LT3757EDD#TRPBF Linear Technology, LT3757EDD#TRPBF Datasheet - Page 25

• Manufacturer Part Number: LT3757EDD#TRPBF
• Description: IC CTRLR DC/DC ADJ 10-DFN
• Manufacturer: Linear Technology
• Type: Step-Up (Boost), Inverting, Flyback, Sepicr

Specifications of LT3757EDD#TRPBF

• Internal Switch(s): No
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Frequency - Switching: 100kHz ~ 1MHz
• Voltage - Input: 2.9 ~ 40 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 10-DFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Voltage - Output: -
• Power - Output: -

Inverting Converter: Switch Duty Cycle and Frequency
For an inverting converter operating in CCM, the duty cycle
of the main switch can be calculated based on the negative
output voltage (V
The maximum duty cycle (D
has the minimum input voltage:
Inverting Converter: Inductor, Sense Resistor, Power
MOSFET, Output Diode and Input Capacitor Selections
The selections of the inductor, sense resistor, power
MOSFET, output diode and input capacitor of an inverting
converter are similar to those of the SEPIC converter. Please
refer to the corresponding SEPIC converter sections.
Inverting Converter: Output Capacitor Selection
The inverting converter requires much smaller output
capacitors than those of the boost, flyback and SEPIC
converters for similar output ripples. This is due to the fact
that, in the inverting converter, the inductor L2 is in series
with the output, and the ripple current flowing through the
output capacitors are continuous. The output ripple voltage
is produced by the ripple current of L2 flowing through the
ESR and bulk capacitance of the output capacitor:
applicaTions inForMaTion
D
∆
MAX
V
OUT P P
=
( – )
V
OUT
=
V
−
OUT
∆
OUT
V
I
L
D
) and the input voltage (V
2
−
−
•



V
V
ESR
IN MIN
D
MAX
(
COUT
) occurs when the converter
)
+
8
• •
f C
1
OUT
IN



).
After specifying the maximum output ripple, the user can
select the output capacitors according to the preceding
equation.
The ESR can be minimized by using high quality X5R or
X7R dielectric ceramic capacitors. In many applications,
ceramic capacitors are sufficient to limit the output volt-
age ripple.
The RMS ripple current rating of the output capacitor
needs to be greater than:
I
Inverting Converter: Selecting the DC Coupling Capacitor
The DC voltage rating of the DC coupling capacitor
(C
maximum input voltage minus the output voltage (nega-
tive voltage):
V
C
the switch off-time, the current through C
approximately –I
rating of the coupling capacitor is determined by the fol-
lowing equation:
A low ESR and ESL, X5R or X7R ceramic capacitor works
well for C
DC
DC
I
RMS(COUT)
RMS CDC
has nearly a rectangular current waveform. During
CDC
, as shown in Figure 10) should be larger than the
(
> V
DC
IN(MAX)
)
.
>
> 0.3 • ∆I
I
O MAX
(
O
– V
flows during the on-time. The RMS
)
•
OUT
L2
− 1
D
MAX
D
MAX
DC
LT3757
is I
IN

, while
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