LTC4069EDC-4.4-PBF LINER [Linear Technology], LTC4069EDC-4.4-PBF Datasheet - Page 11

• Manufacturer Part Number: LTC4069EDC-4.4-PBF
• Manufacturer: LINER [Linear Technology]

OPERATION
APPLICATIONS INFORMATION
Undervoltage Charge Current Limiting (UVCL)
The LTC4069-4.4 includes undervoltage charge (ΔV
current limiting that prevents full charge current until the
input supply voltage exceeds approximately 220mV above
the battery voltage. This feature is particularly useful if the
LTC4069-4.4 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 LTC4069-4.4 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 V
(approximately 220mV above the battery voltage),
undervoltage charge current limiting will begin to reduce
the charge current in an attempt to maintain ΔV
between the V
CC
input and the BAT output of the IC.
R
NOM
R
NTC
6
0.016 • V
BAT
0.76 • V
0.35 • V
NTC
Figure 3. NTC Circuit Information
+ ΔV
CC
CC
CC
V
UVCL1
CC
UVCL1
UVCL1
)
–
+
–
+
+
–
The LTC4069-4.4 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 LTC4069-4.4 dissipates signifi cantly 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 LTC4069-4.4 to charge at a current above 600mA.
Assume that the LTC4069-4.4 is programmed for 750mA
(i.e., R
PROG
= 1.33k) to ensure that part tolerances maintain
TOO COLD
TOO HOT
NTC_ENABLE
4069 F03
LTC4069-4.4
11
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