ACT8796 datasheet(32/34 Pages) ACTIVE-SEMI

32 / 34 page

LOW-DROPOUT LINEAR REGULATORS

ACT8796

Rev1, 10-Oct-08

Innovative Power

- 32 -

www.active-semi.com

ActivePMU

TM is a trademark of Active-Semi.

2CTM is a trademark of Philips Electronics.

General Description

REG4, REG5, and REG6 are low-noise, low-

dropout linear regulators (LDOs) that are optimized

for low noise and high-PSRR operation, achieving

more than 60dB PSRR at frequencies up to 10kHz.

LDO Output Voltage Programming

All LDOs feature independently-programmable out-

put voltages that are set via the I2C serial interface,

increasing the ACT8796’s flexibility while reducing

total solution size and cost. Set the output voltage

by writing to the REG456CFG/VSETx[ ] registers.

Output Current Capability

REG4, REG5, and REG6 each supply an output

current of 250mA. Excellent performance is

achieved over this load current range.

Output Current Limit

In order to ensure safe operation under over-load

conditions, each LDO features current-limit circuitry

with current fold-back. The current-limit circuitry

limits the current that can be drawn from the output,

providing protection in over-load conditions. For

additional protection under extreme over current

conditions, current-fold-back protection reduces the

current-limit by approximately 30% under extreme

overload conditions.

Enabling and Disabling the LDOs

REG4 is enabled whenever either of the following

conditions are met:

1) nMSTR is driven low, or

2) PWRHLD is asserted high.

Furthermore, once these conditions are met REG5

and REG6 maybe independently enabled or dis-

abled via the I2C serial interface by writing the ap-

propriate REG56/ONx[_] bit.

Power-OK

Each of the LDOs features power-OK status bit 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 pro-

grammed regulation voltage, the corresponding

REG456CFG/OKx[ ] will clear to 0.

Reference Bypass Pin

The ACT8796 contains a reference bypass pin

which filters noise from the reference, providing a

low noise voltage reference to the LDOs. Bypass

REF to G with a 0.01µF ceramic capacitor.

Optional LDO Output Discharge

Each of the ACT8796’s LDOs features an optional,

independent output voltage discharge feature.

When this feature is enabled, the LDO output is

discharged to ground through a 1kΩ resistance

when the LDO is shutdown. This feature may be

enabled or disabled via the I2C interface by writing

to the REG456CFG/DISx[ ] bits.

Output Capacitor Selection

REG4, REG5, and REG6 each require only a small

ceramic capacitor for stability. For best perform-

ance, each output capacitor should be connected

directly between the OUTx and G pins as possible,

with a short and direct connection. To ensure best

performance for the device, the output capacitor

should have a minimum capacitance of 1µF, and

ESR value between 10mΩ and 200mΩ. High quality

ceramic capacitors such as X7R and X5R dielectric

types are strongly recommended.

FUNCTIONAL DESCRIPTION

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