ACT3704 データシートの表示（PDF） - Active-Semi, Inc

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ACT3704

12V Linear-Mode Battery Charger for Li+/Li-polymer Cells

Active-Semi, Inc 

ACT3704

Rev2, 26-Jul-07

ture at which the thermal regulation begins to pro-

tect the IC is given by :

TA = 120 °C − PD × θ JA

(4)

( ) TA = 120 °C - VIN - VBAT × IBAT × θ JA

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:

TA = 120 °C - (5V - 3.4V )× (700 mA )× 45 °C

TA = 120 °C − 1.12W × 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 − TA )

( ) VIN − VBAT × 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

=

(5V

(120 °C - 70°C )

- 3.4V )× 45°C /

W

= 50°C

72°C / A

TA = 694mA

(7)

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

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.

State Machine

Precondition State

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)

Which is 10% of the programmed maximum fast-

charge constant current, IBAT.

Once VBAT reaches the Precondition Threshold Volt-

age the state machine jumps to the NORMAL state.

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

CTIMER 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).

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.

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.

Innovative Products. Active Solutions.

-9-

www.active-semi.com

Copyright © 2007 Active-Semi, Inc.

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