LM3561TMX National Semiconductor Corporation, LM3561TMX Datasheet - Page 29

• Manufacturer Part Number: LM3561TMX
• Description: Synchronous Boost Converter With 600ma High Side Led Driver And I2c-compatible Interface
• Manufacturer: National Semiconductor Corporation

Applications Information
OUTPUT CAPACITOR SELECTION
The LM3561 is designed to operate with a at least a 10µF
ceramic output capacitor. When the boost converter is run-
ning the output capacitor supplies the load current during the
boost converters on-time. When the NMOS switch turns off
the inductor energy is discharged through the internal PMOS
switch supplying power to the load and restoring charge to the
output capacitor. This causes a sag in the output voltage dur-
ing the on-time and a rise in the output voltage during the off-
time. The output capacitor is therefore chosen to limit the
output ripple to an acceptable level depending on load current
and input/output voltage differentials and also to ensure the
converter remains stable.
For proper LED operation the output capacitor must be at
least a 10µF ceramic. Larger capacitors such as 22µF can be
used if lower output voltage ripple is desired. To estimate the
output voltage ripple considering the ripple due to capacitor
discharge (ΔV
(ΔV
For continuous conduction mode, the output voltage ripple
due to the capacitor discharge is:
INDUCTOR SELECTION
The LM3561 is designed to use a 1µH to 2.2µH inductor.
Table 13
LM3561. When the device is boosting (V
tor will typically be the biggest area of efficiency loss in the
circuit. Therefore, choosing an inductor with the lowest pos-
sible series resistance is important. Additionally, the satura-
tion rating of the inductor should be greater than the maximum
operating peak current of the LM3561. This prevents excess
efficiency loss that can occur with inductors that operate in
saturation. For proper inductor operation and circuit perfor-
Manufacturer
ESR
TDK Corporation
TDK Corporation
TDK Corporation
Manufacturer
Coilcraft
) use the following equations:
TDK
TDK
TDK
TDK
TDK
Murata
Murata
lists various inductors that can work well with the
Q
) and the ripple due to the capacitors ESR
1µH
1µH
1µH
1µH
1µH
1µH
L
GRM21BR60J226ME39L
GRM21BR61A106KE19
TABLE 12. Recommended Input/Output Capacitors (X5R Dielectric)
C2012JB1A106M
C1608JB0J106M
C2012JB0J226M
Part Number
OUT
VLS252010ET-1R0N
VLS20160ET-1R0N
VLS252012T-1R0N
VLS2012ET-1R0N
XPL2010-102ML
VLS2010-1R0N
> V
TABLE 13. Recommended Inductors
Part Number
IN
) the induc-
Value
10µF
10µF
22µF
10µF
22µF
29
The output voltage ripple due to the output capacitors ESR is
found by:
In ceramic capacitors the ESR is very low so assume that 80%
of the output voltage ripple is due to capacitor discharge and
20% from ESR.
ious output capacitors and their case sizes suitable for use
with the LM3561.
INPUT CAPACITOR SELECTION
Choosing the correct size and type of input capacitor helps
minimize the voltage ripple caused by the switching of the
LM3561’s boost converter and reduces noise on the devices
input terminal that can feed through and disrupt internal ana-
log signals. In the Typical Application Circuit a 10µF ceramic
input capacitor works well. It is important to place the input
capacitor as close as possible to the LM3561’s input (IN) ter-
minals. This reduces the series resistance and inductance
that can inject noise into the device due to the input switching
currents.
ed for use with the LM3561.
mance ensure that the inductor saturation and the peak cur-
rent limit setting of the LM3561 is greater than I
be calculated by:
ƒ
Characteristics plots.
SW
2mm x 1.6mm x 0.95mm
Dimensions (L×W×H)
2mm×2.5mm×1.2mm
2mm x 2mm x 1.2mm
2.5mm x 2mm x 1mm
= 2MHz, and η can be found in the Typical Performance
2mm x 2mm x 1mm
2mm×1.9mm×1mm
0805(2mm×1.25mm×1.25mm)
0805(2mm×1.25mm×1.25mm)
0805(2mm×1.25mm×1.25mm)
0805(2mm×1.25mm×1.25mm)
0603(1.6mm×0.8mm×0.8mm)
Table 12
Case Size
Table 12
lists various input capacitors recommend-
lists different manufacturers for var-
100mΩ
81mΩ
73mΩ
90mΩ
71mΩ
70mΩ
R
DC
Voltage Rating
PEAK
6.3V
6.3V
6.3V
10V
10V
www.national.com
1.65A
1.65A
1.6A
2.7A
1.5A
1.9A
. This can
I
SAT