参数资料
型号: IRDC3842A
厂商: International Rectifier
文件页数: 14/34页
文件大小: 0K
描述: BOARD EVAL SUPIRBUCK IR3842A
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: IR3842A
PD-97510
IR3842AMPbF
I OCSet ( μ A ) =
.......... .......... .......... .....( 2 )
Operating Frequency
The switching frequency can be programmed
between 250kHz – 1200kHz by connecting an
external resistor from R t pin to Gnd. Table 1
tabulates the oscillator frequency versus R t .
Table 1. Switching Frequency and I OCSet vs.
External Resistor ( R t )
1400
R t (k Ω )
Table 1. shows I OCSet at different switching
frequencies. The internal current source
develops a voltage across R OCSet . When the low
side MOSFET is turned on, the inductor current
flows through the Q2 and results in a voltage at
OCSet which is given by:
V OCSet = ( I OCSet ? R OCSet ) ? ( R DS (on ) ? I L ) .......... .(3)
R t (k ? )
47.5
35.7
28.7
23.7
20.5
17.8
15.8
14.3
12.7
11.5
F s (kHz)
300
400
500
600
700
800
900
1000
1100
1200
I ocset ( μ A)
29.4
39.2
48.7
59.07
68.2
78.6
88.6
97.9
110.2
121.7
Shutdown
The IR3842A can be shutdown by pulling the
Enable pin below its 1 V threshold. This will tri-
state both, the high side driver as well as the low
side driver. Alternatively, the output can be
shutdown by pulling the soft-start pin below 0.3V.
Fig. 7. Connection of over current sensing resistor
An over current is detected if the OCSet pin goes
below ground. Hence, at the current limit
threshold, V OCset =0. Then, for a current limit
setting I Limit , R OCSet is calculated as follows:
Normal operation is resumed by cycling the
voltage at the Soft Start pin.
R OCSet =
R
DS ( on ) * I Limit
I OCSet
.......... .......... .... (4)
An overcurrent detection trips the OCP
Over-Current Protection
The over current protection is performed by
sensing current through the R DS(on) of low side
MOSFET. This method enhances the converter’s
efficiency and reduces cost by eliminating a
current sense resistor. As shown in figure 7, an
external resistor (R OCSet ) is connected between
OCSet pin and the switch node (SW) which sets
the current limit set point.
An internal current source sources current ( I OCSet
) out of the OCSet pin. This current is a function
of the switching frequency and hence, of R t .
Rev 13.0
comparator, latches OCP signal and cycles the
soft start function in hiccup mode.
The hiccup is performed by shorting the soft-start
capacitor to ground and counting the number of
switching cycles. The Soft Start pin is held low
until 4096 cycles have been completed. The
OCP signal resets and the converter recovers.
After every soft start cycle, the converter stays in
this mode until the overload or short circuit is
removed.
The OCP circuit starts sampling current typically
160 ns after the low gate drive rises to about 3V.
This delay functions to filter out switching noise.
14
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