LT3513EUHF#TRPBF Linear Technology, LT3513EUHF#TRPBF Datasheet - Page 16

• Manufacturer Part Number: LT3513EUHF#TRPBF
• Description: IC REG 5-OUT FOR TFT-LCD 38QFN
• Manufacturer: Linear Technology

Specifications of LT3513EUHF#TRPBF

• Applications: Converter, TFT, LCD
• Voltage - Input: 4.5 ~ 30 V
• Number Of Outputs: 5
• Voltage - Output: 0.8 ~ 40 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 38-QFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

operaTion
LT3513
output. The minimum load current generally goes to zero
once the circuit has started. Even without an output load
current, in many cases the discharged output capacitor
will present a load to the switcher that will allow it to start.
INVERTER/STEP-UP CONSIDERATIONS
Regulating Positive Output Voltages
The output voltage is programmed with a resistor divider
between the output and the FB pin. Choose the resistors
according to:
R4 should be 10k or less to avoid bias current errors.
Regulating Negative Output Voltages
The LT3513 contains an inverting op amp with a gain of 1.
The NFB4 pin works just as the other FB pins. Choose the
resistors according to:
R5 should be 2.5kΩ or less to avoid bias current errors.
Duty Cycle Range
The maximum duty cycle (DC) of the LT3513 switching
regulator is 75% for SW2, and 84% for SW3 and SW4.
16
R3 = R4
R6 =

 
V
OUT
V
1.25
1.25
OUT
• R5
– 1

 
– R5
–V
OUT
R6
R5
3513 A2
NFB4
22
The duty cycle for a given application using the step-up
or charge pump topology is:
The duty cycle for a given application using the inverter
or SEPIC is:
The LT3513 can still be used in applications where the duty
cycle, as calculated above, is greater than the maximum.
However, the part must be operated in discontinuous mode
so that the actual duty cycle is reduced.
Inductor Selection
Table 1 lists several inductor vendors and types that are
suitable to use with the LT3513. Consult each manufacturer
for detailed information and for their entire selection of
related parts. Use ferrite core inductors to obtain the best
efficiency, as core losses at frequencies above 1MHz are
much lower for ferrite cores than for powdered-iron units.
A 10µH to 22µH inductor will be the best choice for most
LT3513 step-up and charge pump designs. Choose an
inductor that can carry the entire switch current without
saturating. For inverting and SEPIC regulators, a coupled
inductor, or two separate inductors is an option. When
using coupled inductors, choose one that can handle
at least the switch current without saturating. If using
uncoupled inductors, each inductor need only handle ap-
proximately one-half of the total switch current. A 4.7µH
to 15µH coupled inductor or two 10µH to 22µH uncoupled
inductors will usually be the best choice for most LT3513
inverting and SEPIC designs.
Dc =
Dc =
V
V
IN
OUT
V
V
+ V
OUT
OUT
– V
OUT
IN
3513fc