LTC4124 datasheet(21/24 Pages) AD

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LTC4126-ADJ

Rev. 0

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APPLICATIONS INFORMATION

used to set the hot and cold thresholds independently to

60°C and –5°C. Using the same Vishay thermistor with

β25/85 = 3950k whose nominal value at 25°C is 100k, the

formula results in RBIAS = 147k and RD = 52.3k for the

closest 1% resistor values.

PC BOARD LAYOUT CONSIDERATIONS

Since the exposed pad of the LTC4126-ADJ package is

the only ground pin and serves as the return path for both

the charger and the DC/DC converter, it must be soldered

to the PC board ground for a good electrical connection.

Although the LTC4126-ADJ is a low power IC, the shunt

circuitry in the AC power control block can cause a fair

amount of on-chip power dissipation if the available AC

power is excessive. If the heat is not dissipated properly

on the PC board, the temperature of the die and subse-

quently, the temperature of the battery may rise above

the hot temperature threshold set by the NTC thermistor

causing the charger to pause charging. For optimum ther-

mal performance, there should be a group of vias directly

under the exposed pad on the backside leading directly

down to an internal ground plane. To minimize parasitic

inductance, the ground plane should be as close as pos-

sible to the top plane of the PC board (Layer 2).

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