43
8048C–AVR–02/12
ATtiny43U
The inductor must be able to tolerate the following input current:
... where
η is the efficiency of the converter at given voltages and load current. See “Boost Con- The inductor must also be able to tolerate short peak currents. At steady state, i.e. when the
converter has stabilised after a constant load current has been introduced, the peak current is
calculated as follows:
... where D is the duty cycle and T
S the switching period of the boost converter. See “Boost Con- follows:
Overall efficiency of the boost converter is affected by the series resistance and the core loss of
the inductor.
8.6.2
Diode
It is recommended to use a Schottky diode with forward voltage, V
F, and reverse leakage cur-
rent, I
R, values as low as possible. This is because converter efficiency mainly depends on the
forward voltage of the diode when I
LOAD is at maximum and VBAT is at minimum. It should be
noted that the reverse leakage current easily becomes a dominant factor, especially in Active
Low Current Mode. For reference, see converter current consumption during Low Current Mode
The diode is subject to peak currents the same magnitude as the inductor. See
“Inductor” onIt should be noted that reverse leakage current is a highly temperature dependent variable.
8.6.3
Input Capacitors
A voltage drop occurs between the voltage source and inductor L
1 because voltage sources are
not ideal and tracks have a non-zero resistance. The voltage drop is application specific and
depends on the quality of the voltage source, inductor current, track size and track length.
I
IN
V
CC
I
LOAD
×
V
BAT
η
×
--------------------------------
=
I
PEAK
V
BAT
T
S
D
×
L
------------------------------------
=
D
V
CC
V
BAT
-------------
1
2
---
–
I
LOAD
×
=