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參數(shù)資料
| 型號： | UCC2974 |
| 廠商： | Texas Instruments, Inc. |
| 英文描述： | DUAL COLD CATHODE FLUORESCENT LAMP CONTROLLER |
| 中文描述： | 雙冷陰極熒光燈控制器 |
| 文件頁數(shù)： | 11/12頁 |
| 文件大小： | 210K |
| 代理商： | UCC2974 |
SLUS485A
–
JULY 2001
–
REVISED NOVEMBER 2001
11
www.ti.com
startup sequence
t0
t2
t1
t3
t4
LFD ENABLE
OPEN LAMP
DETECT ENABLE
OUTPUT ENABLE
DEVICE ENABLE
0.0
0.5
3.0
4.0
MODE
UDG
–
01026
Figure 5. Start-Up Sequence
Figure 5 describes what happens during a typical startup sequence. At t0, power is applied to the system. A
constant current source begins charging the external capacitor connected to the MODE pin. Until the voltage
on the MODE pin reaches 0.5 V (t1), the internal circuitry on the device is disabled and nothing happens at the
outputs. As the voltage crosses 0.5 V, the internal circuitry is powered up. When the voltage crosses 1 V at t2,
the outputs are enabled, allowing the buck stages to begin to charge up and to supply current to the royer stages.
During the period from t2 to t3, the open lamp detection circuitry is disabled, preventing a false trip of the open
lamp detector circuit when the lamp is trying to ignite for the first time. As a precaution against severe
overvoltage on the high-voltage secondary of the transformer, a clamp circuit is included in the UCC3974. The
function of the clamp circuit is to monitor the voltage on the BUCK pins and prevent that voltage to drop more
than 8.7-V below the input rail. This is accomplished by sourcing a current from the FB pin when the BUCK
voltage drops more than 8.7 V.
The magnitude of the current sourced from this pin is proportional to the excess drop of the BUCK voltage
beyond 8.7 V. The maximum current sourced from this pin is approximately 200
μ
A. Consequently, the
impedance at the FB pin affects the speed at which this clamp becomes effective. A small capacitor and large
resistors in the feedback network increases the effectiveness of this feature. From t3 onward, the open lamp
detector circuit is enabled. Each time the BUCK pin drops more than 7.8-V below VIN, a 4-bit counter is clocked.
If the counter reaches a count of 16 (4 bits) it declares an open lamp fault and shuts down the device. Resetting
the device requires a power cycle. The counter in the open lamp detector is an up/down counter. If the BUCK
pin only occasionally dips below the 7.8-V threshold, an open lamp condition is not declared since the counter
is clocked down on each cycle in which BUCK does not cross the 7.8-V threshold. At time t4, LFD is enabled.
Depending on the state of LFDSYNC when this threshold is crossed, DIM is either an analog input or a digital
one.
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| UCC2975PW | 功能描述:LCD 驅(qū)動器 Multi-Topology Piezoelectric RoHS:否 制造商:Maxim Integrated 數(shù)位數(shù)量:4.5 片段數(shù)量:30 最大時鐘頻率:19 KHz 工作電源電壓:3 V to 3.6 V 最大工作溫度:+ 85 C 最小工作溫度:- 20 C 封裝 / 箱體:PDIP-40 封裝:Tube |
| UCC2975PWG4 | 功能描述:LCD 驅(qū)動器 Multi-Topology Piezoelectric RoHS:否 制造商:Maxim Integrated 數(shù)位數(shù)量:4.5 片段數(shù)量:30 最大時鐘頻率:19 KHz 工作電源電壓:3 V to 3.6 V 最大工作溫度:+ 85 C 最小工作溫度:- 20 C 封裝 / 箱體:PDIP-40 封裝:Tube |
| UCC2976PW | 功能描述:LCD 驅(qū)動器 Multi-Topology Piezoelectric RoHS:否 制造商:Maxim Integrated 數(shù)位數(shù)量:4.5 片段數(shù)量:30 最大時鐘頻率:19 KHz 工作電源電壓:3 V to 3.6 V 最大工作溫度:+ 85 C 最小工作溫度:- 20 C 封裝 / 箱體:PDIP-40 封裝:Tube |
| UCC2976PWG4 | 功能描述:LCD 驅(qū)動器 Multi-Topology Piezoelectric RoHS:否 制造商:Maxim Integrated 數(shù)位數(shù)量:4.5 片段數(shù)量:30 最大時鐘頻率:19 KHz 工作電源電壓:3 V to 3.6 V 最大工作溫度:+ 85 C 最小工作溫度:- 20 C 封裝 / 箱體:PDIP-40 封裝:Tube |
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