NCP5425DBR2G データシートの表示（PDF） - ON Semiconductor

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NCP5425DBR2G

Dual Synchronous Buck Controller

ON Semiconductor 

NCP5425

Current Sharing

When used in a two separate input to a single output mode,

the NCP5425 dual controller can provide input power

sharing in either of two ways:

• A preset ratio. For example, Channel 1 could provide

70% of the load current, and Channel 2, the remaining

30%. Practical ratios for Channel 1/Channel 2

contribution to total load current range from 50%−50%

to 80%−20%.

• A preset ratio up to a specific current contribution from

Channel 2. In excess of that limit, all of the additional

load current would be supplied by Channel 1. Figure 7

depicts the actual performance of a NCP5425

configured in a 70%−30% share ratio, with Channel 2

output current limited to 5.0 Amps.

The availability both Channel 2 error amplifier inputs

(signal and reference) at device pins is key to programmable

current ratio sharing. Current sense information from

Vin

Q3

L1

Vout

R3

Q4

R1

C3

R

R

C

Master

Error Amp

−

+

U2

Internal

Reference

VFB1

0.8 V

R4

R

Channel 1 is connected to the reference input of the Channel

2 error amplifier. Current information from Channel 2 is fed

back to the error amplifier’s inverting input. Channel 2 will

therefore act to adjust its current to match the current

information fed to its reference input from Channel 1. If this

information is one−half the voltage developed across the

Channel 1 output inductor, Channel 2 will run at half the

current and supply a approximately 33% of the total load

current. This application is illustrated in Figure 7.

In some applications the power supply designer may not

only wish to draw a known percentage of power from one

source, but also limit the power drawn from that source. The

current limit amplifier on Channel 2 can be programmed to

budget the maximum input power into Channel 2 and all

power in excess of that limit will be supplied solely by

Channel 1. This is accomplished by setting the Channel 2

cycle−by−cycle current limit in conjunction with

programming the current ratio as described above.

Vin

Q1

L2

Q2

C2

C

C1

C

R2

R

VFB2

VREF2

Slave

Error Amp

−

+

U2

Figure 6. Two Phase Current Sharing Circuit

14.00

12.00

10.00

8.00

6.00

4.00

2.00

Iout(1)

Iout(2)

Iin(1)

Iin(2)

Channel 1 output current

share begins to increase

Channel 2 output current

begins to level off at 5

Amps

0.00

0

5

10

15

20

TOTAL OUTPUT CURRENT, AMPS

Figure 7. 70%/30% Current Sharing with Channel 2 Current Limiting

NOTE: Channel 1 input voltage = Channel 2 input voltage = 5.0 V

Output voltage = 1.5 V

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