LTC1430AI datasheet(20/24 Pages) LINER

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LTC1430A

APPLICATI

I FOR ATIO

the sense resistors should be well matched. This is

accomplished by using trace resistors that are laid out

symmetrically. Since they are formed of the same material

and processed identically, they will inherently match very

well. Note that the absolute value of these resistors is not

important; only the match between them is of concern.

The second issue is related to the reference point for the

two sense voltages. In order to avoid the need to use a true

differential amplifier to measure input current, the circuit

is configured such that the input side of these resistors

must be at the exact same potential. If the layout is not

configured this way, the current sharing accuracy will

prove disappointing. With only 0.2

Ω sense resistors, a

seemingly small error will produce a rather large current

mismatch between channels.

The last issue is related to having a very noisy sense

voltage. The current waveshape at the input to a buck

regulator is trapezoidal. Therefore, the sense amplifier

must integrate the two current measurements in order that

the average input currents be compared. The two-stage

RC filter on the sense amplifier provides an adequately

clean signal for the share circuit to operate correctly. High

speed is not required in the current sense loop. In balanced

operation any offsets in the slave regulator are dialed out

by the sense amplifier. If a sudden load change should

occur, both regulators will respond immediately and in the

right direction. If there are any gain differences in the two

loops there will need to be a small correction in the current

share error voltage. This can occur over a relatively long

time period with no adverse effects. As such, the share

amplifier’s bandwidth is on the order of a few hundred Hz,

ensuring good noise immunity.

Figure 18 demonstrates the high efficiency achieved with

this two-phase converter. An efficiency > 90% is realized

from a few amperes up to 30A. In theory and in practice,

this multiphase approach can be extended to even higher

current and output power levels. Consult Linear Technol-

ogy for further details.

Figure 18. Low Voltage 30A Power Supply Efficiency

LOAD CURRENT (A)

1430 F18

100

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