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| 型号： | NCP1530DM33R2 |
| 厂商： | ON Semiconductor |
| 文件页数： | 12/16页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK 3.3V 0.6A MICRO8 |
| 产品变化通告： | LTB Notification 03/Jan/2008 |
| 标准包装： | 4,000 |
| 类型： | 降压（降压） |
| 输出类型： | 固定 |
| 输出数： | 1 |
| 输出电压： | 3.3V |
| 输入电压： | 4.3 V ~ 5.5 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 600kHz |
| 电流 - 输出： | 600mA |
| 同步整流器： | 无 |
| 工作温度： | 0°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-TSSOP，8-MSOP（0.118"，3.00mm 宽） |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | Micro8? |
NCP1530
Power Saving Pulse?Frequency?Modulation (PFM)
Control Scheme
With the SYN pin (pin 2) connected to ground or left
open, the converter will operate in PWM/PFM auto mode.
Under this operating mode, NCP1530 will stay in constant
frequency PWM operation in moderate to heavy load
conditions. When the load decreases down to a threshold
point, the operation will switch to the power saving PFM
operation automatically. The switchover mechanism
depends on the input voltage, output voltage and the
inductor current level. The mode change circuit will
determine whether the converter should be operated in
PWM or PFM mode. In order to maintain stable and smooth
switching mode transition, a small hysteresis on the load
current level for mode transition was implemented. The
detailed mode transition characteristics for each voltage
option are illustrated in Figures 11 and 14. PFM mode
operation provides high conversion efficiency even at very
light loading conditions. In PFM mode, most of the circuits
inside the device will be turned off and the converter
operates just as a simple voltage hysteretic converter.
When the load current increases, the converter returns to
PWM mode automatically.
External Synchronization Control
The NCP1530 has an internal fixed frequency oscillator
of 600 kHz or can be synchronized to an external clock
signal at SYN pin (pin 2). Connecting the SYN pin with an
external clock signal will force the converter to operate in
a pure PWM mode and the switching frequency will be
synchronized. The external clock signal should be in the
range of 600 kHz to 1.2 MHz and the pulse width should
not be less than 300 ns. The detection of the pulse train is
edge sensitive and independent of duty ratio. In the case
where the external clock frequency is too low, the detection
circuit may not be able to follow and will treat it as a
disturbance, thus affecting the converters normal
operation. The internal control circuit detects the rising
edge of the pulse train and the switching frequency
synchronized to the external clock signal. If the external
clock signal ceases for several clock cycles, the converter
will switch back to use the internal oscillator automatically.
Output Overvoltage Protection (OVP)
In order to prevent the output voltage from going to high
(when the load current is close to zero in a pure PWM mode
and other abnormal conditions), an Output Overvoltage
protection circuit is included in the NCP1530. In case the
output voltage is higher than its nominal level by more than
12% maximum, the protection circuitry will stop the
switching immediately.
Internal Thermal Shutdown
Internal thermal shutdown circuitry is provided to
protect the integrated circuit in the event that the maximum
junction temperature is exceeded. The protection will be
activated at about 145 ° C with a hysteresis of 15 ° C. This
feature is provided to prevent failures from unexpected
overheating.
Input Capacitor Selection
For a PWM converter operating in continuous current
mode, the input current of the converter is a square wave
with a duty ratio of approximately V OUT /V IN . The
pulsating nature of the input current transient can be a
source of EMI noise and system instability. Using an input
bypass capacitor can reduce the peak current transients
drawn from the input supply source, thereby reducing
switching noise significantly. The capacitance needed for
the input bypass capacitor depends on the source
impedance of the input supply. For NCP1530, a low ESR,
low profile ceramic capacitor of 22 m F can be used for most
of the cases. For effective bypass results, the input
capacitor should be placed just next to V IN pin (pin 1)
whenever it is possible.
Inductor Value Selection
Selecting the proper inductance for the power inductor
is a trade?off between inductor ’s physical sizes, transient
response, power delivering capability, output voltage
ripple and power conversion efficiency. Low value
inductor saves cost, PC board space and provides fast
transient response, however suffers high inductor ripple
current, core loss and lower overall conversion efficiency.
The relationship between the inductance and the inductor
ripple current is given by the equation in below.
Power Saving Shutdown Mode
NCP1530 can be disabled whenever the EN pin (pin 5)
is tied to ground. In shutdown mode, the internal reference,
L +
TON(VIN * RDS(ON) IOUT * VOUT)
IL_RIPPLE(P * P)
oscillator and most of the control circuitries are turned off.
With the device put in shutdown mode, the device current
consumption will be as low as 0.5 m A (typ).
Input Undervoltage Lockout Protection (UVLO)
To prevent the P?Channel MOSFETs from operating
below safe input voltage levels, an Undervoltage Lockout
protection is incorporated in NCP1530. Whenever the
Where L is the inductance required;
T ON is the nominal ON time within a switching cycle;
R DS(ON) is the ON resistance of the internal MOSFET;
V IN is the worst?case input voltage;
V OUT is the output voltage;
I OUT is the maximum allowed loading current;
I L_RIPPLE(P?P) is the acceptable inductor current ripple
level.
input voltage, V IN drops below approximately 2.0 V, the
protection circuitry will be activated and the converter
operation will be stopped.
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