LM2825 datasheet(7/12 Pages) NSC

7 / 12 page

Test Circuit

Application Information

PROGRAMMING OUTPUT VOLTAGE

(Selecting R1 and R2 as shown in

Figure 3)

The LM2825 is available in two adjustable output versions.

The LM2825-ADJ has been optimized for output voltages

between 1.23V and 8V, while the LM2825H-ADJ covers the

output voltage range of 7V to 15V. Both adjustable versions

are set in the following way.

Select a value for R1 between 240

Ω and 1.5 kΩ. The lower

resistor values minimize noise pickup at the sensitive adjust

pin. (For lowest temperature coefficient and the best stability

with time, use 1% metal film resistors.)

Select R2 with the following equation.

When programming V

OUT, keep in mind that VIN must be

greater than V

OUT + 2V for proper operation.

OPTIONAL EXTERNAL COMPONENTS

SOFT-START CAPACITOR

SS: A capacitor on this pin provides the regulator with a

Soft-start feature (slow start-up). The current drawn from the

source starts out at a low average level with narrow pulses,

and ramps up in a controlled manner as the pulses expand

to their steady-state width. This reduces the startup current

considerably, and delays and slows down the output voltage

rise time.

DS012661-19

*Optional—Required if package is more than 6" away from main filter or bypass capacitor.

**Optional Soft-start Capacitor

VIN = 40V (max)

VOUT = 3.3V or 5V @ 1A or 12V @ 0.75A

FIGURE 2. Standard Test Circuit

(Fixed Output Voltage Versions)

DS012661-30

*Optional—Required if package is more than 6" away from main filter or bypass capacitor.

**Optional Soft-start Capacitor

***Optional—See Application Information.

VIN = 40V (max)

VOUT = 1.23V to 8V (LM2825-ADJ)

7V to 15V (LM2825H-ADJ)

ILOAD = IMAX (See derating curves)

FIGURE 3. Standard Test Circuit

(Adjustable Output Voltage Versions)

LM2825 Datasheet(PDF) 7 Page - National Semiconductor (TI)

LM2825 Datasheet(HTML) 7 Page - National Semiconductor (TI)

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