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參數資料
| 型號： | LT1939IDD#TRPBF |
| 廠商： | Linear Technology |
| 文件頁數： | 21/24頁 |
| 文件大小： | 349K |
| 描述： | IC REG DL BUCK/LINEAR 12DFN |
| 標準包裝： | 2,500 |
| 拓撲： | 降壓（降壓）（1），線性（LDO）（1） |
| 功能： | 任何功能 |
| 輸出數： | 2 |
| 頻率 - 開關： | 500kHz ~ 2.4MHz |
| 電壓/電流 - 輸出 1： | 0.8 V ~ 24.25 V，2A |
| 電壓/電流 - 輸出 2： | 0.8 V ~ 24.25 V，1A |
| 帶 LED 驅動器： | 無 |
| 帶監控器： | 無 |
| 帶序列發生器： | 無 |
| 電源電壓： | 3 V ~ 25 V |
| 工作溫度： | -40°C ~ 125°C |
| 安裝類型： | 表面貼裝 |
| 封裝/外殼： | 12-WFDFN 裸露焊盤 |
| 供應商設備封裝： | 12-DFN |
| 包裝： | 帶卷 (TR) |
LT1939
21
1939f
APPLICATIONS INFORMATION
one location, ideally at the ground terminal of the output
capacitor C2. Additionally, the SW and BST traces should
be kept as short as possible. The topside metal from the
DC1069A demonstration board in Figure 12 illustrates
proper component placement and trace routing.
Thermal Considerations
The PCB must also provide heat sinking to keep the
LT1939 cool. The exposed metal on the bottom of the
Figure 11. Subtracting the Current when the Switch is On (11a) from the Current when the Switch is Off (11b) Reveals the Path of the
High Frequency Switching Current (11c). Keep this Loop Small. The Voltage on the SW and BST Traces will Also be Switched; Keep
These Traces as Short as Possible. Finally, Make Sure the Circuit is Shielded with a Local Ground Plane
package must be soldered to a ground plane. This ground
should be tied to other copper layers below with thermal
vias; these layers will spread the heat dissipated by the
LT1939. Place additional vias near the catch diodes. Adding
more copper to the top and bottom layers and tying this
copper to the internal planes with vias can further reduce
thermal resistance. With these steps, the thermal resis-
tance from die (or junction) to ambient can be reduced to
?/DIV>
JA
= 45癈/W.
Power dissipation within the LT1939 can be estimated
by calculating the total power loss from an ef ciency
measurement and subtracting the catch diode loss. The
die temperature is calculated by multiplying the LT1939
power dissipation by the thermal resistance from junction
to ambient.
The power dissipation in the other power components
such as catch diodes, boost diodes and inductors, cause
additional copper heating and can further increase what
the IC sees as ambient temperature. See the LT1767 data
sheets Thermal Considerations section.
Other Linear Technology Publications
Application notes AN19, AN35 and AN44 contain more
detailed descriptions and design information for buck
regulators and other switching regulators. The LT1376
data sheet has a more extensive discussion of output
ripple, loop compensation and stability testing. Design
note DN100 shows how to generate a dual (+ and ) output
supply using a buck regulator.
Figure 12. LT1939 Demonstration Circuit Board DC1293A
V
IN
GND
(11a)
LT1939
SW
V
IN
GND
1939 F11
(11c)
LT1939
SW
V
IN
GND
(11b)
LT1939
SW
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