LM2825N-12 National Semiconductor, LM2825N-12 Datasheet - Page 8

• Manufacturer Part Number: LM2825N-12
• Description: SWITCHING REG 1A 12V, 2825, DIP24
• Manufacturer: National Semiconductor

Specifications of LM2825N-12

• Primary Input Voltage: 24V
• No. Of Outputs: 1
• Output Voltage: 12V
• Output Current: 1A
• Voltage Regulator Case Style: DIP
• No. Of Pins: 24
• Operating Temperature Range: -40°C To +85°C
• Svhc: No SVHC
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

www.national.com
Application Information
It is especially useful in situations where the input power
source is limited in the amount of current it can deliver, since
you avoid loading down this type of power supply.
Under some operating conditions, a Soft-start capacitor is
required for proper operation. Figure 5 indicates the input
voltage and ambient temperature conditions for which a
Soft-start capacitor may be required.
This curve is typical for full guaranteed output current and
can be used as a guideline. As the output current decreases,
the operating area requiring a Soft-start capacitor de-
creases. Capacitor values between 0.1 µF and 1 µF are rec-
ommended. Tantalum or ceramic capacitors are appropriate
for this application.
INPUT CAPACITOR
C
more than 6" away from the main filter or bypass capacitor. A
low ESR aluminum or tantalum bypass capacitor is recom-
mended between the input pin and ground to prevent large
voltage transients from appearing at the input. In addition, to
be conservative, the RMS current rating of the input capaci-
tor should be selected to be at least
With a 1A load, a capacitor with a RMS current rating of at
least 500 mA is recommended.
The voltage rating should be approximately 1.25 times the
maximum input voltage. With a nominal input voltage of 12V,
an aluminum electrolytic capacitor (Panasonic HFQ series or
Nichicon PL series or equivalent) with a voltage rating
greater than 15V (1.25 x V
Solid tantalum input capacitors should only be used where
the input source is impedance current limited. High dV/dt ap-
plied at the input can cause excessive charge current
through low ESR tantalum capacitors. This high charge cur-
rent can result in shorting within the capacitor. It is recom-
mended that they be surge current tested by the manufactur-
er.The TPS series available from AVX, and the 593D series
from Sprague are both surge current tested.
Use caution when using ceramic capacitors for input bypass-
ing, because it may cause ringing at the V
LOWERING OUTPUT RIPPLE
When using the adjustable parts, one can achieve lower out-
put ripple voltage by shorting a resistor internal to the
LM2825. However, if this resistor is shorted, a feed forward
capacitor must be used to keep the regulator stable. For this
reason, this resistor must be left open on all of the fixed out-
put voltage versions or instability will result. See the feed for-
ward capacitor selection below. Shorting the internal resistor
is accomplished by shorting pins 8 and 9 on the LM2825,
and will typically reduce output ripple by 25 to 33%.
FEED FORWARD CAPACITOR SELECTION (C
When using an adjustable part and pins 8 and 9 are shorted
to reduce output ripple, a feed forward capacitor is required.
This capacitor is typically between 680 pF and 2700 pF. The
table of Figure 4 shows the value for C
voltage and feedback resistor R
IN
: An optional input capacitor is required if the package is
IN
) would be needed.
2
(R1 = 1 k ).
1
⁄
2
FF
the DC load current.
(Continued)
for a given output
IN
pin.
FF
)
8
SHUTDOWN
The circuit shown in Figure 10 shows 2 circuits for the
Shutdown/Soft-start feature using different logic signals for
shutdown and using a 0.1 µF Soft-start capacitor.
THERMAL CONSIDERATIONS
The LM2825 is available in a 24-pin through hole DIP. The
package is molded plastic with a copper lead frame. When
the package is soldered to the PC board, the copper and the
board are the heat sink for the LM2825.
V
FIGURE 5. Usage of the Soft-start Capacitor
10
11
12
13
14
15
OUT
2
3
4
5
6
7
8
7
8
9
FIGURE 4. C
LM2825H-ADJ
LM2825-ADJ
1.43k
2.26k
3.09k
3.92k
4.75k
5.49k
4.75k
5.49k
6.34k
7.15k
8.06k
8.87k
9.53k
10.5k
11.3k
630
R2
FF
Selection Table
2700 pF
2700 pF
2200 pF
1800 pF
1500 pF
2700 pF
2200 pF
1800 pF
1500 pF
1000 pF
820 pF
680 pF
680 pF
680 pF
C
N/A
N/A
FF
DS012661-22