LM3559TLX National Semiconductor Corporation, LM3559TLX Datasheet - Page 36

• Manufacturer Part Number: LM3559TLX
• Description: Synchronous Boost Flash Driver With Dual 900 Ma High Side Current Sources 1.8a Total Flash Current
• Manufacturer: National Semiconductor Corporation

www.national.com
Applications Information
OUTPUT CAPACITOR SELECTION
The LM3559 is designed to operate with at least a 10 µF ce-
ramic output capacitor. When the boost converter is running
the output capacitor supplies the load current during the boost
converters on-time. When the NMOS switch turns off the in-
ductor 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
during 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 operation the output capacitor must be at least a
10 µF ceramic. Larger capacitors such as a 22 µF or capaci-
tors in parallel can be used if lower output voltage ripple is
desired. To estimate the output voltage ripple considering the
ripple due to capacitor discharge (ΔV
the capacitors ESR (ΔV
For continuous conduction mode, the output voltage ripple
due to the capacitor discharge is:
The output voltage ripple due to the output capacitors ESR is
found by:
INDUCTOR SELECTION
The LM3559 is designed to use a 1 µH or 2.2 µH inductor.
Table 19
can work well with the LM3559. When the device is boosting
(V
efficiency loss in the circuit. Therefore choosing an inductor
with the lowest possible series resistance is important. Addi-
tionally, the saturation rating of the inductor should be greater
than the maximum operating peak current of the LM3559.
This prevents excess efficiency loss that can occur with in-
ductors that operate in saturation and prevents over heating
TDK Corporation
TDK Corporation
TDK Corporation
Murata
Murata
Murata
Manufacturer
OUT
Manufacturer
TOKO
TOKO
TOKO
TOKO
TOKO
> V
lists various inductors and their manufactures that
IN
) the inductor will typically be the largest area of
2.2 µH
1.5µH
2.2µH
ESR
1µH
1µH
L
GRM21BR60J226ME39L
) use the following equations:
GRM21BR61A106KE19
TABLE 18. Recommended Input/Output Capacitors (X5R Dielectric)
GRM188R60J06M
C2012JB1A106M
C1608JB0J106M
C2012JB0J226M
Part Number
Q
) and the ripple due to
FDSD0312-H-2R2M
FDSD0312-H-1R0M
FDSD0312-H-1R5M
FDSD0312-2R2M
FDSD0312-1R0M
TABLE 19. Recommended Inductors
Part Number
Value
10 µF
10 µF
22 µF
10 µF
10 µF
22 µF
36
In ceramic capacitors the ESR is very low so a close approx-
imation is to assume that 80% of the output voltage ripple is
due to capacitor discharge and 20% from ESR.
different manufacturers for various output capacitors and their
case sizes suitable for use with the LM3559.
INPUT CAPACITOR SELECTION
Choosing the correct size and type of input capacitor helps
minimize the voltage ripple caused by the switching of the
LM3559’s boost converter, and reduces noise on the boost
converter's input terminal that can feed through and disrupt
internal analog signals. In the Typical Application Circuit a 10
µF ceramic input capacitor works well. It is important to place
the input capacitor as close as possible to the LM3559’s input
(IN) terminal. This reduces the series resistance and induc-
tance that can inject noise into the device due to the input
switching currents.
or recommended for use with the LM3559.
of the inductor and further efficiency loss. For proper inductor
operation and circuit performance ensure that the inductor
saturation and the peak current limit setting of the LM3559 is
greater than I
ƒ
formance Characteristics plots.
SW
= 2MHz, and efficiency can be found in the Typical Per-
Dimensions (L×W×H)
3mm x 3mm x 1.2mm
3mm x 3mm x 1.2mm
0805 (2mm×1.25mm×1.25mm)
0805 (2mm×1.25mm×1.25mm)
0805 (2mm×1.25mm×1.25mm)
0805 (2mm×1.25mm×1.25mm)
3mm×3.2mm×1.2mm
3mm×3.2mm×1.2mm
3mm×3.2mm×1.2mm
0603 (1.6mm×0.8mm×0.8mm)
0603 (1.6mmx0.8mmx0.8mm)
PEAK
Case Size
in the following calculation:
Table 18
lists various input capacitors that
2.3A
3.4A
2.8A
2.3A
3.4A
I
SAT
Voltage Rating
Table 18
6.3V
6.3V
6.3V
6.3V
10V
10V
105 mΩ
145 mΩ
43 mΩ
71 mΩ
70mΩ
R
DC
lists