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参数资料
| 型号： | IRU3039CHTR |
| 厂商： | International Rectifier |
| 文件页数： | 8/22页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM VM 20-MLPQ |
| 标准包装： | 1 |
| PWM 型： | 电压模式 |
| 输出数： | 1 |
| 频率 - 最大： | 400kHz |
| 占空比： | 88% |
| 电源电压： | 4.75 V ~ 20 V |
| 降压： | 是 |
| 升压： | 无 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | 0°C ~ 70°C |
| 封装/外壳： | 20-MLPQ |
| 包装： | 剪切带 (CT) |
| 其它名称： | *IRU3039CHTR IRU3039CHTRCT |
IRU3039(PbF)
APPLICATION INFORMATION
Design Example:
The following example is a typical application for IRU3039,
the schematic is Figure 17 on page 16.
V IN = 18V
V OUT = 3.3V
I OUT = 8A
? V OUT = 100mV (output voltage ripple ? 3% of V OUT )
f S = 200KHz
Output Voltage Programming
Output voltage is programmed by reference voltage and
external voltage divider. The Fb pin is the inverting input
of the error amplifier, which is referenced to the voltage
on non-inverting pin of error amplifier. For this applica-
tion, this pin (V P ) is connected to reference voltage (V REF ).
The output voltage is defined by using the following equa-
Css ? 20 × t START ( μ F) ---(8)
Where t START is the desired start-up time (ms)
For a start-up time of 5ms, the soft-start capacitor will
be 0.1 μ F. Choose a ceramic capacitor at 0.1 μ F.
Boost Supply Vc
To drive the high side switch, it is necessary to supply a
gate voltage at least 4V grater than the bus voltage. This
is achieved by using a charge pump configuration as
shown in Figure 9. This method is simple and inexpen-
sive. The operation of the circuit is as follows: when the
lower MOSFET is turned on, the capacitor (C1) is pulled
down to ground and charges, up to V OUT2 value, through
the diode (D1). The bus voltage will be added to this
(
tion:
V OUT = V P × 1 +
R 6
R 5
)
---(7)
voltage when upper MOSFET turns on in next cycle,
and providing supply voltage (Vc) through diode (D2). Vc
is approximately:
V P = V REF = 0.8V
When an external resistor divider is connected to the
output as shown in Figure 8.
V OUT
Vc ? V OUT2 + V BUS - (V D1 + V D2 )
Capacitors in the range of 0.1 μ F and 1 μ F are generally
adequate for most applications. The diode must be a
fast recovery device to minimize the amount of charge
fed back from the charge pump capacitor into V OUT2 . The
IRU3039
R 6
diodes need to be able to block the full power rail volt-
age, which is seen when the high side MOSFET is
V REF
V P
Fb
R 5
switched on. For low voltage application, schottky di-
odes can be used to minimize forward drop across the
diodes at start up.
D1
Figure 8 - Typical application of the IRU3039 for
programming the output voltage.
V OUT2
C3
D2
( )
R 6 = R 5 ×
-1
Equation (7) can be rewritten as:
V OUT
V P
Regulator
Vc
C2
C1
V BUS
Q1
L2
Choose R 5 = 1K
This will result to R 6 = 3.16K
IRU3039
HDrv
Q2
If the high value feedback resistors are used, the input
bias current of the Fb pin could cause a slight increase
in output voltage. The output voltage set point can be
more accurate by using precision resistor.
Soft-Start Programming
The soft-start timing can be programmed by selecting
the soft-start capacitance value. The start-up time of the
converter can be calculated by using:
Figure 9 - Charge pump circuit.
Input Capacitor Selection
The input filter capacitor should be based on how much
ripple the supply can tolerate on the DC input line. The
ripple current generated during the on time of upper
MOSFET should be provided by input capacitor. The RMS
value of this ripple is expressed by:
8
www.irf.com
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