms
OUTPUT_ High Voltage Sourcing 2mA V3.3VAUXIN
- 0.3
V
3.3 V AU X IN
V
OUTPUT_ Low Voltage Sinking 2mA
0.4
V
Note 1: 100% production tested at TA= +25°C. Parameters over temperature are guaranteed by design.
Note 2: PWRGD_ asserts a time tPOR_HL after VPGTH12, VPGTH3.3, and VPGTH3.3AUX conditions are met.
Note 3: The UVLO for the 3.3V supply is sensed at 3.3SA+.
Note 4: This is the time that ON_ or AUXON_ must stay low when resetting a fault condition.
MAX5946
Dual PCI Express, Hot-Plug
Controller
_______________________________________________________________________________________ 5
12VIN INPUT SUPPLY CURRENT
vs. TEMPERATURE
MAX5946 toc01
TEMPERATURE (°C)
SUPPLY CURRENT (mA)
603510-15
0.491
0.492
0.493
0.494
0.495
0.496
0.497
0.498
0.499
0.500
0.501
0.502
0.503
0.504
0.505
0.490
-40 85
3.3VAUXIN SUPPLY CURRENT
vs. TEMPERATURE
MAX5946 toc02
TEMPERATURE (°C)
SUPPLY CURRENT (mA)
603510-15
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
0
-40 85
ON AND AUXON LOW-TO-HIGH THRESHOLD
VOLTAGE vs. TEMPERATURE
MAX5946 toc03
TEMPERATURE (°C)
THRESHOLD VOLTAGE (V)
603510-15
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2.0
1.0
-40 85
ON_ OR AUXON_
3.3VAUXO_ OUTPUT VOLTAGE vs. CURRENT
MAX5946 toc04
OUTPUT CURRENT (A)
OUTPUT VOLTAGE (V)
0.50.40.30.20.1
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0
00.6
12G_ AND 3.3G_ GATE CHARGE
CURRENT vs. TEMPERATURE
MAX5946 toc05
TEMPERATURE (°C)
GATE CHARGE CURRENT (µA)
603510-15
4.90
4.95
5.00
5.05
5.10
5.15
5.20
5.25
5.30
5.35
4.85
-40 85
12G_
3.3G_
12G_ AND 3.3G_ GATE DISCHARGE
CURRENT vs. TEMPERATURE
MAX5946 toc06
TEMPERATURE (°C)
GATE DISCHARGE CURRENT (µA)
603510-15
150
155
160
165
170
145
-40 85
3.3G_
12G_
3.3VAUX INTERNAL SWITCH
MAXIMUM DROPOUT vs. TEMPERATURE
MAX5946 toc07
TEMPERATURE (°C)
DROPOUT VOLTAGE (V)
603510-15
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
0.20
0
-40 85
AUXILIARY OUTPUT CURRENT = 375mA
12V AND 3.3V CURRENT-LIMIT THRESHOLD
VOLTAGE vs. TEMPERATURE
MAX5946 toc08
TEMPERATURE (°C)
CURRENT-LIMIT THRESHOLD VOLTAGE (mV)
603510-15
10
20
30
40
50
60
0
-40 85
12V CURRENT-SENSE
THRESHOLD
3.3V CURRENT-SENSE
THRESHOLD
AUXILIARY CURRENT LIMIT
vs. TEMPERATURE
MAX5946 toc09
TEMPERATURE (°C)
AUXILIARY CURRENT LIMIT (A)
603510-15
0.455
0.460
0.465
0.470
0.475
0.480
0.485
0.490
0.495
0.500
0.450
-40 85
Typical Operating Characteristics
(V12VIN = V12SA+ = 12V, V3.3VAUXIN = V3.3S_+ = VON_ = VAUXON_ = VINPUT_ = 3.3V, PRES-DET_ = GND, FON_ = PORADJ = TIM =
float, FAULT_ = 10kΩto 3.3VAUXIN, PWRGDA = 10kΩto 3.3VAUXO_, TA= +25°C, unless otherwise noted, see the Typical
Application Circuit.)
MAX5946
Dual PCI Express, Hot-Plug
Controller
6_______________________________________________________________________________________
Typical Operating Characteristics (continued)
(V12VIN = V12SA+ = 12V, V3.3VAUXIN = V3.3S_+ = VON_ = VAUXON_ = VINPUT_ = 3.3V, PRES-DET_ = GND, FON_ = PORADJ = TIM =
float, FAULT_ = 10kΩto 3.3VAUXIN, PWRGDA = 10kΩto 3.3VAUXO_, TA= +25°C, unless otherwise noted, see the Typical
Application Circuit.)
12VIN UNDERVOLTAGE LOCKOUT
THRESHOLD vs. TEMPERATURE
MAX5946 toc10
TEMPERATURE (°C)
UVLO THRESHOLD (V)
6035-15 10
9.85
9.90
9.95
10.00
10.05
10.10
10.15
10.20
9.80
-40 85
3.3VAUXIN UNDERVOLTAGE LOCKOUT
THRESHOLD vs. TEMPERATURE
MAX5946 toc11
TEMPERATURE (°C)
UVLO THRESHOLD (V)
603510-15
2.62
2.64
2.66
2.68
2.70
2.60
-40 85
12V TURN-ON/OFF TIME
MAX5946 toc12
12G_
20V/div
PWRGD_
5V/div
ON_
5V/div
12V OUTPUT
10V/div
40ms/div
3.3V TURN-ON/OFF TIME
MAX5946 toc13
3.3G_
10V/div
PWRGD_
5V/div
ON_
5V/div
3.3V OUTPUT
5V/div
40ms/div
3.3V AUXILIARY TURN-ON/OFF TIME
MAX5946 toc14
40ms/div
3.3AUXO_
OUTPUT VOLTAGE
2V/div
AUXON_
2V/div
PWRGD
2V/div
12V POWER-UP
MAX5946 toc15
12V OUTPUT
10V/div
PWRGD_
5V/div
12VIN, 12V INPUT
10V/div
12G_
20V/div
40ms/div
MAX5946
Dual PCI Express, Hot-Plug
Controller
_______________________________________________________________________________________ 7
Typical Operating Characteristics (continued)
(V12VIN = V12SA+ = 12V, V3.3VAUXIN = V3.3S_+ = VON_ = VAUXON_ = VINPUT_ = 3.3V, PRES-DET_ = GND, FON_ = PORADJ = TIM =
float, FAULT_ = 10kΩto 3.3VAUXIN, PWRGDA = 10kΩto 3.3VAUXO_, TA= +25°C, unless otherwise noted, see the Typical
Application Circuit.)
