Datasheet

LM3243
SNVS782B –OCTOBER 2010–REVISED FEBRUARY 2013 www.ti.com
Table 3. Suggested Inductors and Their Suppliers
Model Vendor Size I
SAT
−30% DCR
DFE201610C-1R5M
TOKO 2.0 mm x 1.6 mm x 1.0 mm 2.2A 120 mΩ
(1285AS-H-1R5M)
PSD20161T-1R5MS CYNTEC 2.0 mm x 1.6 mm x 1.0 mm 1.6A 143 mΩ
TFM201610-1R5M TDK 2.0 mm x 1.6 mm x 1.0 mm 2.2A 140 mΩ
Capacitor Selection
The LM3243 is designed to use ceramic capacitors for its input and output filters. Use a 10 µF capacitor for the
input and approximately 10 µF actual total output capacitance. Capacitor types such as X5R, X7R are
recommended for both filters. These provide an optimal balance between small size, cost, reliability and
performance for cell phones and similar applications. Table 4 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. For even smaller total solution size, 0402 case size capacitors are recommended for filtering. Use of
multiple 2.2 µF or 1 µF capacitors can also be considered. For RF Power Amplifier applications, split the output
capacitor between DC-DC converter and RF Power Amplifiers: 10 µF (C
OUT1
) + 4.7 µF (C
OUT2
) + 3 x 1.0 µF
(C
OUT3
) is recommended. The optimum capacitance split is application dependent, and for stability the actual
total capacitance (taking into account effects of capacitor DC bias, temperature de-rating, aging and other
capacitor tolerances) should target 10 µF with 2.5V DC bias (measured at 0.5 V
RMS
). Place all the output
capacitors very close to the respective device. A high-frequency capacitor (3300 pF) is highly recommended to
be placed next to C
OUT1
.
Table 4. Suggested Capacitors and Their Suppliers
Capacitance Model Size (Wx L) (mm) Vendor
10 µF GRM185R60J106M 1.6 x 0.8 Murata
10 µF CL05A106MQ5NUN 1.0 x 0.5 Samsung
4.7 µF CL05A475MQ5NRN 1.0 x 0.5 Samsung
1.0 µF CL03A105MQ3CSN 0.6 x 0.3 Samsung
3300 pF GRM022R60J332K 0.4 x 0.2 Murata
EN Input Control
Use the system controller to drive the EN HIGH or LOW with a comparator, Schmitt trigger or logic gate. Set EN
= HIGH (>1.2V) for normal operation and LOW (<0.5V) for shutdown mode to reduce current consumption to
0.02 µA (typ.) current.
Startup
The waveform Figure 24 in shows the startup condition. First, V
IN
should take on a value between 2.7V and 5.5V.
Next, EN should go HIGH (>1.2V). Finally, VCON should be set to a value that corresponds to the required
output voltage (V
OUT
= VCON x 2.5). V
OUT
will reach its steady-state value in less than 50 µs. To optimize the
startup time and behavior of the output voltage, the LM3243 will always start up in PWM mode (even when
MODE = HIGH and output load current ≤ 75mA), then seamlessly transition into PFM mode.
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