LM3691TL-0.9 NSC [National Semiconductor], LM3691TL-0.9 Datasheet - Page 15

• Manufacturer Part Number: LM3691TL-0.9
• Description: High Accuracy, Miniature 1A, Step-Down DC-DC Converter for Portable Applications
• Manufacturer: NSC [National Semiconductor]

Application Information
INDUCTOR SELECTION
DC bias current characteristics of inductors must be consid-
ered. Different manufacturers follow different saturation cur-
rent rating specifications, so attention must be given to
details. DC bias curves should be requested from them as
part of the inductor selection process.
Minimum value of inductance to guarantee good perfor-
mance is 0.5 µH at 1.5A (I
ambient temp range. The inductor’s DC resistance should
be less than 0.1Ω for good efficiency at high current condition.
The inductor AC loss (resistance) also affects conversion ef-
ficiency. Higher Q factor at switching frequency usually gives
better efficiency at light load to middle load.
Table 1 lists suggested inductors and suppliers
INPUT CAPACITOR SELECTION
A ceramic input capacitor of 4.7 µF, 6.3V/10V is sufficient for
most applications. Place the input capacitor as close as pos-
sible to the V
or higher voltage rating may be used to improve input voltage
filtering. Use X7R, X5R or B types; do not use Y5V or F. DC
bias characteristics of ceramic capacitors must be considered
when selecting case sizes like 0402. Minimum input capac-
itance to guarantee good performance is 2.2 µF at maxi-
mum input voltage DC bias including tolerances and over
ambient temp range.
The input filter capacitor supplies current to the PFET (high-
side) switch in the first half of each cycle and reduces voltage
ripple imposed on the input power source. A ceramic
capacitor's low ESR provides the best noise filtering of the
input voltage spikes due to this rapidly changing current. Se-
lect an input filter capacitor with sufficient ripple current rating.
The input current ripple can be calculated as:
4.7 µF for C
LQM2HPN1R0MG0
KSLI252010AG1R0
C1608X5R1A475K
C1608X5R0J475K
MIPSZ2012D1R0
MLP2520S1R0L
IN
IN
Model
Model
pin and GND pin of the device. A larger value
and C
OUT
LIM
typ.) bias current over the
TABLE 2. Suggested Capacitors and Their Suppliers
TABLE 1. Suggested Inductors and Their Suppliers
Ceramic
Ceramic
Type
HItachi Metals
Vendor
Murata
TDK
FDK
15
Vendor
TDK
TDK
Dimensions LxWxH (mm)
OUTPUT CAPACITOR SELECTION
Use a 4.7μF, 6.3V ceramic capacitor, X7R, X5R or B types;
do not use Y5V or F. DC bias voltage characteristics of ce-
ramic capacitors must be considered. DC bias characteristics
vary from manufacturer to manufacturer, and DC bias curves
should be requested from them as part of the capacitor se-
lection process. The output filter capacitor smooths out cur-
rent flow from the inductor to the load, helps maintain a steady
output voltage during transient load changes and reduces
output voltage ripple. These capacitors must be selected with
sufficient capacitance and sufficiently low ESR to perform
these functions. Minimum output capacitance to guaran-
tee good performance is 2.2 µF at the output voltage DC
bias including tolerances and over ambient temp range.
The output voltage ripple is caused by the charging and dis-
charging of the output capacitor and also due to its R
can be calculated as:
Voltage peak-to-peak ripple due to capacitance =
Voltage peak-to-peak ripple due to ESR =
V
Because these two components are out of phase the rms val-
ue can be used to get an approximate value of peak-to-peak
ripple.
Voltage peak-to-peak ripple, root mean squared =
Note that the output voltage ripple is dependent on the current
ripple and the equivalent series resistance of the output ca-
pacitor (R
temperature dependent); make sure the value used for cal-
culations is at the switching frequency of the part.
Table 2 lists suggested capacitors and suppliers.
PP-ESR
2.0 x 1.25 x 1.0
2.5 x 2.0 x 1.0
2.5 x 2.0 x 1.0
2.5 x 2.0 x 1.0
= (2 * I
ESR
). The R
Voltage Rating (V)
RIPPLE
) * R
10.0
ESR
6.3
ESR
is frequency dependent (as well as
D.C.R (mΩ)
0603 (1608)
0603 (1608)
Inch (mm)
Case Size
55
60
80
90
www.national.com
ESR
and