LM3676SD-ADJEV National Semiconductor, LM3676SD-ADJEV Datasheet - Page 2

• Manufacturer Part Number: LM3676SD-ADJEV
• Description: BOARD EVALUATION LM3676SD-ADJ
• Manufacturer: National Semiconductor

Specifications of LM3676SD-ADJEV

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 1 ~ 3.3V
• Current - Output: 600mA
• Voltage - Input: 2.9 ~ 5.5V
• Regulator Topology: Buck
• Frequency - Switching: 2MHz
• Board Type: Fully Populated
• Utilized Ic / Part: LM3676
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -
• Lead Free Status / Rohs Status: Not Compliant

www.national.com
Output Voltage Selection for
LM3676SD-ADJ
The output voltage of the adjustable parts can be pro-
grammed through the resistor network connected from V
to FB to GND. The resistor from FB to GND (R
200kΩ to keep the current drawn throught this network small,
but large enough that it is not susceptible to noise. If R
200kΩ, and given the V
the resistor feedback network will be 2.5µA. The output volt-
age formula is:
V
Powering the LM3676 for Bench
Measurement
When powering the LM3676 with a bench power supply, it is
recommended to place a 100µF tantalum capacitor across
the VIN and GND supply terminals of the bench power supply.
This capacitor will reduce the input spike caused by the power
OUT
V
: output voltage (V)
1.875
OUT
1.0
1.1
1.2
1.5
1.6
1.7
1.8
2.5
2.8
3.3
(V)
R
1
200
191
280
357
442
432
464
523
402
464
562
(kΩ )
FB
TABLE 1. LM3676-ADJ Configurations for Various V
is 0.5V, then the current through
R
2
200
158
200
178
200
178
178
191
100
100
100
(kΩ )
C
2
) should be
1
8.2
8.2
8.2
6.8
8.2
8.2
6.8
18
18
12
10
(pF)
OUT
2
is
C
None
None
None
None
None
None
None
None
None
2
2
33
33
(pF)
V
R
R
For the fixed output voltage parts the feedback resistors are
internal. The bypass capacitors C
feedback resistors are chosen for stable operation. Below are
the formulas for C
supply and long power cables. The combination of the power
supply and inductance within the power cables produce a
large voltage spike that may damage the device. In addition,
consideration must given to the enable pin of the device. The
enable should never be taken high, until minimum guaranteed
operating voltage of 2.7V is reached. The enable pin should
also never exceed the input voltage.
FB
1
2
: feedback resistor from V
: feedback resistor from FB to GND (Ω)
: feedback voltage (0.5V typical)
L (µH)
2.2
2.2
2.2
2.2
2.2
2.2
2.2
2.2
2.2
2.2
2.2
out
(Circuit of Figure 2)
1
and C
C
IN
2
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
.
(µF)
OUT
to FB(Ω )
1
and C
2
in parallel with the
C
OUT
10
10
10
10
10
10
10
10
10
10
10
(µF)