Remote Sense Adjust Modes

The two remote sense adjust modes (positive and negative)

achieve current sharing by controlling either remote sense

input of the power converter. These configurations for the

LM5080 are shown in Figures 3 and 4. To understand the

sharing mechanism, assume for a moment the SHR pin is

disconnected from the share bus. Connecting RSO and

CSO configures the current sharing amplifier as a differential

amplifier with a gain of one. The CSP and RSO voltage will

be identical and independent of the voltage across the sense

resistor. Hence the voltage regulation loop of each power

converter is unaffected by the LM5080 when the SHR bus is

open.

When the SHR pins are connected, the small signal transfer

functions between the sense resistor voltages (VRS) and the

power supplies negative remote sense voltages (VSNS) are:

VSNS1 = A/4 x (VRS1 – VRS2)

VSNS2 = A/4 x (VRS2 – VRS1)

where

gm = current share amplifier transconductance (8.7mA/V)

Ro = output impedance of TRO pin (typically 6 M

Ω).

Provided the current sharing is equal (VRS1=VRS2), the

VSNS voltages will remain unchanged. However, any differ-

ence between VRS1 and VRS2 will drive the VSNS1 and

VSNS2 voltages in opposite polarities. As a result the power

converter

output

voltages

will

be

adjusted

to

force

VRS1=VRS2.

A capacitor from TRO to ground will compensate the differ-

ential amplifier as well as set the dominant pole of the

current share loop. CTRO should be at least 2 nF to insure

stability of the differential amplifier. In some systems a small

resistor (RTRO) in series with CTRO will improve stability of

the current share loop by introducing a zero at high frequen-

cies.

In the remote sense modes, it is essential the CSP pins of all

LM5080’s be tied to the exact same location on the PC

board. Any mismatch in the CSP voltages between

LM5080’s will contribute to current share errors. As in the

reference adjust mode, the current sense resistors should be

located as close to the load as possible to minimize trace

resistance in series with the sense resistors. In the remote

sense positive 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.

20157807

FIGURE 3. Remote Sense Negative Mode Implementation

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