LM3207TL-2.53 National Semiconductor, LM3207TL-2.53 Datasheet - Page 19

• Manufacturer Part Number: LM3207TL-2.53
• Description: LM3207 650mA Miniature, Adjustable, Step-Down DC-DC Converter for RF Power Amplifiers with Integrated Vref LDO; Package: MICRO SMD; No of Pins: 9; Qty per Container: 250; Container: Reel
• Manufacturer: National Semiconductor

NR3015T3R3M
DO3314-332MXC
MIPW3226D3R0M
INDUCTOR SELECTION
A 3.3µH inductor with saturation current rating over 1200mA
and low inductance drop at the full DC bias condition is rec-
ommended for almost all applications. The inductor’s DC
resistance should be less than 0.2Ω for good efficiency. For
low dropout voltage, lower DCR inductors are advantageous.
The lower limit of acceptable inductance is 1.7µH at 1200mA
over the operating temperature range. Full attention should
be paid to this limit, because some small inductors show large
inductance drops at high DC bias. These can not be used with
the LM3207. Table 2 suggests some inductors and suppliers.
If a smaller inductance inductor is used in the application, the
LM3207 may become unstable during line and load transients
and V
cost applications, an unshielded bobbin inductor is suggest-
ed. For noise critical applications, a toroidal or shielded-
bobbin inductor is recommended. A good practice is to layout
the board with footprints accommodating both types for de-
sign flexibility. This allows substitution of a low-noise toroidal
inductor, in the event that noise from low-cost bobbin models
is unacceptable. Saturation occurs when the magnetic flux
density from current through the windings of the inductor ex-
ceeds what the inductor’s core material can support with a
corresponding magnetic field. This can result in poor efficien-
cy, regulation errors or stress to DC-DC converter like the
LM3207.
DC-DC CONVERTER CAPACITOR SELECTION
The LM3207 is designed with a ceramic capacitor for its input
and output filters. Use a 10µF ceramic capacitor for input and
a 4.7µF ceramic capacitor for output. They should maintain at
least 50% capacitance at DC bias and temperature condi-
tions. Ceramic capacitors types such as X5R, X7R are rec-
ommended for both filters. These provide an optimal balance
between small size, cost, reliability and performance for cell
phones and similar applications. Table 3 lists suggests ac-
ceptable part numbers and their suppliers. DC bias charac-
teristics of the capacitors must be considered when selecting
the voltage rating and case size of the capacitor. If it is nec-
essary to choose a 0603-size capacitor for V
of the LM3207should be carefully evaluated on the system
board. Output capacitors with smaller case sizes mitigate
piezo electric vibrations when the output voltage is stepped
up and down at fast rates. However, they have a larger per-
centage drop in value with dc bias. Use of multiple 2.2µF or
1µF capacitors in parallel may also be considered.
TABLE 1. Suggested capacitors and their suppliers
TABLE 2. Suggested inductors and their suppliers
C1005X5R0J224KT, 220nF, 6.3V
Model
C1005X5R1A104KT, 100nF, 10V
CON
transient response times may be affected. For low-
Model
Size (WxLxH) [mm]
3.0 x 3.0 x 1.5
3.3 x 3.3 x 1.4
3.2 x 2.6 x 1.0
Taiyo-Yuden
Coilcraft
FDK
IN
, the operation
Vendor
Vendor
TDK
TDK
19
The input filter capacitor supplies AC current drawn by the
PFET switch of the LM3207 in the first part of each cycle and
reduces the voltage ripple imposed on the input power
source. The output filter capacitor absorbs the AC inductor
current, helps maintain a steady output voltage during tran-
sient load changes and reduces output voltage ripple. These
capacitors must be selected with sufficient capacitance and
sufficiently low ESR (Equivalent Series Resistance) to per-
form these functions. The ESR of the filter capacitors is
generally a factor in voltage ripple.
EN PIN CONTROL
Drive the EN and EN
turn the LM3207 ON and OFF. Use a comparator, Schmidt
trigger or logic gate to drive the EN and EN
high (>1.2V) for normal operation and low (<0.5V) for a
0.01µA (typ.) shutdown mode.
Set EN low to turn off the LM3207 during power-up and under
voltage conditions when the power supply is less than the
2.7V minimum operating voltage. The part is out of regulation
when the input voltage is less than 2.7V. The LM3207 is de-
signed for mobile phones where the system controller con-
trols operation mode for maximizing battery life and require-
ments for small package size outweigh the additional size
required for inclusion of UVLO (Under Voltage Lock-Out) cir-
cuitry.
Micro SMD PACKAGE ASSEMBLY AND USE
Use of the Micro SMD package requires specialized board
layout, precision mounting and careful re-flow techniques, as
detailed in National Semiconductor Application Note 1112.
Refer to the section Surface Mount Technology (SMD) As-
sembly Considerations. For best results in assembly, align-
ment ordinals on the PC board should be used to facilitate
placement of the device. The pad style used with Micro SMD
package must be the NSMD (non-solder mask defined) type.
This means that the solder-mask opening is larger than the
pad size. This prevents a lip that otherwise forms if the solder-
mask and pad overlap, from holding the device off the surface
of the board and interfering with mounting. See Application
Note 1112 for specific instructions.
The 9-Bump package used for LM3207 has 300 micron solder
balls and requires 10.82mil pads for mounting the circuit
board. The trace to each pad should enter with a 90° entry
angle to prevent debris from being caught in deep corners.
Initially, the trace to each pad should be 6-7mil wide, for a
section approximately 6mil long or longer, to provide thermal
relief. Each trace should then neck up or down to its optimal
width. The important criterion is symmetry. This ensures the
solder bumps re-flow evenly and that the device solders level
to the board. In particular, special attention must be paid to
the pads for bumps A1, A3 and B3. Because P
are typically connected to large copper planes, inadequate
thermal relief’s may result in late or inadequate re-flow of
these bumps. The Micro SMD package is optimized for the
smallest possible size in applications with red or infrared
opaque cases. Because the Micro SMD package lacks the
TABLE 3. Suggested capacitors and their suppliers
C2012X5R1A475M, 4.7uF, 6.3V
C1608X5R0J475M, 4.7uF, 6.3V
C1608X5R0J106M, 10µF, 6.3V
C2012X5R0J106M, 10uF, 6.3V
0805ZD475KA, 4.7µF, 10V
Model
LDO
pins using the system controller to
LDO
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GND
Vendor
pins. Set EN
www.national.com
TDK
TDK
TDK
TDK
and PV
IN