LTC2972 datasheet(56/112 Pages) LINER

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LTC2972

2972fa

For more information www.linear.com/LTC2972

Figure 19. Electronic Analogy for Inductor Temperature Model

PMBus COMMAND DESCRIPTION

I = PI

PI = CURRENT REPRESENTING THE POWER DISSIPATED BY THE INDUCTOR

(VDCR • READ_IOUT WHERE VDCR = (VISENSEP – VISENSM))

Cτ = CAPACITANCE REPRESENTING THERMAL HEAT CAPACITY OF THE INDUCTOR

(INCLUDED IN MFR_IOUT_CAL_GAIN_TAU_INV)

TI = VOLTAGE REPRESENTING THE TEMPERATURE OF THE INDUCTOR

θIS = RESISTANCE REPRESENTING THE THERMAL RESISTANCE FROM THE DCR

TO THE REMOTE TEMPERATURE SENSOR (MFR_IOUT_CAL_GAIN_THETA)

TS = VOLTAGE REPRESENTING THE TEMPERATURE AT THE REMOTE

TEMPERATURE SENSOR

2972 F19

C = Cτ

R = θIS

VS = TS

VI = TI

OT_FAULT_LIMIT, OT_WARN_LIMIT, UT_WARN_LIMIT and UT_FAULT_LIMIT

These commands provide supervising limits for temperature as measured by the external diode.

MFR_TEMP_1_GAIN and MFR_TEMP_1_OFFSET

The MFR_TEMP_1_GAIN command specifies the inverse of the temperature sensor ideality factor. The MFR_TEMP_1_

OFFSET allows an offset to be applied to the measured temperature.

Calculations using these paged commands are:

READ_TEMPERATURE_1 = TEXT • MFR_TEMP_1_GAIN – 273.15 + MFR_TEMP_1_OFFSET

where:

TEXT = Measured external temperature in degrees Kelvin.

READ_TEMPERATURE_2 is substituted for READ_TEMPERATURE_1 if the associated TSENSE network fails to detect

a valid temperature. Under these conditions MFR_TEMP_1_GAIN and MFR_TEMP_1_OFFSET will have no effect. See

READ_TEMPERATURE_1 for more information.

MFR_TEMP_1_GAIN Data Contents

BIT(S) SYMBOL

OPERATION

b[15:0] Mfr_temp_1_gain[15:0]

16-bit integer representing inverse of temperature non-ideality factor. Value = Y • 214 where Y = b[15:0] is an

unsigned integer. Example:

MFR_TEMP_1_GAIN = 1.0

For b[15:0] = 0x4000

Value = 16384 • 2–14 = 1.0

MFR_T_SELF_HEAT, MFR_IOUT_CAL_GAIN_TAU_INV and MFR_IOUT_CAL_GAIN_THETA

The LTC2972 uses an innovative (US patent 8920026) algorithm to dynamically model the temperature rise from the

external temperature sensor to the inductor core. This temperature rise is called MFR_T_SELF_HEAT and is used to

calculate the final temperature correction required by IOUT_CAL_GAIN. The temperature rise is a function of the power

dissipated in the inductor DCR, the thermal resistance from the inductor core to the remote temperature sensor and

the thermal time constant of the inductor to board system. The algorithm simplifies the placement requirements for

the external temperature sensor and compensates for the significant steady state and transient temperature error from

the inductor core to the primary inductor heat sink.

LTC2972 Datasheet(PDF) 56 Page - Linear Technology

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