8

7

6

1

2

R*

* R

8

7

6

1

2

a) EXTERNAL npn SWITCH

b) EXTERNAL npn SATURATED SWITCH (see Note A)

7

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MC33063A, MC34063A

SLLS636N – DECEMBER 2004 – REVISED JANUARY 2015

www.ti.com

9 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

9.1 Application Information

9.1.1 External Switch Configurations for Higher Peak Current

A.

If the output switch is driven into hard saturation (non-Darlington configuration) at low switch currents (

≤300 mA) and

high driver currents (

≥30 mA), it may take up to 2 μs to come out of saturation. This condition will shorten the off time

at frequencies

≥30 kHz and is magnified at high temperatures. This condition does not occur with a Darlington

configuration because the output switch cannot saturate. If a non-Darlington configuration is used, the output drive

configuration in Figure 7b is recommended.

8

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