LT3513EUHF#PBF Linear Technology, LT3513EUHF#PBF Datasheet - Page 15

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

Specifications of LT3513EUHF#PBF

• 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

The low ESR and small size of ceramic capacitors make
them the preferred type for LT3513 applications. However,
not all ceramic capacitors are the same. Many of the higher
value capacitors use poor dielectrics with high temperature
and voltage coefficients. In particular, Y5V and Z5U types
lose a large fraction of their capacitance with applied volt-
age and at temperature extremes.
Because loop stability and transient response depend on
the value of C
X7R and X5R types. Electrolytic capacitors are also an
option. The ESRs of most aluminum electrolytic capacitors
are too large to deliver low output ripple. Tantalum and
newer, lower ESR organic electrolytic capacitors intended
for power supply use are suitable, and the manufacturers
will specify the ESR. Chose a capacitor with a low enough
ESR for the required output ripple. Because the volume
of the capacitor determines its ESR, both the size and the
value will be larger than a ceramic capacitor that would
give similar ripple performance. One benefit is that the
larger capacitance may give better transient response
for large changes in load current. Table 2 lists several
capacitor vendors.
Table 2. Low ESR Surface Mount Capacitors
DIODE SELECTION
The catch diode (D1 from Figure 1) conducts current only
during switch-off time. Average forward current in normal
operation can be calculated from:
operaTion
Taiyo Yuden
Panasonic
VENDOR
Kemet
Sanyo
AVX
TDK
OUT
, this loss may be unacceptable. Use
Ta or Al Organic
Ta Organic
Al Organic
Al Organic
Tantalum
Tantalum
Ceramic
Ceramic
Ceramic
TYPE
T491, T494, T495
X5R, X7R
X5R, X7R
X5R, X7R
POSCAP
SERIES
SP CAP
T520
A700
TPS
The only reason to consider a diode with a larger current
rating than necessary for nominal operation is for the
worst-case condition of shorted output. The diode current
will then increase to the typical peak switch current. Peak
reverse voltage is equal to the regulator input voltage.
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 applica-
tion 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
Characteristics section shows a plot of the minimum load
current to start as a function of input voltage for a 3.3V
I
D(AVG)
=I
OUT
V
R
20
40
40
40
20
40
40
V
(V)
IN
– V
V
IN
I
AVE
OUT
1
1
2
3
1
2
3
(A)
V
FAT
530
550
500
1A (mV)
LT3513
V
F
at 2A (mV)
450
500
450
15
3513fc