LTC4069EDC-TRPBF(RevB) データシートの表示（PDF） - Linear Technology

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LTC4069EDC-TRPBF
(Rev.:RevB)

Standalone 750mA Li-Ion Battery Charger in 2 × 2 DFN with NTC Thermistor Input

Linear Technology 

OPERATION

VCC

RNOM

–

0.76 • VCC

NTC

+

6

RNTC

–

+

0.35 • VCC

+

0.016 • VCC

–

TOO COLD

TOO HOT

NTC_ENABLE

LTC4069

4069 F03

Figure 3. NTC Circuit Information

APPLICATIONS INFORMATION

Undervoltage Charge Current Limiting (UVCL)

The LTC4069 includes undervoltage charge (ΔVUVCL1)

current limiting that prevents full charge current until the

input supply voltage exceeds approximately 200mV above

the battery voltage. This feature is particularly useful if the

LTC4069 is powered from a supply with long leads (or any

relatively high output impedance).

For example, USB-powered systems tend to have highly

variable source impedances (due primarily to cable

quality and length). A transient load combined with such

impedance can easily trip the UVLO threshold and turn the

charger off unless undervoltage charge current limiting

is implemented.

Consider a situation where the LTC4069 is operating under

normal conditions and the input supply voltage begins to

droop (e.g., an external load drags the input supply down).

If the input voltage reaches VBAT + ΔVUVCL1 (approximately

220mV above the battery voltage), undervoltage charge

current limiting will begin to reduce the charge current

in an attempt to maintain ΔVUVCL1 between the VCC input

and the BAT output of the IC. The LTC4069 will continue

to operate at the reduced charge current until the input

supply voltage is increased or constant voltage mode

reduces the charge current further.

Operation from Current Limited Wall Adapter

By using a current limited wall adapter as the input supply,

the LTC4069 dissipates significantly less power when

programmed for a current higher than the limit of the

supply as compared to using a non-current limited supply

at the same charge current.

Consider a situation where an application demands a

600mA charge current for an 800mAh Li-Ion battery. If a

typical 5V (non-current limited) input supply is used, the

charger’s peak power dissipation can exceed 1W.

Now consider the same scenario, but with a 5V input

supply with a 600mA current limit. To take advantage of

the current limited supply, it is necessary to program the

LTC4069 to charge at a current above 600mA. Assume

that the LTC4069 is programmed for 750mA (i.e.,

RPROG = 1.33k) to ensure that part tolerances maintain

a programmed current higher than 600mA. Since the

4069fb

11

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