参数资料
| 型号： | NCP5217AMNTXG |
| 厂商： | ON Semiconductor |
| 文件页数： | 11/16页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM 14-QFN |
| 标准包装： | 3,000 |
| PWM 型： | 电流/电压模式 |
| 输出数： | 1 |
| 频率 - 最大： | 330kHz |
| 电源电压： | 4.5 V ~ 27 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： | -40°C ~ 85°C |
| 封装/外壳： | 14-VFQFN 裸露焊盘 |
| 包装： | 带卷 (TR) |
| 其它名称： | NCP5217AMNTXG-ND NCP5217AMNTXGOSTR |
NCP5217A
Overcurrent Protection (OCP)
The NCP5217A protects power system if over current
event occurs. The current is continuously monitored by the
differential current sensing circuit. The current limit
threshold voltage VOCSET can be programmed by resistor
Rocset connecting at the IDRP/OCP pin. However, fixed
default VOCSET can be achieved if Rocset is less than 2 k W .
If the inductor current exceeds the current threshold
continuously, the top gate driver will be turned off cycle by
cycle. If it happens over consecutive 16 clock cycles time
(16 x 1/f SW ), the device is latched off such that top and
bottom gate drivers are off. EN resets or power recycle the
device can exit the fault. The following diagram shows the
typical behavior of OCP.
It should be noted that there are two configurations for
Rocp resistor. If Adaptor Voltage Position (AVP) is used, the
Rocp should be connected to FB pin. If AVP is not used, the
Rocp should be connected to ground. At the IDRP/OCP pin,
there is a constant current(24 m A typ.) flowing out during the
programming stage at system start up. This is used to sense
the voltage level which is developed by a resistor R ocp so as
to program the overcurrent detection threshold voltage. For
typical application, the V octh is set as default value (40 mV
typ) by setting R ocp = 0 W , or directly short the IDRP/OCP
pin to ground. It has the benefit of saving one component at
application board. For other programming values of V octh ,
please refer to the electrical table of “Overcurrent Protection
Setting” section.
Guidelines for selecting OCP Trip Component
1. Choose the value of R ocp for V octh selection.
(typical is 0 W for V octh = 40 mV typical)
2. Define the DC value of OCP trip point (I OCP_DC )
that you want. The typical value is 1.5 to 1.8 times
of maximum loading current. For example, if
maximum loading is 10 A, then set OCP trip point
at 15 A to 18 A.
3. Calculate the inductor peak current (I pk )which is
estimated by the equation:
I pk + I OCP_DC )
V O * (V IN * V O )
2 * V IN * f SW * L O
(eq. 4)
Top to Bottom : SWN, V o , PGOOD, I o
Figure 20. Overcurrent Protection
4. Check with inductor datasheet to find out the value
of inductor DC resistance DCR, then calculate the
RS1, RS2 dividing factor k based on the equation:
The NCP5217A uses lossless inductor current sensing for
acquiring current information. In addition, the threshold
OCP voltage can be programmed to some desired value by
setting the programming resistor Rocp.
V OCth
k +
I pk * DCR
5. Select Cs value between 100 nF to 200 nF.
Typically, 100 nF will be used.
(eq. 5)
Rs1 +
Vo
Rt
Rb
FB
+
COMP
6. Calculate Rs1 value by the equation:
L
k * DCR * Cs
(eq. 6)
IDRP
? Vref
IDRP
Rs2 +
V OCth
I pk +
L
DCR
Vo
Rs1
Cs
Rt
Rb
IDRP/OCP
Rocp
CS+
Rs2
CS ?
FB
Rocp
IDRP/OCP
+
+
Gi
Without AVP
+
+
? Vref
COMP
7. Calculate Rs2 value by the equation:
k * Rs1
(eq. 7)
1 * k
8. Hence, all the current sense components Rs1, Rs2,
Cs have been found for target I OCP_DC .
9. If Rs2 is not used (open), set k = 1, at that
moment, the I pk will be restricted by:
(eq. 8)
DCR
Overvoltage Protection (OVP)
L
DCR
Rs1
Cs
Rs2
CS+
CS ?
+
Gi
When V FB voltage is above 115% (typical) of the nominal
V FB voltage for over 1.5 m s blanking time, an OV fault is set.
At that moment, the top gate drive is turned off and the
With AVP
Figure 21. OCP Configurations
bottom gate drive is turned on until the V FB below lower
under voltage (UV) threshold and bottom gate drive is
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