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ADP3162JR

5-Bit Programmable 2-Phase Synchronous Buck Controller

Analog Devices 

ADP3162

Cycle-by-Cycle Operation

During normal operation (when the output voltage is regulated),

the voltage-error amplifier and the current comparator are the

main control elements. The voltage at the CT pin of the oscilla-

tor ramps between 0 V and 3 V. When that voltage reaches 3 V,

the oscillator sets the driver logic, which sets PWM1 high. Dur-

ing the ON time of Phase 1, the driver IC turns on the high-side

MOSFET. The CS+ and CS– pins monitor the current through

the sense resistor that feeds both high-side MOSFETs. When

the voltage between the two pins exceeds the threshold level

set by the voltage error amplifier (gm), the driver logic is reset

and the PWM output goes low. This signals the driver IC to turn

off the high-side MOSFET and turn on the low-side MOSFET.

On the next cycle of the oscillator, the driver logic toggles and

sets PWM2 high. On each following cycle of the oscillator, the

outputs toggle between PWM1 and PWM2. In each case, the

current comparator resets the PWM output low when the current

comparator threshold is reached. As the load current increases,

the output voltage starts to decrease. This causes an increase in

the output of the gm amplifier, which in turn leads to an increase

in the current comparator threshold, thus programming more

current to be delivered to the output so that voltage regulation is

maintained.

Active Current Sharing

The ADP3162 ensures current balance in the two phases by

actively sensing the current through a single sense resistor. During

one phase’s ON time, the current through the respective high-side

MOSFET and inductor is measured through the sense resistor

(R4 in Figure 2). When the comparator (CMP1 in the Functional

Block Diagram) threshold programmed by the gm amplifier is

reached, the high-side MOSFET turns off. In the next cycle the

ADP3162 switches to the second phase. The current is measured

with the same sense resistor and the same internal comparator,

ensuring accurate matching. This scheme is immune to imbalances

in the MOSFETs’ RDS(ON) and inductors’ parasitic resistances.

If for some reason one of the phases fails, the other phase will still

be limited to its maximum output current (one-half of the short

circuit current limit). If this is not sufficient to supply the load,

the output voltage will droop and cause the PWRGD output to

signal that the output voltage has fallen out of its specified range.

Short Circuit Protection

The ADP3162 has multiple levels of short circuit protection to

ensure fail-safe operation. The sense resistor and the maximum

current sense threshold voltage given in the specifications set the

peak current limit.

When the load current exceeds the current limit, the excess current

discharges the output capacitor. When the output voltage is below

the foldback threshold VFB(LOW), the maximum deliverable output

current is cut by reducing the current sense threshold from the

current limit threshold, VCS(CL), to the foldback threshold,

VCS(FOLD). Along with the resulting current foldback, the oscilla-

tor frequency is reduced by a factor of five when the output is

0 V. This further reduces the average current in short circuit.

Power-Good Monitoring

The Power-Good comparator monitors the output voltage of the

supply via the FB pin. The PWRGD pin is an open drain output

whose high level (when connected to a pull-up resistor) indi-

cates that the output voltage is within the specified range of

the nominal output voltage requested by the VID DAC. PWRGD

will go low if the output is outside this range.

Output Crowbar

The ADP3162 includes a crowbar comparator that senses when

the output voltage rises higher than the specified trip thresh-

old, VCROWBAR. This comparator overrides the control loop and

sets both PWM outputs low. The driver ICs turn off the high side

MOSFETs and turn on the low-side MOSFETs, thus pulling the

output down as the reversed current builds up in the inductors. If

the output overvoltage is due to a short of the high side MOSFET,

this action will current limit the input supply or blow its fuse,

VIN 5V

VIN RTN

12V VCC

+

C12

+

+

+

C13

C14

C15

1000␮F ؋ 4

R6

10⍀

RA

10.1k⍀

1%

FROM

CPU

RB

19.1k⍀

1%

COC

3.3nF

U1

ADP3162

1 VID3

VCC 16

2 VID2

REF 15

3 VID1

CS– 14

4 VID0 PWM1 13

5 VID25 PWM2 12

6 COMP CS+ 11

7 FB PWRGD 10

8 CT

GND 9

C1

91pF

C4

4.7␮F

C22 1nF

R7

20⍀

C21

15nF

R8

330⍀

C23

330pF

C26

4.7␮F

R5

2.4k⍀

Z1

ZMM5236BCT

D1

MBR052LTI

Q5

FMMT18

1

R4

4m⍀

C9

1␮F

U2

ADP3412

BST DRVH 8

2 IN

SW 7

3 DLY PGND 6

C5

C7

1␮F 15pF

4 VCC DRVL 5

Q1

IRL3803

L1

1␮H

Q2

IRL3803

D2

C10

MBR052LTI

1␮F

U3

ADP3412

1 BST DRVH 8

2 IN

SW 7

Q3

IRL3803

L2

1␮H

1000␮F ؋ 8

RUBYCON ZA SERIES

24m⍀ ESR (EACH)

C2

100pF

R1

1k⍀

C6

C8

1␮F 15pF

3 DLY PGND 6

4 VCC DRVL 5

Q4

IRL3803

C16 C17 C18 C19 C20 C27 C28 C29

VCC(CORE)

1.7V

30A

VCC(CORE)RTN

Figure 2. 23 A Pentium® III CPU Supply Circuit

Pentium is a registered trademark of Intel Corporation.

–6–

REV. A

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