LM3578AM datasheet(7/30 Pages) TI

7 / 30 page

LM2578A, LM3578A

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SNVS767E – AUGUST 2000 – REVISED APRIL 2013

TEST CIRCUIT*

Parameter tests can be made using the test circuit shown. Select the desired Vin, collector voltage and duty cycle

with adjustable power supplies. A digital volt meter with an input resistance greater than 100 M

Ω should be used

to measure the following:

Input Reference Voltage to Ground; S1 in either position.

Level Shift Accuracy (%) = (TP3(V)/1V) × 100%; S1 at I1 = I2 = 1 mA

Input Current (mA) = (1V

− Tp3 (V))/1 MΩ: S1 at I1 = I2 = 0 mA.

Oscillator parameters can be measured at Tp4 using a frequency counter or an oscilloscope.

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 Vin terminal. Set the duty cycle to

90% and monitor test point TP5 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.

Op amp supplies are ±15V

DVM input resistance >100 M

*LM2578 max duty cycle is 90%

Definition of Terms

Input Reference Voltage: The voltage (referred to ground) that must be applied to either the inverting or non-

inverting input to cause the regulator switch to change state (ON or OFF).

Input Reference Current: The current that must be drawn from either the inverting or non-inverting input to

cause the regulator switch to change state (ON or OFF).

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