参数资料
型号: IRDC3856W
厂商: International Rectifier
文件页数: 13/34页
文件大小: 0K
描述: BOARD EVAL SUPIRBUCK IR3856W
产品培训模块: SupIRBuck? Family and POL Design Tools Overview
标准包装: 1
系列: SupIRBuck™
主要目的: DC/DC,步降
输出及类型: 1,非隔离
输出电压: 1.8V
电流 - 输出: 6A
输入电压: 12V
稳压器拓扑结构: 降压
频率 - 开关: 600kHz
板类型: 完全填充
已供物品:
已用 IC / 零件: IR3856W
PD-97506
IR3856WMPbF
Fig. 5. Pre-Bias startup pulses
Soft-Start
The IR3856W has a programmable soft-start to
control the output voltage rise and to limit the
Fig. 3c. Recommended startup sequence,
Sequenced operation
Pre-Bias Startup
IR3856W is able to start up into pre-charged
output, which prevents oscillation and
disturbances of the output voltage.
The output starts in asynchronous fashion and
keeps the synchronous MOSFET off until the first
current surge at the start-up. To ensure correct
start-up, the soft-start sequence initiates when
the Enable and Vcc rise above their UVLO
thresholds and generate the Power On Ready
(POR) signal. The internal current source
(typically 20uA) charges the external capacitor
C ss linearly from 0V to 3V. Figure 6 shows the
waveforms during the soft start.
The start up time can be estimated by:
gate signal for control MOSFET is generated.
Figure 4 shows a typical Pre-Bias condition at
start up.
T start =
( 1.4 - 0.7 ) * C SS
20 μ A
- - - - - - - - - - - - - - - - - - - - (1)
The synchronous MOSFET always starts with a
narrow pulse width and gradually increases its
duty cycle with a step of 25%, 50%, 75% and
100% until it reaches the steady state value. The
number of these startup pulses for the
synchronous MOSFET is internally programmed.
Figure 5 shows a series of 32, 16, 8 startup
pulses.
Fig. 4. Pre-Bias startup
Rev 9.0
During the soft start the OCP is enabled to
protect the device for any short circuit and over
current condition.
Fig. 6. Theoretical operation waveforms
during soft-start
13
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