参数资料
| 型号： | NCP5252MNTXG |
| 厂商： | ON Semiconductor |
| 文件页数： | 12/16页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK SYNC ADJ 2A 16QFN |
| 标准包装： | 1 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 0.6 V ~ 5 V |
| 输入电压： | 4.5 V ~ 13.2 V |
| 频率 - 开关： | 333kHz ~ 1MHz |
| 电流 - 输出： | 2A |
| 同步整流器： | 是 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 16-VFQFN 裸露焊盘 |
| 包装： | 标准包装 |
| 供应商设备封装： | 16-QFN（3x3） |
| 其它名称： | NCP5252MNTXGOSDKR |
NCP5252
DETAILED OPERATING DESCRIPTION
General
The NCP5252 is a PWM regulator intended for DC ? DC
conversion from 5 V & 12 V buses and supplies up to a 2 A
load. The NCP5252 is a step down synchronous ? rectifier
buck topology regulator with integrated high ? side and a
low ? side NMOS switches. The output voltage of the
converter can be precisely regulated down to 600 mV ± 1.0%
when the V FB pin is tied to V OUT . The switching frequency
can be adjusted to 333 kHz, 500 kHz, or 1 MHz. A skip mode
can be enabled to provide light load efficiency.
The NCP5252 includes the following features: power
good monitor, internal soft ? start, cycle ? by ? cycle current
limit, short circuit protection, output undervoltage/
overvoltage protection, and thermal shutdown.
crosses zero from positive to negative, the low ? side
MOSFET is shut off so that current is not pulled out of the
output capacitor. A high ? side MOSFET turn on is not
initiated until the COMP voltage exceeds the bottom of the
PWM ramp.
Transient Response Enhancement (TRE)
To improve transient response in CCM, a transient
response enhancement circuitry is implemented inside the
NCP5252.
In CCM operation, the controller continuously monitors
the COMP pin voltage of the error amplifier and detects load
transient events. The functional block diagram of TRE is
shown as follows:
Control Logic
During start ? up the internal LDO is activated and
power ? on reset occurs which resets the logic and all
protection faults. The device will begin its start up sequence
and the functionality will be determined by the voltage at the
COMP
R
C
+
-
TRE
EN/SKIP pin. When voltage of EN/SKIP is below
VEN_DISABLE, the converter will shut down. If the
voltage of EN/SKIP is set between VEN_FPWM and
VEN_SKIP, the device will be in PWM mode of operation.
When the voltage level of EN/SKIP is above VEN_SKIP,
the device will operate in PFM power saving mode. Once
V REF reaches its regulation voltage, an internal signal will
wake up the output undervoltage supply monitor which will
assert a “GOOD” condition. In addition, the NCP5252
continuously monitors the V CC level with an undervoltage
lockout (UVLO) function.
Forced PWM Operation (FPWM Mode)
To place the device into force PWM mode, the EN/SKIP
pin voltage should be set between VEN_FPWM and
VEN_SKIP thresholds. During the soft ? start operation, the
NCP5252 will automatically run as FPWM mode until the
output voltage is higher than the internal soft ? start ramp.
In FPWM mode in each switching cycle, the high ? side
MOSFET turns on for a time period defined by the ratio of
input voltage to output voltage known as duty ratio. After a
short period of time following high ? side MOSFET turn off,
the low ? side MOSFET turns on and remains on for the
remainder of the switching cycle. At currents below the
critical conduction point, the low ? side MOSFET will sync
current out of the output capacitor, reducing overall
converter efficiency at light loads.
Pulse Skipping Operation (Skip Mode/PFM)
The device operates in skip mode if the EN/SKIP pin
voltage is greater than 2.9 V. Skip mode can reduce the
switching loss in light load conditions.
When the converter inductor current is greater than the
critical conduction point, the converter will run in
continuous ? conduction ? mode (CCM) which behaves
exactly the same as FPWM mode. When the inductor current
Internal TRE_TH
Figure 25. Block Diagram of TRE Circuit
If a large transient occurs, the COMP signal will exceed
the comparator threshold indicating that a transient has
occurred and action is required. When the comparator trips
an extra high ? side pulse is generated and the converter
appears to run at a higher frequency. Once the transient has
passed, the converter returns to normal operation and
normal switching frequency.
Voltage Feed Forward
The NCP5252 has a voltage feed forward derived ramp.
Voltage feed ? forward is employed to ease loop
compensation for wide ? input ? range designs and provide
better line transient response. The ramp generator provides
voltage feed ? forward control by varying the PWM ramp
slope with line voltage. One important thing to note is that
since the slope changes with the input voltage, the ramp
height will also change, resulting in an almost constant gain
over input voltages. Varying the PWM ramp directly with
line voltage provides excellent response to line variations,
because the PWM is not required to wait for loop delays
before changing the duty cycle.
The peak to peak ramp voltage can be calculated using the
following equation:
V RAMP_PP = 0.25 V IN
Overcurrent Protection (OCP)
The NCP5252 will protect the system if an overcurrent
event occurs. The regulator will continuously monitor the
output current through the internal MOSFETs. If the
high ? side MOSFET current exceeds the internal current
limit threshold, it will be turned off. If a repetitive
overcurrent event occurs, both MOSFETs will be turned off
and the device will hold for 3 normal soft ? start periods
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