NB679, 28 V VIN, FIXED 5V-8A BUCK CONVERTER WITH LDO

NB679 Rev. 1.03

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14

7/27/2017

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set to provide enough hysteresis to allow for any

input supply variations.

Figure 5

—Adjustable UVLO

To avoid too much sink current on EN, the EN

resistor (Rup) is usually in the range of 1 M-2 M

Ω.

A typical pull-up resistor is 2 M

Ω.

Thermal Shutdown

Thermal shutdown is employed in the NB679.

The junction temperature of the IC is monitored

internally. If the junction temperature exceeds the

threshold value (140ºC, typically), the converter

shuts off. This is a non-latch protection. There is

about

25ºC

hysteresis.

Once

the

junction

temperature drops to about 115ºC, it initiates a

SS.

Output Discharge

NB679 discharges the output when EN is low, or

the controller is turned off by the protection

functions UVP, OCP, OCP, OVP, UVLO, and

thermal shutdown. The part discharges outputs

using an internal 6

Ω MOSFET.