adm1075-2aruz-rl7 Analog Devices, Inc., adm1075-2aruz-rl7 Datasheet - Page 20

• Manufacturer Part Number: adm1075-2aruz-rl7
• Description: −48 V Hot Swap Controller And Digital Power Monitor With Pmbus Interface
• Manufacturer: Analog Devices, Inc.

ADM1075
THEORY OF OPERATION
When circuit boards are inserted into a live backplane,
discharged supply bypass capacitors draw large transient
currents from the backplane power bus as they charge. Such
transient currents can cause permanent damage to connector
pins, as well as dips on the backplane supply that can reset other
boards in the system.
The
of a board in a controlled manner, allowing the board to be
removed from, or inserted into, a live backplane by protecting it
from excess currents. The
backplane or on the removable board.
A minimal load current requirement is assumed when charging
the load capacitance. If the load current is too large relative to
the regulation current, it may not be possible to charge the load
capacitance. The PWRGD pin can be used to disable the load
until the load capacitance is fully charged.
POWERING THE ADM1075
The
−35 V to −80 V and can tolerate transient voltages of up to
−200 V. The VIN pin is a positive supply pin with respect to
chip ground. It is a current-driven supply and is shunt regulated
to 12 V internally. It should be connected to the most positive
supply terminal (usually −48 V RTN or 0 V) through a dropper
resistor. The resistor should be chosen such that it always
supplies enough current to overcome the maximum quiescent
supply current of the chip while not exceeding the maximum
allowable shunt current. After the system supply range has been
established, an appropriate value for the dropper resistor can be
calculated.
where:
V
80 V).
V
sheet specifications (see Table 1).
I
shunt current).
I
I
temperature (T
temperature (T
from Table 4. Worst-case internal power is at VIN
Table 1.
SHUNT_MIN
SHUNT_MAX
SHUNT_MAX
IN_MIN
SHUNT_MIN
ADM1075
ADM1075
R
R
I
SHUNT
SHUNT
SHUNT
and V
is the maximum quiescent supply current (minimum
is the maximum shunt input current.
can be calculated based on the maximum ambient
and V
_
_
_
MAX
MIN
MAX
IN_MAX
J(MAX)
A(MAX)
is intended to control the powering on and off
typically operates from a negative supply of
SHUNT_MAX



T
V
are the supply voltage extremes (that is, 35 V,
V

) in the application, the maximum junction
= 105°C), and the θ
J
IN
IN
(
JA
MAX
_
_

MAX
MIN
I
VIN
I
)
SHUNT
are the shunt regulator voltage data
ADM1075
SHUNT



T
A
(
V
V
MAX
(
_
SHUNT
MAX
SHUNT
_
MAX
MIN
)
)
_
_
can reside either on the
MIN
MAX
JA
value of the package
(MAX)
from
Rev. 0 | Page 20 of 52
For example, the maximum shunt current with a TSSOP device
at 80°C maximum ambient can be calculated as
Tolerance of supplies and resistors should also be accounted for
to ensure that the shunt current is always within the desired range.
Care must be taken to ensure that the power rating of the shunt
resistor is sufficient. The power may be as high as 2 W at
extreme supply conditions. Multiple shunt resistors can be used
in series or in parallel to share power between resistors.
where:
The power dissipation in the shunt resistor can be saved if a
suitable voltage rail is available to power the chip directly. This
voltage rail must be well regulated to ensure that it is always
greater than the UVLO threshold but less than the minimum
shunt regulation voltage. The power directly without shunt
specification in Table 1 shows the limits this voltage rail must
meet. Note that this voltage is referenced to VEE.
The VIN pin provides the majority of the bias current for the
device. The remainder of the current needed to control the gate
drive and to best regulate the V
SENSE± pins. The VEE and SENSE− pins are connected to the
same voltage rail, although through separate traces to prevent
accuracy loss in the sense voltage measurement (see Figure 41).
The available shunt current range should be wide enough to
accommodate most telecommunication input voltage ranges.
In an application where a wider input voltage range is possible,
some external circuitry may be required to meet the shunt
regulation current specifications. The applications diagram in
Figure 42 shows an example of such a circuit, using a Zener
diode and a bipolar junction transistor (BJT) device as an
external pre-regulator on the −48 V supply. This ensures that
the shunt regulation current is always within specification even
at the extremes of supply voltage.
I
P
I
SHUNT
MAX
R
_
SHUNT
1µF

–48V RTN
VEE
_
MAX
V
IN

VI
_

MAX
Figure 41. Powering the ADM1075
68

105
R
VIN
R
(


SHUNT
V
SHUNT
ADM1075
C/W
V

IN
C
SHUNT
_

VEE
MAX

80
13
_


MIN
GS
C
V
V
voltage is supplied by the
SHUNT

28
GATE
SENSE+
SENSE–
_
mA
MIN
C
LOAD
)

Data Sheet
I
MAX
Q1
R
SENSE