BQ24725A_17 Datasheet, PDF (16/47 Pages) Texas Instruments – 1-4 Cell Li+ Battery SMBus Charge Controller with N-Channel Power MOSFET Selector and Advanced Circuit Protection

bq24725A
SLUSAL0A – SEPTEMBER 2011 – REVISED AUGUST 2014
Feature Description (continued)
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A
B
t_LOW t _HIGH
SMBCLK
SMBDATA
Figure 12. SMBus Write Timing
C
D
EF
G
H
I
J
K
A = START CONDITION
B = MSB OF ADDRESS CLOCKED INTO SLAVE
C = LSB OF ADDRESS CLOCKED INTO SLA VE
D = R/W BIT CLOCKED INTO SLAVE
E = SLAVE PULLS SMBDATA LINE LOW
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER
G = MSB OF DATA CLOCKED INTO MASTER
H = LSB OF DATA CLOCKED INTO MASTER
Figure 13. SMBus Read Timing
I = ACKNOWLEDGE CLOCK PULSE
J = STOP CONDITION
K = NEW START CONDITION
8.4 Device Functional Modes
8.4.1 Adapter Detect and ACOK Output
The bq24725A uses an ACOK comparator to determine the source of power on VCC pin, either from the battery
or adapter. An external resistor voltage divider attenuates the adapter voltage before it goes to ACDET. The
adapter detect threshold should typically be programmed to a value greater than the maximum battery voltage,
but lower than the maximum allowed adapter voltage.
The open drain ACOK output requires external pull up resistor to system digital rail for a high level. It can be
pulled to external rail under the following conditions:
• V_VCC > UVLO;
• 2.4V < V_ACDET < 3.15V (not in ACOVP condition, nor in low input voltage condition);
• V_VCC–V_SRN > 275mV (not in sleep mode);
The first time after IC POR always gives 150ms ACOK rising edge delay no matter what the ChargeOption
register value is. Only after the ACDET pin voltage is pulled below 2.4V (but not below 0.6V, which resets the IC
and forces the next ACOK rising edge deglitch time to be 1.3s) and the ACFET has been turned off at least one
time, the 1.3s (or 150ms) delay time is effective for the next time the ACDET pin voltage goes above 2.4V. To
change this option, the VCC pin voltage must above UVLO, and the ACDET pin voltage must be above 0.6V
which enables the IC SMBus communication and sets ChargeOption() bit[15] to 0 which sets the next ACOK
rising deglitch time to be 150ms. The purpose of the default 1.3s rising edge deglitch time is to turn off the
ACFET long enough when the ACDET pin is pulled below 2.4V by excessive system current, such as over
current or short circuit.
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