Texas Instruments LM3671 Evaluation Board LM3671LC-1.8EV/NOPB LM3671LC-1.8EV/NOPB 데이터 시트
제품 코드
LM3671LC-1.8EV/NOPB
Fp =
1
2 *
S
* (R1 R2) * (C1+C2)
Fz =
1
(2 *
S
* R1 * C1)
C2 =
1
(2 *
S
* R2 * 45 kHz)
C1 =
1
(2 *
S
* R1 * 45 kHz)
V
OUT
= V
FB
1 +
R1
R2
R2
¹
·
©
§
SNVS294Q – NOVEMBER 2004 – REVISED NOVEMBER 2013
APPLICATION INFORMATION
Output Voltage Selection for LM3671-ADJ
The output voltage of the adjustable parts can be programmed through the resistor network connected from V
OUT
to FB, then to GND. V
OUT
is adjusted to make the voltage at FB equal to 0.5V. The resistor from FB to GND (R2)
should be 200 k
Ω to keep the current drawn through this network well below the 16 µA quiescent current level
(PFM mode) but large enough that it is not susceptible to noise. If R2 is 200 k
Ω, and V
FB
is 0.5V, the current
through the resistor feedback network will be 2.5 µA. The output voltage of the adjustable parts ranges from 1.1V
to 3.3V.
to 3.3V.
The formula for output voltage selection is:
where
•
V
OUT
: output voltage (volts)
•
V
FB
: feedback voltage = 0.5V
•
R1: feedback resistor from V
OUT
to FB
•
R2: feedback resistor from FB to GND
(2)
For any output voltage greater than or equal to 1.1V, a zero must be added around 45 kHz for stability. The
formula for calculation of C1 is:
formula for calculation of C1 is:
(3)
For output voltages higher than 2.5V, a pole must be placed at 45 kHz as well. If the pole and zero are at the
same frequency the formula for calculation of C2 is:
same frequency the formula for calculation of C2 is:
(4)
The formula for location of zero and pole frequency created by adding C1 and C2 is given below. By adding C1,
a zero as well as a higher frequency pole is introduced.
a zero as well as a higher frequency pole is introduced.
(5)
(6)
See the "LM3671-ADJ configurations for various V
OUT
" table.
Table 1. LM3671-ADJ Configurations For Various V
OUT
(Circuit of
)
(Refer to Note 11 for VIN requirements)
V
OUT
(V)
R1(k
Ω)
R2 (k
Ω)
C1 (pF)
C2 (pF)
L (µH)
C
IN
(µF)
C
OUT
(µF)
0.90
160
200
22
none
2.2
4.7
10
1.1
240
200
15
none
2.2
4.7
10
1.2
280
200
12
none
2.2
4.7
10
1.3
320
200
12
none
2.2
4.7
10
1.5
357
178
10
none
2.2
4.7
10
1.6
442
200
8.2
none
2.2
4.7
10
1.7
432
178
8.2
none
2.2
4.7
10
1.8
464
178
8.2
none
2.2
4.7
10
1.875
523
191
6.8
none
2.2
4.7
10
2.5
402
100
8.2
none
2.2
4.7
10
2.8
464
100
8.2
33
2.2
4.7
10
3.3
562
100
6.8
33
2.2
4.7
10
Copyright © 2004–2013, Texas Instruments Incorporated
19
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