Design an LDO with external reference input signal using NE57814

[yihuang]

Hi, I am designing a general purpose LDO with external input reference. I have the samples of NE57814. Can someone help me regarding the following questions?

(1) From the datahsheet it says max VD and VDD=3.6V. If I am using VD=VDD=5.5V, will it break the circuit or make it unfunctional? I am not doing mass production. So as far as it still functions, that is good for me.

(2) Can I connect external resistor dividers to close the feedback loop (I do not want VTT=VREF, but VTT=K*VREF, where K is a number greater than 1)? If so, how can I connect it? The question is illustrated in the attachment.

(3) If I cannot use NE57814, are there any other products I can choose, which can be used as the LDO with external input reference signal?

Thank you!

[reyes]

Hi,

(1) From the datasheet it says max VD and VDD=3.6V. If I am using VD=VDD=5.5V, will it break the circuit or make it un-functional? I am not doing mass production. So as far as it still functions, that is good for me.

A1. Voltages above 3.6V may cause permanent damage to the device. Supply VD and VDD of the NE57814 with 5.5V is definitely not recommended. I would recommend you to add a small resistor divider (for test purposes) to down the 5.5V to about 2.5V.

(2) Can I connect external resistor dividers to close the feedback loop (I do not want VTT=VREF, but VTT=K*VREF, where K is a number greater than 1)? If so, how can I connect it? The question is illustrated in the attachment.

A2. Yes, the NE57814 allows use of an external reference voltage applied to the ExtRefIn pin to set the VTT output voltage. This pin is used for applications where the VTT voltage is not equal to VDD divided by 2. The internal reference voltage is set by two matched 100 kΩ resistors connected in a resistor divider between the VDD and Vss pins of the NE57814. Setting the value of Vref or VTT can be done in two ways: by using an external resistor divider whose resistor values are less than 5 kΩ each or by connecting the output of an operational amplifier which is outputting the reference voltage to the ExtRefIn pin. If the external resistor divider is used, place a 0.01 µF ceramic bypass capacitor between the ExtRefIn pin (pin 6) and the VSS pin (pin 1).

(3) If I cannot useNE57814, are there any other products I can choose, which can be used as the LDO with external input reference signal?

A3. I think that you can use the NE57814 for your test purposes, but if you want to check for different devices I recommend you to take a look at section 2 of the selector guide.

Have a great day,
Jose

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