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Date: 2/1/05 SP6654 High Efficiency 800mA Synchronous Buck Regulator © Copyright 2005 Sipex Corporation
APPLICATION INFORMATION
Output Voltage Program
The output voltage is programmed by the external
divider, as shown in the typical application circuit
on page 1. First pick a value for R
I
that is no larger
than 300K. Too large a value of R
I
will reduce the
AC voltage seen by the loop comparator since the
internal FB pin capacitance can form a low pass
filter with R
F
in parallel with R
I
. The formula for
R
F
with a given R
I
and output voltage is:
R
F
= (
V
OUT
- 1
) • R
I
0.8V
Output Voltage Ripple Frequency
An important consideration in a power supply
application is the frequency value of the output
ripple. Given the control technique of the SP6654
(as described in the operations section), the
frequency of the output ripple will vary when in
light to moderate load in the discontinuous or
PFM mode. For moderate to heavy loads greater
than about 100mA inductor current ripple, (for
the typical 10µH inductor application on 100mA
is half the 200mA inductor current ripple), the
output ripple frequency will be fairly constant.
From the operations section, this maximum loop
frequency in continuous conduction mode is:
1 V
OUT
(V
IN
- V
OUT
)
F
LP
≈
K
ON
*
V
IN
*
Data for loop frequency, as measured from
output voltage ripple frequency, can be found in
the typical performance curves.
Layout Considerations
Proper layout of the power and control circuits is
necessary in a switching power supply to obtain
good output regulation with stability and a mini-
mum of output noise. The SP6654 application
circuit can be made very small and reside close to
the IC for best performance and solution size, as
long as some layout techniques are taken into
consideration. To avoid excessive interference
between the SP6654 high frequency converter and
INDUCTORS SURFACE MOUNT
Inductor Specification
Inductance Manufacturer/Part No. Series R Ω I
SAT
(A) Size Inductor Type Manufacturer
(µH) LxW(mm) Ht. (mm) Website
10 Sumida CDRH5D28-100 0.048 1.30 5.7 x 5.5 3.0 Shielded Ferrite Core sumida.com
10 TDK RLF5018T-100MR94 0.056 0.94 5.6 x 5.2 2.0 Shielded Ferrite Core tdk.com
10 Coilcraft DO1608C-103 0.160 1.10 6.6 x 4.5 2.9 Unshielded Ferrite Core coilcraft.com
10 Coilcraft LPO6013-103 0.300 0.70 6.0 x 5.4 1.3 Unshielded Ferrite Core coilcraft.com
6.8 Sumida CDRH5D28-6R8 0.081 1.12 4.7 x 4.5 3.0 Shielded Ferrite Core sumida.com
6.8 TDK RLF5018T-6R8M1R1 0.47 1.10 5.6 x 5.2 2.0 Shielded Ferrite Core tdk.com
6.8 Coilcraft DO1608C-682 0.130 1.20 6.6 x 4.5 2.9 Unshielded Ferrite Core coilcraft.com
6.8 Coilcraft LPO6013-103 0.200 0.60 6.0 x 5.4 1.3 Unshielded Ferrite Core coilcraft.com
CAPACITORS - SURFACE MOUNT
Capacitor Specification
Capacitance Manufacturer/Part No. ESR RippleCurrent Size Voltage Capacitor Type Manufacturer
(µF) Ω (max) (A) @ 45°C LxW(mm) Ht. (mm) (V) Website
22 TDK C3216X5R0J226M 0.002 3.00 3.2 x 1.6 1.6 6.3 X5R Ceramic tdk.com
22 SANYO 6APA22M 0.040 1.90 7.3 x 4.3 2.0 6.3 POSCAP sanyovideo.com
47 TDK C3225X5R0J46M 0.002 4.00 3.2 x 1.6 1.6 6.3 X5R Ceramic tdk.com
47 SANYO 6TPA47M 0.040 1.90 6.0 x 3.2 2.8 6.3 POSCAP sanyovideo.com
Table 2 Component Selection
Note: Components highlighted in bold are those used on the SP6654 Evaluation Board.
