SP6659_06 Datasheet, PDF (9/11 Pages) Sipex Corporation – 1.5MHz, 600mA Synchronous Buck Regulator

THEORY OF OPERATION
choose an inductor with DC series resis-
tance in the 50mΩ to 150mΩ range. For
higher efficiency at heavy loads (above
200mA), or minimal load regulation (but
some transient overshoot), the resistance
should be kept below 100mΩ. The DC cur-
rent rating of the inductor should be at least
equal to the maximum load current plus half
the ripple current to prevent core saturation
(600mA+105mA).
Table 1 lists some typical surface mount
inductors that meet target applications for
the SP6659.
SP6659 Inductor Selection Chart
Part #
Inductor Max DCR Rated DC Size WxLxH
(µH)
(mΩ) Current
(mm)
(Amps)
Murata
LQH32CN2R2M11
1.0
78
1
3.2x2.5x1.55
Murata
LQH32CN2R2M11
2.2
Murata
4.7
LQH32CN4R7M11
1.4
Sumida CR43
2.2
3.3
4.7
1.5
Sumida CDRH4D18 ^2.2
3.3
4.7
1.5
Toko D312C
2.2
3.3
4.7
126
195
56.2
71.2
86.2
108.7
75
110
162
120
140
180
240
0.79 3.2x2.5x1.55
0.6 5
2.52
1.5
1.44
1.15
3.2x2.5x1.55
4.5x4.0x3.5
1.32
4.7x4.7x2.0
1.04
0.84
1.29
1.14
3.6x3.6x1.2
0.98
0.79
Inductor inBold is used on the SP6659EB evaluation Board
Table 1: Typical Surface Mount Inductors
________________ INPUT CAPACITOR
SELECTION
The input capacitor reduces the surge cur-
rent drawn from the input and switching
noise from the device. The input capacitor
impedance at the switching frequency shall
be less than input source impedance to
prevent high frequency switching current
from passing to the input. A low ESR (Equiva-
lent Series Resistance) input capacitor sized
for maximum RMS current must be used.
Ceramic capacitors with X5R or X7R dielec-
trics are highly recommended because of
their low ESR and small temperature coeffi-
cients. A 4.7μF ceramic capacitor for most
applications is sufficient.
______________ OUTPUT CAPACITOR
SELECTION
The output capacitor is required to keep the
output voltage ripple small and to ensure
regulation loop stability. The output capaci-
tor must have low impedance at the switch-
ing frequency. Ceramic capacitors with X5R
or X7R dielectrics are recommended due to
their low ESR and high ripple current. The
output ripple ΔV_OUT is determined by:
ΔV_OUT ≤
{ + } VOUT X (VINMax - VOUT) X ESR
V_INMax X L X ƒ_OSC
1
(8X
ƒ
OSC
X
C_OUT)
Date: 9/25/06 Rev C
SP6659 1.5MHz, 600mA Synchronous Buck Regulator
9
© 2006 Sipex Corporation