Rainbow Electronics LM20 - Manual (Page 4)

Electrical Characteristics
(Continued)
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is
functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. The guaranteed
specifications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test
conditions.
Note 2: When the input voltage (V I ) at any pin exceeds power supplies (V I
< GND or V I
> V + ), the current at that pin should be limited to 5 mA.
Note 3: The human body model is a 100 pF capacitor discharged through a 1.5 k Ω resistor into each pin. The machine model is a 200 pF capacitor discharged
directly into each pin.
Note 4: Reflow temperature profiles are different for lead-free and non-lead-free packages.
Note 5: The junction to ambient thermal resistance ( θ
JA
) is specified without a heat sink in still air using the printed circuit board layout shown in Figure 1.
Note 6: Typicals are at T
J
= T
A
= 25˚C and represent most likely parametric norm.
Note 7: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).
Note 8: Accuracy is defined as the error between the measured and calculated output voltage at the specified conditions of voltage, current, and temperature
(expressed in˚C).
Note 9: Non-Linearity is defined as the deviation of the calculated output-voltage-versus-temperature curve from the best-fit straight line, over the temperature
range specified.
Note 10: Regulation is measured at constant junction temperature, using pulse testing with a low duty cycle. Changes in output due to heating effects can be
computed by multiplying the internal dissipation by the thermal resistance.
Note 11: Negative currents are flowing into the LM20. Positive currents are flowing out of the LM20. Using this convention the LM20 can at most sink −1 µA and
source +16 µA.
Note 12: Load regulation or output impedance specifications apply over the supply voltage range of +2.4V to +5.5V.
Note 13: Line regulation is calculated by subtracting the output voltage at the highest supply input voltage from the output voltage at the lowest supply input voltage.
Typical Performance Characteristics
Temperature Error vs Temperature
10090825
PCB Layouts Used for Thermal Measurements
1.0 LM20 Transfer Function
The LM20’s transfer function can be described in different
ways with varying levels of precision. A simple linear transfer
function, with good accuracy near 25˚C, is
V
O
= −11.69 mV/˚C x T + 1.8663 V
Over the full operating temperature range of −55˚C to
+130˚C, best accuracy can be obtained by using the para-
bolic transfer function
V
O
= (−3.88x10 −6 xT 2 ) + (−1.15x10 −2 xT) + 1.8639
solving for T:
10090829
a) Layout used for no heat sink measurements.
10090830
b) Layout used for measurements with small heat hink.
FIGURE 1. PCB Lyouts used for thermal measurements.
LM20
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