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参数资料
| 型号： | NCP1599GEVB |
| 厂商： | ON Semiconductor |
| 文件页数： | 11/15页 |
| 文件大小： | 0K |
| 描述： | BOARD EVALUATION NCP1599 |
| 设计资源： | NCP1599GEVB BOM NCP1599GEVB Schematic NCP1599GEVB Gerber Files |
| 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： | 最低可调至 0.8V |
| 电流 - 输出： | 3A |
| 输入电压： | 3 ~ 5.5 V |
| 稳压器拓扑结构： | 降压 |
| 频率 - 开关： | 1MHz |
| 板类型： | 完全填充 |
| 已供物品： | 板 |
| 已用 IC / 零件： | NCP1599 |
| 其它名称： | NCP1599GEVBOS |
NCP1599
PROTECTIONS
Undervoltage Lockout (UVLO)
The undervoltage lockout feature prevents the controller
from switching when the input voltage is too low to power
the internal power supplies and reference. Hysteresis must
be incorporated in the UVLO comparator to prevent
resistive drops in the wiring or PCB traces from causing
ON/OFF cycling of the controller during heavy loading at
power up or power down.
The UVLO threshold allows steady ? state operation at
input voltages as low as 3.3 V. However, the current limit at
these input voltage levels may not function appropriately
due to increased R DSon . This could cause excessive heating
and possible device failure.
Overcurrent Protection (OCP)
NCP1599 detects high side switch current and then
compares to a voltage level representing the overcurrent
threshold limit. If the current through the high side FET
exceeds the overcurrent threshold limit for seven
consecutive switching cycles, overcurrent protection is
triggered.
Once the overcurrent protection occurs, hiccup mode
engages. First, hiccup mode turns off both FETs and
discharges the internal compensation network at the COMP
pin. Next, the IC waits typically 2 ms and then resets the
another normal soft ? start. During soft ? start, the overcurrent
protection threshold is increased to prevent false
overcurrent detection while charging the output capacitors.
The hiccup mode scheme reduces input supply current and
power dissipation during a short ? circuit. It also allows for
much improved system up ? time by allowing auto ? restart
upon removal of a temporary short ? circuit.
Pre ? Bias Startup
In some applications the controller will be required to start
switching when its output capacitors are charged anywhere
from slightly above 0 V to just below the regulation voltage.
This situation occurs for a number of reasons: the
converter ’s output capacitors may have residual charge on
them or the converter ’s output may be held up by a low
current standby power supply. NCP1599 supports pre ? bias
start up by holding the low side FETs off till soft start ramp
reaches the FB Pin voltage.
Thermal Shutdown
The NCP1599 protects itself from over heating with an
internal thermal monitoring circuit. If the junction
temperature exceeds the thermal shutdown threshold the
voltage at the COMP pin will be pulled to GND and both the
upper and lower MOSFETs will be shut OFF.
overcurrent counter. After this reset, the circuit attempts
APPLICATION INFORMATION
Programming the Output Voltage
The output voltage is set using a resistive voltage divider
from the output voltage to FB pin (see Figure 25). So the
L +
V out
f @ I ripple
@ 1 *
V out
V in(max)
(eq. 2)
V out + V FB @
output voltage is calculated according to Eq.1.
R 1 ) R 2
R 2
V out
R1
FB
R2
(eq. 1)
Where V out ? the output voltage;
f ? switching frequency, 1.0 MHz;
I ripple ? Ripple current, usually it’s 20% ? 30% of output
current;
V in(max) ? maximum input voltage.
Choose a standard value close to the calculated value to
maintain a maximum ripple current within 30% of the
maximum load current. If the ripple current exceeds this
30% limit, the next larger value should be selected.
The inductor ’s RMS current rating must be greater than
the maximum load current and its saturation current should
be about 30% higher. For robust operation in fault conditions
(start ? up or short circuit), the saturation current should be
high enough. To keep the efficiency high, the series
Figure 25. Output divider
Inductor Selection
The inductor is the key component in the switching
regulator. The selection of inductor involves trade ? offs
among size, cost and efficiency. The inductor value is
selected according to the equation 2.
resistance (DCR) should be less than 0.1 W , and the core
material should be intended for high frequency applications.
Output Capacitor Selection
The output capacitor acts to smooth the dc output voltage
and also provides energy storage. So the major parameter
necessary to define the output capacitor is the maximum
allowed output voltage ripple of the converter. This ripple is
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