ACT5880 datasheet(64/87 Pages) ACTIVE-SEMI

64 / 87 page

ACT5880

Rev 2, 03-Sep-13

- 64 -

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

General Description

REG1 and REG2 are fixed-frequency, current-mode,

synchronous PWM step-down DC/DC converters that

achieve peak efficiencies of up to 97%. These

regulators operate at a fixed frequency around 2MHz,

minimizing noise in sensitive applications and

allowing the use of small external components.

Additionally, REG1 and REG2 are available with a

variety of standard and custom output voltages, and

may be software-controlled via the I2C interface for

systems that require advanced power management

functions. Finally, REG2 features a unique SLEEP

mode function that significantly reduces quiescent

power consumption yet maintains a regulated output

voltage that can supplies up to 10mA nominal (50mA

maximum).

By default, REG1 and REG2 operate in fixed-

frequency PWM mode at medium to heavy load, then

transit to a proprietary power-saving mode at light

load for having better efficiency. In applications where

low noise is critical, fixed-frequency PWM operation

may be retained across the entire load current range

(in compromising of the light-load efficiency) by

setting the respective MODE[ ] bit via I2C.

REG1 and REG2 are capable of operating at up to

100% duty cycle. During 100% duty-cycle operation,

the

high-side

power

MOSFET

held

continuously, providing a direct connection from the

input to the output (through the inductor), ensuring

the lowest possible dropout voltage in battery

powered applications.

REG1 has 2 banks of registers for setting the output

voltage, with the VSEL input to select to output

voltage set in which bank.

REG2 has a buck unit and a synergetic linear

regulation unit, which is designed to replace the buck

unit in light load operation. The linear unit has almost

the same programmable features as an LDO, but

with a bit to program if to turn on when the buck is

tuned off, and it should not be set to active discharge

in shutdown.

Manipulation

The output voltages and few other operation options

of REG1, the buck unit and synergetic linear unit in

REG2 are programmable through the I2C operation.

Refer to the REGISTER AND BIT DESCRIPTIONS

section for details and the step-down DC/DC

converter and LDO Voltage Setting for the code to

voltage cross.

Summary of key specifications

Table 3:

Key Specifications of Step-down DC/DC

Converters

Soft-Start Step Transient

Both REG1 and REG2 implement constant slope

control for soft start ramping in 400μs nominal, as

well as the step up transition for outputting two

different voltages. This assures no overshoot during

start up and changes of voltages. The output

voltage drop is load condition dependent during

turning off or step down transition.

REG2 Sleep Mode

When set the EVENT4 bit of the system register,

the buck operation of REG2 stops and the linear

regulator unit starts smoothly with no dropping at

output. When the "Enable Key" is pressed or the

EVENT4 is cleared, the REG2 is set back to buck

operation and the linear regulation unit stops, also

in seamless smooth transition. The EVENT4 bit

should be cleared by software when wanting the

REG2 resumes from the sleep mode to normal

mode.

When REG2 is set off before the set of EVENT4,

the assertion of EVENT4 starts REG2 in sleep

mode. In this condition the clear of EVENT4 sets

the REG2 off, without turning it into buck operation.

Irregular Conditions

Both REG1 and REG2 are output short-circuit safe.

The

over

current

protection

and

the

over

temperature shutdown protection prevent the

ACT5880 from being damaged by thermal over

stress. When the output voltage drops about 7% off

the normal output voltage, the OK bit for the

regulator is cleared. When interrupt is unmasked,

STEP-DOWN DC/DC REGULATORS

PARAMETER

VOLUME

Operation Voltage

2.7V to 5.5V

Active Mode Quiescent

Supply Current

65μA

Sleep Mode Quiescent

Supply Current

23μA

Shutdown Current

1μA

Default Output Voltage

1.2V and 1.2V/REG1, 1.8V/

REG2

Output Range

0.6V to 3.9V

1.2A/REG1, 0.6A/REG2

10mA/REG2 in Sleep Mode

Maximum Output Current

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