LTC4063 LINER [Linear Technology], LTC4063 Datasheet - Page 15

• Manufacturer Part Number: LTC4063
• Description: Standalone Linear Li-Ion Charger with Micropower Low Dropout Linear Regulator
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
Regulator Output Noise
Noise measurements on the output should be made with
care to ensure accurate results. Coaxial connections and
proper shielding should be used to maintain measurement
integrity. Figure 7 shows a test setup for taking the
measurement. When the output is set to 3V and a 100mA
load is applied, the LTC4063 output noise power in the
10Hz to 100kHz band is typically measured to be 135µV
For more information on obtaining accurate noise mea-
surements for LDOs, see Application Note 83.
Power Dissipation
When designing the battery charger circuit, it is not
necessary to design for worst-case power dissipation
scenarios because the LTC4063 automatically reduces the
charge current during high power conditions. The condi-
tions that cause the LTC4063 to reduce charge current
through thermal feedback can be approximated by con-
sidering the power dissipated in the IC. Most of the power
dissipation is generated from the internal charger MOSFET
(the LDO generates considerably less heat in most appli-
cations). Thus, the power dissipation is calculated to be
approximately:
P
V
The approximate ambient temperature at which the ther-
mal feedback begins to protect the IC is:
IN
D
BAT
P
T
T
is the power dissipated, V
A
A
D
is the battery voltage and I
= 105°C – P
= 105°C – (V
= (V
5Hz SINGLE ORDER
CC
HIGHPASS
– V
BAT
D
CC
U
) • I
• θ
– V
JA
BAT
BAT
U
CC
) • I
is the input supply voltage,
GAIN = 60dB
BAT
BAT
W
is the charge current.
• θ
Figure 7. Filter Structure for Noise Testing LDOs
JA
U
BUTTERWORTH HP
10Hz 2nd ORDER
RMS
.
Example: An LTC4063 operating from a 5V wall adapter is
programmed to supply 800mA full-scale current to a
discharged Li-Ion battery with a voltage of 3.3V. Assuming
θ
temperature at which the LTC4063 will begin to reduce the
charge current is approximately:
The LTC4063 can be used above 50.6°C ambient, but the
charge current will be reduced from 800mA. The approxi-
mate current at a given ambient temperature can be
approximated by:
Using the previous example with an ambient temperature
of 60°C, the charge current will be reduced to approximately:
It is important to remember that LTC4063 applications
do not need to be designed for worst-case thermal
conditions, since the IC will automatically reduce power
dissipation when the junction temperature reaches ap-
proximately 105°C.
JA
T
T
T
I
I
I
BAT
BAT
BAT
is 40°C/W (see Thermal Considerations), the ambient
A
A
A
= 105°C – (5V – 3.3V) • (800mA) • 40°C/W
= 105°C – 1.36W • 40°C/W = 105°C – 54.4°C
= 50.6°C
100kHz 4th ORDER
BUTTERWORTH LP
=
=
=
662
(
(
5
V
V
CC
mA
105
105
– .
–
3 3
V
°
°
BAT
C T
C
V
–
–
)
)
•
60
• θ
A
40
°
5Hz SINGLE ORDER
JA
C
°
C W
HIGHPASS
/
=
68
45
°
C A
°
C
/
LTC4063
10Hz TO 100kHz
15
4063 F07
4063fb