Datasheet

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 V
3.3SA+
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 V
3.3VAUXIN
is not
present.
When an output is enabled, a programmable startup
timer (t
SU
) begins to count the startup time duration.
The value of t
SU
is set to 2x the fault timeout period
(t
FAULT
). R
TIM
externally connected from TIM to GND
sets the duration of t
FAULT
.
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 (t
DEG
).