Specifications

LM3269
SNVS793D –NOVEMBER 2011 –REVISED MAY 2015 www.ti.com
Typical Application (continued)
8.2.1 Design Requirements
DESIGN PARAMETER EXAMPLE VALUE
Minimum input voltage 2.7 V
Minimum output voltage 0.6 V
Output current 0 to 750 mA
Switching frequency 2.4 MHz (typical)
8.2.2 Detailed Design Procedure
8.2.2.1 Recommended External Components
8.2.2.1.1 Inductor Selection
A 2.2-μH inductor with a saturation current rating over 1500 mA and low inductance drop at the full DC bias
condition is recommended for almost all applications. An inductor with a smaller DC resistance, such as 110 mΩ
(depending on case size of resistor), should be used for good efficiency.
Table 2. Suggested 2.2-µH Inductors
I
SAT
I
RATING
VENDOR MODEL DIMENSIONS (mm) DCR
(30% drop) (Δ40°)
FDK MIPSZ2520D2R2 2.5 x 2.0 x 1.0 1.5 A 1.1 A 110 mΩ
Murata LQH2HPN1R0NG0 2.5 x 2.0 x 1.2 2 A 1.2 A 112 mΩ
Samsung CIG22H2R2MNE 2.5 x 2.0 x 1.2 1.9 A 1.6 A 116 mΩ
TDK TFM201610A2R2M 2.0 x 1.6 x 1.0 1.7 A 1.3 A 180 mΩ
TOKO DFE201612C2R2N 2.0 x 1.6 x 1.2 2.1 A 1.3 A 155 mΩ
8.2.2.1.2 Input Capacitor Selection
A ceramic input capacitor of 10 µF, 6.3 V, 0603 (1608) is recommended for use in most applications. Place the
input capacitor as close as possible to the PVIN pin and PGND pin of the device. A larger value of higher voltage
rating may be used to improve input filtering. Use X7R, X5R, or B types; do not use Y5V or F. DC board
characteristics of ceramic capacitors must be considered when selecting case sizes like 0402 (1005). The input
filter capacitor supplies current to the PFET (high-side) switch in first half of each cycle and reduces voltage
ripple imposed on the input power source. A ceramic capacitor’s low equivalent series resistance (ESR) provides
the best noise filtering of the input voltage spikes due to this rapidly changing current.
8.2.2.1.3 Output Capacitor Selection
Use a 4.7 µF capacitor for the output capacitor. Use of capacitor types such as X5R, X7R are recommended for
the filter. These provide an optimal balance between small size, cost, reliability, and performance for cell phones
and similar applications. Table 3 lists suggested part numbers and suppliers. DC bias characteristics of the
capacitors must be considered while selecting the voltage rating and case size of the capacitor. Smaller case
sizes for the output capacitor mitigate piezo-electric vibrations of the capacitor when the output voltage is
stepped up and down at fast rates. However, they have a bigger percentage drop in value with DC bias. A 0603
(1608) case size capacitor is recommended for output. For RF Power Amplifier applications, split the output
capacitor between DC-DC converter and RF Power Amplifier(s). (4.7 μF (0402 (1005)) + PA input cap
(0402(1005)/0201(0603)) is recommended.) The optimum capacitance split is application dependent. Place all
the output capacitors very close to their respective device.
NOTE
If using a 4.7 µF, 0402 (1005) as the output capacitor, the total recommended actual
capacitance on V
OUT
bus should be at least 7 µF (4.7 µF + PA decoupling caps) to take
into account the 0402 (1005) DC bias degradation and other tolerances.
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