Datasheet

Table Of Contents
LMZ31530
SLVSBC7B OCTOBER 2013REVISED DECEMBER 2013
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Frequency Select
The LMZ31530 switching frequency can be selected from several values as shown in Table 2. To select a
switching frequency, a resistor (R
FREQ
) must be connected between the FREQ_SEL pin and either PGND or V5V
(pin 61) as shown in Table 2. For all output voltages, the recommended switching frequency is 500 kHz which
can be configured by leaving the FREQ_SEL pin open. Table 2 also shows the output voltage range for each
frequency.
Table 2. Frequency Selection
V
OUT
RANGE (V)
Frequency Select (kHz) R
FREQ
(kΩ) Connect To MIN MAX
300 66 PGND 0.6 3.6
400 498 PGND 0.6 3.6
500 open - 0.6 3.6
650 745 V5V 0.8 3.6
750 188 V5V 1.0 3.6
850 short V5V 1.2 3.6
CAPACITOR RECOMMENDATIONS FOR THE LMZ31530 POWER SUPPLY
Capacitor Technologies
Electrolytic, Polymer-Electrolytic Capacitors
Aluminum electrolytic capacitors provide adequate decoupling over the frequency range of 2 kHz to 150 kHz.
When using electrolytic capacitors, high-quality, polymer-electrolytic capacitors are recommended. Polymer-
electrolytic type capacitors are recommended for applications where the ambient operating temperature is less
than 0°C. The Panasonic OS-CON capacitor series is suggested due to the lower ESR, higher rated surge,
power dissipation, ripple current capability, and small package size.
Ceramic Capacitors
The performance of ceramic capacitors is most effective above 150 kHz. Multilayer ceramic capacitors have a
low ESR and a resonant frequency higher than the bandwidth of the regulator. They can be used to reduce the
reflected ripple current at the input as well as improve the transient response of the output.
Tantalum, Polymer-Tantalum Capacitors
Polymer-tantalum type capacitors are recommended for applications where the ambient operating temperature is
less than 0°C. The Panasonic POSCAP series and Kemet T530 capacitor series are recommended rather than
many other tantalum types due to their lower ESR, higher rated surge, power dissipation, ripple current
capability, and small package size. Tantalum capacitors that have no stated ESR or surge current rating are not
recommended for power applications.
Input Capacitor
The LMZ31530 requires a minimum input capacitance of 44 μF of ceramic type. The voltage rating of input
capacitors must be greater than the maximum input voltage. The input RMS ripple current is a function of the
output current and the duty cycle for any application. The input capacitor must be rated for the application's RMS
ripple current. Table 3 includes a preferred list of capacitors by vendor.
Output Capacitor
The required output capacitance of the LMZ31530 can be comprised of either all ceramic capacitors, or a
combination of ceramic and bulk capacitors. The required output capacitance must include at least 100 µF of
ceramic type. When adding additional non-ceramic bulk capacitors, low-ESR devices like the ones recommended
in Table 3 are required. The required capacitance above the minimum is determined by actual transient deviation
requirements. See Table 4 for typical transient response values for several output voltage, input voltage and
capacitance combinations. Table 3 includes a preferred list of capacitors by vendor.
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