ACT8600 datasheet(39/51 Pages) ACTIVE-SEMI

39 / 51 page

ACT8600

Rev 3, 15-Nov-12

Innovative Power

ActivePMU

TM and ActivePathTM are trademarks of Active-Semi.

2CTM is a trademark of NXP.

- 39 -

www.active-semi.com

General Description

The step-up DC/DC is a highly efficient step-up

DC/DC converter that employs a fixed frequency,

current-mode, PWM architecture. This regulator is

optimized for 5V applications as well as white-LED

bias applications consisting of up to ten white-

LEDs.

5V Applications

The boost converter is configured by default to

provide a fixed 5V output voltage, without requiring

external feedback resistors. Contact the factory for

other voltage options.

In order to provide improved operation under very

low duty-cycle conditions, such as when operating

from a fully-charged Li+ cell to 5V, the boost

converter may optionally be configured to operate

at half of the frequency of the buck regulators.

Compensation and Stability

The boost regulator utilizes current-mode control

and an internal compensation network to optimize

transient performance, ease compensation, and

improve stability over a wide range of operating

conditions.

Inductor Selection

REG4 is optimized for operation with inductors in

the 4.7uH to 10uH range, although larger inductor

values of up to 22uH can be used to achieve the

highest possible efficiency.

Input and Output Capacitor Selection

For 5V operation, a 10uF ceramic capacitor should

be connected to the input and output of OUT4

respectively. A larger output capacitor may be used

to minimize output voltage ripple if needed.

Rectifier Selection

The boost regulator requires a Schottky diode to

rectify the inductor current. Select a low forward

voltage drop Schottky diode with a forward current

rating that is sufficient to support the maximum

switch current of 900mA (typ) and a sufficient peak

repetitive reverse voltage (VRRM) to support the

output voltage.

Configuration Options

Output Voltage Programming

By default, the boost regulator powers up and

regulates to its default output voltages. Once the

system is enabled, the output voltages may be

modified through either the I2C interface by writing to

the VSET[ ] register. Using I2C, the output voltage

may be programmed to any voltage as shown in

Table 6.

Enabling the Boost Regulator

The

boost

regulator

feature

independent

enable/disable control via the I2C serial interface.

Independently enable or disable the boost by

writing to the ON[ ] bit for REG4.

Power-OK

The boost regulator features a power-OK status bit

(OK[ ]) that can be read by the system

microprocessor via the I2C interface. If an output

voltage is lower than the power-OK threshold,

typically 6% below the programmed regulation

voltage, this bit clears to 0.

CONFIGURABLE STEP-UP DC/DC

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