LM5080MM datasheet(10/13 Pages) NSC

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Remote Sense Adjust Modes (Continued)

Feedback Adjustment Mode

The feedback adjust mode configuration is shown in Figure

5. It is very similar to the reference adjust mode except the

current sensing is done on the high side of the load and the

correction is applied to the feedback resistor divider in the

voltage regulation loop.

Similar to the reference adjust mode, the transfer functions

between the sense resistor voltages (VRS) and the currents

injected into the power converter TRIM pin (IT) are:

IT1 = 0.9 x gm x (VRS1 - VRS2)

IT2 = 0.9 x gm x (VRS2 - VRS1)

where gm = current share amplifier transconductance

(8.7mA/V).

As previously described, provided the current sharing is

equal (VRS1=VRS2), the correction current to the reference

(IT) will be zero. However, any difference between VRS1

and VRS2 will drive the TRIM pin currents in opposite po-

larities. As a result the power converter output voltages will

be adjusted to force VRS1=VRS2.

In this mode, VCC must be biased at least 2V higher than the

output regulation voltage to maintain CSP and CSM in the

proper common mode range. It is essential the VCC pins of

all LM5080’s be tied to the same point in this mode. Any

mismatch in the VCC voltages between LM5080’s will con-

tribute to current share errors. For the same reasons as

discussed in the above two operating modes, the current

sense resistors should be located as close to the load as

possible. In this mode, the best accuracy will be achieved

with lower VCC values since any mismatch in the gain

resistors internal to the LM5080 will affect the current share

accuracy.

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FIGURE 4. Remote Sense Positive Mode Implementation

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FIGURE 5. Feedback Adjust Mode Implementation

LM5080MM Scheda tecnica(PDF) 10 Page - National Semiconductor (TI)