LTM4620AMPY 查看數據表（PDF） - Linear Technology

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LTM4620AMPY

Dual 13A or Single 26A DC/DC µModule Regulator

Linear Technology 

LTM4620A

APPLICATIONS INFORMATION

values of ID), and VG0 is the band gap voltage of 1.2V

extrapolated to absolute zero of –273°C Kelvin. Figure 8

shows a plot of the diode temperature characteristic of

the diode connected PNP transistor biased with a 100µA

current source. This plot would extend to the left back to

1.2V at –273°C Kelvin. This curve is stop at –55°C due to

the test system limits.

If we take the IS equation and substitute into the VD equa-

tion, then we get:

VD

=

VG0

–

Kt

 q

ln

 I0 

 ID

,

VT

=

kT

 q

The expression shows that the junction voltage of the PNP

connected diode decreases linearly if Io were constant

from a value VG0 of 1.2V at absolute zero to a decreasing

value with increased temperature.

If we take this equation and differentiate it with respect to

temperature T, then:

dVD = – (VG0 – VD) / T This dVD

dT

dT

change as a function of temperature is the typical

~–2mV/°C. This equation is simplified for the first order

derivation.

Solving for T, T = –(VG0 – VD)/ dVD provide the

temperature.

1st Example: Figure 4 for 27°C, or 300°C Kelvin the diode

voltage is 0.598V, thus, 300°C = –(1200mV – 598mV)/

–2mV/°C)

2nd Example: Figure 4 for 75°C, or 350°C Kelvin the diode

voltage is 0.50V, thus, 350°C = –(1200mV – 500mV)/

–2mV/°C)

Converting the Kelvin scale to Celsius is simply taking the

Kelvin temp and subtracting –273°C Kelvin from it.

A typical forward voltage is measured and placed in the

electrical characteristics section of the data sheet, and

Figure 8 is the plot of this forward voltage. Measure this

forward voltage at 27°C to establish a reference point.

Then use the above expression while measuring the

0.8

ID = 100µA

0.7

0.6

0.5

0.4

0.3

–50 –25

0 25 50 75 100 125

TEMPERATURE (°C)

4620A F08

Figure 8. Diode Voltage VD vs Temperature

T(°C) for Different Bias Currents

forward voltage over temperature will provide a general

temperature monitor.

The diode connected PNP transistor can be pulled up to

VIN with a resistor to set the current to 100µA for using

this diode connected transistor as a general temperature

monitor by monitoring the diode voltage drop with tem-

perature. See Figure 27 for an example.

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 JESD 51-9 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

µModule package mounted to a hardware test board—

also defined by JESD 51-9 (“Test Boards for Area Array

Surface Mount Package Thermal Measurements”). The

motivation for providing these thermal coefficients in

found in JESD 51-12 (“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

µModule regulator’s thermal performance in their appli-

cation at various electrical and environmental operating

For more information www.linear.com/LTM4620A

4620afc

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