参数资料
型号: LT3782AEFE#TR
厂商: LINEAR TECHNOLOGY CORP
元件分类: 稳压器
英文描述: SWITCHING CONTROLLER, PDSO28
封装: 4.40 MM, PLASTIC, TSSOP-28
文件页数: 2/20页
文件大小: 233K
代理商: LT3782AEFE#TR
LT3782A
10
3782af
then RFREQ1 + RFREQ2 should be 80k and VDELAY should
be 1V, with VRSET = 2.3V then RFREQ1 = 47.5k and RFREQ2
= 32.5k (see Figure 3).
Duty Cycle Limit
When DCL pin is shorted to RSET pin and switching fre-
quency is less than 250kHz (RFREQ > 80k), the maximum
duty cycle of LT3782A will be at least 90%. The maximum
duty cycle can be clamped to 50% by grounding the DCL
pin or to 75% by forcing the VDCL voltage to 1.2V with a
resistor divider from RSET pin to ground. The typical DCL
pin input current is 0.2μA.
Slope Compensation
The LT3782A is designed for high voltage and/or high
current applications, and very often these applications
generate noise spikes that can be picked up by the cur-
rent sensing amplier and cause switching jitter. To avoid
switching jitter, careful layout is absolutely necessary to
minimize the current sensing noise pickup. Sometimes
increasing slope compensation to overcome the noise
can help to reduce jitter. The built-in slope compensa-
tion can be increased by adding a resistor RSLOPE from
SLOPE pin to ground. Note that smaller RSLOPE increases
slope compensation and the minimum RSLOPE allowed is
RFREQ/2.
Layout Considerations
To prevent EMI, the power MOSFETs and input bypass
capacitor leads should be kept as short as possible. A
ground plane should be used under the switching circuitry
to prevent interplane coupling and to act as a thermal
spreading path. Note that the bottom pad of the package
is the heat sink, as well as the IC signal ground, and must
be soldered to the ground plane.
In a boost converter, the conversion gain (assuming 100%
efciency) is calculated as (ignoring the forward voltage
drop of the boost diode):
V
OUT
V
IN
=
1
1D
where D is the duty ratio of the main switch. D can then
be estimated from the input and output voltages:
D =1
V
IN
V
OUT
;D
MAX = 1
V
IN(MIN)
V
OUT
Figure 3. Increase Delay Time
RSET
DELAY
LT3782A
RFREQ2
32.5k
RFREQ1
47.5k
3782A F03
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