3.3V INPUT/3.3V AUXILIARY INPUT
POWER-UP
MAX5946 toc16
3.3V OUTPUT
5V/div
PWRGD_
5V/div
3.3VAUXO_
5V/div
3.3G_
10V/div
100ms/div
3.3S_+
5V/div
TURN-ON DELAY 3.3V OUTPUT AND
3.3V AUXILIARY OUTPUT
MAX5946 toc17
4ms/div
5V/div
5V/div
5V/div
5V/div
10V/div
3.3VAUXO_
OUTPUT VOLTAGE
3.3 OUTPUT VOLTAGE
3.3 INPUT,
3.3VAUXIN
3.3G_
PWRGD
FAULT CONDITION ON 12V OUTPUT
(AUTORESTART OPTION MAX5946A)
MAX5946 toc18
12G_
20V/div
FAULT_
5V/div
12V OUTPUT CURRENT
5A/div
100ms/div
12V OUTPUT VOLTAGE
10V/div
tRESTART
RLOAD STEP TO 1.5Ω
FAULT CONDITION ON 3.3V OUTPUT
(AUTORESTART OPTION MAX5946A)
MAX5946 toc19
3.3G_
10V/div
FAULT_
5V/div
3.3V MAIN OUTPUT CURRENT
2A/div
100ms/div
3.3V OUTPUT VOLTAGE
5V/div
tRESTART
RLOAD STEP TO 0.5Ω
FAULT CONDITION ON AUXILIARY OUTPUT
(AUTORESTART OPTION MAX5946A)
MAX5946 toc20
FAULT_
2V/div
3.3VAUXO_ OUTPUT CURRENT
500mA/div
100ms/div
3.3VAUXO_ OUTPUT VOLTAGE
2V/div
tRESTART
RLOAD STEP TO 4Ω
FAULT CONDITION ON 12V OUTPUT
(LATCH OPTION MAX5946L)
MAX5946 toc21
12G_
20V/div
FAULT_
5V/div
12V OUTPUT CURRENT
5A/div
100ms/div
12V OUTPUT VOLTAGE
10V/div
RLOAD STEP TO 1.5Ω
MAX5946
Dual PCI Express, Hot-Plug
Controller
8_______________________________________________________________________________________
Typical Operating Characteristics (continued)
(V12VIN = V12SA+ = 12V, V3.3VAUXIN = V3.3S_+ = VON_ = VAUXON_ = VINPUT_ = 3.3V, PRES-DET_ = GND, FON_ = PORADJ = TIM =
float, FAULT_ = 10kΩto 3.3VAUXIN, PWRGDA = 10kΩto 3.3VAUXO_, TA= +25°C, unless otherwise noted, see the Typical
Application Circuit.)
FAULT CONDITION ON 12V OUTPUT
MAX5946 toc22
12G_
20V/div
FAULT_
5V/div
12V OUTPUT CURRENT
5A/div
4ms/div
12V OUTPUT VOLTAGE
10V/div
RLOAD
STEP TO 1.5Ω
tFAULT
FAULT CONDITION ON 3.3V OUTPUT
(LATCH OPTION MAX5946L)
MAX5946 toc23
3.3G_
10V/div
FAULT_
5V/div
3.3V OUTPUT CURRENT
2A/div
100ms/div
3.3V OUTPUT VOLTAGE
5V/div
RLOAD STEP TO 0.5Ω
FAULT CONDITION ON 3.3V MAIN OUTPUT
MAX5946 toc24
3.3G_
10V/div
FAULT_
5V/div
3.3V OUTPUT CURRENT
2A/div
4ms/div
3.3V OUTPUT VOLTAGE
5V/div
RLOAD
STEP TO 0.5Ω
tFAULT
FAULT CONDITION ON AUXILIARY OUTPUT
(LATCH OPTION MAX5946L)
MAX5946 toc25
FAULT_
2V/div
3.3VAUXO_ OUTPUT CURRENT
500mA/div
100ms/div
3.3VAUXO_ OUTPUT VOLTAGE
2V/div
RLOAD STEP TO 4Ω
FAULT CONDITION ON AUXILIARY OUTPUT
MAX5946 toc26
FAULT_
2V/div
3.3VAUXO_ OUTPUT CURRENT
500mA/div
4ms/div
3.3VAUXO_ OUTPUT VOLTAGE
2V/div
RLOAD
STEP TO 4Ω
tFAULT
SHORT CIRCUIT ON 12V OUTPUT
MAX5946 toc27
12G_
20V/div
FAULT_
5V/div
12V OUTPUT CURRENT
5A/div
2ms/div
12V OUTPUT VOLTAGE
10V/div
MAX5946
Dual PCI Express, Hot-Plug
Controller
_______________________________________________________________________________________ 9
Typical Operating Characteristics (continued)
(V12VIN = V12SA+ = 12V, V3.3VAUXIN = V3.3S_+ = VON_ = VAUXON_ = VINPUT_ = 3.3V, PRES-DET_ = GND, FON_ = PORADJ = TIM =
float, FAULT_ = 10kΩto 3.3VAUXIN, PWRGDA = 10kΩto 3.3VAUXO_, TA= +25°C, unless otherwise noted, see the Typical
Application Circuit.)
