ACT5880
Rev 2, 03-Sep-13
output capacitor, the inductor and then the input
capacitor.
Inversion Regulation Option
When programmed as an inversion regulator
option, the error amplifier in the FB3 feedback path
is phase inverted for the negative output regulation.
An external positive reference voltage is employed
for bias an external divider, whose tap connects to
the FB3. The voltage at FB3 is still regulated at
200mV in inversion application.
Irregular Conditions
When the load condition, or input to output ratio pull
the output out of regulation, the switch current limit
prevent the circuit from over stress. As the rectifier
diode is serial in the output path, short the output to
a voltage lower than input voltage would cause
excessive high current through the diode and might
damage the diode. Current limit switch or thermal
fuse is desired if there is possibility of shorting the
boost output.
Component Selection
Table 4 lists the suitable component specifications.
The better high frequency performance is important
to both inductor and capacitor. Capacitors with X5R
or X7R serial dielectrics are recommended.
The inductor DC saturation current should be at
least 30% over the limit of switch current. For
applications that do not require high current, options
with lower current limit are available upon ordering,
which is necessary when selecting the inductor with
smaller saturation current.
Table 4:
The Components Selection for REG3.
L
(μH)
COUT
(μF)
CIN
(μF)
Operation conditions
Voltage, 500mA, 5V
Voltage, 35mA, 40V
Current 35mA, 40V
Current 100mA, 20V
10~15
22
22~27
0.68
2.2
2.2
2.2
2.2
22
0.47
15
0.68
PCB Layout Considerations
The inductor current alternately goes into the output
capacitor and the power switch, place the output
capacitor close to the switch node SW3 and
connect the capacitor ground to the same current
loop back node GP3 would reduce the risk of
excessive noise conducting. Practically it might be
difficult to place all components close to the chip.
When the available space is constraint, the order
for being close to the chip is the rectifier diode, the
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