LTC3872ETS8#TRMPBF Linear Technology, LTC3872ETS8#TRMPBF Datasheet - Page 12

• Manufacturer Part Number: LTC3872ETS8#TRMPBF
• Description: IC DC/DC CNTRLR TSOT23-8
• Manufacturer: Linear Technology
• Type: Step-Up (Boost)r

Specifications of LTC3872ETS8#TRMPBF

• Internal Switch(s): No
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 1.2 ~ 60 V
• Current - Output: 10A
• Frequency - Switching: 550kHz
• Voltage - Input: 2.75 ~ 9.8 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: TSOT-23-8, TSOT-8
• Primary Input Voltage: 9.8V
• No. Of Outputs: 1
• Output Voltage: 60V
• No. Of Pins: 8
• Operating Temperature Range: -40°C To +85°C
• Msl: MSL 1 - Unlimited
• Supply Voltage Range: 2.75V To 9.8V
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Other names: LTC3872ETS8#TRMPBF; LTC3872ETS8#TRMPBFTR

LTC3872
applicaTions inForMaTion
For a 1% contribution to the total ripple voltage, the ESR
of the output capacitor can be determined using the fol-
lowing equation:
where:
For the bulk C component, which also contributes 1% to
the total ripple:
For many designs it is possible to choose a single capacitor
type that satisfies both the ESR and bulk C requirements
for the design. In certain demanding applications, however,
the ripple voltage can be improved significantly by con-
necting two or more types of capacitors in parallel. For
example, using a low ESR ceramic capacitor can minimize
the ESR step, while an electrolytic capacitor can be used
to supply the required bulk C.
Once the output capacitor ESR and bulk capacitance have
been determined, the overall ripple voltage waveform
should be verified on a dedicated PC board (see Board
Layout section for more information on component place-
ment). Lab breadboards generally suffer from excessive
series inductance (due to inter-component wiring), and
these parasitics can make the switching waveforms look
significantly worse than they would be on a properly
designed PC board.
The output capacitor in a boost regulator experiences
high RMS ripple currents, as shown in Figure 7. The RMS
output capacitor ripple current is:
Note that the ripple current ratings from capacitor manu-
facturers are often based on only 2000 hours of life. This
makes it advisable to further derate the capacitor or to
12
ESR
I
I
C
RMS(COUT)
IN(PEAK)
OUT
COUT
≥
0.01• V
= 1+
≤
I

 
O(MAX)
≈I
0.01• V
I
IN(PEAK)
O(MAX)
χ
2
O

 
• f
•
O
1– D
I
•
O(MAX)
V
MAX
O
V
– V
IN(MIN)
IN(MIN)
choose a capacitor rated at a higher temperature than
required. Several capacitors may also be placed in parallel
to meet size or height requirements in the design.
Manufacturers such as Nichicon, United Chemicon and
Sanyo should be considered for high performance through-
hole capacitors. The OS-CON semiconductor dielectric
capacitor available from Sanyo has the lowest product of
ESR and size of any aluminum electrolytic, at a somewhat
higher price.
In surface mount applications, multiple capacitors may
have to be placed in parallel in order to meet the ESR or
RMS current handling requirements of the application.
Aluminum electrolytic and dry tantalum capacitors are
Figure 6. Switching Waveforms for a Boost Converter
6e. Output Voltage Ripple Waveform
V
(AC)
I
OUT
SW
I
I
D
L
6b. Inductor and Input Currents
6d. Diode and Output Currents
V
IN
t
ON
6a. Circuit Diagram
6c. Switch Current
L
SW
V
t
ESR
OFF
D
V
COUT
C
OUT
RINGING DUE TO
TOTAL INDUCTANCE
(BOARD + CAP)
V
OUT
I
IN
R
L
I
O
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