SHORT CIRCUIT ON 12V OUTPUT
MAX5946 toc28
12G_
20V/div
FAULT_
5V/div
12V OUTPUT CURRENT
25A/div
4µs/div
12V OUTPUT VOLTAGE
10V/div
0V
0V
0V
SHORT CIRCUIT ON 3.3V OUTPUT
MAX5946 toc29
3.3G_
5V/div
FAULT_
5V/div
3.3V OUTPUT CURRENT
2A/div
2ms/div
3.3V OUTPUT VOLTAGE
5V/div
SHORT CIRCUIT ON 3.3V OUTPUT
MAX5946 toc30
3.3G_
5V/div
FAULT_
5V/div
3.3V OUTPUT CURRENT
10A/div
2µs/div
3.3V OUTPUT VOLTAGE
5V/div
0V
SHORT CIRCUIT ON 3.3AUXO_
MAX5946 toc31
FAULT_
5V/div
3.3VAUXO_ OUTPUT CURRENT
500mA/div
2ms/div
3.3VAUXO_ OUTPUT VOLTAGE
2V/div
SHORT CIRCUIT ON 3.3VAUXO_
MAX5946 toc32
FAULT_
5V/div
3.3VAUXO_ OUTPUT CURRENT
5A/div
2µs/div
3.3VAUXO_ OUTPUT VOLTAGE
2V/div
POWER-UP INTO FAULT
(AUXILIARY SUPPLY)
MAX5946 toc33
3.3VAUXO_ OUTPUT VOLTAGE
2V/div
FAULT_
5V/div
3.3VAUXO_ OUTPUT CURRENT
500mA/div
4ms/div
AUXON_
5V/div
tSU
RLOAD = 4Ω
MAX5946
Dual PCI Express, Hot-Plug
Controller
10 ______________________________________________________________________________________
Typical Operating Characteristics (continued)
(V12VIN = V12SA+ = 12V, V3.3VAUXIN = V3.3S_+ = VON_ = VAUXON_ = VINPUT_ = 3.3V, PRES-DET_ = GND, FON_ = PORADJ = TIM =
float, FAULT_ = 10kΩto 3.3VAUXIN, PWRGDA = 10kΩto 3.3VAUXO_, TA= +25°C, unless otherwise noted, see the Typical
Application Circuit.)
POWER-UP INTO FAULT
(3.3V MAIN)
MAX5946 toc34
3.3V OUTPUT VOLTAGE
2V/div
FAULT_
5V/div
3.3V OUTPUT CURRENT
4A/div
4ms/div
ON_, AUXON_
5V/div
tSU
RLOAD = 0.5Ω
3.3G_
5V/div
POWER-UP INTO FAULT
(12V OUTPUT)
MAX5946 toc35
12V OUTPUT VOLTAGE
10V/div
FAULT_
5V/div
12V OUTPUT CURRENT
5A/div
4ms/div
ON_, AUXON_
5V/div
tSU
12G_
10V/div
PRESENT-DETECT (ON/OFF) OPERATION
MAX5946 toc36
40ms/div
5V/div
5V/div
5V/div
10V/div 12V OUTPUT VOLTAGE
3.3VAUXO_
OUTPUT VOLTAGE
PWRGD
PRES-DET_
PRESENT-DETECT (ON/OFF) OPERATION
MAX5946 toc37
4ms/div
5V/div
5V/div
5V/div
10V/div 12V OUTPUT VOLTAGE
3.3VAUXO_
OUTPUT VOLTAGE
PWRGD
PRES-DET_
FORCED-ON (ON/OFF) OPERATION
MAX5946 toc38
40ms/div
5V/div
5V/div
5V/div
10V/div 12V OUTPUT VOLTAGE
3.3VAUXO_
OUTPUT VOLTAGE
PWRGD
FON_
FORCED-ON (ON/OFF) OPERATION
MAX5946 toc39
4ms/div
5V/div
5V/div
5V/div
10V/div 12V OUTPUT VOLTAGE
3.3VAUXO_
OUTPUT VOLTAGE
PWRGD
FON_
MAX5946
Dual PCI Express, Hot-Plug
Controller
______________________________________________________________________________________ 11
Typical Operating Characteristics (continued)
(V12VIN = V12SA+ = 12V, V3.3VAUXIN = V3.3S_+ = VON_ = VAUXON_ = VINPUT_ = 3.3V, PRES-DET_ = GND, FON_ = PORADJ = TIM =
float, FAULT_ = 10kΩto 3.3VAUXIN, PWRGDA = 10kΩto 3.3VAUXO_, TA= +25°C, unless otherwise noted, see the Typical
Application Circuit.)
DEBOUNCED ON/OFF OPERATION
MAX5946 toc40
INPUT_
2V/div
10ms/div
OUTPUT_
2V/div
POWER-ON-RESET TIME
vs. PORADJ RESISTOR
MAX5946 toc41
RPORADJ (kΩ)
tPOR_HL (ms)
900800600 700200 300 400 500100
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
2400
2600
2800
3000
0
01000
tFAULT TIME DELAY vs. TIM RESISTOR
MAX5946 toc42
RTIM (kΩ)
tFAULT (ms)
900800600 700200 300 400 500100
20
40
60
80
100
120
140
160
180
200
0
01000
MAX5946
Dual PCI Express, Hot-Plug
Controller
12 ______________________________________________________________________________________
PIN NAME FUNCTION
1
PRES-DETA
Present-Detect Input A. PRES-DETA accepts inputs from the PRSNT#2 pin on a PCI express connector.
PRES-DETA has an internal pullup to 3.3VAUXIN. When PRES-DETA is low, the outputs follow the
command from ONA and AUXONA after a 4ms debounced time. When PRES-DETA goes from low to
high, all outputs of the respective slot shut down with no delay (see Table 2).
