参数资料
型号: LT3686IDD#TRPBF
厂商: LINEAR TECHNOLOGY CORP
元件分类: 稳压器
英文描述: 2.65 A SWITCHING REGULATOR, 2500 kHz SWITCHING FREQ-MAX, PDSO10
封装: 3 X 3 MM, LEAD FREE, PLASTIC, MO-229WEED-2, DFN-10
文件页数: 3/28页
文件大小: 509K
代理商: LT3686IDD#TRPBF
LT3686
11
3686fc
ApplicAtions inForMAtion
Figure 3. Continuous Mode Operation Near Minimum On Time
When the required on time decreases below the typical
minimum on time of 100ns, instead of the switch pulse
width becoming narrower to accommodate the lower duty
cycle requirement, the switch pulse width remains fixed at
100ns. The inductor current ramps up to a value exceed-
ing the load current and the output ripple increases. The
part then remains off until the output voltage dips below
the programmed value before it begins switching again
(Figure 4).
Provided that the load can tolerate the increased output
voltagerippleandthatthecomponentshavebeenproperly
selected, operation while pulse skipping is safe and will
not damage the part. As the input voltage increases, the
inductor current ramps up quicker, the number of skipped
pulses increases, and the output voltage ripple increases.
Inductor current may reach current limit when operating
in pulse skip mode with small valued inductors. In this
case, the LT3686 will periodically reduce its frequency to
keep the inductor valley current to 1.7A (Figure 5). Peak
Figure 4. Pulse Skip Occurs When Required On Time Is
Below 100ns
The maximum input voltage is determined by the absolute
maximum ratings of the VIN and BOOST pins. For fixed
frequency operation, the maximum input voltage is de-
termined by the minimum duty cycle DCMIN:
VIN(MAX) =
VOUT + VD
DCMIN
– VD + VSW
DCMIN can be adjusted with frequency. Note that this is a
restrictionontheoperatinginputvoltageforfixedfrequency
operation; the circuit will tolerate transient inputs up to
the absolute maximum ratings of the VIN and BOOST pins.
Minimum On Time
As the input voltage is increased, the LT3686 is required
to switch for shorter periods of time. Delays associated
with turning off the power switch dictate the minimum on
time of the part. The minimum on time for the LT3686 is
100ns (Figure 3).
VIN = 18V
VOUT = 3.3V
L = 6.8H
COUT = 22F
ILOAD = 1.2mA
VOUT
100mV/DIV
AC
VSW
10V/DIV
IL
500mA/DIV
500ns/DIV
3686 F03
VIN = 35V
VOUT = 3.3V
L = 6.8H
COUT = 22F
IOUT = 300mA
VSW
20V/DIV
IL
500mA/DIV
VOUT
100mA/DIV
AC
2s/DIV
3686 F04
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