参数资料
型号: MC34653EFR2
厂商: Freescale Semiconductor
文件页数: 11/24页
文件大小: 1649K
描述: IC CTRLR HOT SWAP NEG V 8-SOIC
标准包装: 2,500
类型: 热交换开关
应用: 通用
内部开关:
电流限制: 1A
电源电压: 36 V ~ 80 V
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)
供应商设备封装: 8-SOICN
包装: 带卷 (TR)
Analog Integrated Circuit Device Data
Freescale Semiconductor
11
34653
FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
rchived by Freescale Semiconductor, Inc., 2008
 Figure 7. Power MOSFET Turn-On and the Gradual
Increase in the Charging Current from 0 A to I
CHG
 
(2.0 ms in Example)
The I
CHG
 current charges up the load capacitor relatively
slowly. When the load capacitor is fully charged, the Power
MOSFET reaches its full enhancement, which triggers the
current limit detection to change from I
CHG
 to I
LIM
 and the load 
current to decrease (Point C in Figure 6
, page 10
). The
current spike at Point C in Figure 6
 is better displayed in
Figure 8
. We can see that when the 淰
OUT
 - V
IN
 ? 0.5 V, the
Power MOSFET fully turns on to reach its full enhancement,
charging the capacitor an additional 0.5 V with a higher
current value that quickly ramps down. This eliminates the
need for a current slew rate control because the hazard for a
voltage change is less than 0.5 V. The power good output
signals activate after a 20 ms delay (Point D in Figure 6
),
which in turn enables the load. The 34653 is now in normal
operation mode and the retry counter resets.
 Figure 8. Full Power MOSFET Turn-On and Current
Spike Associated with It. End of Charging Process
NORMAL MODE
If one of the start-up conditions (list on page 
10
) is violated
any time from the start of the Power MOSFET enhancement
process and thereafter during normal operation, the Power
MOSFET turns off and the power good output signals
deactivate, disabling the load, and a new timer cycle starts as
explained previously. The 34653 also monitors the load
current to prevent any overload or short circuit conditions
from happening to protect the load from damage.
LOAD CURRENT CONTROL
When in normal operation mode, the 34653 monitors the
load and provides two modes of current control as explained
in the paragraphs below.
Overcurrent Mode
The 34653 monitors the load for overcurrent conditions. If
the current going through the load becomes larger than the
overcurrent limit for longer than the overcurrent limit filter
timer of 100 約, the overcurrent signal is asserted and the
gate of the Power MOSFET is discharged to try to regulate
the current at the I
LIM
value (Point A in Figure 9
). The 34653
is in overcurrent mode for 3.0 ms. If after a 3.0 ms filter timer
the device is still in overcurrent mode, the device turns off the
Power MOSFET and deactivates the power good output
signals (Point B in Figure 9
). The 34653 then initiates another
start-up timer and goes back through the enhancement
process. If during the 3.0 ms timer the fault was cleared, then
the 34653 goes back to the normal operation mode and the
power good output signals stay activated as shown in
Figure 10
. This way the device overcomes temporary
overcurrent situations and at the same time protects the load
from a more severe overcurrent situation.
Short Circuit Mode
If the current going through the load becomes > 5.0 A, the
Power MOSFET is discharged very fast (in less than 10 約)
to try to regulate the current at the I
LIM
value, and the 34653
is in the overcurrent mode for 3.0 ms. Then it follows the
pattern outlined in the Overcurrent Mode paragraph above.
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