ACT8946A Datasheet, PDF (26/37 Pages) Active-Semi, Inc – Advanced PMU for Hisilicon Processors

FUNCTIONAL DESCRIPTION
I²C Interface
The ACT8946A 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 ACT8946A, and I²C read-byte
commands are used to read the ACT8946A’s
internal registers. The ACT8946A 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, go to the NXP website:
http://www.nxp.com.
Voltage Monitor and Interrupt
Programmable System Voltage Monitor
The ACT8946A 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 3.
SYSLEV[ ] is set to 3.0V by default. There is a
200mV rising hysteresis on SYSLEV[ ] threshold
such that V_VSYS 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 V_VSYS
relative to the SYSLEV[-] voltage threshold, the
value of nSYSTAT[-] = 1 when V_VSYS is lower than
the SYSLEV[-] voltage threshold, and nSYSTAT[-] =
0 when V_VSYS 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 V_VSYS 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 ACT8946A 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 is unmasked
(nSYSLEVMSK[ ]=1) and V_VSYS falls below the
ACT8946AQJ203-T
Rev 1.0, 08-Jul-16
programmable threshold, the ACT8946A 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 V_VSYS
rises up again above the SYSLEV rising threshold
and nSYSSTAT[-] is read via I²C.
2) If nSYSMODE[-] = 0, when V_VSYS falls below the
programmable threshold the ACT8946A 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 3: SYSLEV Falling Threshold
SYSLEV[3:0]
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
SYSLEV Falling Threshold
(Hysteresis = 200mV)
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3.0
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
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, as shown in
Functional Block Diagram. The output of the
comparator is present at the nLBO open-drain
output.
Thermal Shutdown
The ACT8946A integrates thermal shutdown
protection circuitry to prevent damage resulting from
excessive thermal stress, as may be encountered
under fault conditions. This circuitry disables all
regulators if the ACT8946A die temperature exceeds
160°C, and prevents the regulators from being
enabled until the IC temperature drops by 20°C
(typ).
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