LM3670MF-1.2EV National Semiconductor, LM3670MF-1.2EV Datasheet - Page 2

• Manufacturer Part Number: LM3670MF-1.2EV
• Description: BOARD EVALUATION LM3670MF-1.2
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM3670MF-1.2EV

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 1.2V
• Current - Output: 350mA
• Voltage - Input: 2.5 ~ 5.5V
• Regulator Topology: Buck
• Frequency - Switching: 1MHz
• Board Type: Fully Populated
• Utilized Ic / Part: LM3670
• Lead Free Status / RoHS Status: Not applicable / Not applicable
• Power - Output: -
• Lead Free Status / Rohs Status: Not Compliant

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Output Voltage Selection for
LM3670MF-ADJ
The output voltage of the adjustable parts can be pro-
grammed through the resistor network connected from V
to V
at least 100kΩ to keep the current sunk through this network
well below 15µA quiescent current level (PFM mode with no
switching) but large enough that it is not susceptible to noise.
If R
through the resistor feedback network will be 2.5µA (I
0.5V/R
V
Powering the LM3670 for Bench
Measurements
When powering the LM3670 with a bench power supply, it is
recommended to place a 100µF tantalum capacitor across
the V
This capacitor will reduce the input spike caused by the power
V
0.7
0.8
0.9
1.0
1.1
1.2
1.24
1.24
1.5
1.6
1.7
1.875
2.5
OUT
OUT
2
FB
: output voltage (V)
IN
is 200kΩ, and given the V
(V)
to GND. The resistor from V
2
and GND supply terminals of the bench power supply.
). The output voltage formula is:
R
80.6
120
160
200
240
280
300
221
402
442
487
549
806
1
(kΩ )
R
200
200
200
200
200
200
200
150
200
200
200
200
200
TABLE 1. Adjustable LM3670 Configurations for Various V
2
FB
(kΩ )
FB
is 0.5V, then the current
to GND (R
C
200
130
100
82
68
56
56
75
39
39
33
30
22
1
(pF)
2
) should be
FB
OUT
C
150
none
none
none
none
none
none
120
none
none
none
none
82
=
2
(pF)
2
V
R
R
For the fixed output voltage parts the feedback resistors are
internal and R
The bypass capacitors C
uation Board) in parallel with the feedback resistors are cho-
sen for increased stability. Below are the formulas for C
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 also be looked at 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
2
: feedback resistor from V
: feedback resistor from V
.
: feedback voltage (0.5V typical)
L (µH)
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
10
10
10
10
10
1
is 0Ω.
C
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
IN
(µF)
1
and C
OUT
OUT
FB
to GND (Ω)
2
to V
(labeled C
C
10
10
10
10
10
10
10
10
10
10
10
14.7 (10 || 4.7)
22
FB
OUT
(Ω )
(µF)
4
and C
5
on Eval-
1
and