LTC4425EDD#PBF Linear Technology, LTC4425EDD#PBF Datasheet - Page 13

• Manufacturer Part Number: LTC4425EDD#PBF
• Description: IC SUPERCAP CHARGER 12-DFN
• Manufacturer: Linear Technology

Specifications of LTC4425EDD#PBF

• Applications: Supercapacitor Charger
• Current - Supply: 20µA
• Voltage - Supply: 2.7 V ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 12-DFN
• Battery Type: Li-Ion/Li-Pol
• Output Current: 3A
• Output Voltage: 5.5V
• Operating Supply Voltage (min): 2.7V
• Operating Supply Voltage (max): 5.5V
• Operating Temp Range: -40C to 125C
• Mounting: Surface Mount
• Pin Count: 8
• Operating Temperature Classification: Automotive
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIONS INFORMATION
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:
If θ
temperature, then the die temperature can be calculated as:
When the part is in thermal regulation, the die temperature
is 105°C and for a given V
can be determined by the following equation:
For example, if the LTC4425 in the DFN package is used in
LDO mode to charge a completely discharged supercap stack
(V
the charge current, at fi rst, will be limited to approximately:
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:
Using the previous example, for full charge current, the
output voltage has to rise to at least:
OUT
P
T
I
I
V
V
CHRG
CHRG
JA
DIE
D
OUT
OUT
= 0V) at a room temperature of 25°C from a 5V source,
= (V
is the thermal resistance and T
= T
=
=
=
=
IN
A
5
V
(
(
IN
5 0
+ P
V
– V
V
IN
–
105
–
–
D
OUT
2
105 –
I
–
(
)
CHRG
• θ
105 25
A
°
V
105
V
) • I
C
•
OUT
•
JA
–
43
43
–
–
25
•
CHRG
T
)
°
A
°
T
θ
•
C W
C W
IN
A
°
JA
θ
)
C
/
/
°
and V
JA
C
=
=
5
OUT
215
V
80
–
, the charge current
°
86
°
C A
A
C
80
/
is the ambient
°
C V
°
C
=
/
372
=
4 07
mA
.
V
Figure 4 shows the graph of charge current vs output
voltage when the charge current profi le is turned off by
shorting the FB pin to GND and the charge current is
limited by thermal regulation.
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
NESS CAP
Maxwell
Bussmann
AVX
Illinois Capacitor
Tecate Group
Figure 4. Charge Current vs Output Voltage under Thermal
Regulation (LDO Mode)
Figure 5. Charging a Single Supercapacitor
2.5
2.0
1.5
1.0
0.5
C1 = C2 ≥ 100μF
0
LTC4425
0
372mA
V
R
T
FB PIN GROUNDED
IN
A
PROG
THERMAL REGULATION
= 25°C
V
V
GND
= 5V
OUT
MID
1
= 500Ω
≈ 105°C
OUTPUT VOLTAGE (V)
2
www.cap-xx.com
www.nesscap.com
www.maxwell.com
www.cooperbussmann.com
www.avx.com
www.illcap.com
www.tecategroup.com
C1
C2
3
4425 F05
4
C
4.07V
SUP
V
OUT
LTC4425
5
4425 F04
6
13
4425f