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| 型号： | NCV8843PWG |
| 厂商： | ON Semiconductor |
| 文件页数： | 10/16页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK 1.5A 16SOIC |
| 标准包装： | 47 |
| 类型： | 降压（降压） |
| 输出数： | 1 |
| 输入电压： | 4.5 V ~ 40 V |
| PWM 型： | 混合物 |
| 频率 - 开关： | 340kHz |
| 电流 - 输出： | 1.5A |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 150°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 16-SOIC（0.295"，7.50mm 宽）裸露焊盘 |
| 包装： | 管件 |
| 供应商设备封装： | 16-SOIC W |
NCV8843
(VIN * VO ) O )
VIN
WBASE + O
WSAT +
IS
VSAT
V 2
WDRV + 12 mA
The base current of a bipolar transistor is equal to collector
current divided by beta of the device. Beta of 60 is used here
to estimate the base current. The Boost pin provides the base
current when the transistor needs to be on. The power
dissipated by the IC due to this current is
V 2 IS
VIN 60
where:
I S = DC switching current.
When the power switch turns on, the saturation voltage
and conduction current contribute to the power loss of a
non ? ideal switch. The power loss can be quantified as
VO
VIN
where:
V SAT = saturation voltage of the power switch which is
shown in Figure 7.
The switching loss occurs when the switch experiences
both high current and voltage during each switch transition.
This regulator has a 30 ns turn ? off time and associated
power loss is equal to
COMPONENT SELECTION
Input Capacitor
In a buck converter, the input capacitor supplies pulsed
current with an amplitude equal to the load current. This
pulsed current and the ESR of the input capacitors determine
the V IN ripple voltage, which is shown in Figure 13. For V IN
ripple, low ESR is a critical requirement for the input
capacitor selection. The pulsed input current has a
significant AC component, which is absorbed by the input
capacitors. The RMS current of the input capacitor can be
calculated using:
IRMS + IO D(1 * D)
where:
D = switching duty cycle which is equal to V O /V IN .
I O = load current.
WS + S
I
2
VIN
30 ns
fS
The turn ? on time is much shorter and thus turn ? on loss is
not considered here.
The total power dissipated by the IC is sum of all the above
WIC + WQ ) WDRV ) WBASE ) WSAT ) WS
The IC junction temperature can be calculated from the
ambient temperature, IC power dissipation and thermal
resistance of the package. The equation is shown as follows,
Figure 13. Input Voltage Ripple in a Buck Converter
To calculate the RMS current, multiply the load current
with the constant given by Figure 14 at each duty cycle. It is
a common practice to select the input capacitor with an RMS
TJ + WIC
R q JA ) TA
current rating more than half the maximum load current. If
multiple capacitors are paralleled, the RMS current for each
Minimum Load Requirement
As pointed out in the previous section, a minimum load is
required for this regulator due to the pre ? driver current
feeding the output. Placing a resistor equal to V O divided by
12 mA should prevent any voltage overshoot at light load
conditions. Alternatively, the feedback resistors can be
valued properly to consume 12 mA current.
capacitor should be the total current divided by the number
of capacitors.
0.6
0.5
0.4
0.3
0.2
0.1
0
0
0.2
0.4
0.6
0.8
1.0
DUTY CYCLE
Figure 14. Input Capacitor RMS Current can be
Calculated by Multiplying Y Value with Maximum Load
Current at any Duty Cycle
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