TPS61023: SOT package 1V

Hi Kami,

TPS61021A should be suitable for your application and its minimum startup voltage is only 0.9V. Its package is QFN.

TPS61022, TPS61023 startup voltage needs to be 1.8V.

Hello Zack,

Customer do not want to use QFN package due their maintenance workers are not very skilled. I want to find an IC with legs. I found
LM2623, but the packaging seems a bit bigger. Can you suggest a new IC?

Best Regards,

Kami Huang

Hi Kami,

As far as the chips I'm involved in, there are no other chips can meet the specifications. Beside, LM2623 requires external diode while TPS61021A is integrated. Its start-up voltage is 1.1V and may have large inrush current when start up. TPS61021A is recommended in this situation, the performance and package is better and the system design is easier as well.

Best Regards,

Eric Yue

Hello Zack and Eric,

Please let me explain, the customer's application environment, Boost Converter is connected to all systems. As shown in the picture below. The battery is used to power the system after sleep, and the Boost Converter will be activated once it needs to be activated. If you use TPS61021A, you still need to add Diode. Please help me to confirm the appearance of the application, the following specifications, which IC is recommended?

Vin 1V~3V (Target 0.8V~3V) , (Start up voltage)

Vout=3.3V, Max. Iout=0.3A.

Best Regards,

Kami Huang

Hi Kami,

TPS61021A integrates high side synchronous FET inside IC, so typically external diode is not needed, which is shown below. Does customer need external diode for any other requirements？

TPS61021A also has better performance such as lower start-up voltage, inrush current and easy design...TPS61021A is recommended if no other specification is required.

Regards,

Eric Yue

Hello Eric and Zack,

I look at the datasheet of LM2623 and calculate the conditions of the customer's requirement.  1.1V input voltage and output 3.3V/0.3A. I found that the switching frequency of LM2623 varies with the input voltage, right? I want to confirm that when the input voltage is 1.1V (not hit UVLO) and RT=75K, can LM2623 generate 3.3V? What is the switching frequency after 3.3V generation?

Best Regards,

Kami Huang

Hi Kami,

1. Yes. The switching frequency of LM2623 varies with the input voltage. Actually, LM2623 works in PFM mode instead of PWM mode, similar to hysteresis track control, so its switching frequency is not fixed, critical speaking. Details can be found in datasheet 7.4.1.

2. LM2623 can generate 3.3V in this condition.

3. The switching frequency and duty cycle changes with R3 and C3 from different Vin and Vout. Switching frequency is about 300kHz from datasheet. 

Besides, LM2623 is more suitable for applications where input/output voltage is fixed. Because switching frequency changes with Vin and duty cycle changes with C3. When testing, please notice that choosing correct C3 capacitor to get the appropriate duty cycle for a particular application circuit is a trial and error process according to datasheet.

Regards,

Eric Yue

Hello Eric,

Thanks for your reply. 

The customer's input is using a battery, if the customer's input range is from 3.3V to 1.1V. So, different input voltages of LM2623 will have different switching frequency?

Because the switching frequency of boost Converter used by customers is fixed frequency 450Khz. I hope that the LM2623 switching frequency is 450Khz when the input voltage is 1.1V, and the switching frequency does not exceed 2Mhz when the input voltage is 3.0V. How much should the RT resistance be set? Or would you suggest that the RT resistance design is 75Kohm, and I will use the lowest input voltage of 1.1V and the switching frequency of 300Khz to design the inductance?

Best Regards,

Kami Huang

Hi Kami,

1. Yes. Switching frequency of LM2623 is different for different input voltages.

2. From datasheet, I think switching frequency cannot reach 450Khz when the input voltage is 1.1V. switching frequency will not exceed 2Mhz when the input voltage is 3.0V in most designs (e.g. RT= 75k, 150k),

3. Since in this condition input voltage is changed, so inductor may be designed in worst working condition and result in large size.

4.  LM2623 is suitable for applications where input/output voltage is fixed. To have better performance, for various input voltages, C3 is changed with different input voltages and the suitable value cannot be calculated, best done by trial and error.

Regards,

Eric Yue

Hello Eric,

I discussed LM2623 with customer RD today. Because their products use battery power, he is very concerned about this parameter. He has question with the parameters of the quiescent current. Customers talked about the meaning of quiescent current that EN pulls Low, Vin power goes in, and LM2623 consumes current when LM2623 is no switching. I don't quite understand the above datasheet parameter list. May I know the Typical value and maximum value of LM2623 quiescent current?

Best Regards,

Kami Huang

Hi Kami,

I think customers referred to shutdown quiescent current, it can be obtained from 6.5 of datasheet.

Regards,

Eric Yue

Hello Eric,

Sorry, I still have a question. The IC that the customer designs now is Richtek RT9266. The customer's application circuit does not add external mosfet.
Which specification of RT9266 mapping to the shutdown quiescent current parameter you told me? Which TI specification mapping to Swith-off current I (VDD) in the RT9266 specification?

Best Regards,

Kami Huang

Hi Kami,

LM2623 integrates low side FET and need external high side diode.

I think Shutdown Current of RT9266 mapping to the shutdown quiescent current I mentioned before. I am not sure what switch-off current is of RT9266, it may be current into the VDD pin when IC is not switching. Operating quiescent current of LM2623 is current into the VDD pin when operating. 

Best Regards,

Eric Yue

Hello Eric,

Excuse me, the Vdd of LM2623 is 6V. May I know, What is the switch-off current (typical and max) of LM2623?

Best Regards,

Kami Huang

Hi Kami,

LM2623 has no such specific data exactly compared to switch-off current of RT9266. Operating quiescent current of LM2623 is current into the VDD pin when chip operates.

Regards,

Eric Yue

Hello Eric,

I have got new question from customer. Customer's application is mobile device.

1. What is the minimum capacitance value of C1, C2 (Input and output cap)?
2. What is the value range of L1?
3. Refer to the following picture for the corresponding relationship between the resistance of R3 and the frequency?

If so~ Is the red circle 150 150R or 150K?

Best Regards,

Kami Huang