参数资料
| 型号： | NCV5173EDR2G |
| 厂商： | ON Semiconductor |
| 文件页数： | 13/19页 |
| 文件大小： | 0K |
| 描述： | IC REG MULTI CONFIG 1.5A 8SOIC |
| 标准包装： | 2,500 |
| 类型： | 升压（升压），反相，回扫，正向转换器，Sepic |
| 输出数： | 1 |
| 输入电压： | 2.7 V ~ 30 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 560kHz |
| 电流 - 输出： | 1.5A |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm 宽） |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 8-SOICN |
NCV5171, NCV5173
Reducing the Current Limit
In some applications, the designer may prefer a lower
limit on the switch current than 1.5 A. An external shunt can
be connected between the V C pin and ground to reduce its
clamp voltage. Consequently, the current limit of the
internal power transistor current is reduced from its nominal
value.
Another solution to the current limiting problem is to
externally measure the current through the switch using a
sense resistor. Such a circuit is illustrated in Figure 32.
V CC
The voltage on the V C pin can be evaluated with the
equation
VC + ISWREAV
V IN
PGND AGND
V C
C2
RSENSE
where:
R E = 0.063 W , the value of the internal emitter resistor;
A V = 5 V/V, the gain of the current sense amplifier.
Since R E and A V cannot be changed by the end user, the
only available method for limiting switch current below
1.5 A is to clamp the V C pin at a lower voltage. If the
maximum switch or inductor current is substituted into the
equation above, the desired clamp voltage will result.
A simple diode clamp, as shown in Figure 31, clamps the
V C voltage to a diode drop above the voltage on resistor R3.
Unfortunately, such a simple circuit is not generally
acceptable if V IN is loosely regulated.
V IN
V CC
R2
R1
C1
R2
Q1
C3
Output
R SENSE Ground
Figure 32. Current Limiting using a Current Sense
Resistor
The switch current is limited to
VBE(Q1)
ISWITCH(PEAK) +
where:
V BE(Q1) = the base ? emitter voltage drop of Q1, typically
0.65 V.
The improved circuit does not require a regulated voltage
to operate properly. Unfortunately, a price must be paid for
R3
D1
V C
this convenience in the overall efficiency of the circuit. The
designer should note that the input and output grounds are
no longer common. Also, the addition of the current sense
resistor, R SENSE , results in a considerable power loss which
increases with the duty cycle. Resistor R2 and capacitor C3
form a low ? pass filter to remove noise.
R1
C1
C2
Figure 31. Current Limiting using a Diode Clamp
http://onsemi.com
13
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