ACT5880 datasheet(69/87 Pages) ACTIVE-SEMI

69 / 87 page

ACT5880

Rev 2, 03-Sep-13

- 69 -

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

The Always-on LDO and the Backup

Battery Charger

Two regulators are specialized for always-on

powers, as a backup battery charger and a low

voltage, low quiescent current always-on regulator.

The backup battery charger is a low power voltage

regulator with preset current limit of up to 5mA

nominal as a constant-voltage and constant-current

charger. If applications like the RAM data keeping

requires larger current option, contact factory for

ordering.

The always-on LDO and the backup battery charger

have programmable output voltages, which are set

individually as other LDOs but the backup battery

charger uses different code to voltage cross as

what in the VBBAT OUTPUT VOLTAGE SETTING

table. As the VBBAT is internally connected to

power the always-on LDO, and the always-on LDO

powers the RTC, if the RTC function is used, the

outputs of both regulator should have enough

headroom for the RTC operation.

The backup battery charger LDO outputs at slightly

lower voltage than the code voltage with a current

related drop before it falls into current regulation,

which would have output the exact code voltage

when the output current were zero. This drop has

close to logarithmic trend to the load current (i.e.,

doubled every decade change of load current).

Typically the backup battery charger input, the

BBCIN connects to the main battery; Its output, the

VBBAT connects to a backup battery coin cell or a

super cap, charges and floats at the programmed

voltage. Its precise voltage setting and current

setting accommodate to various battery chemicals

of 1.5V to 3.6V output and super caps. When the

input power removes, the backup battery charger

turns itself shutdown with almost 0 leakage

backward from the cell.

The input of the always-on regulator is internally

routed to available powers, which is the internal

bias in the ACT5880, the VSYS, or the VBBAT. The

always-on regulator output is internally connected

to power the RTC block. When the RTC function is

enabled, the minimum voltage to start oscillation or

to maintain the RTC functional is greater than the

minimum available programmable output voltage.

The data in register bits for the always-on LDO

output voltage setting are kept until both the system

power and VALIVE fail.

Two accesses are designed for change the VBBAT

regulation voltage. The first access is to set

UNLOCK bit, to allow the change to the voltage

configuration byte, then the VBBAT is changed by

writing to the byte. It is highly recommended to

reset the UNLOCK bit after each writing, to avoid

possible accidental change to the voltage setting for

VBBAT.

For configuration and manipulation, refer to THE

REGISTERS and BITS DESCRIPTION

for detail.

Irregular Conditions

The LDO circuit monitors the output and asserts

interrupt if out of regulation happens, if the function

is allowed. When short circuit or over current

happens, the output current limit folds back to about

the 0.45 times of the maximum output current. Each

LDO is safe in output short circuit.

The individual LDO does not have its own over

temperature protection circuit. Subject to the whole

die's thermal condition, the LDOs are turned off

when die over temperature happens.

Component Selection

Input Capacitor Selection

Each LDO requires a small ceramic input capacitor

to supply current to support fast transients at the

input of the LDO.

Output Capacitor Selection

Each LDO requires a small ceramic output

capacitor for stability. Each output capacitor should

be connected directly between the output and GA

pins, as close to the output as possible, and with a

short, direct connection.

The input and output capacitor values are listed in

Table 6. High quality ceramic capacitors such as

X7R and X5R dielectric types are strongly

recommended.

Table 6

Component Recommendation for LDOs

LDO NAME

OUTPUT CAP

(μF)

INPUT CAP

(μF)

REG4, REG6,

REG7, REG8

3.3

REG5, REG9, REG12

2.2

REG10, REG13

1.5

REG11

LDO tied in REG2

1~1.5

Backup Battery

Charger

1~1.5

Always-on LDO

1~1.5

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