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RT9018B 参数 Datasheet PDF下载

RT9018B图片预览
型号: RT9018B
PDF下载: 下载PDF文件 查看货源
内容描述: 最大3A ,超低压差稳压器 [Maximum 3A, Ultra Low Dropout Regulator]
分类和应用: 稳压器
文件页数/大小: 12 页 / 143 K
品牌: RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
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RT9018A/B  
Application Information  
Adjustable Mode Operation  
Power Good  
The output voltage of RT9018A/B is adjustable from 0.8V  
to VIN by external voltage divider resisters as shown in  
TypicalApplication Circuit (Figure 2). The value of resisters  
R1 and R2 should be more than 10kΩ to reduce the power  
loss.  
The power good function is an open-drain output. Connects  
100kΩ pull up resistor to VOUT to obtain an output voltage.  
The PGOOD pin will output high immediately after the  
output voltage arrives 90% of normal output voltage. The  
PGOOD pin will output high with typical 1.5ms delay time.  
Enable  
Thermal-Shutdown Protection  
The RT9018A/B goes into shutdown mode when the EN  
pin is in the logic low condition. During this condition, the  
pass transistor, error amplifier, and band gap are turned  
off, reducing the supply current to 10uA typical. The  
RT9018A/B goes into operation mode when the EN pin is  
in the logic high condition. If the EN pin is floating, NOTE  
that the RT9018A/B internal initial logic level. For RT9018A,  
the EN pin function pulls high level internally. So the  
regulator will be turn on when EN pin is floating. For  
RT9018B, the EN pin function pulls low level internally.  
So the regulator will be turn off when EN pin is floating.  
Thermal protection limits power dissipation to prevent IC  
over temperature in RT9018A/B. When the operation  
junction temperature exceeds 160°C, the over-temperature  
protection circuit starts the thermal shutdown function  
and turns the pass transistor off. The pass transistor turn  
on again after the junction temperature cools by 30°C.  
RT9018A/B lowers its OTP trip level from 160°C to 110°C  
when output short circuit occurs (VOUT < 0.4V). It limits  
IC case temperature under 100°C and provides maximum  
safety to customer while output short circuit occurring.  
Power Dissipation  
Output Capacitor  
For continuous operation, do not exceed absolute  
maximum operation junction temperature 125°C. The  
power dissipation definition in device is:  
The RT9018A/B is specifically designed to employ ceramic  
output capacitors as low as 10uF. The ceramic capacitors  
offer significant cost and space savings, along with high  
frequency noise filtering.  
PD = (VIN VOUT) x IOUT + VIN x IQ  
The maximum power dissipation depends on the thermal  
resistance of IC package, PCB layout, the rate of  
surroundings airflow and temperature difference between  
junctions to ambient. The maximum power dissipation can  
be calculated by following formula:  
Input Capacitor  
Good bypassing is recommended from input to ground to  
help improve AC performance. A 10uF input capacitor or  
greater located as close as possible to the IC is  
recommended.  
PD(MAX) = ( TJ(MAX) TA ) / θJA  
Where TJ(MAX) is the maximum operation junction  
Current Limit  
temperature 125°C, TAis the ambient temperature and the  
The RT9018A/B contains an independent current limit and  
the short circuit current protection to prevent unexpected  
applications. The current limit monitors and controls the  
pass transistors gate voltage, limiting the output current  
to higher than 4.5A typical. When the output voltage is  
less than 0.4V, the short circuit current protection starts  
the current fold back function and maintains the loading  
current 1.8A. The output can be shorted to ground  
indefinitely without damaging the part.  
θJA is the junction to ambient thermal resistance.  
For recommended operating conditions specification of  
RT9018A/B, where TJ (MAX) is the maximum junction  
temperature of the die (125°C) and TA is the maximum  
ambient temperature. The junction to ambient thermal  
resistance for SOP-8 (Exposed Pad) package is 75°C/W  
on the standard JEDEC 51-7 (4 layers, 2S2P) thermal  
test board. The copper thickness is 2oz. The maximum  
power dissipation at TA = 25°C can be calculated by  
following formula:  
DS9018A/B-04 September 2007  
www.richtek.com  
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