ltc4350 Linear Technology Corporation, ltc4350 Datasheet - Page 8

• Manufacturer Part Number: ltc4350
• Description: Hot Swappable Load Share Controller
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
LTC4350
drives the SB pin (or share bus). If the FB pin is above the
reference, the COMP1 pin is grounded and the SB pin is
disconnected from the COMP1 pin using the series diode.
The LTC4350 with the highest reference will drive the SB
pin and the 20k loads connected to the SB pin. All of the
other LTC4350’s COMP1 pins are pulled low because their
FB pins are at a higher voltage than their references. The
series diode between the COMP1 pin and the SB pin is
actually a low impedance buffer amplifier with a diode in
the output stage. Therefore, the master LTC4350’s E/A1
drives the share bus to the proper value that keeps the
output voltage tightly regulated. The buffer amplifier is
capable of driving at least fifty 20k loads (each 20k load
represents an LTC4350).
OUTPUT VOLTAGE ADJUSTMENT
The LTC4350 is designed to work with supplies featuring
remote sense. The output voltage of each power supply
needs to be adjusted below the final output voltage at the
8
OUT
+
THE POWER SUPPLY CURRENT
THIS VOLTAGE REPRESENTS
MEASURED USING A SENSE
SUPPLY AND TO HOT-SWAP A
DISCONNECT A BAD POWER
C
G
DRIVE
PASS-FET USED TO
GATE
POWER SUPPLY
U
RESISTOR
U
3
+
1
R
I
SENSE
SENSE
R
GAIN
g
2
–
W
m
4
= 1m
Ω
Figure 3. Simplified Block Diagram
REF
FB PIN
U
–
+
+
–
E/A1
E/A2
COMP1 PIN
COMP2 PIN
THIS AMPLIFIER FORCES THE POWER
SUPPLY CURRENT TO EQUAL THE
REFERENCE CURRENT VALUE
(i.e., SHARE BUS)
NEEDED TO FORCE THE OUTPUT
THIS VOLTAGE REPRESENTS
VOLTAGE TO EQUAL THE REF
THE REFERENCE CURRENT
common load. For example, a 5V system would require the
power supply output be set to 4.90V or some value below
5V. This is normally done using the trim pin of the module.
The power supply output is then increased by artificially
reducing the positive sense voltage by a small amount.
The LTC4350 would then adjust the output voltage to 5V,
an increase of 2%. The maximum range of adjustment can
be set from 2% to 5% to compensate for voltage drops in
the wiring, but no more than 300mV.
In most power supplies, the voltage sense is tied directly
to the output voltage. If a small valued resistor, R
placed in series with the power supply sense line, a voltage
drop across R
requires the power supply to increase its output voltage to
compensate. Thus, the LTC4350 exercises complete con-
trol of the final output voltage.
The I
a current that flows through R
voltage at COMP2 increases, the current in R
VALUE (i.e., SHARE BUS)
OUT
block converts the E/A2 output (COMP2 pin) to
+
–
20k
I
OUT
OUT
SENSE
SHARE BUS
appears as a lower sensed voltage. This
+
I
OUT
PIN
R
–
R
SET
4350 F03
SET
THIS AMPLIFIER CONVERTS
THE E/A2 VOLTAGE OUTPUT TO
A CURRENT OUTPUT (I
R
OUT
PIN
THIS RESISTOR CONVERTS I
TO A VOLTAGE TO MODIFY THE
REMOTE SENSE INPUT OF THE
POWER SUPPLY (SENSE
CREATES AN ARTIFICIAL
SENSE
ADJUSTS THE POWER
SUPPLY’S OUTPUT VOLTAGE
UP OR DOWN
+
OUT
I
ADJ
+
(see Figure 3). As the
VOLTAGE THAT
LOAD
ADJ
)
+
). IT
ADJ
OUT
4350fa
OUT
, is