LTC3550EDHC-1#TR Linear Technology, LTC3550EDHC-1#TR Datasheet - Page 16

• Manufacturer Part Number: LTC3550EDHC-1#TR
• Description: IC,Battery Management,CMOS,LLCC,16PIN,PLASTIC
• Manufacturer: Linear Technology
• Type: Battery Chargerr

Specifications of LTC3550EDHC-1#TR

• Battery Type: Li-Ion
• Output Current: 800mA
• Output Voltage: 4.2V
• Operating Supply Voltage (min): 2.5V
• Operating Supply Voltage (max): 5.5V
• Operating Temp Range: -40C to 85C
• Mounting: Surface Mount
• Pin Count: 16
• Operating Temperature Classification: Industrial
• Lead Free Status / Rohs Status: Not Compliant

LTC3550-1
APPLICATIO S I FOR ATIO
The DC current rating of the inductor should be at least
equal to the maximum load current plus half the ripple
current to prevent core saturation. Thus, a 720mA rated
inductor should be enough for most applications (600mA
+ 120mA). For best effi ciency, choose a low DC-resistance
inductor.
The inductor value also has an effect on Burst Mode opera-
tion. The transition to low current operation begins when
the inductor current peaks fall to approximately 200mA.
Lower inductor values (higher ΔI
at lower load currents, which can cause a dip in effi ciency
in the upper range of low current operation. In Burst Mode
operation, lower inductance values will cause the burst
frequency to increase.
Inductor Core Selection
Different core materials and shapes will change the
size/current and price/current relationship of an induc-
tor. Toroid or shielded pot cores in ferrite or permalloy
materials are small and don’t radiate much energy, but
generally cost more than powdered iron core inductors
with similar electrical characteristics. The choice of which
style inductor to use often depends more on the price vs
size requirements and any radiated fi eld/EMI requirements
than on what the LTC3550-1 requires to operate. Table 2
shows some typical surface mount inductors that work
well in LTC3550-1 applications.
16
Table 2. Representative Surface Mount Inductors
PART
NUMBER
Sumida
CDRH3D16
Sumida
CMD4D06
Panasonic
ELT5KT
Murata
LQH32CN
VALUE
(µH)
1.5
2.2
3.3
4.7
2.2
3.3
4.7
3.3
4.7
1.0
2.2
4.7
U
(Ω MAX)
0.043
0.075
0.110
0.162
0.116
0.174
0.216
0.060
0.097
0.150
DCR
0.17
0.20
U
CURRENT (A)
MAX DC
L
0.950
0.770
0.750
) will cause this to occur
1.55
1.20
1.10
0.90
1.00
0.95
1.00
0.79
0.65
W
W × L × H (mm)
3.8 × 3.8 × 1.8
3.5 × 4.3 × 0.8
4.5 × 5.4 × 1.2
2.5 × 3.2 × 2.0
U
SIZE
C
In continuous mode, the source current of the top MOSFET
is a square wave of duty cycle V
voltage transients, a low ESR input capacitor sized for the
maximum RMS current must be used. The maximum RMS
capacitor current is given by:
This formula has a maximum at V
= I
used for design because even signifi cant deviations do not
offer much relief. Note that the capacitor manufacturer’s
ripple current ratings are often based on 2000 hours of
life. This makes it advisable to further derate the capaci-
tor, or choose a capacitor rated at a higher temperature
than required. Always consult the manufacturer if there
is any question.
The selection of C
series resistance (ESR).
Typically, once the ESR requirement for C
met, the RMS current rating generally far exceeds the
I
determined by:
where f = operating frequency, C
and ΔI
voltage, the output ripple voltage is highest at maximum
input voltage since ΔI
Aluminum electrolytic and solid tantalum capacitors are
both available in surface mount confi gurations. In the case
of tantalum, it is critical that the capacitors are surge tested
for use in switching power supplies. An excellent choice is
the AVX TPS series of surface mount tantalum. These are
specially constructed and tested for low ESR so they give
the lowest ESR for a given volume. Other capacitor types
include Sanyo POSCAP, Kemet T510 and T495 series, and
Sprague 593D and 595D series. Consult the manufacturer
for other specifi c recommendations.
C
RIPPLE(P-P)
IN
IN
OUT
∆
and C
required I
V
/2. This simple worst-case condition is commonly
OUT
L
= ripple current in the inductor. For a fi xed output
OUT
≅ ∆
requirement. The output ripple ΔV
Selection
I ESR
RMS
L
⎛
⎝ ⎜
OUT
≅
L
is driven by the required effective
I
OMAX
increases with input voltage.
+
8
fC
1
OUT
OUT
V
OUT
OUT
CC
⎞
⎠ ⎟
/V
= output capacitance
= 2V
CC
(
V
V
. To prevent large
CC
CC
OUT
−
OUT
, where I
V
OUT
has been
OUT
)
35501f
RMS
(2)
(3)
is