Datasheet

LM2578A, LM3578A
www.ti.com SNVS767E –AUGUST 2000–REVISED APRIL 2013
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) × 100%; S1 at I
1
= I
2
= 1 mA
Input Current (mA) = (1V − T
p3
(V))/1 MΩ: S1 at I
1
= I
2
= 0 mA.
Oscillator parameters can be measured at T
p4
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 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 I
1
= I
2
= 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 MΩ
*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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