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HV9922N3-G 参数 Datasheet PDF下载

HV9922N3-G图片预览
型号: HV9922N3-G
PDF下载: 下载PDF文件 查看货源
内容描述: 3引脚开关模式LED灯驱动器IC [3-Pin Switch-Mode LED Lamp Driver ICs]
分类和应用: 驱动器开关接口集成电路
文件页数/大小: 10 页 / 652 K
品牌: SUPERTEX [ Supertex, Inc ]
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HV9921/HV9922/HV9923  
Functional Description  
where ITH is the current sense comparator threshold.  
The ripple current introduces a peak-to-average error in  
the output current setting that needs to be accounted for.  
Due to the constant off-time control technique used in the  
HV9921/22/23, the ripple current is independent of the input  
AC or DC line voltage variation. Therefore, the output current  
will remain unaffected by the varying input voltage.  
The HV9921/22/23 are PWM peak current controllers  
for controlling a buck converter topology in continuous  
conduction mode (CCM). The output current is internally  
preset at 20mA (HV9921), 50mA (HV9922), or 30mA  
(HV9923).  
When the input voltage of 20 to 400V appears at the  
DRAIN pin, the internal high-voltage linear regulator seeks  
to maintain a voltage of 7VDC at the VDD pin. Until this  
voltage exceeds the internally programmed under-voltage  
threshold, the output switching MOSFET is non-conductive.  
When the threshold is exceeded, the MOSFET turns on. The  
input current begins to flow into the DRAIN pin. Hysteresis  
is provided in the under-voltage comparator to prevent  
oscillation.  
Adding a filter capacitor across the LED string can reduce  
the output current ripple even further, thus permitting a  
reduced value of L1. However, one must keep in mind that  
the peak-to-average current error is affected by the variation  
of T . Therefore, the initial output current accuracy might  
be sOaFcFrificed at large ripple current in L1.  
Another important aspect of designing an LED driver with the  
HV9921/22/23 is related to certain parasitic elements of the  
circuit, including distributed coil capacitance of L1, junction  
capacitance and reverse recovery of the rectifier diode D1,  
capacitance of the printed circuit board traces CPCB and output  
capacitance CDRAIN of the controller itself. These parasitic  
elements affect the efficiency of the switching converter and  
could potentially cause false triggering of the current sense  
comparator if not properly managed. Minimizing these  
parasitics is essential for efficient and reliable operation of  
the HV9921/22/23.  
When the input current exceeds the internal preset level,  
a current sense comparator resets an RS flip-flop, and the  
MOSFET turns off. At the same time, a one-shot circuit  
is activated that determines the duration of the off-state  
(10.5µS typ.). As soon as this time is over, the flip-flop sets  
again. The new switching cycle begins.  
A “blanking” delay of 300nS is provided that prevents false  
triggering of the current sense comparator due to the leading  
edge spike caused by circuit parasitics.  
Coil capacitance of inductors is typically provided in the  
manufacturer’s data books either directly or in terms of the  
self-resonant frequency (SRF).  
SRF = 1/(2π L CL )  
Application Information  
The HV9921/22/23 is a low-cost off-line buck converter IC  
specifically designed for driving multi-LED strings. It can be  
operated from either universalAC line range of 85 to 264VAC,  
or 20 to 400VDC, and drives up to tens of high brightness  
LEDs. All LEDs can be run in series, and the HV9921/22/23  
regulates at constant current, yielding uniform illumination.  
The HV9921/22/23 is compatible with triac dimmers. The  
output current is internally fixed at 20mA for the HV9921,  
50mA for the HV9922, and 30mA for HV9923. These parts  
are available in space saving TO-92 and SOT-89 packages.  
where L is the inductance value, and CL is the coil  
capacitance.) Charging and discharging this capacitance  
every switching cycle causes high-current spikes in the LED  
string. Therefore, connecting a small capacitor CO (~10nF) is  
recommended to bypass these spikes.  
Using an ultra-fast rectifier diode for D1 is recommended  
to achieve high efficiency and reduce the risk of false  
triggering of the current sense comparator. Using diodes  
with shorter reverse recovery time trr and lower junction  
capacitance CJ achieves better performance. The reverse  
voltage rating V of the diode must be greater than the  
maximum input Rvoltage of the LED lamp.  
Selecting L1 and D1  
There is a certain trade-off to be considered between  
optimal sizing of the output inductor L1 and the tolerated  
output current ripple. The required value of L1 is inversely  
proportional to the ripple current IO in it.  
The total parasitic capacitance present at the DRAIN pin of  
the HV9921/22/23 can be calculated as:  
VO TOFF  
(1)  
L1 =  
(3)  
CP = CDRAIN + CPCB + CL + CJ  
IO  
When the switching MOSFET turns on, the capacitance CP  
is discharged into the DRAIN pin of the IC. The discharge  
current is limited to about 150mA typically. However, it  
may become lower at increased junction temperature. The  
duration of the leading edge current spike can be estimated  
VO is the forward voltage of the LED string. T  
is the off-  
time of the HV9921/22/23. The output currenOtFFin the LED  
string (IO) is calculated then as:  
1
(2)  
IO = ITH − ⋅ IO  
2
NR092005  
5