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参数资料
| 型号： | LT3500IMSE#PBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 3.5 A SWITCHING REGULATOR, 2800 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封装： | LEAD FREE, PLASTIC, MSOP-16 |
| 文件页数： | 6/28页 |
| 文件大小： | 318K |
| 代理商： | LT3500IMSE#PBF |
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LT3500
14
3500fc
APPLICATIONS INFORMATION
To maintain output regulation, this peak current must be
less than the LT3500’s switch current limit, ILIM. ILIM is
guaranteed to be greater than 2.3A over the entire duty
cycle range. The maximum output current is a function
of the chosen inductor value:
I
OUT1(MAX) = ILIM
ΔI
L
2
=2.3 –
ΔI
L
2
If the inductor value is chosen so that the ripple current
is small, then the available output current will be near the
switch current limit.
One approach to choosing the inductor is to start with the
simple rule given above, look at the available inductors
and choose one to meet cost or space goals. Then use
these equations to check that the LT3500 will be able to
deliver the required output current. Note again that these
equations assume that the inductor current is continuous.
Discontinuous operation occurs when IOUT1 is less than
IL/2 as calculated above.
Figure 4 illustrates the inductance value needed for a 3.3V
output with a maximum load capability of 2A. Referring
to Figure 4, an inductor value between 3.3μH and 4.7μH
will be sufcient for a 15V input voltage and a switch
frequency of 750kHz. There are several graphs in the
Typical Performance Characteristics section of this data
sheet that show inductor selection as a function of input
voltage and switch frequency for several popular output
voltages and output ripple currents. Also, low inductance
may result in discontinuous mode operation, which is
okay, but further reduces maximum load current. For
details of maximum output current and discontinuous
mode operation, see Linear Technology Application Note
44. Finally, for duty cycles greater than 50% (VOUT1/VIN
> 0.5), there is a minimum inductance required to avoid
subharmonic oscillations. See Application Note 19 for
more information.
Input Capacitor Selection
Bypass the input of the LT3500 circuit with a 4.7μF or
higher ceramic capacitor of X7R or X5R type. A lower
value or a less expensive Y5V type can be used if there
is additional bypassing provided by bulk electrolytic or
tantalum capacitors. The following paragraphs describe
the input capacitor considerations in more detail.
Step-down regulators draw current from the input sup-
ply in pulses with very fast rise and fall times. The input
capacitor is required to reduce the resulting voltage
ripple at the LT3500 and to force this very high frequency
switching current into a tight local loop, minimizing EMI.
The input capacitor must have low impedance at the
switching frequency to do this effectively, and it must
have an adequate ripple current rating.
A conservative value is the RMS input current is given
by:
I
CIN(RMS) =
I
OUT1 VOUT1 VIN VOUT1
()
0.5
V
IN
<
I
OUT1
2
and is largest when VIN = 2VOUT1 (50% duty cycle).
Figure 4. Inductor Values for 2A Maximum Load Current
(VOUT1 = 3.3V, IRIPPLE = 1A)
INPUT VOLTAGE (V)
5
250
FREQUENCY
(kHz)
500
1000
1250
1500
25
2500
3500 F04
750
15
10
30
35
20
40
1750
2000
2250
L = 6.8μH
L = 4.7μH
L = 3.3μH
L = 2.2μH
L = 1.5μH
L = 1μH
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相关代理商/技术参数 |
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|---|---|
| LT3500IMSE-TRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Monolithic 2A Step-Down Regulator Plus Linear Regulator/Controller |
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| LT3501_12 | 制造商:LINER 制造商全称:Linear Technology 功能描述:Monolithic Dual Tracking 3A Step-Down Switching |
| LT3501EFE | 制造商:Linear Technology 功能描述:Conv DC-DC Dual Step Down 3.1V to 25V 20-Pin TSSOP EP |
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