LTC3410_15 Datasheet, PDF (13/16 Pages) Linear Technology – 2.25MHz, 300mA Synchronous Step-Down Regulator in SC70

LTC3410
APPLICATIO S I FOR ATIO
Substituting V_OUT = 3V, V_IN = 4.2V, ∆I_L = 100mA
and f = 2.25MHz in Equation (3) gives:
L
=
2.25MH3zV(100mA)^{⎛⎝⎜1−}
3V
4.2V
⎞⎠⎟
=
3.8µH
A 4.7µH inductor works well for this application. For best
efficiency choose a 350mA or greater inductor with less
than 0.3Ω series resistance.
C_IN will require an RMS current rating of at least 0.125A ≅
I_LOAD(MAX)/2 at temperature and C_OUT will require an ESR
of less than 0.5Ω. In most cases, a ceramic capacitor will
satisfy this requirement. From Table 2, Capacitance Selec-
tion, C_OUT = 10µF and C_IN = 4.7µF.
For the feedback resistors, choose R1 = 301k. R2 can
then be calculated from equation (2) to be:
R2 = ^{⎛⎝⎜}
V_OUT
0.8
− 1^{⎞⎠⎟} R1= 827.8k;use
825k
Figure 6 shows the complete circuit along with its
efficiency curve.
100
90
80
70
60
50
40
30
20
10
0
0.1
V_IN
2.7V
TO 4.2V
C_IN^††
4.7µF
CER
4
V_IN
3
SW
LTC3410
1
RUN
6
V_FB
GND
2, 5
4.7µH*
10pF
V_OUT
3V
C_OUT^†
10µF
CER
825k
301k
3410 F06a
†_{TAIYO YUDEN JMK212BJ106}
††_{TAIYO YUDEN JMK212BJ475}
*MURATA LQH32CN4R7M23
Figure 6a
V_OUT
100mV/DIV
AC COUPLED
I_L
200mA/DIV
V_IN = 3.6V
V_IN = 4.2V
1
10
100
I_LOAD (mA)
1000
3410 F06b
Figure 6b
I_LOAD
200mA/DIV
20µs/DIV
V_IN = 3.6V
V_OUT = 3V
I_LOAD = 100mA TO 300mA
Figure 6c
3410 F06c
3410fb
13