LM2578A, LM3578A

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SNVS767E – AUGUST 2000 – REVISED APRIL 2013

Figure 14. Value of Timing Capacitor vs Oscillator Frequency

OUTPUT TRANSISTOR

The output transistor is capable of delivering up to 750 mA with a saturation voltage of less than 0.9V. (see

Collector Saturation Voltage and Emitter Saturation Voltage curves).

The emitter must not be pulled more than 1V below ground (this limit is 0.6V for TJ ≥ 100°C). Because of this

limit, an external transistor must be used to develop negative output voltages (see the Inverting Regulator Typical

Application). Other configurations may need protection against violation of this limit (see the Emitter Output

section of the Applications Information).

CURRENT LIMIT

The LM2578A's current limit may be referenced to either the ground or the Vin pins, and operates on a cycle-by-

cycle basis.

The current limit section consists of two comparators: one with its non-inverting input referenced to a voltage

110 mV below Vin, the other with its inverting input referenced 110 mV above ground (see FUNCTIONAL

DIAGRAM). The current limit is activated whenever the current limit terminal is pulled 110 mV away from either

Vin or ground.

Applications Information

CURRENT LIMIT

As mentioned in the functional description, the current limit terminal may be referenced to either the Vin or the

ground terminal. Resistor R3 converts the current to be sensed into a voltage for current limit detection.

Figure 15. Current Limit, Ground Referred

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