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| 型号： | NCP5425DBG |
| 厂商： | ON Semiconductor |
| 文件页数： | 17/22页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM VM 20TSSOP |
| 标准包装： | 75 |
| PWM 型： | 电压模式 |
| 输出数： | 2 |
| 频率 - 最大： | 938kHz |
| 占空比： | 100% |
| 电源电压： | 4.75 V ~ 13.2 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 ~ 125°C |
| 封装/外壳： | 20-TSSOP（0.173"，4.40mm 宽） |
| 包装： | 管件 |
NCP5425
RSENSE + 0.070 V
Control IC Power Dissipation
The power dissipation of the IC varies with the MOSFETs
used, VCC, and the NCP5425 operating frequency. The
average MOSFET gate charge current typically dominates
the control IC power dissipation, and is given by:
PCONTROL(IC) + ICC1VCC1 ) IBSTVBST
) PGATE(H)1 ) PGATE(L)1
Sense Resistor
A sense resistor can be added in series with the inductor.
When the voltage drop across the sense resistor exceeds the
internal voltage threshold of 70 mV, a limit condition is set.
The sense resistor value is calculated by:
ILIMIT
where:
) PGATE(H)2 ) PGATE(L)2
In a high current supply, the sense resistor will be a very
low value, typically less than 10 m W . Such a resistor can be
either a discrete component or a PCB trace. The resistance
P CONTROL(IC) = control IC power dissipation;
I CC1 = IC quiescent supply current;
V CC1 = IC supply voltage;
P GATE(H) = upper MOSFET gate driver (IC) losses;
P GATE(L) = lower MOSFET gate driver (IC) losses.
The upper (switching) MOSFET gate driver (IC) losses
are given by:
of a discrete component can be more precise than a PCB
trace, but the cost is also greater. Setting the current limit
using an external sense resistor is very precise because all
the values can be designed to specific tolerances. However,
the disadvantage of using a sense resistor is its additional
constant power loss and heat generation. Trace resistance
can vary as much as " 10% due to copper plating variations.
PGATE(H) + QGATE(H)
fSW
VBST
Inductor ESR
where:
P GATE(H) = upper MOSFET gate driver (IC) losses;
Q GATE(H) = total upper MOSFET gate charge at VCC;
f SW = switching frequency.
The lower (synchronous) MOSFET gate driver (IC)
Another means of sensing current is to use the intrinsic
resistance of the inductor. A model of an inductor reveals
that the windings have an effective series resistance (ESR).
The voltage drop across the inductor ESR can be measured
with a simple parallel circuit: an RC integrator. If the value
of RS1 and C are chosen such that:
losses are:
PGATE(L) + QGATE(L)
fSW
VCC
L
ESR
+ RS1C
RS1 +
ILIM + 0.070 V
where:
P GATE(L) = lower MOSFET gate driver (IC) losses;
Q GATE(L) = total lower MOSFET gate charge at VCC;
f SW = switching frequency.
The junction temperature of the control IC is primarily a
function of the PCB layout, since most of the heat is removed
through the traces connected to the pins of the IC.
CURRENT SENSING AND CURRENT SHARING
Current Sharing Errors
The three main errors in current are from board layout
imbalances, inductor mismatch, and input offsets in the error
amplifiers. The first two sources of error can be controlled
through careful component selection and good layout
then the voltage measured across the capacitor C will be:
VC + ESR ILIM
Inductor Sensing Component Selection
Select the capacitor C first. A value of 0.1 m F is
recommended. The value of RS1 can be calculated by:
L
ESR C
Typical values for inductor ESR range in the low
milliohms; consult manufacturer ’s data sheets for specific
values. Selection of components at these values will result
in a current limit of:
ESR
practice. With a 4.0 m W (parasitic winding resistance)
inductor, for example, one mV of input offset error will
represent 0.25 A of measurement error. One way to diminish
this effect is to use higher resistance inductors, but the
penalty is higher power losses in the inductors.
Current Limiting Options
The current supplied to the load can be sensed using the
IS+ and IS? pins. These pins sense a voltage, proportional
V CC
GATE(H)
GATE(L)
IS+
IS?
L
RS1
ESR
C
Co
to the output current, and compare it to a fixed internal
voltage threshold. When the differential voltage exceeds
70 mV, the internal overcurrent protection system goes into
a cycle?by?cycle limiting mode. Two methods for sensing
the current are available.
http://onsemi.com
17
Figure 11. Inductor ESR Current Sensing
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| NCP5425DBR2 | 功能描述:DC/DC 开关控制器 Dual Synchronous RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
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| NCP5425DOEVB | 功能描述:电源管理IC开发工具 ANA SW REG EVAL BRD RoHS:否 制造商:Maxim Integrated 产品:Evaluation Kits 类型:Battery Management 工具用于评估:MAX17710GB 输入电压: 输出电压:1.8 V |
| NCP5425S0EVB | 制造商:ON Semiconductor 功能描述: |
| NCP5425SOEVB | 功能描述:电源管理IC开发工具 ANA SW REG EVAL BRD RoHS:否 制造商:Maxim Integrated 产品:Evaluation Kits 类型:Battery Management 工具用于评估:MAX17710GB 输入电压: 输出电压:1.8 V |
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