ACT3704
Rev2, 26-Jul-07
ture at which the thermal regulation begins to pro-
tect the IC is given by :
T
A
=
120
°
C
−
P
D
×
θ
JA
T
A
=
120
°
C -
(
V
IN
- V
BAT
)
×
I
BAT
×
θ
JA
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.
(4)
State Machine
Precondition State
A new charging cycle begins with the PRECONDI-
TION state, and operation continues in this state
until V
BAT
exceeds the Precondition Threshold Volt-
age of 2.8V.
When operating in PRECONDITION state, the cell
is charged at a reduced current given by:
(8)
Which is 10% of the programmed maximum fast-
charge constant current, I
BAT.
Once V
BAT
reaches the Precondition Threshold Volt-
age the state machine jumps to the NORMAL state.
If V
BAT
does not reach the Precondition Threshold
Voltage before the Precondition Timeout period
(T
PRECONDITION
) 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
C
TIMER
capacitor, or it can be increased with a larger
value capacitor. See the
Safely Timers section
for
more information.
Normal State
Normal state is made up of two operating modes,
fast charge Constant-Current (CC) and Constant-
Voltage (CV).
I
PRECONDITION
=
2.200
×
(
V
ISET
/ R
ISET
)
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
θ
JA
is 45°C/W, the ambi-
ent temperature at which the device will begin to
reduce the charge current is approximately:
T
A
=
120
°
C -
(
5V - 3.4V
)
×
(
700 mA
)
×
45
°
C
T
A
=
120
°
C
−
1 . 12 W
×
45
°
C
=
120
°
C
−
50 . 4
°
C
T
A
=
69 . 6
°
C
(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:
I
BAT
=
(
120
°
C
−
T
A
)
(
V
IN
−
V
BAT
)
×
θ
JA
(6)
Using the previous example with an ambient tem-
perature of 70°C, the charge current will be reduced
to approximately:
I
BAT
(
120
°
C - 70
°
C
)
=
(
5V - 3.4V
)
×
45
°
C / W
50
°
C
=
72
°
C / A
(7)
T
A
=
694 mA
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
Innovative Products.
Active Solutions.
In CC mode, the ACT3704 charges at the current
programmed by R
ISET
(see the
Charge Current Pro-
gramming
section for more information). During a
normal charge cycle fast-charge continues in CC
mode until V
BAT
reaches the charge termination volt-
age (V
TERM
), 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 (I
BAT
), at which point the
state machine jumps to the TOP-OFF state.
If V
BAT
does not proceed out of the NORMAL state
before the Normal Timeout period (T
NORMAL
) 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 C
TIMER
capacitor or can be changed with a larger value
external capacitor. See the
Safety Times
section for
more information.
-9-
www.active-semi.com
Copyright © 2007 Active-Semi, Inc.
ACTIVE-SEMI [ ACTIVE-SEMI, INC ]
