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参数资料
| 型号： | LT1573CS8-3.3 |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 基准电压源/电流源 |
| 英文描述： | Low Dropout PNP Regulator Driver |
| 中文描述： | 3.3 V FIXED POSITIVE LDO REGULATOR, PDSO8 |
| 封装： | 0.150 INCH, PLASTIC, SO-8 |
| 文件页数： | 9/16页 |
| 文件大小： | 200K |
| 代理商： | LT1573CS8-3.3 |
9
LT1573
Resistor R
B
helps to turn off the PNP (Q
OUT
in Figure 2).
Smaller values for R
B
turn off the PNP faster but will
increase input current. The recommended value for R
B
is
50
. For circuits that do not require high output current or
fast transient response, the value of R
B
can be increased
up to 200
. For the D45H11, the emitter-base voltage is
a function of base and collector current. Table 2 lists some
useful operating points for the D45H11. These points were
empirically determined using a sampling of devices.
Table 2. D45H11 V
BE
I
B
(mA)
1
7
23
45
66
100
I
C
(A)
0.2
1
2
3
4
5
V
BE
AT 25
°
C
(V)
0.65
0.75
0.80
0.85
0.90
0.95
Design Example
Given the following operating requirements:
4.5V < V
IN
< 5.5V
I
OUT(MAX)
= 5A
V
OUT
= 3.3V
1. The first step is to determine the required drive current
for the D45H11. Dropout voltage must be less than 1.2V
at 5A output current. From Table 1, a drive current of
100mA will give 0.7V dropout voltage at an output
current of 5A. This satisfies the operating require-
ments.
2. The next step is to determine the value of R
D
. Assume
R
B
is 50
. From Table 2, the maximum emitter-base
voltage for this design is 0.95V. The current through
R
B
is:
I
RB
= V
BE
/R
B
= 0.95/50 = 19mA
V
DRIVE
is the DRIVE pin saturation voltage when the
DRIVE pin current equals 119mA, which can be read
from the typical performance characteristics curve to
be 0.39V. Resistor R
D
now can be calculated from
Eq (1):
R
D
= (4.5 – 0.95 – 0.39)V/(100 + 19)mA = 26.6
The next lowest 5% value is 24
.
Overcurrent Latch-Off
In addition to limiting the base drive current, the resistor
R
D
is included in the circuit for the overcurrent protection
latch-off function. There is a minimum value for this
resistance. It is calculated by Equation 1 with the drive
current I
DRIVE
set to the minimum available drive current
(= 250mA) from the LT1573. At high currents, R
D
also
limits the power dissipation in the LT1573. In some
conditions, resistor R
D
can be replaced with a short. This
is possible in circuits where an overload is unlikely and the
input voltage and drive requirements are low. If resistor R
D
is not included in the circuit, the regulator is protected
against the overcurrent condition only by the thermal
shutdown function. After the resistor R
D
is determined, a
certain amount of base drive current is available to the
external PNP transistor. An overcurrent or output short
condition will demand a base drive current greater than the
LT1573 can supply. The internal drive transistor will
saturate. A time-out latch will be triggered by this
overcurrent condition to turn off the regulator system. The
time-out period is determined by an external capacitor
connected between the LATCH and GND pins. The time-
out period is equal to the time it takes for the capacitor to
charge from 0V to the latch threshold which is equal to
2V
BE
. The latch charging current is set by an internal
current source and is a function of input voltage and
temperature as shown in the typical performance charac-
teristics curve. At 25
°
C, the typical latch charging current
ranges from 7.2
μ
A with 3V input to 8
μ
A with 7V input. If
the overcurrent or output short condition persists longer
than the time-out period, the regulator will be shut down.
Otherwise, the regulator will function normally. In the
latch-off mode, some extra current is drawn from the input
to maintain the latch. The latching current is a function of
input voltage and temperature as shown in the typical
performance characteristic curve. At 25
°
C, the typical
latching current ranges from 0.3mA with 3V input to
9.5mA with 7V input. The latch can be reset by recycling
input power, by grounding the LATCH pin or by putting the
device into shutdown.
APPLICATIOU
W
U
U
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相关代理商/技术参数 |
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| LT1573CS8TR | 制造商:Linear Technology 功能描述: |
| LT1573I | 制造商:LINER 制造商全称:Linear Technology 功能描述:Low Dropout PNP Regulator Driver |
| LT1573IS8 | 功能描述:IC REG CTRLR SGL POS ADJ 8-SOIC RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - 线性晶体管驱动器 系列:- 产品培训模块:More Information on LDOs 标准包装:2,500 系列:- 类型:正，固定式 输出数:2 输出电压:2.8V，3.3V 电流 - 电源:12mA 输入电压:5 V ~ 22 V 工作温度:0°C ~ 70°C 封装/外壳:16-SOIC（0.154"，3.90mm 宽） 供应商设备封装:16-SOIC 包装:带卷 (TR) |
| LT1573IS8#PBF | 功能描述:IC REG CTRLR SGL POS ADJ 8-SOIC RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - 线性晶体管驱动器 系列:- 产品培训模块:More Information on LDOs 标准包装:2,500 系列:- 类型:正，固定式 输出数:2 输出电压:2.8V，3.3V 电流 - 电源:12mA 输入电压:5 V ~ 22 V 工作温度:0°C ~ 70°C 封装/外壳:16-SOIC（0.154"，3.90mm 宽） 供应商设备封装:16-SOIC 包装:带卷 (TR) |
| LT1573IS8#TR | 功能描述:IC REG CTRLR SGL POS ADJ 8SOIC RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - 线性晶体管驱动器 系列:- 产品培训模块:More Information on LDOs 标准包装:2,500 系列:- 类型:正，固定式 输出数:2 输出电压:2.8V，3.3V 电流 - 电源:12mA 输入电压:5 V ~ 22 V 工作温度:0°C ~ 70°C 封装/外壳:16-SOIC（0.154"，3.90mm 宽） 供应商设备封装:16-SOIC 包装:带卷 (TR) |
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