LTM2987 datasheet(92/114 Pages) AD

92 / 114 page

LTC2971

Rev. 0

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APPLICATIONS INFORMATION

OVERVIEW

The LTC2971 is a 2-channel Power System Management

IC that is capable of sequencing, margining, trimming,

supervising output voltage for OV/UV conditions, fault

management, voltage/current/temperature readback for

two DC/DC converter channels, and readback of high side

input current, input voltage, input power, input energy,

and junction temperature. Multiple Analog Devices Power

System Managers can coordinate operation using the

SHARE_CLK, FAULTB, and CONTROL pins. The LTC2971

utilizes a PMBus compliant interface and command set.

POWERING THE LTC2971

The LTC2971 can be powered two ways. In one method,

power from an external 4.5V to 60V supply is applied to

the VPWR pin. See Figure 22. An internal linear regulator

convertsVPWRto3.3V,whichdrivestheLTC2971'sinternal

circuitry. High VPWR levels cause excessive internal power

dissipation and self-heating. Although the LTC2971 works

with60VVPWRlevels,itisadvisedtouseanexternalswitch-

ing regulator to drop VPWR for external supplies above 24V.

Figure 22. Powering LTC2971 from External 4.5V to 60V Supply

Alternatively, power from an external 3.13V to 3.47V sup-

ply is applied to the VDD33 and VPWR pins. See Figure 23.

All functionality is availiable when using this method, and

internal power is minimized.

SETTING COMMAND REGISTER VALUES

The command register settings described herein are in-

tendedasareferenceandforthepurposeofunderstanding

the registers in a software development environment. In

actualpractice,theLTC2971canbecompletelyconfigured

for stand-alone operation with the DC1613 USB to I2C/

SMBus/PMBuscontrollerandLTpowerPlayusingintuitive

menu driven objects.

MEASURING INPUT CURRENT

The LTC2971 is capable of measuring the current of the

input power source. The device also measures the input

supply voltage, enabling it to calculate input power. The

LTC2971 has an accurate internal time base allowing the

chip to calculate input energy since energy is the product

of power and time. The units for each of the measured

parameters are amps, volts, watts, and millijoules.

Input current is measured by placing a sense resistor,

RSENSE, in series with the desired current load path as

shown in Figure 24. If RSENSE has low thermal drift char-

acteristics, the MFR_IIN_CAL_GAIN_TC register value

may be set to zero. Otherwise, choose a setting for the

MFR_IIN_CAL_GAIN_TC value in units of ppm/°C to cor-

rect for RSENSE thermal drift.

For best results, it is recommended to locate RSENSEclose

to and isothermal with the LTC2971.

Figure 23. Powering LTC2971 from External 3.3V Supply

Figure 24. Measuring Input Current

VPWR

VDD33

VDD25

VIN_SNS

LTC2971*

0.1µF

4.5V < VPWR < 60V

GND

0.1µF

*SOME DETAILS

OMITTED FOR CLARITY

2971 F22

VDD33

VDD25

VPWR

LTC2971*

0.1µF

GND

*SOME DETAILS

OMITTED FOR CLARITY

2971 F23

EXTERNAL 3.3V

VIN_SNS

4.5V < VIN_SNS < 60V

IIN_SNSP

IIN_SNSM

LTC2971*

GND

*SOME DETAILS OMITTED FOR CLARITY

2971 F24

RSENSE

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