参数资料
型号: LT3688EUF#PBF
厂商: Linear Technology
文件页数: 24/28页
文件大小: 0K
描述: IC REG BUCK ADJ 0.8A DL 24QFN
标准包装: 91
类型: 降压(降压)
输出类型: 可调式
输出数: 2
输出电压: 0.8 V ~ 32.4 V
输入电压: 3.8 V ~ 36 V
PWM 型: 电流模式,Burst Mode?
频率 - 开关: 500kHz ~ 2.1MHz
电流 - 输出: 800mA
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: 24-WFQFN 裸露焊盘
包装: 管件
供应商设备封装: 24-QFN(4x4)
LT3688
APPLICATIONS INFORMATION
V IN
D4
V IN
BIAS
BOOST
keep thermal resistance low, extend the ground plane as
much as possible, and add thermal vias under and near
LTC3688
the LT3688 to additional ground planes within the circuit
SW
V OUT
board and on the bottom side.
EN/UVLO
DA
FB
+
High Temperature Considerations
GND
3688 F13
Figure 13. Diode D4 Prevents a Shorted Input from Discharging
a Backup Battery Tied to the Output; It Also Protects the Circuit
from a Reversed Input. The LT3688 Runs Only When the Input
Is Present
3688 F14
Figure 14. Top Layer PCB Layout in the LT3688
Demonstration Board
these components should be as small as possible. These
components, along with the inductor and output capacitor,
should be placed on the same side of the circuit board.
Place a local, unbroken ground plane below these com-
ponents. The SW and BST nodes should be as small as
possible. Finally, keep the FB node small so that the ground
traces will shield them from the SW and BST nodes.
The exposed pad on the bottom of the package must be
soldered to ground so that the pad acts as a heat sink. To
The PCB must provide heat sinking to keep the LT3688
cool. The exposed pad on the bottom of the package must
be soldered to a ground plane. This ground should be tied
to large copper layers below with thermal vias; these lay-
ers will spread the heat dissipated by the LT3688. Placing
additional vias can reduce thermal resistance further. With
these steps, the thermal resistance from die (or junction)
to ambient can be reduced to θ JA = 40°C/W or less. With
100 LFPM air?ow, this resistance can fall by another 25%.
Further increases in air?ow will lead to lower thermal re-
sistance. Because of the large output current capability of
the LT3688, it is possible to dissipate enough heat to raise
the junction temperature beyond the absolute maximum
of 125°C (150°C for H Grade). When operating at high
ambient temperatures, the maximum load current should
be derated as the ambient temperature approaches 125°C
(150°C for H Grade). Power dissipation within the LT3688
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
LT3688 power dissipation by the thermal resistance from
junction-to-ambient. Thermal resistance depends on the
layout of the circuit board, but values from 30°C/W to
60°C/W are typical. Die temperature rise was measured
on a 4-layer, 5cm ? 7.5cm circuit board in still air at a load
current of 0.8A (f SW = 800kHz). For a 12V input to 3.3V
output the die temperature elevation above ambient was
14°C; for 12V IN to 5V OUT the rise was 15°C and for 12V IN
to 5V OUT and 3.3V OUT the rise was 30°C.
Other Linear Technology Publications
Application Notes 19, 35 and 44 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 318
shows how to generate a bipolar output supply using a
buck regulator.
3688f
24
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