2FONA
Forced-On Input A. FONA has a 50kΩ internal pullup to 3.3VAUXIN. A logic-low on FONA turns on all
slot A outputs as long as the power inputs are within their operating range, regardless of the status of
the other input signals. Leave FONA open for normal operation (see Table 2).
3ONA Slot A 12V And 3.3V Outputs Enable. A logic-high at ONA turns on the 12V and 3.3V outputs of slot A
(see Table 2).
4AUXONA Slot A 3.3V Auxiliary Output Enable. A logic-high at AUXONA turns on the slot A auxiliary output
(3.3VAUXOA), see Table 2.
512SA+ Slot A 12V Positive Current-Sense Input. Connect the positive terminal of the current-sense resistor to
12SA+ using the Kelvin-sensing technique to assure accurate current sensing.
612SA- Slot A 12V Negative Current-Sense Input. Connect 12SA- to the negative side of the current-sense
resistor using the Kelvin-sensing technique to assure accurate current sensing.
712GA Slot A 12V Gate-Drive Output. Connect 12GA to the gate of slot A’s 12V MOSFET. At power-up, V12GA
is raised to the internal charge-pump voltage level by a constant current.
83.3SA+
Slot A 3.3V Positive Current-Sense Input. Connect the positive side of the current-sense resistor to
3.3SA+ using the Kelvin-sensing technique to assure accurate current sensing. This input is also used
for the 3.3V supply’s UVLO function.
93.3SA- Slot A 3.3V Negative Current-Sense Input. Connect to the negative side of the sense resistor using the
Kelvin-sensing technique to assure accurate current sensing.
10 3.3GA S l ot A 3.3V G ate- D r i ve O utp ut. C onnect 3.3G A to the g ate of sl ot A’ s 3.3V M OS FE T. At p ow er - up , V
3 .3 GA
i s char g ed to 5.5V ab ove the 3.3V sup p l y b y a constant cur r ent d er i ved fr om V
1 2V IN
.
11 FAULTA
Open-Drain Fault Output Signal. FAULTA latches active low whenever the slot A outputs are shut down
due to a fault. A fault is either of:
• An overcurrent condition lasting longer than the overcurrent timeout.
• A device over temperature condition.
If the fault is detected in the main outputs, FAULTA must be reset by toggling the ONA input. If the fault
is in the auxiliary output, FAULTA must be reset by toggling both ONA and AUXONA. For the auto-
restart version, FAULTA is reset when the part initiates the next power-on cycle.
12 PWRGDA Open-Drain Power-Good Output. PWRGDA goes low tPOR_HL after all outputs of slot A reach their final
value and the power MOSFETs are fully enhanced.
13
3.3VAUXOA
Slot A 3.3V Auxiliary Power-Supply Output
14
3.3VAUXIN
3.3V Auxiliary Supply Input. 3.3VAUXIN is the input to a charge pump that drives the internal MOSFETs
connecting 3.3VAUXIN to 3.3VAUXOA and 3.3VAUXOB. V3.3VAUXIN is also used to power the internal
control logic and analog references of the MAX5946.
15
3.3VAUXOB
Slot B 3.3V Auxiliary Power Output
16 PWRGDB Slot B Power-Good Output. See PWRGDA function.
17 FAULTB Slot B Open-Drain Fault Output. See FAULTA function.
18 3.3GB Slot B 3.3V Gate-Drive Output. See 3.3GA function.
Pin Description
Detailed Description
The MAX5946 dual hot-plug controller is designed for
PCI express applications. The device provides hot-plug
control for 12V, 3.3V, and 3.3V auxiliary supplies of two
PCI express slots. The MAX5946’s logic inputs/outputs
allow interfacing directly with the system hot-plug-man-
agement controller or through an SMBus with an exter-
nal I/O expander. An integrated debounced attention
switch and present-detect signals are included to sim-
plify system design.
The MAX5946 drives four external n-channel MOSFETs
to control the 12V and 3.3V main outputs. The 3.3V aux-
iliary outputs are controlled through internal 0.24Ωn-
channel MOSFETs. Internal charge pumps provide a
gate drive for the 12V outputs while the gate drive of
the 3.3V output is driven by the 12V input supply. The
3.3V auxiliary outputs are completely independent from
the main outputs with their own charge pumps.
At power-up, the MAX5946 keeps all of the external
MOSFETs off until all supplies rise above their respec-
tive UVLO thresholds. The device keeps the internal
MOSFETs off only until the 3.3VAUXIN supply rises
above its UVLO threshold. Upon a turn-on command,
the MAX5946 enhances the external and internal
MOSFETs slowly with a constant gate current to limit
the power-supply inrush current. The MAX5946 actively
limits the current of all outputs at all times and shuts
down if an overcurrent condition persists for longer
than a programmable overcurrent timeout. Thermal-
protection circuitry also shuts down all outputs if the die
temperature exceeds +150°C. After an overcurrent or
overtemperature fault condition, the MAX5946L latches
off while the MAX5946A automatically restarts after a
restart time delay.
The power requirement for PCI express connectors is
defined by the PCI express card specification and
summarized in Table 1.
MAX5946
Dual PCI Express, Hot-Plug
Controller
______________________________________________________________________________________ 13
PIN NAME FUNCTION
19 3.3SB- Slot B 3.3V Negative Current-Sense Input. See 3.3SA- function.
20 3.3SB+ Slot B 3.3V Positive Current-Sense Input. Connect the positive side of the current-sense resistor to
3.3SB+ using the Kelvin-sensing technique to assure accurate current sensing.
21 12GB Slot B 12V Gate-Drive Output. See 12GA function.
22 12SB- Slot B 12V Negative Current-Sense Input. See 12SA- function.
23 12SB+ Slot B 12V Positive Current-Sense Input. See 12SA+ function.
