LTM4662 datasheet(21/34 Pages) LINER

21 / 34 page

LTM4662

4662f

For more information www.linear.com/LTM4662

Figure 7. Diode Voltage VD vs Temperature T(°C)

for Different Bias Currents

where VD appears to increase with temperature. It is com-

mon knowledge that a silicon diode biased with a current

source has an approximate –2mV/°C temperature rela-

tionship (Figure 7), which is at odds with the equation

term, increases with temperature, reducing the ln(ID/IS)

absolute value yielding an approximate –2mV/°C com-

posite diode voltage slope.

APPLICATIONS INFORMATION

Solving for temperature:

T(KELVIN) =

∆VD

K'D

T(KELVIN) = [°C]+ 273.15,

[°C] = T(KELVIN) − 273.15

means that if we take the difference in voltage across the

diode measured at two currents with a ratio of 10, the

resulting voltage is 198V per Kelvin of the junction with

a zero intercept at 0 Kelvin. The diode connected NPN

transistor at the TEMP+, TEMP–pins can be used to moni-

tor the internal temperature of the LTM4662. A general

temperature monitor can be implemented by connecting

a resistor between TEMP+ and VIN to set the current to

100 A, grounding the TEMP– pin and then monitoring

the diode voltage drop with temperature. A more accurate

temperature monitor can be achieved with a circuit inject-

ing two currents that are at a 10:1 ratio. See LTC2997

data sheet.

Thermal Considerations and Output Current Derating

The thermal resistances reported in the Pin Configuration

section of the data sheet are consistent with those param-

eters defined by JESD51-12 and are intended for use with

finite element analysis (FEA) software modeling tools that

leverage the outcome of thermal modeling, simulation,

and correlation to hardware evaluation performed on a

Module® package mounted to a hardware test board.

The motivation for providing these thermal coefficients

is found in JESD51-12 (“Guidelines for Reporting and

Using Electronic Package Thermal Information”). Many

designers may opt to use laboratory equipment and a test

vehicle such as the demo board to anticipate the Module

regulator’s thermal performance in their application at

various electrical and environmental operating conditions

to compliment any FEA activities. Without FEA software,

the thermal resistances reported in the Pin Configuration

section are in-and-of themselves not relevant to provid-

ing guidance of thermal performance; instead, the derat-

ing curves provided in the data sheet can be used in a

manner that yields insight and guidance pertaining to

one’s application-usage, and can be adapted to corre-

late thermal performance to one’s own application. The

4662 F07

TEMPERATURE (°C)

–173

–73

127

0.4

0.6

0.8

1.0

∆VD

ID = 100µA

ID = 10µA

To obtain a linear voltage proportional to temperature,

we cancel the IS variable in the natural logarithm term to

remove the IS dependency from the following equation.

This is accomplished by measuring the diode voltage at

two currents I1, and I2, where I1 = 10 • I2.

Subtracting we get:

∆VD = T(KELVIN) • KD •In

− T(KELVIN) • KD •In

Combining like terms, then simplifying the natural log

terms yields:

∆VD = T(KELVIN) • KD • In(10)

and redefining constant

K’D = KD • In(10) = 198µV/k

yields

∆VD = K’D • T(KELVIN)

LTM4662 Datasheet(PDF) 21 Page - Linear Technology

LTM4662 Datasheet(HTML) 21 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

Datasheet Download

Link URL