LTM4677 datasheet(60/116 Pages) AD

60 / 116 page

LTC3883/LTC3883-1

Rev. F

For more information www.analog.com

The ripple will be 4.79A (32%). The peak inductor current

will be the maximum DC value plus one-half the ripple

current or 17.39A. The minimum on time occurs at the

maximum VIN, and should not be less than 45ns:

tON(MIN) =

VOUT

VIN(MAX) • f

1.8V

20V 500kHz

(

)

= 180ns

The Vishay IHLP4040DZ-11 1µH (2.3mΩ DCRTYP at 25°C)

is the chosen inductor.

Assuming the temperature measurement of the inductor

temperatureisaccurateandC1issetto0.2µF,RDisinfinite

and removed from the equations.

R1=

DCR at 25°C

(

) • C1

1µH

2.5mΩ • 0.2µF

= 1.37k

The maximum power loss in R0 is related to the duty

cycle, and will occur in continuous mode at the maximum

input voltage:

PLOSSR1=

VIN(MAX) – VOUT

(

) • VOUT

20 – 1.8

(

) • 1.8

1.37k

= 23.91mW

The current limit will be set 20% higher than the peak

value to assure variation in components and noise in the

system do not limit the average current.

VILIMIT = IPEAK • RDCR(MAX) = 17.39A • 2.5mΩ = 43mV

TheclosestVILIMITsettingis42.9mVor46.4mV.Thevalues

are entered with the IOUT_OC_FAULT_LIMIT command.

Based on expected variation and measurement in the lab

across the sense capacitor the user can determine the

optimal setting.

The power dissipation on the topside MOSFET can be

easily estimated. Choose a M1: INFINEON BSC050NE2LS

topside MOSFET. RDS(ON) = 5.7mΩ, CMILLER = 35pF. At

maximum input voltage with T estimated = 50°C and a

bottom side MOSFET a M2: INFINEON BSC010NE2LSI,

RDS(ON) = 1.1mΩ:

APPLICATIONS INFORMATION

PMAIN =

1.8V

20V

• 17.25

(

)

2 • 1+ 0.005

(

) 50°C – 25°C

(

)

⎡⎣

⎤⎦

• 5.7mΩ + 20V

(

)

2 8.695A

(

) •

5 – 2.3

2.3

⎛

⎝⎜

⎞

⎠⎟

35pF

(

) 500kHz

(

) = 0.221W

The loss in the bottom side MOSFET is:

PSYNC =

20V – 1.8V

(

)

20V

• 17.25A

(

)

2 •

1+ 0.005

(

) 50°C – 25°C

(

)

⎡⎣

⎤⎦ • 1.1mΩ

= 0.335W

Both MOSFETS have I2R losses while the PMAIN equation

includes an additional term for transition losses, which

are highest at high input voltages.

CIN is chosen for an RMS current rating of:

CIN Required IRMS =

17.25

1.8

( ) • 20 – 1.8

(

)

⎡⎣

⎤⎦

1/2

= 4.9A

at temperature. COUT is chosen with an ESR of 0.006Ω for

low output ripple. The output ripple in continuous mode

will be highest at the maximum input voltage. The output

voltage ripple due to ESR is

VORIPPLE = R(∆IL) = 0.006Ω • 5.5A = 33mV.

CONNECTING THE USB TO I2C/SMBus/PMBus

CONTROLLER TO THE LTC3883 IN SYSTEM

The ADI USB to I2C/SMBus/PMBus controller can be

interfaced to the LTC3883 on the user’s board for pro-

gramming, telemetry and system debug. The controller,

when used in conjunction with LTpowerPlay, provides a

powerful way to debug an entire power system. Faults are

quicklydiagnosedusingtelemetry,faultstatuscommands

and the fault log. The final configuration can be quickly

developed and stored to the LTC3883 EEPROM.

Figure 29 illustrates the application schematic for power-

ing, programming and communication with one or more

LTC3883s via the ADI I2C/SMBus/PMBus controller

regardless of whether or not system power is present.

LTM4677 Datasheet(PDF) 60 Page - Analog Devices

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