24 AUXONB Slot B 3.3V Auxiliary Output Enable. See AUXONA function.
25 ONB Slot B 12V And 3.3V Outputs Enable. See ONA function.
26 FONB Slot B Forced-On Input. See FONA function.
27
PRES-DETB
Slot B Present-Detect Input. See PRES-DETA function.
28 TIM
Overcurrent Timeout Programming Input. Connect a resistor between 500Ω and 500kΩ from TIM to GND
to program tFAULT. Leave TIM floating for a default timeout of 11ms.
29 INPUT2 Digital Logic Gate Input
30 OUTPUT2 Digital Output. 4ms debounced digital output of INPUT2.
31 OUTPUT1 Digital Output. 4ms debounced digital output of INPUT1.
32 INPUT1 Digital Logic Gate Input
33 12VIN 12V Supply Input. V12VIN drives the gates of the MOSFETs connected to 3.3GA and 3.3GB. 12VIN
powers an internal charge pump that drives the gates of the MOSFETs connected to 12GA and 12GB.
34 GND Ground
35 PGND Power Ground. Connect externally to GND.
36 PORADJ Power-On-Reset Programming Input. Connect a resistor between 500Ω and 500kΩ from PORADJ to
GND to program the POR timing. Leave floating for a default value of 160ms.
Pin Description (continued)
MAX5946
Dual PCI Express, Hot-Plug
Controller
14 ______________________________________________________________________________________
5µA
12SA-
12GA
12SA+
54mV 500mV
RSENSE12A -
+
150µA
-
+
50µA
3.3SA-
3.3GA
3.3SA+
20mV 100mV
CONTROL LOGIC
AUX-SLOT A
INPUT COMPARATORS AND CHIP-CONTROL LOGIC
CONTROL LOGIC
MAIN-SLOT A
CHARGE
PUMP
tFAULT
OSCILLATOR
tPOR
OSCILLATOR
RSENSE3.3A -
+
150µA
-
+
10µA
100mA
10µA
VREF
CHARGE
PUMP
-
+
150mA
BIAS
REFERENCES AND UVLO
5µA
12SB-
12GB
12SB+
54mV
500mV RSENSE12B
RTIM RPORADJ
150µA
5µA
3.3SB-
3.3GB
3.3VAUXOB3.3VAUXOA
3.3VAUXIN
ONA
PGND GND
AUXONA FONA PRES-DETA ONB AUXONB FONB PRES-DETB
3.3SB+
20mV
100mV
CONTROL LOGIC
AUX-SLOT B
CONTROL LOGIC
MAIN-SLOT B
CHARGE
PUMP
DEBOUNCE
FAST
OSCILLATOR
150µA
VREF
CHARGE
PUMP
RSENSE3.3B
10µA
100µA
10µA
150µA
-
+
-
+
-
+
-
+
-
+
PWRGDA FAULTA FAULTBTIM
INPUT1
OUTPUT1
INPUT2
OUTPUT2
12VIN
PORADJ PWRGDB
10µA
100mA
10µA
150mA
MAX5946
Figure 1. Functional Diagram
Startup
The main supply outputs can become active only after
all the following events have occurred:
•V
3.3VAUXIN is above its UVLO threshold
•V
12VIN and V3.3SA+ are both above their UVLO
threshold
•ON_ is driven high
•PRES-DET_ is low for more than 4ms
The auxiliary supply output is made available only after
the following events have occurred:
•V
3.3VAUXIN is above its UVLO threshold
•AUXON_ is driven high
•PRES-DET_ is low for more than 4ms
The FON_ input overrides all other control signals and
turns on the respective slot when driven low, as long as
the UVLO thresholds have been reached. Table 2 sum-
marizes the logic conditions required for startup.
The auxiliary supply input powers the internal control
logic and analog references of the MAX5946, so the
main supplies cannot be enabled if V3.3VAUXIN is not
present.
When an output is enabled, a programmable startup
timer (tSU) begins to count the startup time duration.
The value of tSU is set to 2x the fault timeout period
(tFAULT). RTIM externally connected from TIM to GND
sets the duration of tFAULT.
MAX5946
Dual PCI Express, Hot-Plug
Controller
______________________________________________________________________________________ 15
Table 1. Power Requirements for PCI Express Connectors
POWER RAIL X1 CONNECTOR X4/8 CONNECTOR X16 CONNECTOR
3.3V
Voltage Tolerance ±9% (max) ±9% (max) ±9% (max)
Supply Current 3.0A (max) 3.0A (max) 3.0A (max)
Capacitive Load 1000µF (max) 1000µF (max) 1000µF (max)
12V
Voltage Tolerance ±8% (max) ±8% (max) ±8% (max)
Supply Current 0.5A (max) 2.1A (max) 5.5A (max)
Capacitive Load 300µF (max) 1000µF (max) 2000µF (max)
3.3V AUXILIARY
Voltage Tolerance ±9% (max) ±9% (max) ±9% (max)
Supply Current,
Wake Enabled 375mA (max) 375mA (max) 375mA (max)
Supply Current, Non-Wake
Enabled 20mA (max) 20mA (max) 20mA (max)
Capacitive Load 150µF (max) 150µF (max) 150µF (max)
Table 2. Control Logic Truth Table
ON_ AUXON_ FON_ PRES-DET_ 12V_ AND 3.3V_
OUTPUTS
3.3VAUXO_
AUXILIARY
OUTPUTS
XXLow X On On
XXHigh High Off Off
Low Low High Low* Off Off
High Low High Low* On Off
Low High High Low* Off On
High High High Low* On On
*
PRES-DET_
high-to-low transition has a 4ms delay (tDEG).
MAX5946
12V and 3.3V Outputs Normal Operation
The MAX5946 monitors and actively limits the current of
the 12V and 3.3V outputs after the startup period. Each
output has its own overcurrent threshold. If any of the
monitored output currents rise above the overcurrent
threshold for a period tFAULT, FAULT_ asserts and the
controller disengages both the 12V and 3.3V outputs for
the particular slot (see the Fault Management section).
