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參數(shù)資料
| 型號(hào)： | LT3513IUHF#TRPBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 3.5 A SWITCHING REGULATOR, 2220 kHz SWITCHING FREQ-MAX, PQCC38 |
| 封裝： | 5 X 7 MM, LEAD FREE, PLASTIC, MO-220WHKD, QFN-38 |
| 文件頁數(shù)： | 10/22頁 |
| 文件大?。?/td> | 374K |
| 代理商： | LT3513IUHF#TRPBF |
LT3513
18
3513fc
below the rated voltage of the capacitor. Be sure to place
the 1F ceramic as close as possible to the VIN and GND
pins on the IC for optimal noise immunity.
A final 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.Ifpowerisappliedquickly(forexamplebyplugging
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 shut-
down 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
~30A. An internal 2A 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
current will generate a voltage ramp on these pins. This
voltage clamps the VC pin, limiting the peak switch current
and therefore input current during start-up. The RUN-SS1
pin clamps VC1, the RUN-SS2 pin clamps VC1 and the
RUN-SS3/4 pin clamps the VC3 and VC4 pins. A good value
for the soft-start capacitors is COUT/10,000, where COUT
is the value of the largest output capacitor.
VON Pin Considerations
TheVONpinisthedelayedoutputforswitchingregulator 3.
When the CT pin reaches 1.1V, the output disconnect PNP
turns on, connecting VON to E3. The VON pin is current
limited and will protect the LT3513 and input source from
a shorted output.
The VON pin output is also controlled from the VON_CLK
pin. When VON_CLK is low, the VON output will turn on if the
CT pin is greater than 1.1V. When VON_CLK is high, greater
than 1.5V, the VON output is disabled and the VONSINK open
collector device turns on. If the VONSINK pin is connected
to VON through a resistor, the VON voltage will decay with
a high VON_CLK. VON_CLK may be synced to the horizontal
scanning frequency to improve LCD image quality.
Low Voltage Dropout Linear Regulator
The LT3513 features an output to drive an external NPN
transistorLDOtoprovidealowervoltagelogicsupplyvolt-
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
=R7
VLDO
0.625V
– 1
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 2.2F and 20F.
X7R dielectrics are preferred, followed by X5R, as these
materials retain their capacitance over wide voltage and
temperature ranges.
Printed Circuit Board Layout
For proper operation and minimum EMI, care must be
taken during printed circuit board (PCB) layout. Figure 3
shows the high current paths in the step-down regula-
tor circuit. Note that in the step-down regulators, large,
switched currents flow in the power switch, the catch
diode and the input capacitor. In the step-up regulators,
large, switched currents flow through the power switch,
the switching diode and the output capacitor. In SEPIC and
operaTion
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