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Shelf Manager ACB-VI
Fan Control
15
R1.2, March 2018
9 Fan Control
The Shelf Manager provides fan control functionality through the ADT7490 fan controllers.
The fan speed is controlled by a PWM signal generated on the ADT7490 0x2E. The PWM
output from the ADT7490 is buffered and enabled by the Carrier_Active signal so that only
the active Shelf Manager controls the fan speed. The PWM signal is opto-isolated and routed
to the backplane connector.
For voltage-regulated Fans the Shelf Manager provides an integrator that converts the PWM
signal into a DC-voltage of 0 V to 10 V, referenced to the ground level of the Fan Tray
electronics (FAN_24V_RTN), which is also available on the backplane connector.
The tachometer signals from the Fans are routed through the backplane connector to the
opto-isolated tachometer inputs of the 3 ADT7490.
Three digital inputs to the PCA9555 (I/O 1.0....I/O 1.2) are used to detect presence of the Fan
Trays. The Fan Tray grounds the signal to indicate that it is installed.
The Shelf Manager’s fan tachometer inputs and fan control outputs (DC, PWM) are optically
isolated from primary voltages of the fans. The primary side of the opto couplers is powered
by a 24 V voltage (FAN_24V) which is generated on the Fan Trays and routed together with
the Fan Tray ground reference (FAN _24V_RTN) to the Shelf Manager.
Figure 13: Shelf Manager Fan Control Block Diagram
ADT7490
0x2C
Fan 1...3 Tachometer
20 V Power Supply
for Opto-couplers
24 VDC generated on Fan Trays
Fan Tray Ground reference
(FAN_24V_RTN)
PWM Fan Control Signal
0....10 V DC Fan Control Signal
local I²C-Bus
VRTN_B
-48V_A
VRTN_A
Fan_Tach
48 V
Backplane Connector
FAN_24V
FAN_24V_RTN
24 V
-48V_B
/
3
Backplane Connector
/
3
ADT7490
0x2D
Fan 4...6 Tachometer
Fan_Tach
/
3
/
3
ADT7490
0x2E
Fan 7...9 Tachometer
Fan_Tach
/
3
/
3
PWM Contr. Fans
Volt. Contr. Fans
from Fan Tray 2
from Fan Tray 3
Fan Tray 1
PWM
PCA9555
0x25
Fan Tray 2
Fan Tray 3