LT3513EUHF#PBF Linear Technology, LT3513EUHF#PBF Datasheet - Page 17

• 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

Output Capacitor Selection
Use low ESR (equivalent series resistance) capacitors at
the output to minimize the output ripple voltage. Multilayer
ceramic capacitors are an excellent choice, as they have
an extremely low ESR and are available in very small pack-
ages. X7R dielectrics are preferred, followed by X5R, as
these materials retain their capacitance over wide voltage
and temperature ranges. A 10µF to 22µF output capaci-
tor is sufficient for most LT3513 applications. Even less
capacitance is required for outputs with |V
|I
also work, but they will occupy more board area and will
have a higher ESR than a ceramic capacitor. Always use
a capacitor with a sufficient voltage rating.
Diode Selection
A Schottky diode is recommended for use with the
LT3513 switcher 2 and switcher 4. The Schottky diode for
switcher 3 is integrated inside the LT3513. Choose diodes
for switcher 2 and switcher 4 rated to handle an average
current greater than the load current and rated to handle
the maximum diode voltage. The average diode current in
the step-up and SEPIC is equal to the load current. Each of
the two diodes in the charge pump configurations carries
an average diode current equal to the load current. The
ground connected diode in the charge pump is integrated
into the LT3513. The maximum diode voltage in the step-
up and charge pump configurations is equal to |V
The maximum diode voltage in the SEPIC and inverting
configurations is V
Input Capacitor Selection
Bypass the input of the LT3513 circuit with a 4.7µF or higher
ceramic capacitor of X7R or X5R type. A lower value or
a less expensive Y5V type will work if there is additional
bypassing provided by bulk electrolytic capacitors or if the
operaTion
OUT
| < 100mA. Solid tantalum or OS-CON capacitors will
IN
+ |V
OUT
|.
OUT
| > 20V or
OUT
|.
input source impedance is low. The following paragraphs
describe the input capacitor considerations in more detail.
Step-down regulators draw current from the input sup-
ply in pulses with very fast rise and fall times. The input
capacitor is required to reduce the resulting voltage ripple
at the LT3513 input and to force this switching current
into a tight local loop, minimizing EMI. The input capaci-
tor must have low impedance at the switching frequency
to do this effectively and it must have an adequate ripple
current rating. The input capacitor RMS current can be
calculated from the step-down output voltage and current,
and the input voltage:
and is largest when V
ripple current contribution from the other channels will
be minimal. Considering that the maximum load current
from switcher 1 is ~3A, RMS ripple current will always be
less than 1.5A. The high frequency of the LT3513 reduces
the energy storage requirements of the input capacitor, so
that the capacitance required is less than 10µF . The com-
bination of small size and low impedance (low equivalent
series resistance or ESR) of ceramic capacitors makes
them the preferred choice. The low ESR results in very
low voltage ripple. Ceramic capacitors can handle larger
magnitudes of ripple current than other capacitor types of
the same value. Use X5R and X7R types. An alternative to
a high value ceramic capacitor is a lower value along with
a larger electrolytic capacitor, for example a 1µF ceramic
capacitor in parallel with a low ESR tantalum capacitor. For
the electrolytic capacitor, a value larger than 10µF will be
required to meet the ESR and ripple current requirements.
Because the input capacitor is likely to see high surge
currents when the input source is applied, only consider a
tantalum capacitor if it has the appropriate surge current
rating. The manufacturer may also recommend operation
c
IN(RMS)
= I
OUT
V
OUT
IN
= 2V
(
V
V
IN
IN
OUT
– V
(50% duty cycle). The
OUT
)
<
I
OUT
LT3513
2
17
3513fc