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参数资料
| 型号： | L6997DTR |
| 厂商： | STMICROELECTRONICS |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING CONTROLLER, PDSO20 |
| 封装： | MO-153AC, TSSOP-20 |
| 文件页数： | 2/30页 |
| 文件大小： | 591K |
| 代理商： | L6997DTR |
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L6997
10/30
so considering zero the output load the output voltage is given by:
(9))
indicating with Vout the final value, the output charging time can be estimated as:
(10)
the minimum CSS value is given imposing this condition:
Tout =TSS
(11)
4.5 Current limit
The current limit comparator senses the inductor current through the low side MOSFET RDSON drop and com-
pares this value with the ILIM pin voltage value. While the current is above the current limit value, the control
inhibits the high side MOSFET Turn On.
To properly set the current limit threshold, it should be noted that this is a valley current limit. The Average cur-
rent depends on the inductor value, VIN VOUT and switching frequency.
The average output current in current limit is given by:
(12)
Thus, to set the current threshold, choose RILIM according to the following equation:
(13)
In overcurrent conditions the system keeps the current constant until the output voltage meets the undervoltage
threshold. The negative valley current limit, for the sink mode, is set automatically at the same value of the pos-
itive valley current limit. The average negative current limit differs from the positive average current limit by the
ripple current; this difference is due to the valley control technique.
The current limit system accuracy is function of the precision of the resistance connected to the ILIM pin and
the low side MOSFET RDSON accuracy. Moreover the voltage on ILIM pin must range between 10mV and 1V
to ensure the system linearity.
Figure 9. Current limit schematic
V
out t,CSS
()
Qt,C
SS
()
C
out
-------------------------
R
ilim /Rdson
K
ILIM
I
SS
t
2
()
C
out
V
SS
C
SS
2
()
-----------------------------------------------------------------------------
==
V
out CSS
()
V
out
C
out
V
SS
C
SS
2
()
R
ilim /Rdson
K
ILIM
I
SS
()
----------------------------------------------------------------------------
0.5
=
I
OUT
CL
I
max valley
I
2
-----
+
=
I
max valley
R
ILim
Rds
on
----------------- K
ILIM
=
Positive and negative current limit
R
ILIM
5A
Current
Comparator
To
logic
PGN
D
PHASE
To inductor
LS
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相关代理商/技术参数 |
参数描述 |
|---|---|
| L6997S | 功能描述:DC/DC 开关控制器 STEP DOWN CONTROLLER Lo Vltg Operations RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
| L6997STR | 功能描述:DC/DC 开关控制器 3.0 to 5.5V Step-Dwn RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
| L6998-0 | 制造商:Johanson Manufacturing 功能描述:TUNING ELEMENT |
| L6998-1 | 制造商:Johanson Manufacturing 功能描述:TUNING ELEMENT |
| L6998-5 | 制造商:Johanson Manufacturing 功能描述:TUNING ELEMENT |
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