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参数资料
| 型号： | LT1572 |
| 厂商： | Linear Technology Corporation |
| 英文描述： | 100kHz, 1.25A Switching Regulator with Catch Diode(100kHz, 1.25A 开关稳压器(带箝位二极管）) |
| 中文描述： | 100kHz时，1.25A的开关稳压抓住二极管（100kHz时，1.25A的开关稳压器（带钳位二极管）） |
| 文件页数： | 9/12页 |
| 文件大小： | 222K |
| 代理商： | LT1572 |
9
LT1572
switch “on” resistance by 2:1, but reduces switch current
limit by 2:1 also, resulting in a net 2:1 reduction in I
2
R
switch dissipation under current limit conditions.
The third approach is to clamp the V
C
pin to a voltage less
than its internal clamp level of 2V. The LT1172 switch
current limit is zero at approximately 1V on the V
C
pin and
2A at 2V on the V
C
pin. Peak switch current can be
externally clamped between these two levels with a diode.
See AN19 for details.
Diode Characteristics
The catch diode used in the LT1572 is a power Schottky
diode with a very low storage time and low forward
voltage. This gives good efficiency in switching regulator
applications, but some thought must be given to maxi-
mum operating voltage and high temperature reverse
leakage. Peak repetitive reverse voltage rating on he diode
is 20V In a boost converter, maximum diode reverse
voltage is equal to regulated output voltage, so this limits
maximum output voltage to 20V. In a negative-to-positive
converter, maximum diode voltage will be equal to the
sum of output voltage plusinput voltage. Use the equa-
tions in Application Note 19 or SwitcherCAD or calculate
maximum diode voltage for other topologies.
Diode reverse leakage increases rapidly with temperature.
This leakage is not high enough to significantly impact
efficiency or diode power dissipation, but it can be of
concern in shutdown mode if the diode is connected in
such a way that the leakage adds to regulator shutdown
current. Use the graphs of diode leakage versus voltage
and temperature to ensure proper high temperature sys-
tem performance.
The LT1572 diode is internally bonded to more than two
package pins to reduce internal bond wire currents. All
pins must be used to prevent excessive current in the
individual internal bond wires This is important in low
load current applications because the LT1572 will draw
high surge currents during start-up (to charge the output
capacitor) even with no output load current.
OPERATIOU
Average supply current (including driver current) is:
I
IN
≈
6mA + I
SW
(0.004 + DC/40)
I
SW
= switch current
DC = switch duty cycle
Switch power dissipation is given by:
P
SW
= (I
SW
)
2
×
R
SW
×
DC
R
SW
= LT1572 switch “on” resistance (1
maximum)
Total power dissipation is the sum of supply current times
input voltage plus switch power:
P
REG
= I
IN
×
V
IN
+ P
SW
In a typical example, using a boost converter to generate
12V at 0.12A from a 5V input, duty cycle is approximately
60%, and switch current is about 0.65A, yielding:
I
IN
= 6mA + 0.65(0.004 + DC/40) = 18mA
P
SW
= (0.65)
2
×
1
×
0.6 = 0.25W
P
REG
= 5V
×
0.018A + 0.25 = 0.34W
Approximate diode power dissipation for boost and buck
converters is shown below. For other topologies or more
accurate results, see Application Note 19 or use
SwitcherCAD.
Boost: P
DIODE
= I
OUT
×
V
f
Buck: P
DIODE
= I
OUT
×
V
f
×
(V
IN
– V
OUT
)/V
IN
V
f
= diode forward voltage at a current equal to I
OUT
for a
buck converter and I
OUT
×
V
OUT
/V
IN
for a boost converter.
In most applications, full load current is used to calculate
die temperature. However, if overload conditions must
also be accounted for, three approaches are possible.
First, if loss of regulated output is acceptable under
overload conditions, the internal thermal limitof the
LT1572 will protect the die in most applications by shut-
ting off switch current. Thermal limit is not a tested
parameter however, and should be considered only for
noncritical applications with temporary overloads.
The second approach for lower current applications is to
leave the second switch emitter (E2) open. This increases
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| LT1572CS | 功能描述:IC REG MULTI CONFIG 1.25A 16SOIC 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: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 |
| LT1572CS#PBF | 功能描述:IC REG MULTI CONFIG 1.25A 16SOIC 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 |
| LT1572CS#TR | 功能描述:IC REG MULTI CONFIG 1.25A 16SOIC 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: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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