ACT8941A datasheet(29/42 Pages) ACTIVE-SEMI

29 / 42 page

ACT8941A

Rev 0, 12-Mar-13

- 29 -

www.active-semi.com

ActivePMU

TM and ActivePathTM are trademarks of Active-Semi.

I2CTM is a trademark of NXP.

Innovative PowerTM

Active-Semi Proprietary―For Authorized Recipients and Customers

I2C Interface

The ACT8941A features an I2C interface that allows

advanced programming capability to enhance overall

system performance. To ensure compatibility with a

wide range of system processors, the I2C interface

supports clock speeds of up to 400kHz (“Fast-Mode”

operation) and uses standard I2C commands. I2C

write-byte commands are used to program the

ACT8941A, and I2C read-byte commands are used

to read the ACT8941A’s internal registers. The

ACT8941A always operates as a slave device, and

is addressed using a 7-bit slave address followed by

an eighth bit, which indicates whether the transaction

is a read-operation or a write-operation, [1011011x].

SDA is a bi-directional data line and SCL is a clock

input. The master device initiates a transaction by

issuing a START condition, defined by SDA

transitioning from high to low while SCL is high. Data

is transferred in 8-bit packets, beginning with the

MSB, and is clocked-in on the rising edge of SCL.

Each packet of data is followed by an “Acknowledge”

(ACK) bit, used to confirm that the data was

transmitted successfully.

For more information regarding the I2C 2-wire serial

interface,

the

NXP

website:

http://www.nxp.com.

Voltage Monitor and Interrupt

Programmable System Voltage Monitor

The ACT8941A features a programmable system-

voltage monitor, which monitors the voltage at VSYS

and compares it to a programmable threshold

voltage. The programmable voltage threshold is

programmed by SYSLEV[3:0], as shown in Table 5.

SYSLEV[ ] is set to 3.0V by default. There is a

200mV rising hysteresis on SYSLEV[ ] threshold

such that VVSYS needs to be 3.2V(typ) or higher in

order to power up the IC.

The nSYSSTAT[-] bit reflects the output of an

internal voltage comparator that monitors VVSYS

relative to the SYSLEV[-] voltage threshold, the

value of nSYSTAT[-] = 1 when VVSYS is lower than

the SYSLEV[-] voltage threshold, and nSYSTAT[-] =

0 when VVSYS is higher than the SYSLEV[-] voltage

threshold. Note that the SYSLEV[-] voltage threshold

is defined for falling voltages, and that the

comparator produces about 200mV of hysteresis at

VSYS. As a result, once VVSYS falls below the

SYSLEV threshold, its voltage must increase by

more than about 200mV to clear that condition.

After the IC is powered up, the ACT8941A responds

in one of two ways when the voltage at VSYS falls

below the SYSLEV[-] voltage threshold:

1) If nSYSMODE[-] = 1 (default case), when system

voltage

level

interrupt

unmasked

(nSYSLEVMSK[ ]=1) and VVSYS falls below the

programmable threshold, the ACT8941A asserts

nIRQ, providing a software “under-voltage alarm”.

The response to this interrupt is controlled by the

CPU, but will typically initiate a controlled shutdown

sequence either or alert the user that the battery is

low. In this case the interrupt is cleared when VVSYS

rises up again above the SYSLEV rising threshold

and nSYSSTAT[-] is read via I2C.

2) If nSYSMODE[-] = 0, when VVSYS falls below the

programmable threshold the ACT8941A shuts down,

immediately disabling all regulators. This option is

useful for implementing a programmable “under-

voltage lockout” function that forces the system off

when the battery voltage falls below the SYSLEV

threshold voltage. Since this option does not support

a controlled shutdown sequence, it is generally used

as a "fail-safe" to shut the system down when the

battery voltage is too low.

Table 5:

SYSLEV Falling Threshold

Precision Voltage Detector

The LBI input connects to one input of a precision

voltage comparator, which can be used to monitor a

system voltage such as the battery voltage. An

external resistive-divider network can be used to set

voltage

monitoring

thresholds,

shown

Functional Block Diagram

. The output of the

comparator is present at the nLBO open-drain

output.

SYSLEV[3:0]

SYSLEV Falling Threshold

(Hysteresis = 200mV)

0000

2.3

0001

2.4

0010

2.5

0011

2.6

0100

2.7

0101

2.8

0110

2.9

0111

3.0

1000

3.1

1001

3.2

1010

3.3

1011

3.4

1100

3.5

1101

3.6

1110

3.7

1111

3.8

FUNCTIONAL DESCRIPTION

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