LTC4065-4.4 Linear Technology, LTC4065-4.4 Datasheet - Page 10

• Manufacturer Part Number: LTC4065-4.4
• Description: Standalone 750mA Li-Ion Battery Charge
• Manufacturer: Linear Technology

www.DataSheet4U.com
OPERATIO
LTC4065-4.4
CHRG Status Output Pin
The charge status indicator pin has three states: pull-
down, pulse at 2Hz (see Trickle Charge and Defective
Battery Detection) and high impedance. The pull-down
state indicates that the LTC4065-4.4 is in a charge cycle.
A high impedance state indicates that the charge current
has dropped below 10% of the full-scale current, the timer
has ended or the LTC4065-4.4 is disabled. Figure 2 shows
the CHRG status under various conditions.
Charge Current Soft-Start and Soft-Stop
The LTC4065-4.4 includes a soft-start circuit to minimize
the inrush current at the start of a charge cycle. When a
charge cycle is initiated, the charge current ramps from
zero to the full-scale current over a period of approximately
180µs. Likewise, internal circuitry slowly ramps the charge
current from full-scale to zero when the charger is shut off
or self terminates. This has the effect of minimizing the
transient current load on the power supply during start-up
and charge termination.
Constant-Current/Constant-Voltage/
Constant-Temperature
The LTC4065-4.4 use a unique architecture to charge a
battery in a constant-current, constant-voltage and con-
stant-temperature fashion. Figures 1 show simplified block
diagrams of the LTC4065-4.4. Three of the amplifier
feedback loops shown control the constant-current, CA,
constant-voltage, VA, and constant-temperature, TA
modes. A fourth amplifier feedback loop, MA, is used to
increase the output impedance of the current source pair;
M1 and M2 (note that M1 is the internal P-channel power
MOSFET). It ensures that the drain current of M1 is exactly
1000 times greater than the drain current of M2.
10
U
Amplifiers CA and VA are used in separate feedback loops
to force the charger into constant-current or constant-
voltage mode, respectively. Diodes D1 and D2 provide
priority to either the constant-current or constant-voltage
loop; whichever is trying to reduce the charge current the
most. The output of the other amplifier saturates low
which effectively removes its loop from the system. When
in constant-current mode, CA servos the voltage at the
PROG pin to be precisely 1V. VA servos its inverting input
to an internal reference voltage when in constant-voltage
mode and the internal resistor divider, made up of R1 and
R2, ensures that the battery voltage is maintained at 4.4V.
The PROG pin voltage gives an indication of the charge
current during constant-voltage mode as discussed in
“Programming Charge Current”.
Transconductance amplifier, TA, limits the die tempera-
ture to approximately 115°C when in constant-tempera-
ture mode. Diode D3 ensures that TA does not affect the
charge current when the die temperature is below approxi-
mately 115°C. The PROG pin voltage continues to give an
indication of the charge current.
In typical operation, the charge cycle begins in constant-
current mode with the current delivered to the battery
equal to 1000V/R
LTC4065-4.4 results in the junction temperature ap-
proaching 115°C, the amplifier (TA) will begin decreas-
ing the charge current to limit the die temperature to
approximately 115°C. As the battery voltage rises, the
LTC4065-4.4 either return to constant-current mode or
enter constant-voltage mode straight from constant-tem-
perature mode. Regardless of mode, the voltage at
the PROG pin is proportional to the current delivered to
the battery.
PROG
. If the power dissipation of the
406544f