LTC2972 datasheet(90/112 Pages) LINER

90 / 112 page

LTC2972

2972fa

For more information www.linear.com/LTC2972

APPLICATIONS INFORMATION

OVERVIEW

The LTC2972 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 LTC2972

utilizes a PMBus compliant interface and command set.

POWERING THE LTC2972

The LTC2972 can be powered two ways. The first method

requires that a voltage between 4.5V and 15V be applied

to the VPWR pin. See Figure 22. An internal linear regula-

tor converts VPWR down to 3.3V which drives all of the

internal circuitry of the LTC2972.

Alternatively, power from an external 3.3V supply may be

applied directly to the VDD33pins11and12usingavoltage

between 3.13V and 3.47V. See Figure 23. Tie VPWR to the

VDD33 pins. All functionality is available when using this

Figure 22. Powering LTC2972 Directly from an Intermediate Bus

alternate power method. The higher voltages needed for

the VOUT_EN pins and bias for the VSENSE pins are charge

pumped from VDD33.

SETTING COMMAND REGISTER VALUES

The command register settings described herein are in-

tendedasareferenceandforthepurposeofunderstanding

the registers in a software development environment. In

actualpractice,theLTC2972canbecompletelyconfigured

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

SMBus/PMBuscontrollerandsoftwareGUIusingintuitive

menu driven objects.

MEASURING INPUT CURRENT

The LTC2972 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

LTC2972 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 LTC2972.

Figure 23. Powering LTC2972 from External 3.3V Supply

Figure 24. Measuring Input Current

VPWR

VDD33

VDD25

VIN_SNS

LTC2972*

0.1µF

4.5V < VPWR < 15V

GND

0.1µF

*SOME DETAILS

OMITTED FOR CLARITY

2972 F22

VDD33

VDD25

VPWR

LTC2972*

0.1µF

GND

*SOME DETAILS

OMITTED FOR CLARITY

2972 F23

EXTERNAL 3.3V

VIN_SNS

4.5V < VIN_SNS < 15V

IIN_SNSP

IIN_SNSM

VIN_SNS_CAP

LTC2972*

GND

*SOME DETAILS OMITTED FOR CLARITY

CIN

0.1µF

350Ω

2972 F24

RSENSE

LOAD

LTC2972 Datasheet(PDF) 90 Page - Linear Technology

LTC2972 Datasheet(HTML) 90 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL