ACT3780 datasheet(11/20 Pages) ACTIVE-SEMI

11 / 20 page

ACT3780

Rev 8, 09-Jul-13

Innovative PowerTM

- 11 -

www.active-semi.com

Active-Semi Proprietary―For Authorized Recipients and Customers

ActivePath

TM is a trademark of Active-Semi.

kHOT(@TC) = VTHH/(RNOM × (ITH + (VCHG_IN - VTHH)/R))

kHOT(@TC) = 0.5V/(6.8kΩ × (100µA + (5V - 0.5V)/82kΩ))

= 0.4748

Reviewing the characteristic curves, the upper

threshold is found to move to 45°C, a change of

about 14°C. Adding the parallel resistance has

allowed us to achieve our desired lower threshold of

0°C with an operating temperature range of 0°C to

45°C, vs. our design target of 0°C to 40°C.

Thermal Regulation and Protection

The

ACT3780

features

internal

thermal

regulation loop that reduces the charging current as

necessary to ensure that the die temperature does

not rise beyond the thermal regulation threshold of

110°C. This feature protects the ACT3780 against

excessive junction temperature and makes the

device more accommodating to aggressive thermal

designs. Note, however, that attention to good

thermal designs is required to achieve the fastest

possible charge time by maximizing charge current.

In order to account for the extended total charge

time resulting from operation in thermal regulation

mode, the charge timeout periods are extended

proportionally to the reduction in charge current.

The conditions that cause the ACT3780 to reduce

charge current in accordance to the internal thermal

regulation loop can be approximated by calculating

the power dissipated in the part.

The ACT3780 also features thermal shutdown for

further protection. When the device temperature

exceeds 160°C, the device will automatically turn

off to prevent the IC from damage. After the die

temperature decreases below 135°C, the IC will

automatically restart.

Charging Safety Timers

The ACT3780 features a programmable safety

charging timer by setting an external resistor from

BTR pin to G (RBTR). The time out period is

calculated as shown in Figure 2. The maximum RBTR

should not be larger than 68kΩ.

If the timeout period expires without change

termination, the ACT3780 will jump to EOC state.

If the ACT3780 detects that the charger remains in

precondition for longer than the precondition time

out period (which determined as TNORMAL/3), the

ACT3780 turns off the charger and generates a

FAULT to ensure prevent charging a bad cell.

Figure 3:

Fix VTHL Configuration

Figure 4:

Fix VTHH Configuration

Figure 2:

RBTR (kΩ)

TNORMAL vs. RBTR

190

160

130

100

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