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参数资料
| 型号： | LT1871IMS-7#TR |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING CONTROLLER, 1000 kHz SWITCHING FREQ-MAX, PDSO10 |
| 封装： | PLASTIC, MSOP-10 |
| 文件页数： | 11/32页 |
| 文件大小： | 461K |
| 代理商： | LT1871IMS-7#TR |
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LTC1871-7
19
18717fc
APPLICATIONS INFORMATION
During this inductor charging interval, the output capacitor
must supply the load current and a signicant droop in
the output voltage can occur. Generally, it is a good idea
to choose a value of inductor ΔIL between 25% and 40%
of IIN(MAX). The alternative is to either increase the value
of the output capacitor or disable Burst Mode operation
using the MODE/SYNC pin.
Burst Mode operation can be defeated by connecting the
MODE/SYNC pin to a high logic-level voltage (either with
a control input or by connecting this pin to INTVCC). In
this mode, the burst clamp is removed, and the chip can
operate at constant frequency from continuous conduction
mode (CCM) at full load, down into deep discontinuous
conduction mode (DCM) at light load. Prior to skipping
pulses at very light load (i.e., <5% of full load), the control-
ler will operate with a minimum switch on-time in DCM.
Pulse skipping prevents a loss of control of the output at
very light loads and reduces output voltage ripple.
Efciency Considerations
The efciency of a switching regulator is equal to the out-
put power divided by the input power (100%). Percent
efciency can be expressed as:
% Efciency = 100% – (L1 + L2 + L3 + …),
where L1, L2, etc. are the individual loss components as a
percentage of the input power. It is often useful to analyze
individual losses to determine what is limiting the efciency
and which change would produce the most improvement.
Although all dissipative elements in the circuit produce
losses, four main sources usually account for the majority
of the losses in LTC1871-7 application circuits:
1. The supply current into VIN. The VIN current is the sum
of the DC supply current IQ (given in the Electrical Char-
acteristics) and the MOSFET driver and control currents.
The DC supply current into the VIN pin is typically about
650μA and represents a small power loss (much less
than 1%) that increases with VIN. The driver current
results from switching the gate capacitance of the power
MOSFET; this current is typically much larger than the
DC current. Each time the MOSFET is switched on and
then off, a packet of gate charge QG is transferred from
INTVCC to ground. The resulting dQ/dt is a current that
must be supplied to the INTVCC capacitor through the
VIN pin by an external supply. If the IC is operating in
CCM:
IQ(TOT) ≈ IQ = f QG
PIC = VIN (IQ + f QG)
2. Power MOSFET switching and conduction losses:
PFET =
IO(MAX)
1–DMAX
2
RDS(ON) DMAX T
+ k VO2
IO(MAX)
1–DMAX
CRSS f
3. The I2R losses in the sense resistor can be calculated
almost by inspection.
PR(SENSE) =
IO(MAX)
1–DMAX
2
RSENSE DMAX
4. The losses in the inductor are simply the DC input cur-
rent squared times the winding resistance. Expressing
this loss as a function of the output current yields:
PR(WINDING) =
IO(MAX)
1–DMAX
2
RW
5. Losses in the boost diode. The power dissipation in the
boost diode is:
PDIODE = IO(MAX) VD
The boost diode can be a major source of power loss
in a boost converter. For 13.2V input, 42V output at
1.5A example given in Figure 9, a Schottky diode with
a 0.4V forward voltage would dissipate 600mW, which
represents about 1% of the input power. Diode losses
can become signicant at low output voltages where
the forward voltage is a signicant percentage of the
output voltage.
6. Other losses, including CIN and CO ESR dissipation and
inductor core losses, generally account for less than
2% of the total losses.
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LT1871IMS-7-TRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:High Input Voltage,Current Mode Boost, Flyback and SEPIC Controller |
| LT1873-41 | 制造商:未知厂家 制造商全称:未知厂家 功能描述:Optoelectronic |
| LT1873-41UR | 制造商:未知厂家 制造商全称:未知厂家 功能描述:Optoelectronic |
| LT1880 | 制造商:LINER 制造商全称:Linear Technology 功能描述:SOT-23, Rail-to-Rail Output, Picoamp Input Current Precision Op Amp |
| LT1880CS5 | 制造商:Linear Technology 功能描述:OP Amp Single GP R-R O/P ±18V/36V 5-Pin TSOT-23 |
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