3.3V Auxiliary Output Normal Operation
The auxiliary output current is internally monitored and
actively limited to the maximum current-limit value. An
overcurrent fault condition occurs when the output
current exceeds the overcurrent threshold for longer
then tFAULT. A fault on an auxiliary channel causes all
supplies of the affected channel to be disabled after a
programmable time period tFAULT (see the Fault
Management section).
Power-Good (
PPWWRRGGDD__
)
Power-good (PWRGD_) is an open-drain output that
pulls low a time (tPOR_HL) after all of the outputs of the
respective slot are fully on. All outputs are considered
fully on when 3.3G_ has risen to VPGTH3.3, 12G_ has
risen to VPGTH12, and V3.3AUXO_is less then
VPGTH3.3AUX. tPOR_HL is adjustable from 2.5ms to
1.5s by connecting a resistor from PORADJ to GND.
See the Setting the Power-On-Reset Timeout Period
(tPOR)section.
Thermal Shutdown
When the die temperature goes above (TSD) +150°C, an
overtemperature fault occurs and the MAX5946 shuts
down all outputs. The device waits for the junction temper-
ature to decrease below TSD - Hysteresis before entering
fault management (see the Fault Management section).
Dual PCI Express, Hot-Plug
Controller
16 ______________________________________________________________________________________
VON_,TH
ON_, AUXON_
PWRGD_
FAULT_
12G_, 3.3G_
12VO_, 3.3VO_
3.3VAUXO_
VPGTH12
VPGTH3.3
VPGTH3.3AUX
3.3AUXIN
RISING
EDGE
PWRGD_ IS PULLED UP TO 3.3.
FAULT_ IS PULLED UP TO 3.3AUXIN.
tPOR_HL
Figure 2. Power-Up Timing, No Fault
FAULT_
3.3VAUXIN
RISING
EDGE
PWRGD_ IS PULLED UP TO 3.3VAUXO_.
FAULT_ IS PULLED UP TO 3.3VAUXIN.
A FAULT ON THE 3.3V OUTPUT OR 3.3VAUXO_ OUTPUT PRODUCES SIMILAR RESULTS.
VON_,TH
ON_
2 x tFAULT
PWRGD_
12G_
12V OUTPUT
CURRENT
3.3VAUXO_
V12ILIM,TH
RSENSE
Figure 3. 12V Power-Up Timing (Turn-On into Output
Overcurrent/Short Circuit)
FAULT_
PWRGD_ IS PULLED UP TO 3.3VAUXO_.
FAULT_ IS PULLED UP TO 3.3VAUXIN.
A FAULT ON THE 3.3V OUTPUT OR 3.3VAUXO_ OUTPUT PRODUCES SIMILAR RESULTS.
tFAULT
PWRGD_
12G_
12V OUTPUT
CURRENT
V12ILIM,TH
RSENSE
Figure 4. 12 Output Overcurrent/Short Circuit During Normal
Operation
FAULT Management
A fault occurs when an overcurrent lasts longer then
tFAULT or when the device experiences an overtemper-
ature condition.
•A fault on a main output (12V or 3.3V) shuts down
both main outputs of the respective slot. The 3.3V
auxiliary is not affected.
•A fault on the 3.3V auxiliary output shuts down all
three outputs of the respective slot.
The MAX5946A automatically restarts from a fault shut-
down after the tRESTART period, while the MAX5946L
latches off. If an overcurrent fault occurred on a main
output, bring ON_ low for at least tRESET (100µs) and
high again to reset the fault and restart the outputs. If
the overcurrent fault occurred on an auxiliary output or
an overtemperature fault occurred, bring both ON_ and
AUXON_ low for a minimum of tRESET to reset the fault.
Bring ON_ and/or AUXON_ high again to restart the
respective outputs. As an extra protection, the
MAX5946L waits a minimum of tRESTART before it can
be restarted.
Debounced Logic Gate
(Input_ and Output_)
INPUT1 and INPUT2 accept inputs from mechanical
switches. The corresponding outputs are OUTPUT1
and OUTPUT2. OUTPUT_ is debounced for 4ms. When
INPUT_ goes from high to low, OUTPUT_ goes low right
away and stays low for at least 4ms. After the
debounce time OUTPUT_ follows INPUT_. If INPUT_
goes from low to high, OUTPUT_ goes high right away
and stays high for at least 4ms. After the debounce
time, OUTPUT_ follows INPUT_. Figure 5 shows the tim-
ing diagram describing the INPUT_/OUTPUT_
debounced feature.
Present-Detect and Forced-On Inputs
(
PPRREESS--DDEETT__,, FFOONN__
)
PRES-DETA and PRES-DETB inputs detect the
PRSNT#2 pin on a PCI express connector. When the
card is plugged in, PRES-DET_ goes low and allows
the turn-on of the outputs of the respective slot after a
4ms debounced time. When the card is removed, an
internal 50kΩpullup forces PRES-DET_ high and the
respective slot is shut down with no delay. PRES-DET_
works in conjunction with ON_ and VAUXON_ and only
enables the device when ON_ and VAUXON_ are high.
A logic-low on FON_ forces the respective slot (main
supplies and auxiliary) to turn on regardless of the sta-
tus of the other logic inputs provided the UVLO thresh-
olds are exceeded on all of the inputs.
Active Current Limits
Active current limits are provided for all three outputs of
slot A and slot B. Connect a current-sense resistor
between 12S_+ and 12S_- to set the current limit for the
12V outputs. The current limit is set to 54mV/RSENSE12.
RSENSE12 is either R1 or R3 in the Typical Application
Circuit. Connect a current-sense resistor between
3.3S_+ and 3.3S_- to set the current limit for the 3.3V
main outputs to 20mV/RSENSE3.3. RSENSE3.3 is either R2
or R4 in the Typical Application Circuit. For the auxiliary
output (3.3VAUXO_) the current limit is fixed at 470mA.
