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参数资料
| 型号： | LT1776 |
| 厂商： | Linear Technology Corporation |
| 英文描述： | Wide Input Range, High Efficiency, Step-Down Switching Regulator(宽输入范围，高效率，5V输出步降开关稳压器) |
| 中文描述： | 宽输入范围，高效率，降压型开关稳压器（宽输入范围，高效率，5V的输出步降开关稳压器） |
| 文件页数： | 12/20页 |
| 文件大小： | 152K |
| 代理商： | LT1776 |
12
LT1776
APPLICATIO
S I
FOR
ATIO
U
W
U
U
P
AC
= 1/2 V
IN
I
OUT
(t
r
+ t
f
+ 30ns) f
t
r
= (V
IN
/1.6)ns in high dV/dt mode
(V
IN
/0.16)ns in low dV/dt mode
t
f
= (V
IN
/1.6)ns (irrespective of dV/dt mode)
f = switching frequency
Total power dissipation of the die is simply the sum of
quiescent, DC and AC losses previously calculated.
P
D(TOTAL)
= P
Q
+ P
DC
+ P
AC
Frequency Compensation
Loop frequency compensation is performed by connect-
ing a capacitor, or in most cases a series RC, from the
output of the error amplifier (V
C
pin) to ground. Proper
loop compensation may be obtained by empirical meth-
ods as described in detail in Application Note 19. Briefly,
this involves applying a load transient and observing the
dynamic response over the expected range of V
IN
and
I
LOAD
values.
As a practical matter, a second small capacitor, directly
from the V
C
pin to ground is generally recommended to
attenuate capacitive coupling from the V
SW
pin. A typical
value for this capacitor is 100pF. (See Switch Node Con-
siderations).
Switch Node Considerations
For maximum efficiency, switch rise and fall times are
made as short as practical. To prevent radiation and high
frequency resonance problems, proper layout of the com-
ponents connected to the IC is essential, especially the
power path. B field (magnetic) radiation is minimized by
keeping output diode, switch pin and input bypass capaci-
tor leads as short as possible. E field radiation is kept low
by minimizing the length and area of all traces connected
to the switch pin (V
SW
). A ground plane should always be
used under the switcher circuitry to prevent interplane
coupling.
However, remember that oscillator slowdown to achieve
short-circuit protection (discussed above) is dependent
on FB pin behavior, and this in turn, is sensitive to FB node
external impedance. Figure 2 shows the typical relation-
ship between FB divider Thevenin voltage and impedance,
and oscillator frequency. This shows that as feedback
network impedance increases beyond 10k, complete os-
cillator slowdown is not achieved, and short-circuit pro-
tection may be compromised. And as a practical matter,
the product of FB pin bias current and larger FB network
impedances will cause increasing output voltage error.
(Nominal cancellation for 10k of FB Thevenin impedance
is included internally.)
Thermal Considerations
Care should be taken to ensure that the worst-case input
voltage and load current conditions do not cause exces-
sive die temperatures. The packages are rated at 110
°
C/W
for the 8-pin SO (S8) and 130
°
C/W for 8-pin PDIP (N8).
Quiescent power is given by:
P
Q
= I
IN
V
IN
+ I
VCC
V
OUT
(This assumes that the V
CC
pin is connected to V
OUT
.)
Power loss internal to the LT1776 related to actual output
current is composed of both DC and AC switching losses.
These can be roughly estimated as follows:
DC switching losses are dominated by output switch “ON
voltage”, i.e.,
P
DC
= V
ON
I
OUT
DC
V
ON
= Output switch ON voltage, typically 1V at 500mA
I
OUT
= Output current
DC = ON duty cycle
AC switching losses are typically dominated by power lost
due to the finite rise time and fall time at the V
SW
node.
Assuming, for simplicity, a linear ramp up of both voltage
and current and a current rise/fall time equal to 15ns,
相关PDF资料 |
PDF描述 |
|---|---|
| LT1777C | RADIATION HARDENED HIGH EFFICIENCY, 5 AMP SWITCHING REGULATORS |
| LT1777IS | RADIATION HARDENED HIGH EFFICIENCY, 5 AMP SWITCHING REGULATORS |
| LT1777CS | RADIATION HARDENED HIGH EFFICIENCY, 5 AMP SWITCHING REGULATORS |
| LT1777I | RADIATION HARDENED HIGH EFFICIENCY, 5 AMP SWITCHING REGULATORS |
| LT1777 | Low Noise Step-Down Switching Regulator(低噪声，5V输出步降开关稳压器) |
相关代理商/技术参数 |
参数描述 |
|---|---|
| LT1776C | 制造商:LINER 制造商全称:Linear Technology 功能描述:Wide Input Range, High Efficiency, Step-Down Switching Regulator |
| LT1776CN8 | 功能描述:IC REG BUCK ADJ 0.7A 8DIP RoHS:否 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:升压（升压） 输出类型:可调式 输出数:1 输出电压:1.24 V ~ 30 V 输入电压:1.5 V ~ 12 V PWM 型:电流模式，混合 频率 - 开关:600kHz 电流 - 输出:500mA 同步整流器:无 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:8-SOIC（0.154"，3.90mm 宽） 包装:带卷 (TR) 供应商设备封装:8-SOIC |
| LT1776CN8#PBF | 功能描述:IC REG BUCK ADJ 0.7A 8DIP 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:250 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V 输入电压:2.05 V ~ 6 V PWM 型:电压模式 频率 - 开关:2MHz 电流 - 输出:500mA 同步整流器:是 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:6-UFDFN 包装:带卷 (TR) 供应商设备封装:6-SON（1.45x1） 产品目录页面:1032 (CN2011-ZH PDF) 其它名称:296-25628-2 |
| LT1776CS8 | 功能描述:IC REG BUCK ADJ 0.7A 8SOIC RoHS:否 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:升压（升压） 输出类型:可调式 输出数:1 输出电压:1.24 V ~ 30 V 输入电压:1.5 V ~ 12 V PWM 型:电流模式，混合 频率 - 开关:600kHz 电流 - 输出:500mA 同步整流器:无 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:8-SOIC（0.154"，3.90mm 宽） 包装:带卷 (TR) 供应商设备封装:8-SOIC |
| LT1776CS8#PBF | 功能描述:IC REG BUCK ADJ 0.7A 8SOIC 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:250 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V 输入电压:2.05 V ~ 6 V PWM 型:电压模式 频率 - 开关:2MHz 电流 - 输出:500mA 同步整流器:是 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:6-UFDFN 包装:带卷 (TR) 供应商设备封装:6-SON（1.45x1） 产品目录页面:1032 (CN2011-ZH PDF) 其它名称:296-25628-2 |
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