ACT5880 datasheet(67/87 Pages) ACTIVE-SEMI

67 / 87 page

ACT5880

Rev 2, 03-Sep-13

- 67 -

www.active-semi.com

ActivePMU

TM and ActivePathTM are trademarks of Active-Semi.

I2CTM is a trademark of NXP.

Active-Semi Confidential―Do Not Copy or Distribute

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.

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

output capacitor, the inductor and then the input

capacitor.

Operation conditions

(μH)

COUT

(μF)

Voltage, 500mA, 5V

10~15

22~27

Voltage, 35mA, 40V

0.68

Current 35mA, 40V

0.47

Current 100mA, 20V

0.68

CIN

(μF)

2.2

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