LTM8062EVPBF datasheet(14/20 Pages) LINER

14 / 20 page

LTM8062

8062f

APPLICATIONS INFORMATION

When charging at a 1C rate, tEOC is commonly set to three

hours, which requires a 0.68μF capacitor.

The CHRG status pin continues to signal charging, regard-

less of which termination scheme is used. When timer

termination is used, the CHRG status pin is pulled low

during a charge cycle until the charge current falls below

the C/10 threshold. The charger continues to top off the

battery until timer EOC, when the LTM8062 terminates the

charge cycle and enters standby mode.

Termination at the end of the timer cycle only occurs if the

charge cycle was successful. A successful charge cycle

occurs when the battery is charged to within 2.5% of the

full-charge float voltage. If a charge cycle is not success-

ful at EOC, the timer cycle resets and charging continues

for another full timer cycle. When VBAT drops 2.5% from

the full-charge float voltage, whether by battery loading

or replacement of the battery, the charger automatically

resets and starts charging.

Preconditioning and Bad-Battery Fault

The LTM8062 has a precondition mode, where the charge

current is limited to 15% of the maximum charge current, or

approximately 300mA. Precondition mode is engaged if the

voltage on the BAT pin is below the precondition threshold,

or approximately 70% of the float voltage. Once the BAT

voltage rises above the precondition threshold, normal full-

currentchargingcancommence.TheLTM8062incorporates

90mV hysteresis to avoid spurious mode transitions.

Bad-battery detection is engaged when the internal timer

is used for termination (capacitor tied to TMR). This fault

detection feature is designed to identify failed cells. A

bad-battery fault is triggered when the voltage on BAT

remains below the precondition threshold for greater than

one-eighth of a full timer cycle (one-eighth EOC). A bad-

battery fault is also triggered if a normally charging battery

re-enters precondition mode after one-eighth EOC.

When a bad-battery fault is triggered, the charge cycle

is suspended, and the CHRG status pin becomes high

impedance. The FAULT pin is pulled low to signal that a

fault has been detected.

Cycling the charger’s power or shutdown function initiates

a new charge cycle, but the LTM8062 charger does not

require a manual reset. Once a bad-battery fault is detected,

a new timer charge cycle initiates if the BAT pin exceeds

the precondition threshold voltage. During a bad-battery

fault, a small current is sourced from the charger; removing

the failed battery allows the charger output voltage to rise

above the preconditioning threshold voltage and initiate a

charge cycle reset. A new charge cycle is started by con-

necting another battery to the charger output.

Battery Temperature Fault: NTC

The LTM8062 can accommodate battery temperature

monitoring by using an NTC (negative temperature

coefficient) thermistor close to the battery pack. The

temperature monitoring function is enabled by connect-

ing a 10kΩ,

β ≈ 3380 NTC thermistor from the NTC pin

to ground. If the NTC function is not desired, leave the

pin open. The NTC pin sources 50μA, and monitors the

voltage dropped across the 10kΩ thermistor. When the

voltage on this pin is above 1.36V (0°C) or below 0.29V

(40°C), the battery temperature is out of range, and the

LTM8062 triggers an NTC fault. The NTC fault condition

remains until the voltage on the NTC pin corresponds to

a temperature within the 0°C to 40°C range. Both hot and

cold thresholds incorporate 20% hysteresis, which equates

to about 5°C. If higher operational charging temperatures

are desired, the temperature range can be expanded by

adding series resistance to the 10k NTC resistor. Adding

a 909Ω resistor will increase the effective temperature

threshold to 45°C, for example.

During an NTC fault, charging is halted and both status

pins are pulled low. If timer termination is enabled, the

timer count is suspended and held until the fault condi-

tion is cleared.

Thermal Foldback

The LTM8062 contains a thermal foldback protection feature

that reduces charge current as the IC junction temperature

approaches 125°C. In most cases, on-chip temperatures

servo such that any overtemperature conditions are relieved

with only slight reductions in maximum charge current.

In some cases, the thermal foldback protection feature

can reduce charge currents below the C/10 threshold.

In applications that use C/10 termination (TMR = 0V), the

LTM8062 will suspend charging and enter standby mode

until the overtemperature condition is relieved.

LTM8062EVPBF Datasheet(PDF) 14 Page - Linear Technology

LTM8062EVPBF Datasheet(HTML) 14 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Datasheet Download

Link URL