LM3578A Datasheet, PDF (6/20 Pages) National Semiconductor (TI) – Switching Regulator

Typical Performance Characteristics (Continued)
Current Limit Sense Voltage
vs Supply Voltage
Supply Current
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Supply Current
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Collector Current with
Emitter Output Below Ground
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Test Circuit*
Parameter tests can be made using the test circuit shown.
Select the desired V_in, collector voltage and duty cycle with
adjustable power supplies. A digital volt meter with an input
resistance greater than 100 MΩ should be used to measure
the following:
Input Reference Voltage to Ground; S1 in either position.
Level Shift Accuracy (%) = (T_P3(V)/1V) x 100%; S1 at I₁ = I₂
= 1 mA
Input Current (mA) = (1V − T_p3 (V))/1 MΩ: S1 at I₁ = I₂ =
0 mA.
Oscillator parameters can be measured at T_p4 using a fre-
quency counter or an oscilloscope.
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The Current Limit Sense Voltage is measured by connecting
an adjustable 0-to-1V floating power supply in series with the
current limit terminal and referring it to either the ground or
the V_in terminal. Set the duty cycle to 90% and monitor test
point T_P5 while adjusting the floating power supply voltage
until the LM2578A’s duty cycle just reaches 0%. This voltage
is the Current Limit Sense Voltage.
The Supply Current should be measured with the duty cycle
at 0% and S1 in the I₁ = I₂ = 0 mA position.
*LM2578A specifications are measured using automated
test equipment. This circuit is provided for the customer’s
convenience when checking parameters. Due to possible
variations in testing conditions, the measured values from
these testing procedures may not match those of the factory.
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