參數(shù)資料
型號: LTC4054
廠商: Linear Technology Corporation
元件分類: 熱敏電阻
英文描述: Standalone Linear Li-lon Battery Charger with Thermistor Input
中文描述: 獨(dú)立線性鋰離子電池充電器熱敏電阻輸入
文件頁數(shù): 11/16頁
文件大小: 191K
代理商: LTC4054
11
LTC4054L-4.2
4054l42f
APPLICATIOU
Stability Considerations
The constant-voltage mode feedback loop is stable with-
out an output capacitor provided a battery is connected to
the charger output. With no battery present, an output
capacitor is recommended to reduce ripple voltage. When
using high value, low ESR ceramic capacitors, it is recom-
mended to add a 1
resistor in series with the capacitor.
No series resistor is needed if tantalum capacitors are
used.
In constant-current mode, the PROG pin is in the feedback
loop, not the battery. The constant-current mode stability
is affected by the impedance at the PROG pin. With no
additional capacitance on the PROG pin, the charger is
stable with program resistor values as high as 20k. How-
ever, additional capacitance on this node reduces the
maximum allowed program resistor. The pole frequency
at the PROG pin should be kept above 100kHz. Therefore,
if the PROG pin is loaded with a capacitance, C
PROG
, the
following equation can be used to calculate the maximum
resistance value for R
PROG
:
W
U
U
PROG
10k
R
PROG
C
FILTER
4054L42 F02
CHARGE
CURRENT
MONITOR
CIRCUITRY
LTC4054L
GND
Figure 2. Isolating Capacitive Load on PROG Pin and Filtering
R
C
PROG
PROG
π
1
2
10
5
Average, rather than instantaneous, charge current may
be of interest to the user. For example, if a switching power
supply operating in low current mode is connected in
parallel with the battery, the average current being pulled
out of the BAT pin is typically of more interest than the
instantaneous current pulses. In such a case, a simple RC
filter can be used on the PROG pin to measure the average
battery current as shown in Figure 2. A 10k resistor has
been added between the PROG pin and the filter capacitor
to ensure stability.
Power Dissipation
The conditions that cause the LTC4054L to reduce charge
current through thermal feedback can be approximated by
considering the power dissipated in the IC. Nearly all of
this power dissipation is generated from the internal
MOSFET—this is calculated to be approximately:
P
D
= (V
CC
– V
BAT
) I
BAT
where P
D
is the power dissipated, V
CC
is the input supply
voltage, V
BAT
is the battery voltage and I
BAT
is the charge
current. The approximate ambient temperature at which
the thermal feedback begins to protect the IC is:
T
A
= 120
°
C – P
D
θ
JA
T
A
= 120
°
C – (V
CC
– V
BAT
) I
BAT
θ
JA
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