LT3513 LINER [Linear Technology], LT3513 Datasheet - Page 15

• Manufacturer Part Number: LT3513
• Description: 2MHz High Current 5-Output Regulator for TFT-LCD Panels
• Manufacturer: LINER [Linear Technology]

OPERATION
Use a diode with a reverse voltage rating greater than the
input voltage. Table 3 lists several Schottky diodes and
their manufacturers.
Table 3. Schottky Diodes
PART NUMBER
On Semiconductor
MBRM120E
MBRM140
MBRS240
MBRA340
Diodes Inc.
B120
B240
B340A
BOOST PIN CONSIDERATIONS
The minimum operating voltage of an LT3513 application
is limited by the undervoltage lockout ~4V and by the
maximum duty cycle. The boost circuit also limits the
minimum input voltage for proper start-up. If the input
voltage ramps slowly or the LT3513 turns on when the
output is already in regulation, the boost capacitor may
not be fully charged. Because the boost capacitor charges
with the energy stored in the inductor, the circuit will rely
on some minimum load current to get the boost circuit
running properly. This minimum load will depend on input
and output voltages. The Typical Performance Character-
istics section shows a plot of the minimum load current
to start as a function of input voltage for a 3.3V 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:
V
R
20
40
40
40
20
40
40
(V)
I
AVE
1
1
2
3
1
2
3
(A)
V
FAT
530
550
500
1A (mV)
V
F
at 2A (mV)
450
500
450
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.
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.
R
3
R
DC
DC
=
6
R
=
=
=
4
⎛
⎝ ⎜
V
V
V
OUT
IN
OUT
V
1 25
1 25
OUT
.
V
V
+
.
OUT
OUT
•
V
–
R
OUT
–
V
5
1
IN
⎞
⎠ ⎟
–
R
–V
5
OUT
R6
R5
3513 A2
NFB4
22
LT3513
15
3513fa