ltc4069edc-4.4 Linear Technology Corporation, ltc4069edc-4.4 Datasheet - Page 11

• Manufacturer Part Number: ltc4069edc-4.4
• Description: Standalone 750ma Li-ion Battery Charger In 2 ? 2 Dfn With Ntc Thermistor Input
• Manufacturer: Linear Technology Corporation

OPERATIO
Undervoltage Charge Current Limiting (UVCL)
The LTC4069-4.4 includes undervoltage charge (∆V
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 imped-
ance 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 ∆V
between the V
APPLICATIO S I FOR ATIO
CC
input and the BAT output of the IC. The
U
U
U
W
R
NOM
R
NTC
6
BAT
0.016 • V
0.76 • V
0.35 • V
NTC
Figure 3. NTC Circuit Information
+ ∆V
U
CC
CC
CC
UVCL1
V
UVCL1
UVCL1
CC
)
–
–
–
+
+
+
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 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
LTC4069-4.4 to charge at a current above 600mA. As-
sume that the LTC4069-4.4 is programmed for 750mA
(i.e., R
PROG
= 1.33k) to ensure that part tolerances main-
TOO COLD
TOO HOT
NTC_ENABLE
4069 F03
LTC4069-4.4
11
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