LTC4350IGN Linear Technology, LTC4350IGN Datasheet - Page 13

• Manufacturer Part Number: LTC4350IGN
• Description: IC CNTRLR HOTSWAP LOADSHAR16SSOP
• Manufacturer: Linear Technology
• Type: Hot-Swap Controllerr

Specifications of LTC4350IGN

• Applications: General Purpose
• Internal Switch(s): No
• Voltage - Supply: 17V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-SSOP (0.150", 3.90mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

applicaTions inForMaTion
The resistors R
The voltage on R
by the ratio of R
the output voltage will track the voltage at the R
which is also the voltage on the COMP2 pin minus a diode
voltage. The expression is V
(V
V
output is expressed as V
value for R
If we set R
the output voltage a full 1V adjustment. For the 0.3V range
in this example, the R
there already exists a resistor between the SENSE
and the power output. In this case, the value of R
parallel combination of two resistors, one in the module
and one placed between the SENSE
of the module.
The value of the gain setting resistor, R
the maximum voltage drop across the sense resistor and
the supply voltage V
voltage at the GAIN pin is 1.5V from the V
The maximum voltage on the GAIN pin is expressed as:
V
expression for R
I
is 0.002Ω. Therefore, R
results in 86.6k.
The FB pin divider provides a 1.220V output for a 5V
input. The precision of the FB pin divider resistors will
impact the accuracy of the final output voltage. The UV
resistive divider in this example, turns on the gate when
V
1.220V. The capacitor C
load steps. The OV set point needs to occur above the
adjustment max for V
also is V
to 5.3V. The OV set point in this example is 5.5V on V
when the OV pin is at 1.220V.
The timer capacitor C
timer cycle. The expression is t = C
gate capacitor C
MAX
RSET
GAINMAX
CC
COMP2
increases above 4V. This corresponds to the UV pin at
). In this example, V
is limited to 1V. The maximum adjustment on the
CC
– V
= R
SET
), can start as high as 5V and adjust upwards
SET
DIODE
SENSE
to be 100Ω, then an R
is in the 50Ω to 100Ω range.
OUT
GAIN
G
OUT
) • R
SET
is set to be 0.1µF which sets a slope
and R
CC
• I
/R
: R
OUT
CC
is translated to a voltage on R
OUT
MAX
SET
T
UV
for the chip. The highest possible
GAIN
GAIN
. The power supply output (which
CC
is 30Ω. In some power modules,
is set to be 0.1µF for a 61ms
/R
ADJMAX
. Therefore, the adjustment on
prevents false activation during
SET
• R
is 5V, I
SET
= (V
is 87.5k but using 1% values
ADJ
set the adjustment range.
GAIN
. The maximum voltage at
CC
= (V
= R
MAX
/1k = V
+
– 1.5V) • 1k/(R
and output terminals
RSET
OUT
OUT
T
is 20A and R
• 1.22V/2µA. The
GAIN,
/R
) • R
of 100Ω allows
CC
SET
depends on
– 1.5V. The
CC
OUT
. A normal
OUT
voltage.
/R
SET
SENSE
SENSE
+
is the
SET
OUT
line
pin
CC
=
•
of 10µA/C
must charge up to 9V before the output can ramp to 5V
which happens in 90ms. In this case, the output adjust
soft-start turns on when the gate ramps above 9V. The
soft-start circuitry releases the COMP2 pin allowing the
load sharing loop to function. A 100Ω resistor R
high frequency oscillations from the power FETs at their
turn-on threshold. A 0.1µF bypass capacitor is required on
the V
ply output that is being adjusted, then a 51Ω decoupling
resistor is needed to hold up the supply during a short to
ground on the supply output.
COMPENSATION
The compensation capacitor, C
crossover frequency of the feedback error amplifier E/A1.
The crossover frequency of 200kHz is adequate for most
applications and requires C
The design of the other compensation capacitor will require
some knowledge about the power supply’s bandwidth. The
bandwidth can be measured easily. First, use a storage
oscilloscope to monitor the power supply output voltage.
Then place a 1A resistive fixed load and switch in a second
resistive load that increases the total load current close
to rated maximum. Tapping the second resistor (with
the correct power rating) to the power supply output
creates this load step. Trigger the scope on the falling
edge of the output voltage as it drops more than 100mV
(for example from 5V to 4.8V). The recovery time, t
from the step needs to be measured. t
the 10% to 90% time measurement (see Figure 6). The
CC
pin. If the V
G
or 1V every 10ms. In this case, the GATE pin
90%
10%
Figure 6. t
CC
pin is tied to the same power sup-
R
t
P1
r
Measurement
t
to be 1000pF (0.001µF).
P1
, is needed to set the
0.1∆V
0.1∆V
LTC4350
R
is defined as
4350 F06
∆V
G
prevents

4350fb
R
,