When the voltage across RSENSE12 or RSENSE3.3
reaches the current-limit threshold voltage, the
MAX5946 regulates the gate voltage to maintain the
current-limit threshold voltage across the sense resis-
tor. If the current limit lasts for tFAULT then an overcur-
rent fault occurs. The MAX5946_ shuts down both the
12V and 3.3V outputs and asserts the FAULT_ output of
the respective slot.
When the auxiliary output reaches the current limit
(470mA) for longer then tFAULT, a fault occurs and the
device shuts down all outputs and asserts FAULT of the
respective slot.
Undervoltage Lockout Threshold
The UVLO thresholds prevent the internal auxiliary
MOSFETs and the external main channel MOSFETs
(Q1–Q4 in the Typical Application Circuit) from turning
on if V12VIN, V3.3VIN, and V3.3VAUXIN are not present.
Internal comparators monitor the main supplies and the
auxiliary supply and keep the gate-drive outputs
(12GA, 12GB, 3.3GA, and 3.3GB) low until the supplies
rise above their UVLO threshold. The 12V main supply
is monitored at 12VIN and has a UVLO threshold of
10V. The 3.3V main supply is monitored at 3.3SA+ and
has a UVLO threshold of 2.65V. The auxiliary supply is
monitored at 3.3VAUXIN and has a 2.65V UVLO thresh-
old. For either main channel to operate, V3.3VAUXIN
must be above its UVLO threshold.
MAX5946
Dual PCI Express, Hot-Plug
Controller
______________________________________________________________________________________ 17
INPUT
DEBOUNCED
OUTPUT
tDBC tDBC tDBC
Figure 5. INPUT_ and OUTPUT_ Debounced Feature
MAX5946
Dual PCI Express, Hot-Plug
Controller
18 ______________________________________________________________________________________
N
Y
POWER-ON MAIN
SUPPLIES FAULT
AND PWRGD ARE
HIGH IMPEDANCE
N
ENABLE CHARGE ON
12G_ AND 3.3G_
PINS. START
COUNTING tSU
HAS tSU
ELAPSED?
N
POWER-ON AUXILIARY
SUPPLIES FAULT
AND PWRGD ARE
HIGH IMPEDANCE
N
ENABLE CHARGE ON
INTERNAL AUXILIARY
MOSFET, BEGIN
COUNTING tSU
HAS tSU ELAPSED?
N
Y
N
Y
Y
ARE PWRGD
THRESHOLDS
REACHED?
ASSERT
PWRGD_
AFTER tPOR_HL DELAY
12V AND 3.3V
OUTPUTS
ARE ENABLED
WAS CURRENT
LIMIT DETECTED ON ANY
12V OR
3.3V OUTPUT?
START COUNTING
tFAULT
HAS tFAULT
ELAPSED?
N
Y
RESET tFAULT
COUNTER
Y
SHUT DOWN
12V AND 3.3V OUTPUTS.
ASSERT FAULT_
STAY WAITING FOR
tRESTART
LATCH-OFF
OPTION?
Y
STAY WAITING FOR
ON_ TRANSITION
HIGH->LOW->HIGH
AUX SUPPLY OUTPUT
IS ENABLED
WAS CURRENT LIMIT
DETECTED ON AUXILIARY
OUTPUT?
IS tFAULT
ELAPSED?
NN
Y
Y
SHUT DOWN
ALL OUTPUTS,
ASSERT FAULT_,
STAY WAITING FOR
tRESTART ELAPSED.
LATCH-OFF
OPTION?
Y
RESET FAULT_
AND
RESTART ALL SUPPLIES
STAY WAITING FOR BOTH
ON_ AND AUXON_
TRANSITION
HIGH->LOW->HIGH
RESET FAULT_
AND
RESTART 12V, 3.3V
SUPPLIES
IS FAULT STILL
PRESENT? Y
N
IS FAULT STILL
PRESENT?
N
START COUNTING
tFAULT
RESET tFAULT
COUNTER
RESET
PWRGD_
AFTER tPOR_LH DELAY
3.3AUXIN IS ON
AND ABOVE UVLO
Figure 6. Fault Management Flow Chart
External MOSFET Gate Drivers
(12GA, 12GB, 3.3GA, and 3.3GB)
The gate drive for the external MOSFETs is provided at
12GA, 12GB, 3.3GA, and 3.3GB. 12G_ is the gate drive
for the 12V main supply and is boosted to 5.3V above
V12VIN by an internal charge pump. During turn-on,
12G_ sources 5µA into the external gate capacitance to
control the turn-on time of the external MOSFET. During
turn-off, 12G_ sinks 150µA from the external gate
capacitance to quickly turn off the external MOSFET.
During short-circuit events, an internal 100mA current
activates to rapidly bring the load current into the regu-
lation limits.
3.3G_ is the gate drive for the 3.3V main supply’s
MOSFET and is driven to 5.5V above the 3.3V main sup-
ply. The power for 3.3G_ is supplied from 12VIN and
has no internal charge pump. During turn-on, 3.3G_
sources 5µA into the external gate capacitance to con-
trol the turn-on time of the external MOSFET. During
turn-off, 3.3G_ sinks 150µA to quickly turn off the exter-
nal MOSFET. During short-circuit events, an internal
150mA current activates to rapidly turn off the appropri-
ate external MOSFET.
Auxiliary Supply (3.3VAUXIN)
3.3VAUXIN provides power to the auxiliary outputs as
well as the internal logic and references. The drains of
the internal auxiliary MOSFETs connect to 3.3VAUXIN
through internal sense resistors and the sources con-
nect to the auxiliary outputs (3.3VAUXOA and
3.3VAUXOB). Both MOSFETs have typical on-resistance
of 0.3Ω. An internal charge pump boosts the gate-drive
voltage to fully turn on the internal n-channel MOSFETs.
The auxiliary supplies have an internal current limit set
to 470mA.
