参数资料
| 型号： | EL7642AILTZ |
| 厂商： | Intersil |
| 文件页数： | 15/19页 |
| 文件大小： | 0K |
| 描述： | IC CONV DC/DC TFT-LCD 32-QFN |
| 标准包装： | 72 |
| 应用： | 转换器，TFT，LCD |
| 输入电压： | 2.6 V ~ 5.5 V |
| 输出数： | 7 |
| 输出电压： | 5.5 V ~ 20 V |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 32-WFQFN 裸露焊盘 |
| 供应商设备封装： | 32-TQFN-EP（5x5） |
| 包装： | 散装 |
EL7640A, EL7641A, EL7642A
V OFF supplies. It can be appreciated that should a regular
supply of LX switching edges be interrupted, for example
during discontinuous operation at light boost load currents,
then this may affect the performance of V ON and V OFF
regulation – depending on their exact loading conditions at
the time.
To optimize V ON /V OFF regulation, the boundary of
discontinuous/continuous operation of the boost converter
can be adjusted, by suitable choice of inductor given V IN ,
V OUT , switching frequency and the V BOOST current loading,
to be in continuous operation.
The following equation gives the boundary between
discontinuous and continuous boost operation. For
continuous operation (LX switching every clock cycle) we
require that:
I(V BOOST _load) > D*(1-D)*V IN /(2*L*F OSC )
where the duty cycle, D = (V BOOST – V IN )/V BOOST
For example, with V IN = 5V, F OSC = 1.2MHz and V BOOST =
12V we find continuous operation of the boost converter can
be guaranteed for:
L = 10μH and I(V BOOST ) > 51mA
L = 6.8μH and I(V BOOST ) > 74mA
L = 3.3μH and I(V BOOST ) > 153mA
15
Start-up Sequence
Figure 23 shows a detailed start-up sequence waveform. For
a successful power-up, there should be 6 peaks at V CDEL .
When a fault is detected, the device will latch off until either
EN is toggled or the input supply is recycled.
When the input voltage is higher than 2.4V, an internal
current source starts to charge C CDEL . During the initial slow
ramp, the device checks whether there is a fault condition. If
no fault is found during the initial ramp, C CDEL is discharged
after the first peak. V REF turns on at the peak of the first
ramp.
Initially the boost is not enabled so V BOOST rises to V IN -
V DIODE through the output diode. Hence, there is a step at
V BOOST during this part of the start-up sequence.
V BOOST soft-starts at the beginning of the third ramp, and is
checked at the end of this ramp. The soft-start ramp
depends on the value of the C DEL capacitor. For C DEL of
100nF, the soft-start time is ~7ms.
V OFF turns on at the start of the fourth peak.
V ON is enabled at the beginning of the sixth ramp. V OFF and
V ON are checked at end of this ramp.
FN6270.0
May 15, 2006
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