Load

Power

Converter

Sense-

GND

CSP

CS

Current Sharing

Amplifier

TRO

RSO

R

R

R

R

CS

M

CSO

Remote Sense

Driver

LM5080

SHR

IT

Voltage

Reference

10:

Sense +

Error

Amp

10:

Vou

t

+

Vou

t

-

8R

8R

+VRS -

NRND

LM5080

SNVS387C – SEPTEMBER 2005 – REVISED MARCH 2013

www.ti.com

FEEDBACK ADJUSTMENT MODE

The feedback adjust mode configuration is shown in Figure 17. 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 polarities. 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 contribute 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.

Figure 17. Feedback Adjust Mode Implementation

12

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