Applications Information
Setting the Fault Timeout Period (tFAULT)
tFAULT is the time an overcurrent or overtemperature
fault must remain for the MAX5946 to disable the main
or auxiliary channels of a particular slot. Program the
fault timeout period (tFAULT) by connecting a resistor
(RTIM) from TIM to GND. tFAULT can be calculated by
the following equation:
tFAULT = 166ns / Ωx RTIM
The tFAULT programmed time duration must be chosen
according to the total capacitance load connected to
the 12G_ and 3.3G_ pins. To properly power-up the
main supply outputs, the following constraints need to
be taken:
where tSU = 2 x tFAULT and where
1) ICHG = 5µA.
2) VGATE = 18.4V for 12G_ and VGATE = 9.4V for
3.3G_.
3) CLOAD is the total capacitance load at the gate.
Maximum and minimum values for RTIM are 500Ωand
500kΩ, respectively. Leave TIM floating for a default
tFAULT of 11ms.
Setting the Power-On-Reset
Timeout Period (tPOR_HL)
tPOR_HL is the time from when the gate voltages of all
outputs of a slot reach their power-good threshold to
when PWRGD_ pulls low. Program the power-on-reset
timeout period (tPOR) by connecting a resistor (RPO-
RADJ) from PORADJ to GND. tPOR_HL can be calculat-
ed by the following equation:
tPOR_HL = 2.5µs / Ωx RPORADJ
Maximum and minimum values for RPORADJ are 500Ω
and 500kΩ, respectively. Leave PORADJ floating for a
default tPOR of 160ms.
Component Selection
Select the external n-channel MOSFET according to the
applications current requirement. Limit the switch
power dissipation by choosing a MOSFET with an
RDS_ON low enough to have a minimum voltage drop at
full load. High RDS_ON causes larger output ripple if
there are pulsed loads. High RDS_ON can also trigger
an external undervoltage fault at full load. Determine
the MOSFETs power rating requirement to accommo-
date a short-circuit condition on the board during start-
up. Table 3 lists MOSFETs and sense resistor
manufacturers.
Additional External Gate
External capacitance can be added from the gate of
the external MOSFETs to GND to slow down the dV/dt
of the 12V and 3.3V outputs.
Maximum Load Capacitance
Large capacitive loads at the 12V output, the 3.3V out-
put, and the 3.3V auxiliary output can cause a problem
when inserting discharged PCI cards into live back-
planes. A fault occurs if the time needed to charge the
capacitance of the board is greater than the typical
startup time (2 x tFAULT). The MAX5946 can withstand
tVC
I
SU GATE LOAD
CHG
≥×
MAX5946
Dual PCI Express, Hot-Plug
Controller
______________________________________________________________________________________ 19
MAX5946
large capacitive loads due to their adjustable startup
times and adjustable current-limit thresholds. Calculate
the maximum load capacitance as follows:
VOUT is either the 3.3V output, the 12V output, or the
3.3V auxiliary output for slot A or slot B.
Input Transients
The 12V input (12VIN), the 3.3V input (3.3SA+), and the
3.3V auxiliary (3.3VAUXIN) must be above their UVLO
thresholds before startup can occur. Input transients
can cause the input voltage to sag below the UVLO
threshold. The MAX5496 rejects transients on the input
supplies that are shorter than 4µs typical.
Chip Information
TRANSISTOR COUNT: 10,487
PROCESS: BiCMOS
CtI
V
LOAD SU LIM
OUT
<×
Dual PCI Express, Hot-Plug
Controller
20 ______________________________________________________________________________________
Table 3. Component Manufacturers
COMPONENT MANUFACTURER PHONE WEBSITE
Vishay-Dale 402-564-3131 www.vishay.com
Sense Resistor IRC 704-264-8861 www.irctt.com
Fairchild 888-522-5372 www.fairchildsemi.com
International Rectifier 310-322-3331 www.irf.com
Motorola 602-244-3576 www.mot-sps.com/ppd/
MOSFETs
Vishay-Siliconix — www.vishay.com
MAX5946
Dual PCI Express, Hot-Plug
Controller
______________________________________________________________________________________ 21
MAX5946
Q1
SI7448DP-T1
Q3
SI7448DP-T1
PWRGDA
12GA
12SA-
12SA+
3.3VAUXIN
12VIN
112SB-
12SB+
12GB
3.3VAUXOA
GND
PWRGDB
3.3VAUXOB
PORADJ
10kΩ
PRSNT1
+12V
GND
PWRGD
3.3VAUX
+3.3V
PRSNT2
PRSNT1
+12V
GND
PWRGD
3.3VAUX
+3.3V
PRSNT2
V3.3AUXIN
RPORADJ = OPEN
V3.3AUXIN
R1
8mΩ
R3
8mΩ
R2
5mΩ
10kΩ
R4
5mΩ
0.1µF
0.1µF
10kΩ
Q2
SI7448DP-T1
Q4
SI7448DP-T1
3.3GA
3.3SA-
3.3SA+
AUXONA / AUXONB
ONA / ONB
INPUT1 / INPUT2
OUTPUT1 / OUTPUT2
3.3SB+
TIM
3.3SB-
3.3GB
3.3V INPUT
MAX7313ATG
16-BIT I/O EXPANDER
MRL
ATTENTION
SWITCHES
LED's LED's
SMBus INTAO-2
2
2
RTM =
OPEN
PRES-DETA
PRES-DETB
FAULTA / FAULTB
FONA / FONB
2 2 2 2
2 2
3
2
PCI EXPRESS
SLOT A
PCI EXPRESS
SLOT B
ADD-IN
CARD
IN5819
V12VIN
MRL
1µF
Typical Application Circuit
MAX5946
Dual PCI Express, Hot-Plug
Controller
22 ______________________________________________________________________________________
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
36L,40L, QFN.EPS
MAX5946
Dual PCI Express, Hot-Plug
Controller
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 23
©2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
U