ACT8810 datasheet(36/54 Pages) ACTIVE-SEMI

36 / 54 page

LOW-DROPOUT LINEAR REGULATORS

ACT8810

Rev 9, 15-Nov-12

Innovative Power

- 36 -

www.active-semi.com

ActivePMU

TM and ActivePathTM are trademarks of Active-Semi.

2CTM is a trademark of NXP.

FUNCTIONAL DESCRIPTION

General Description

REG4 and REG5 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

output voltages that are set via the I2C serial

interface, increasing the ACT8810’s flexibility while

reducing total solution size and cost. Set the output

voltage by writing to the REG45CFG/VSETx[ ]

registers.

Output Current Capability

REG4 and REG5 each supply an output current of

360mA. 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 40% under extreme

overload conditions.

Enabling and Disabling the LDOs

All LDOs feature independent enable/disable

control via the I2C serial interface. Independently

enable or disable each output by writing to the

appropriate REG45CFG/ONx[ ] bit.

In addition REG4 or REG5 may be enable when

nPBIN is pushed low via 100kΩ resistance. It

depends on sequence is set. See the Control

Sequence

section for more information.

Power-OK

REG4 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 12% below the

programmed regulation voltage, the corresponding

REG45CFG/OK[ ] will clear to 0.

Reference Bypass Pin

The ACT8810 contains a reference bypass pin

which filters noise from the reference, providing a

low noise voltage reference to the LDOs. Bypass

REFBP to GA with a 0.01μF ceramic capacitor.

Optional LDO Output Discharge

Each of the ACT8810’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 REG45CFG/DISx[ ] bits.

Output Capacitor Selection

REG4 and REG5 each require only a small ceramic

capacitor for stability. For best performance, each

output capacitor should be connected directly

between the OUTx and GA 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.

PCB Layout Considerations

The ACT8810’s LDOs provide good DC, AC, and

noise performance over a wide range of operating

conditions, and are relatively insensitive to layout

considerations. When designing a PCB, however,

careful layout is necessary to prevent other circuitry

from degrading LDO performance. A good design

places input and output capacitors as close to the

LDO inputs and output as possible, and utilizes a

star-ground configuration for all regulators to

prevent noise-coupling through ground. Output

traces should be routed to avoid close proximity to

noisy nodes, particularly the SW nodes of the

DC/DCs. REFBP is a filtered reference noise, and

internally has a direct connection to the linear

regulator controller. Any noise injected onto REFBP

will directly affect the outputs of the linear

regulators, and therefore special care should be

taken to ensure that no noise is injected to the

outputs via REFBP. As with the LDO output

capacitors, the REFBP bypass capacitor should be

placed as close to the IC as possible, with short,

direct connections to the star-ground. Avoid the use

of vias whenever possible. Noisy nodes, such as

from the DC/DCs, should be routed as far away

from REFBP as possible.

ACT8810 数据表(PDF) 36 Page - Active-Semi, Inc

ACT8810 数据表(HTML) 36 Page - Active-Semi, Inc

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54

数据表下载