ACT3704
Rev2, 26-Jul-07
ture at which the thermal regulation begins to pro-
tect the IC is given by :
1000mA to a battery from a 5V supply at 25°C.
Without a good backside thermal connection, this
number could drop to less than 500mA.
TA = 120 °C − PD ×θJA
TA = 120 °C - VIN -VBAT × IBAT ×θJA
(4)
State Machine
(
)
Precondition State
Example: The ACT3704 is operating from a 5V wall
adapter and is programmed to supply 700mA fast
charge current to a discharged Li-Ion battery with a
voltage of 3.4V. Assuming θJA is 45°C/W, the ambi-
ent temperature at which the device will begin to
reduce the charge current is approximately:
A new charging cycle begins with the PRECONDI-
TION state, and operation continues in this state
until VBAT exceeds the Precondition Threshold Volt-
age of 2.8V.
When operating in PRECONDITION state, the cell
is charged at a reduced current given by:
IPRECONDITION = 2.200 ×
VISET / RISET
(8)
TA = 120 °C -
(
5V - 3.4V
)
×
(
700 mA × 45°C
)
Which is 10% of the programmed maximum fast-
charge constant current, IBAT.
TA = 120 °C −1.12W × 45°C = 120 °C − 50.4°C
TA = 69 .6°C
Once VBAT reaches the Precondition Threshold Volt-
age the state machine jumps to the NORMAL state.
(5)
The ACT3704 can be used above 69.6°C ambient,
but the charge current will be reduced from 700mA.
The approximate current at a given ambient tem-
perature can be approximated by:
If VBAT does not reach the Precondition Threshold
Voltage before the Precondition Timeout period
(TPRECONDITION) expires, then a damaged cell is de-
tected and the state machine jumps to the TIME-
OUT-FAULT State. The Precondition Timeout pe-
riod is default to 20mins with an external 2.2nF
(
120°C −TA
)
IBAT
=
(6)
(
VIN −VBAT
)
×θJA
C
TIMER capacitor, or it can be increased with a larger
value capacitor. See the Safely Timers section for
more information.
Using the previous example with an ambient tem-
perature of 70°C, the charge current will be reduced
to approximately:
Normal State
Normal state is made up of two operating modes,
fast charge Constant-Current (CC) and Constant-
Voltage (CV).
(
120°C -70°C
)
50°C
IBAT
=
=
(
5V - 3.4V × 45°C / W 72°C / A
)
(7)
TA = 694mA
In CC mode, the ACT3704 charges at the current
programmed by RISET (see the Charge Current Pro-
gramming section for more information). During a
normal charge cycle fast-charge continues in CC
mode until VBAT reaches the charge termination volt-
age (VTERM), at which point the ACT3704 charges in
CV mode. Charging continues in CV mode until the
charge current drops to 10% of the programmed
maximum charge current (IBAT), at which point the
state machine jumps to the TOP-OFF state.
ACT3704 applications do not need to be designed
for worst-case thermal conditions, since the part will
automatically reduce power dissipation if the ther-
mal regulation threshold of approximately 120°C is
reached.
However, in order to deliver maximum charge cur-
rent under all conditions, it is critical that the ex-
posed metal pad on the backside of the package
exposed pad (EP) is soldered directly to the PC
board ground. Correctly soldered to a double sided
1oz copper board, the ACT3704 has a thermal re-
sistance of approximately 45°C/W with SOP8 and
36.7°C/W with TDFN33-8. Failure to make thermal
contact between the exposed pad on the backside
pf the package and the copper board will result in
thermal resistances far greater than 45°C/W with
SOP8 and 36.7°C/W with TDFN33-8. For example,
a correctly soldered ACT3704 can deliver up to
If VBAT does not proceed out of the NORMAL state
before the Normal Timeout period (TNORMAL) expires,
then a damaged cell is detected and the state ma-
chine jumps to the TIMEOUT-FAULT State.
The Normal Timeout period is default to 30mins, or
it can be increased with an external 2.2nF CTIMER
capacitor or can be changed with a larger value
external capacitor. See the Safety Times section for
more information.
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