L6917B

30/33

Figure 27 shows the device in a high current server power supply application.

Adding an external resistor divider after the remote sense buffer gives the possibility to increase the regulated

voltage. Considering for example a divider by two (two equal resistors) the DAC range is doubled from 2.200V

to 3.700V with 50mV binary steps. The external resistor divider must be designed in order to give negligible ef-

fects to the remote buffer gain, this means that the resistors value must be much lower than the remote buffer

input resistance (20k

Ω). In this way, it is possible to regulate the 3.3V and 2.5V rails from the 12V available from

the AC/DC converter. The 5V rail can be obtained with further modifications to the external divider. The regulator

assures all the advantages of the dual phase conversion especially in the 5V conversion where the duty cycle

is near the 50% and practically no ripple is present in the input capacitors.

for reasonable times considering the overall dynamic thermal capacitance.

Figure 27. Server power supply schematic

The following part list refers to the following application:

– Input Voltage: 12V;

– Output voltage: 3.3V;

– Oscilator frequency: 200kHz;

– Output voltage tolerance (over static and dynamic conditions): ±2.5%.

PGOOD

PGND

PGNDS2

ISEN2

LGATE2

VSEN

FB

PHASE2

UGATE2

BOOT2

VCC

COMP

SGND

OSC / INH

VID0

VID1

VID2

VID3

VID4

PGNDS1

ISEN1

LGATE1

PHASE1

UGATE1

BOOT1

VCCDR

6

24

25

26

27

16

15

2

5

4

3

1

13

14

22

21

20

18

19

7

28

23

10

9

8

11

12

FBR

FBG

17

C1

R7

R8

C2

R4

R3

Q3

Q4

C3

L2

C7

R10

D3

C6

C11..C13

C14,

C23

R1

JP3

R2

S1

S0

S3

S2

S4

R5

R6

Q1

L1

Q2

C4

D4

C5

Vin

GNDin

GNDCORE

VoutCORE

PGOOD

FBG

FBR

U1

L6917B

DZ1

C8

JP2

JP1

R13

R15

R12

R14

C9,C10

R9

R18

D1

R17

R16

Q1a

Q3a

D2

R19

R20

JP5

JP4

Vcc

GNDcc

JP6

To Vcc

Rosc