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

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

OPERATIO
Undervoltage Charge Current Limiting (UVCL)
The LTC4069 includes undervoltage charge (∆V
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 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 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
R
NOM
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 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., R
= 1.33k) to ensure that part tolerances maintain a pro-
grammed current higher than 600mA. Since the LTC4069
TOO COLD
TOO HOT
NTC_ENABLE
4069 F03
LTC4069
11
PROG
4069fa