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参数资料
| 型号： | LT3508IUF#TR |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 3.2 A DUAL SWITCHING CONTROLLER, 1060 kHz SWITCHING FREQ-MAX, PQCC24 |
| 封装： | 4 X 4 MM, PLASTIC, MO-220WGGD-X, QFN-24 |
| 文件页数： | 9/24页 |
| 文件大小： | 365K |
| 代理商： | LT3508IUF#TR |
LT3508
17
3508f
Ratiometric tracking is achieved in Figure 8b by connecting
both the TRACK/SS pins together. In this conguration the
TRACK/SS pin source current is doubled (2.4μA) which
must be taken into account when calculating the output
rise time.
By connecting a feedback network from VOUT1 to the
TRACK/SS2 pin with the same ratio that set the VOUT2
voltage, absolute tracking shown in Figure 8c is imple-
mented. A small VOUT2 voltage offset will be present due
to the TRACK/SS2 1.2μA source current. This offset can
be corrected for by slightly reducing the value of R2. Use
a resistor divider such that when VOUT1 is in regulation,
TRACK/SS2 is pulled up to 1V or greater. If TRACK/SS is
below 1V, the output may regulate FB to a voltage lower
than the 800mV reference voltage.
Figure 8d illustrates output sequencing. When VOUT1
is within 10% of its regulated voltage, PG1 releases
the TRACK/SS2 soft-start pin allowing VOUT2 to soft-
start. In this case PG1 will be pulled up to 1.3V by the
TRACK/SS pin.
If precise output ramp up and down is required, drive the
TRACK/SS pins as shown in Figure 8e.
Multiple Inputs
For applications requiring large inductors due to high VIN
to VOUT ratios, a 2-stage step down approach may reduce
inductor size by allowing an increase in frequency. A dual
step-down application (Figure 9) steps down the input
voltage (VIN1) to the highest output voltage, then uses that
voltage to power the second output (VIN2). VOUT1 must be
able to provide enough current for its output plus the input
current at VIN2 when VOUT2 is at its maximum load.
For applications with multiple input voltages, the LT3508
can accommodate input voltages as low as 3V on VIN2.
This can be useful in applications regulating outputs from
a PCI Express bus, where the 12V input is power limited
and the 3.3V input has power available to drive other
outputs. In this case, tie the 12V input to VIN1 and the
3.3V input to VIN2. See the Typical Application section for
an example circuit.
Do not tie TRACK/SS1 and TRACK/SS2 together if using
multiple inputs. If VIN2 is below 3V, TRACK/SS2 pulls low
and would hold TRACK/SS1 low as well if the two pins
are tied together, which would prevent channel 1 from
operating.
Shorted and Reverse Input Protection
If the inductor is chosen so that it won’t saturate exces-
sively, an LT3508 step-down regulator will tolerate a shorted
output. There is another situation to consider in systems
where the output will be held high when the input to the
LT3508 is absent. This may occur in battery charging
APPLICATIONS INFORMATION
Figure 9. 1MHz, Wide Input Range 5V and 1.8V Outputs
VIN
5.7V TO 36V
BOOST2
LT3508
VIN1
VIN2
GND
3508 F09
RT/SYNC
C7
330pF
C5
47
F
C4
10
F
C1
4.7
F
C2
0.1
F
C3
0.1
F
R6
47k
C6
100pF
R5
39k
R4
15.0k
R8
33.2k
fSW = 1MHz
R1
56.2k
R7
100k
R2
18.7k
R3
10.7k
L2
3.3
H
L1 6.8
H
D1
D2
OUT1
D3
D4
POWER
GOOD
OUT2
1.8V
1A
OUT1
5V
0.9A
C8
1nF
C9
3.3nF
BOOST1
SHDN
SW2
SW1
FB2
FB1
VC2
PG1
VC1
TRACK/SS1
PG2
TRACK/SS2
ON OFF
相关PDF资料 |
PDF描述 |
|---|---|
| LT3508IUF | 3.2 A DUAL SWITCHING CONTROLLER, 1060 kHz SWITCHING FREQ-MAX, PQCC24 |
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相关代理商/技术参数 |
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|---|---|
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| LT3509EDE#TRPBF | 功能描述:IC REG BUCK ADJ 0.7A DL 14DFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:2,500 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V，1.5V，1.8V，2.5V 输入电压:2.7 V ~ 20 V PWM 型:- 频率 - 开关:- 电流 - 输出:50mA 同步整流器:是 工作温度:-40°C ~ 125°C 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽）裸露焊盘 包装:带卷 (TR) 供应商设备封装:10-MSOP 裸露焊盘 |
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