LT8608/LT8608B
42V, 1.5A Synchronous Step-Down Regulator
with 2.5µA Quiescent Current
FEATURES DESCRIPTION Wide Input Voltage Range: 3.0V to 42V
n Ultralow Quiescent Current Burst Mode® Operatio 0.5),
a minimum inductance is required to avoid sub-harmonic
oscillation. See Analog Devices Application Note 19.
Input Capacitor where ∆IL is the inductor ripple current as calculated several paragraphs below and ILOAD(MAX) is the maximum
output load for a given application. IOUT(MAX) = ILIM - The peak-to-peak ripple current in the inductor can be
calculated as follows: Bypass the input of the LT8608 circuit with a ceramic
capacitor of X7R or X5R type. Y5V types have poor performance over temperature and applied voltage, and
should not be used. A 4.7μF to 10μF ceramic capacitor
is adequate to bypass the LT8608 and will easily handle
the ripple current. Note that larger input capacitance is
required when a lower switching frequency is used. If the
input power source has high impedance, or there is significant inductance due to long wires or cables, additional
bulk capacitance may be necessary. This can be provided
with a low performance electrolytic capacitor.
Step-down regulators draw current from the input supply in pulses with very fast rise and fall times. The input
capacitor is required to reduce the resulting voltage ripple at the LT8608 and to force this very high frequency
switching current into a tight local loop, minimizing EMI.
A 4.7μF capacitor is capable of this task, but only if it is
placed close to the LT8608 (see the PCB Layout section).
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