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參數(shù)資料
| 型號： | LTC4425IDD#PBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 電源管理 |
| 英文描述： | 1-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO12 |
| 封裝： | 3 X 3 MM, 0.75 MM HEIGHT, LEAD FREE, PLASTIC, DFN-12 |
| 文件頁數(shù)： | 5/20頁 |
| 文件大?。?/td> | 239K |
| 代理商： | LTC4425IDD#PBF |
LTC4425
13
4425f
Charge Current Reduction by the Thermal Regulator
To protect the part against excessive heat generated by
internal power dissipation, the LTC4425 is equipped with a
thermal regulator which automatically reduces the charge
current to maintain a maximum die temperature of 105°C.
Ignoring the quiescent current, the power dissipation can
be approximated by the following equation:
PD = (VIN – VOUT) ICHRG
If
θJA is the thermal resistance and TA is the ambient
temperature, then the die temperature can be calculated as:
TDIE = TA + PD θJA
When the part is in thermal regulation, the die temperature
is 105°C and for a given VIN and VOUT, the charge current
can be determined by the following equation:
I
T
VV
CHRG
A
IN
OUT
JA
= ()
105 –
–
θ
For example, if the LTC4425 in the DFN package is used in
LDOmodetochargeacompletelydischargedsupercapstack
(VOUT = 0V) at a room temperature of 25°C from a 5V source,
the charge current, at rst, will be limited to approximately:
I
CC
VC W
C
CA
mA
CHRG =
°°
() °
=
°
=
105
25
50
43
80
215
372
–
–/
/
As the output voltage rises, the charge current will gradually
rise to the full charge current programmed by the PROG pin
resistor as long as the constant-current loop is in control.
If the LTC4425 is programmed for a charge current of 2A,
the output voltage at which the part will deliver full charge
current can be determined by the following equation:
VV
T
I
OUT
IN
A
CHRG
JA
=
–
105
θ
Using the previous example, for full charge current, the
output voltage has to rise to at least:
VV
C
AC W
V
C
CV
V
OUT =
()°
°
=
°
=
5
105 25
243
5
80
86
407
–
/
–
/
.
APPLICATIONS INFORMATION
Figure 4 shows the graph of charge current vs output
voltage when the charge current prole is turned off by
shorting the FB pin to GND and the charge current is
limited by thermal regulation.
OUTPUT VOLTAGE (V)
0
CHARGE
CURRENT(A)
2.0
1.5
1.0
0.5
2.5
15
6
234
4425 F04
VIN = 5V
RPROG = 500Ω
TA = 25°C
FB PIN GROUNDED
THERMAL REGULATION
4.07V
≈ 105°C
372mA
Figure 4. Charge Current vs Output Voltage under Thermal
Regulation (LDO Mode)
C1
CSUP
VOUT
C1 = C2 ≥ 100μF
C2
4425 F05
LTC4425
VOUT
VMID
GND
Figure 5. Charging a Single Supercapacitor
Charging a Single Supercapacitor
The LTC4425 can also be used to charge a single super-
capacitor by connecting two series-connected matched
ceramic capacitors with a minimum capacitance of 100μF
in parallel with the supercapacitor as shown in Figure 5.
Refer to Table 1 for supercapacitor manufacturers.
Table 1. Supercapacitor Manufacturers
CAP-XX
www.cap-xx.com
NESS CAP
www.nesscap.com
Maxwell
www.maxwell.com
Bussmann
www.cooperbussmann.com
AVX
www.avx.com
Illinois Capacitor
www.illcap.com
Tecate Group
www.tecategroup.com
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