参数资料
型号: LT1765EFE-2.5#TRPBF
厂商: Linear Technology
文件页数: 9/20页
文件大小: 0K
描述: IC REG BUCK 2.5V 3A 16TSSOP
标准包装: 2,500
类型: 降压(降压)
输出类型: 固定
输出数: 1
输出电压: 2.5V
输入电压: 3 V ~ 25 V
PWM 型: 电流模式
频率 - 开关: 1.25MHz
电流 - 输出: 3A
同步整流器:
工作温度: -40°C ~ 125°C
安装类型: 表面贴装
封装/外壳: 16-TSSOP(0.173",4.40mm)裸露焊盘
包装: 带卷 (TR)
供应商设备封装: 16-TSSOP-EP
LT1765/LT1765-1.8/LT1765-2.5/
LT1765-3.3/LT1765-5
APPLICATIONS INFORMATION
( V OUT IN OUT )
Table 2. Surface Mount Solid Tantalum Capacitor ESR
and Ripple Current
E Case Size ESR (Max, Ω) Ripple Current (A)
I OUT ( MAX ) =
Continuous Mode
I P –
)( V – V
2 ( L )( f )( V IN )
( 5 ) ( 8 ? 5 )
(
)(
)
2 3 . 3 ? 10 1 . 25 ? 10 6 ( 8 )
I OUT ( MAX ) = 3 ?
AVX TPS, Sprague 593D
AVX TAJ
D Case Size
AVX TPS, Sprague 593D
C Case Size
AVX TPS
0.1 to 0.3
0.7 to 0.9
0.1 to 0.3
0.2 (typ)
0.7 to 1.1
0.4
0.7 to 1.1
0.5 (typ)
For V IN = 8V, V OUT = 5V and L = 3.3μH,
? 6
= 3 ? 0 . 23 = 2 . 77 A
Figure 3 shows a comparison of output ripple for a ceramic
and tantalum capacitor at 200mA ripple current.
Note that the worst case (minimum output current avail-
able) condition is at the maximum input voltage. For the
same circuit at 15V, maximum output current would be
only 2.6A.
V OUT USING 47μF, 0.1Ω
TANTALUM CAPACITOR
(10mV/DIV)
V OUT USING 2.2μF
CERAMIC CAPACITOR
(10mV/DIV)
V SW
(5V/DIV)
Inductor Selection
The output inductor should have a saturation current rating
greater than the peak inductor current set by the current
comparator of the LT1765. The peak inductor current will
depend on the output current, input and output voltages
and the inductor value:
0.2μs/DIV
Figure 3. Output Ripple Voltage Waveform
1765 F03
I PEAK = I OUT +
V OUT ( V IN ? V OUT )
2 ( L )( f ) ( V IN )
INDUCTOR CHOICE AND MAXIMUM OUTPUT
CURRENT
Maximum output current for an LT1765 buck converter is
equal to the maximum switch rating (I P ) minus one half
peak to peak inductor ripple current. The LT1765 main-
tains a constant switch current rating at all duty cycles.
(Patent Pending)
For most applications, the output inductor will be in the
1μH to 10μH range. Lower values are chosen to reduce
the physical size of the inductor, higher values allow higher
output currents due to reduced peak to peak ripple current.
The following formula gives maximum output current for
continuous mode operation, implying that the peak to peak
ripple (2x the term on the right) is less than the maximum
switch current.
V IN = Maximum input voltage
f = Switching frequency, 1.25MHz
If an inductor with a peak current lower than the maximum
switch current of the LT1765 is chosen a soft-start circuit
in Figure 10 should be used. Also, short-circuit conditions
should not be allowed because the inductor may saturate
resulting in excessive power dissipation.
Also, consideration should be given to the resistance
of the inductor. Inductor conduction loses are directly
proportional to the DC resistance of inductor. Sometime,
the manufacturers will also provide maximum current
rating based on the allowable losses in the inductor. Care
should be taken, however. At high input voltages and low
DCR, excessive switch current could ?ow during shorted
output condition.
Suitable inductors are available from Coilcraft, Coiltronics,
Dale, Sumida, Toko, Murata, Panasonic and other
manufacturers.
1765fd
9
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