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AN1696 APPLICATION NOTE

each of them is designed to deliver 3.3V/5A to the load. They must be inserted in the motherboard;

minals to the load. This board can accommodate up to three DC-DC converters.

On the motherboard there is the circuitry necessary to perform current sharing (L6615) and to isolate a failed

section from the load; it is designed to be adaptable to all power supplies (whose rating are compatible with

L6615 absolute maximum ratings) having remote sense pins; in fact only changing few components it can be

rearranged for new specs.

It is so possible to build a system to supply a 10A load at +3.3V in 2+1 redundant configuration. That is,

whenever three sections are running, each of them supplies 3.33A, a value lower than its nominal capability.

If one of them is switched off, the system is however able to supply the load and each section will carry 5A.

The DC-DC conversion management is entrusted to the L6910 [4].

It is possible to verify that disabling one section (through the relevant switch on the motherboard) does not cause

either overvoltage on the output or overcurrent in other sections.

At the same way, enabling one section (with other two already running) does not cause output voltage negative

drop or even short to ground and current sharing is established.

Figure 2. System overview

1.0 DAUGHTER BOARD

The L6910 controller drives a synchronous step-down stage at 200KHz; the internal reference is used for the

regulation. The external power mosfet's are included in one SO8 package to save space and increase power

density.

Fig. 3 shows the schematic of each daughter board and in table 1 the part list is indicated (for the description of

this section see [4]).

CURRENT SHARING (L6615),

ORING FET and

AUX. CIRCUITRY

DC-DC

CONVERSION

(daughter board)

CURRENT SHARING (L6615)

ORING FET and

AUX. CIRCUITRY

CURRENT SHARING (L6615)

ORING FET and

AUX. CIRCUITRY

DC-DC

CONVERSION

(daughter board)

R

SENSE

DC-DC

CONVERSION

(daughter board)

+5V

GND

GND

10A@+3.3V

V

SENSE

R

SENSE

V

SENSE

R

SENSE

V

SENSE

motherboard

sh bus

adj

adj

adj

CURRENT SHARING (L6615),

ORING FET and

AUX. CIRCUITRY

DC-DC

CONVERSION

(daughter board)

CURRENT SHARING (L6615)

ORING FET and

AUX. CIRCUITRY

CURRENT SHARING (L6615)

ORING FET and

AUX. CIRCUITRY

DC-DC

CONVERSION

(daughter board)

R

SENSE

DC-DC

CONVERSION

(daughter board)

+5V

GND

GND

10A@+3.3V

V

SENSE

R

SENSE

V

SENSE

R

SENSE

V

SENSE

motherboard

sh bus

adj

adj

adj