LTC3550EDHC#PBF Linear Technology, LTC3550EDHC#PBF Datasheet - Page 17

• Manufacturer Part Number: LTC3550EDHC#PBF
• Description: IC CHARGER BATT DUAL 16-DFN
• Manufacturer: Linear Technology

Specifications of LTC3550EDHC#PBF

• Function: Charge Management
• Battery Type: Lithium-Ion (Li-Ion)
• Voltage - Supply: 4.3 V ~ 8 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-WFDFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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.
Using Ceramic Input and Output Capacitors
Higher capacitance values, lower cost ceramic capacitors
are now becoming available in smaller case sizes. Their
high ripple current, high voltage rating and low ESR make
them ideal for switching regulator applications. Because
the LTC3550’s control loop does not depend on the output
capacitor’s ESR for stable operation, ceramic capacitors
can be used freely to achieve very low output ripple and
small circuit size.
When choosing the input and output ceramic capacitors,
choose the X5R or X7R dielectric formulations. These
dielectrics have the best temperature and voltage charac-
teristics of all the ceramics for a given value and size.
Output Voltage Programming
The output voltage is set by a resistive divider according
to the following formula:
The external resistive divider is connected to the output,
allowing remote voltage sensing as shown in Figure 3.
Effi ciency Considerations
The effi ciency of a switching regulator is equal to the output
power divided by the input power times 100%. It is often
useful to analyze individual losses to determine what is
APPLICATIO S I FOR ATIO
V
OUT
L
= ripple current in the inductor. For a fi xed output
=
0 6
.
V
⎛
⎝ ⎜
1
+
U
R
R
L
2
1
increases with input voltage.
⎞
⎠ ⎟
U
OUT
W
= output capacitance
U
(4)
limiting the effi ciency and which change would produce
the most improvement. Effi ciency can be expressed as:
where L1, L2, etc. are the individual losses as a percent-
age of input power.
Although all dissipative elements in the circuit produce
losses, two main sources usually account for most of
the losses in LTC3550 circuits: V
and I
the effi ciency loss at very low load currents whereas the
I
load currents. In a typical effi ciency plot, the effi ciency
curve at very low load currents can be misleading since
the actual power lost is of no consequence as illustrated
in Figure 4.
1. The V
2
R loss dominates the effi ciency loss at medium to high
Effi ciency = 100% – (L1 + L2 + L3 + ...)
the DC bias current as given in the Electrical Charac-
teristics and the internal main switch and synchronous
2
R losses. The V
0.00001
0.0001
CC
Figure 3. Setting the LTC3550 Output Voltage
0.001
0.01
0.1
quiescent current is due to two components:
1
0.1
Figure 4. Power Lost vs Load Current
LTC3550
1
CC
LOAD CURRENT (mA)
GND
V
FB
quiescent current loss dominates
10
0.6V ≤ V
100
CC
OUT
R1
R2
3550 F03
quiescent current
≤ 5.5V
LTC3550
3550 F04
1000
17
3550fa