LT3513 LINER [Linear Technology], LT3513 Datasheet - Page 17

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

OPERATION
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
below the rated voltage of the capacitor. Be sure to place
the 1μF ceramic as close as possible to the V
pins on the IC for optimal noise immunity.
A fi nal caution is in order regarding the use of ceramic
capacitors at the input. A ceramic input capacitor can
combine with stray inductance to form a resonant tank
circuit. If power is applied quickly (for example by plugging
the circuit into a live power source), this tank can ring,
doubling the input voltage and damaging the LT3513. The
solution is to either clamp the input voltage or dampen the
tank circuit by adding a lossy capacitor (an electrolytic)
in parallel with the ceramic capacitor. For details, see Ap-
plication Note 88.
Soft-Start and Shutdown
The RUN-SS1(Run/Soft-Start) pin is used to place the
switching regulators and the internal bias circuits in
shutdown mode. It also provides a soft-start function,
along with RUN-SS2 and RUN-SS3/4. If the RUN-SS1
pin is pulled to ground, the LT3513 enters its shutdown
mode with all regulators off and quiescent current reduced
to ~30μA. An internal 2μA current source pulls up on the
RUN-SS1, RUN-SS2, and RUN-SS3/4 pins. If the RUN-SS1
pin reaches ~0.6V, the internal bias circuits start and the
quiescent currents increase to their nominal levels.
If a capacitor is tied from the RUN-SS1, RUN-SS2 or
RUN-SS3/4 pins to ground, then the internal pull-up
IN
and GND
current will generate a voltage ramp on these pins. This
voltage clamps the V
and therefore input current during start-up. The RUN-SS1
pin clamps V
RUN-SS3/4 pin clamps the V
for the soft-start capacitors is C
is the value of the largest output capacitor.
V
The V
When the C
turns on, connecting V
limited and will protect the LT3513 and input source from
a shorted output.
The V
pin. When V
C
than 1.5V, the V
collector device turns on. If the V
to V
a high V
scanning frequency to improve LCD image quality.
Low Voltage Dropout Linear Regulator
The LT3513 features an output to drive an external NPN
transistor LDO to provide a lower voltage logic supply volt-
age. The output is capable of providing 10mA of current to
the base of the NPN. The output of the LDO is controlled
by the FB5 pin. Choose the resistor values according to:
R8 should be 10k or less to avoid bias current errors.
The internal compensation of the LDO relies on a low ESR
ceramic capacitor between the values of 2.2μF and 20μF .
X7R dielectrics are preferred, followed by X5R, as these
materials retain their capacitance over wide voltage and
temperature ranges.
ON
T
pin is greater than 1.1V. When V
R
ON
8
Pin Considerations
ON
ON
=
through a resistor, the V
ON_CLK
R
pin is the delayed output for switching regulator 3.
pin output is also controlled from the V
7
⎛
⎝ ⎜
T
ON_CLK
pin reaches 1.1V, the output disconnect PNP
0 625
C1
V
.
ON
. V
LDO
, the RUN-SS2 pin clamps V
ON_CLK
output is disabled and the V
V
is low, the V
C
–
pin, limiting the peak switch current
1
ON
⎞
⎠ ⎟
may be synced to the horizontal
to E3. The V
C3
ON
and V
ON
OUT
ONSINK
output will turn on if the
voltage will decay with
ON_CLK
/10,000, where C
C4
pins. A good value
ON
pin is connected
is high, greater
pin is current
LT3513
ONSINK
C1
and the
17
ON_CLK
open
3513fa
OUT