adm1075-2aruz-rl7 Analog Devices, Inc., adm1075-2aruz-rl7 Datasheet - Page 21

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

Data Sheet
CURRENT SENSE INPUTS
The load current is monitored by measuring the voltage drop
across an external sense resistor, R
sense amplifier provides a gain of 25 or 50 (depending on the
model) to the voltage drop detected across R
compared to an internal reference and detects when an
overcurrent condition occurs.
The SENSE± inputs can be connected to multiple parallel sense
resistors, which can affect the voltage drop detected by the
ADM1075. The current flowing through the sense resistors
creates an offset, resulting in reduced accuracy. To achieve
better accuracy, averaging resistors should be used to sum the
sense nodes of each sense resistor, as shown in Figure 44. The
typical value for the averaging resistors is 10 Ω. The value of the
averaging resistors is chosen to be much greater than the trace
resistance between the sense resistor terminals and the inputs to
the ADM1075. This greatly reduces the effects of differences in
the trace resistances.
–48V RTN
–48V
18V
TO
75V
C
IN
OVER-
CURRENT
ADM1075
11V
Ib = 6µA TO 33µA
Rb1 = 100kΩ
Figure 43. Hot-Swap Current Sense Amplifier
1µF
Figure 42. Wide Input Supply Range
VIN
VEE
+
–
1V REF
VEE
×25/50
10.3V (5.5mA TO 10mA)
Rb2 = 640Ω
VIN
R
ADM1075
DROP
–
SENSE
VEE
= 15Ω
GATE
SENSE+
SENSE–
. An internal current
SENSE
Q1
R
GATE
SENSE+
SENSE–
SENSE
. The result is
C
LOAD
Q
R
1
SENSE
Rev. 0 | Page 21 of 52
CURRENT LIMIT REFERENCE
The current limit reference voltage determines the load current
level to which the
overcurrent event. This is the reference voltage to which the
gained up current sense voltage is compared to determine if the
limit is reached. This current limit voltage, shown in Figure 45,
is then converted to a gate current to regulate the GATE pin.
where g
An internal current limit reference selector block continuously
compares the ISET, soft start, and foldback (derived from PLIM)
voltages, determines which is the lowest at any given time, and
uses it as the current limit reference. This ensures that the
programmed current limit, ISET, is used in normal operation
and the soft start and foldback features reduce the current limit
when required.
The foldback and soft start voltages change during different
stages of operation and are clamped to a lower level of 100 mV
(typical) to prevent zero current flow due to the current limit
being too low.
ISET
Figure 44. Connection of Multiple Sense Resistors to SENSE± Pins
I
GATE
m
, the gate transconductance, = 660 μs.
=
VCAP
ADM1075
V
ADM1075
Figure 45. Current Limit Reference Selection
CURR
SS
10µA
CURRENT
LIMIT
SELECT
ADM1075
REF
1.0V
VIN
_
LIM
×
g
VEE
CURRENT
m
CURRENT
VOLTAGE
CURRENT
CONTROL
BIAS
LIMIT
LIMIT
limits the current during an
VEE
–
LOGIC
DRIVE
GATE
+
TIMEOUT
SENSE+
SENSE–
GATE
FLB
( = 0.1/PLIM)
×25/50
+
–
Q1
ADM1075
PLIM
GATE
SENSE+
SENSE–