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參數(shù)資料
| 型號(hào)： | LTC3496EUFD#TRPBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SWITCHING CONTROLLER, 2300 kHz SWITCHING FREQ-MAX, PQCC28 |
| 封裝： | 4 X 5 MM, LEAD FREE, PLASTIC, MO-220, QFN-28 |
| 文件頁數(shù)： | 15/16頁 |
| 文件大?。?/td> | 296K |
| 代理商： | LTC3496EUFD#TRPBF |
LT3496
8
3496f
Switching Frequency and Soft-Start
The LT3496 switching frequency is controlled by FADJ
pin voltage. Setting FADJ voltage to be less than 1V will
reduce switching frequency.
If FADJ voltage is higher than 1V, the default switch-
ing frequency is 2.1MHz. In general, a lower switching
frequency should be used where either very high or very
low switch duty cycle is required or higher efciency is
desired. Selection of a higher switching frequency will
allow use of low value external components and yield a
smaller solution size and prole.
Connecting FADJ pin to a lowpass lter (R5 and C4 in
Figure 1) from the REF pin provides a soft-start function.
During start-up, FADJ voltage increases slowly from 0V
to the setting voltage. As a result, the switching frequency
increases slowly to the setting frequency. This function
limits the inrush current during start-up.
Undervoltage Lockout
The LT3496 has an undervoltage lockout circuit that
shuts down all the three converters when the input volt-
age drops below 2.4V. This prevents the converter from
switching in an erratic mode when powered from a low
supply voltage.
Input Capacitor Selection
For proper operation, it is necessary to place a bypass
capacitor to GND close to the VIN pin of the LT3496. A
1F or greater capacitor with low ESR should be used. A
ceramic capacitor is usually the best choice.
In the buck mode conguration, the capacitor at PVIN has
large pulsed currents due to the current returned though
the Schottky diode when the switch is off. For the best
reliability, this capacitor should have low ESR and ESL
and have an adequate ripple current rating. The RMS
input current is:
II
D D
IN RMS
LED
()
–
=
()
1
where D is the switch duty cycle. A 1F ceramic type ca-
pacitor placed close to the Schottky diode and the ground
plane is usually sufcient for each channel.
Output Capacitor Selection
The selection of output lter capacitor depends on the load
and converter conguration, i.e., step-up or step-down.
For LED applications, the equivalent resistance of the LED
is typically low, and the output lter capacitor should be
large enough to attenuate the current ripple.
To achieve the same LED ripple current, the required lter
capacitor value is larger in the boost and buck-boost mode
applications than that in the buck mode applications. For the
LED buck mode applications, a 0.22F ceramic capacitor
is usually sufcient for each channel. For the LED boost
and buck-boost applications, a 1F ceramic capacitor is
usually sufcient for each channel.
Use only ceramic capacitors with X7R or X5R dielectric,
as they are good for temperature and DC bias stability of
the capacitor value. All ceramic capacitors exhibit loss of
capacitance value with increasing DC voltage bias, so it
may be necessary to choose a higher value capacitor to get
the required capacitance at the operation voltage. Always
check that the voltage rating of the capacitor is sufcient.
Table 1 shows some recommended capacitor vendors.
Table 1. Ceramic Capacitor Manufacturers
VENDOR
TYPE
SERIES
Taiyo Yuden
Ceramic
X5R, X7R
AVX
Ceramic
X5R, X7R
Murata
Ceramic
X5R, X7R
Kemet
Ceramic
X5R, X7R
APPLICATIONS INFORMATION
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