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参数资料
| 型号： | NCV8843MNR2GEVB |
| 厂商： | ON Semiconductor |
| 文件页数： | 7/16页 |
| 文件大小： | 0K |
| 描述： | EVAL BOARD FOR NCV8843MNR2G |
| 设计资源： | NCV8843 EVB BOM NCV8843MNR2GEVB Gerber Files NCV8843 EVB Schematic |
| 标准包装： | 1 |
| 主要目的： | DC/DC，步降 |
| 输出及类型： | 1，非隔离 |
| 输出电压： | 3.3V |
| 电流 - 输出： | 1A |
| 输入电压： | 5 ~ 16 V |
| 稳压器拓扑结构： | 降压 |
| 频率 - 开关： | 340kHz |
| 板类型： | 完全填充 |
| 已供物品： | 板 |
| 已用 IC / 零件： | NCV8843 |
| 其它名称： | NCV8843MNR2GEVBOS |
NCV8843
102.5
100
97.5
95
92.5
When the switch turns on, the V SW voltage is equal to the
V IN minus switch Saturation Voltage. In the buck regulator,
the V SW voltage swings to one diode drop below ground
when the power switch turns off, and the inductor current is
commutated to the catch diode. Due to the presence of high
pulsed current, the traces connecting the V SW pin, inductor
and diode should be kept as short as possible to minimize the
noise and radiation. For the same reason, the input capacitor
should be placed close to the V IN pin and the anode of the
diode.
The saturation voltage of the power switch is dependent
on the switching current, as shown in Figure 7.
90
? 40 ? 20
0
20
40 60 80
100 120 140
1.0
T J , JUNCTION TEMPERATURE ( ° C)
Figure 4. Oscillator Frequency Versus Junction
Temperature
An external clock signal can sync the NCV8843 to a
higher frequency. The SYNC pin equivalent input circuit is
shown in Figure 5.
0.9
0.8
0.7
0.6
Sync
10k
± 33%
50k
± 33%
0.5
0.4
V Z = 11V
to 20V
50k
± 33%
0.3
0
0.5 1.0 1.5
2.0
IO(MAX) + ILIM * O
GND
Figure 5.
The rising edge of the sync pulse turns on the power
switch to start a new switching cycle, as shown in Figure 6.
There is approximately 0.5 m s delay between the rising edge
of the sync pulse and rising edge of the V SW pin voltage. The
sync threshold is TTL logic compatible, and duty cycle of
the sync pulses can vary from 10% to 90%. The frequency
foldback feature is disabled during the sync mode.
Figure 6. A NCV8843 Buck Regulator is
Synchronized to an External 443 kHz Pulse Signal
Power Switch and Current Limit
The collector of the built ? in NPN power switch is
connected to the V IN pin, and the emitter to the V SW pin.
SWITCHING CURRENT (A)
Figure 7. Power Switch Saturation Versus Switching
Current (Normalized to 1.5 A)
The NCV8843 contains pulse ? by ? pulse current limiting
to protect the power switch and external components. When
the peak of the switching current reaches the Current Limit,
the power switch turns off after the Current Limit Delay. The
switch will not turn on until the next switching cycle. The
current limit threshold is independent of switching duty
cycle. The maximum load current, given by the following
formula under continuous conduction mode, is less than the
Current Limit due to the ripple current.
V (VIN * VO)
2(L)(VIN)(fs)
where:
f S = switching frequency,
I LIM = current limit threshold,
V O = output voltage,
V IN = input voltage,
L = inductor value.
When the regulator runs under current limit, the
subharmonic oscillation may cause low frequency
oscillation, as shown in Figure 8. Similar to current mode
control, this oscillation occurs at the duty cycle greater than
50% and can be alleviated by using a larger inductor value.
The current limit threshold is reduced to Foldback Current
when the FB pin falls below Foldback Threshold. This
feature protects the IC and external components under the
power up or over ? load conditions.
http://onsemi.com
7
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| NCV8843PWG | 功能描述:直流/直流开关转换器 1.5A LO VLT BUCK REG RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
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