ltc4350 Linear Technology Corporation, ltc4350 Datasheet - Page 7

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

APPLICATIO S I FOR ATIO
INTRODUCTION
Many system designers find it economically feasible to
parallel power supplies to achieve redundancy. The sec-
ond trend is providing some load sharing between the
many supplies. In some cases, a failure in any one supply
will trigger a sequence that disconnects the faulty supply
and sends a flag to the system. Then, a service technician
will swap in a good supply. For systems that are continu-
ously powered, there is Hot Swap circuitry to prevent
glitches on the power buses when power cards are
swapped. A block diagram of this system is shown in
Figure 1.
By combining the features of a load share and a Hot Swap
controller into one IC, the LTC4350 simplifies the design
of redundant power supplies. A complete redundant power
supply is a combination of a power module and the
LTC4350 as shown in Figure 2. Note that the power
LOAD
OUTPUT BUS
OUTPUT
SHARE BUS
INPUT BUS
BUS
Figure 1. Redundant Power Card System
SHARE
Figure 2. Redundant Power Supply
BUS
INPUT
BUS
U
CONNECTOR
CONNECTOR
MODULE
POWER
SENSE
SENSE
OUT
OUT
U
+
+
–
–
SWAP
SWAP
HOT
HOT
W
LTC4350
SHARE
SHARE
LOAD
LOAD
U
4350 F02
SUPPLY
SUPPLY
POWER
POWER
4350 F01
module must have accessible feedback network or a
remote sensing pin (SENSE
The LTC4350 provides a means for paralleling power
supplies. It also provides for load sharing, fault isolation
and power supply hot insertion and removal. The power
supply current is accurately measured and then compared
to a share bus signal. The power supply’s output voltage
is adjusted until the load current matches the share bus,
which results in load sharing. There are two optional
power FETs in series with the load that provide a quick
disconnect between a load and a failed power supply.
These same power FETs allow a power supply to be
connected into a powered backplane in a controlled man-
ner or removed without disruption.
CURRENT SHARING
The current sharing components will now be discussed.
Figure 3 shows a simplified block diagram of these com-
ponents. The I
current by amplifying the voltage drop across the sense
resistor. An external resistor on the GAIN pin determines
the gain of the I
sense resistor is divided by a precision 1k resistor to
produce a current at the GAIN pin. For example, a 10mV
sense voltage translates to a 10µA current. If a 10k resistor
is on the GAIN pin, then the voltage gain is 10k/1k or 10.
The voltage at the GAIN pin is compared to the current
share bus using the E/A2 block. The output of E/A2 is used
to adjust the output voltage of the power supply using the
I
GAIN pin voltage to equal the SB pin voltage. When the
GAIN pin voltages of all the LTC4350s in the system equal
the SB pin voltage, the load current is shared.
VOLTAGE MONITOR
Unique to the LTC4350 is tight output voltage regulation.
This is handled by the LTC4350’s error amplifier and
reference and not the power supply’s error amplifier and
reference. The E/A1 amplifier monitors the output voltage
via the feedback divider connected to the FB pin. The FB pin
is compared to the internal reference of the LTC4350. If the
FB pin is at or below the reference, then the output of E/A1
OUT
block. The objective of the E/A2 block is forcing the
SENSE
SENSE
block measures the power supply
block. The voltage drop across the
+
) to interface to the LTC4350.
LTC4350
4350fa
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