TI中文支持网Part Number:LM61460-Q1Other Parts Discussed in Thread:LM61460
Hello Expert
Please support to check below design and give your comments.
Input voltage range: 9-16V
Output voltage range:2-8V, current configure:5V
Output current: max. 5A
fsw=400KHz
Output voltage ripple: 3%
load transient range: 5A to 0.5A
Transient response voltage change: 5%
Q1: consider the cost saving, i choose one Electrolytic capacitor 100uF, esr=35mR, ripple current=1.7A, with 1*10uF and 1*4.7uF, can you check it's OK or not->especially for 100uF EC?
Q2: choose one 10uF with 2*220nF at input pin, it's OK or not?
Q3: Customer want to adjust the output voltage, do you have good solution for current BUCK LM61460?
ping Wu：
Add note: this buck is used for control external LED, then need to consider the short circuit to power supply and GND testing. also iso7637-3a/3b/ESD
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Vivian Gao：
感谢您对TI产品的关注！ 关于你的咨询，我们正在确认你的问题，稍后回复您。
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Vivian Gao：
Please see my comments and questions:
You said:
Output voltage range:2-8V, current configure:5V
How are they planning to implement this:
1. Will a design have a fixed output voltage (between 2 and 8V) or do they need adjustable output voltage?
You said:
Q1: consider the cost saving, i choose one Electrolytic capacitor 100uF, esr=35mR, ripple current=1.7A, with 1*10uF and 1*4.7uF, can you check it's OK or not->especially for 100uF EC?
Q2: choose one 10uF with 2*220nF at input pin, it's OK or not?
Schematic Review:
1. Ensure the voltage ratings of the input capacitors are appropriate. (Rated Voltage > Abs max voltage on the input rail – thumb rule is to use atleast 50V rated caps for 12V automotive systems).
2. Ensure CVcc and CBoot are high quality ceramic caps (Eg: X7R) for good thermal stability. Ensure proper voltage rating.
3. Inductor – Ensure the Saturation current and DC Current rating of the Inductor > ~6.3A (for a 5A design).
4. The output capacitor values seem okay. However, since this is an adjustable output implementation – I would recommend:
a. Have a provision for feedforward cap and resistor.
b. Check the load transient and bode plot at all output voltages to ensure proper operation across different operating conditions.
You said:
Q3: Customer want to adjust the output voltage, do you have good solution for current BUCK LM61460?
Look at this app note: https://www.ti.com/lit/an/slyt777/slyt777.pdf
You said::
Add note: this buck is used for control external LED, then need to consider the short circuit to power supply and GND testing. also iso7637-3a/3b/ESD
These are system level tests and not device specific. You will have to implement external protection if you see the device abs max ratings getting violated.
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ping Wu：
1. Will a design have a fixed output voltage (between 2 and 8V) or do they need adjustable output voltage?
WP: need adjustable output voltage. current we choose LM61460 is adjustable output, and also we want to use external DAC/PWM to configure the output voltage via SW.
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Vivian Gao：
Got it!
Please refer to the design resources and the comments I shared in my previous reply.
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ping Wu：
I want to double confirm with you:
1) Input capacitor use 1*10uF and 2*220nF
2) Output capacitor use 1*100uF Electrolytic Capacitor and 1*10uF and 1*4.7uF.
3) FB consider add CFF=22pF and RFF=1K and
4) inductor use 6.8uH, Saturation current is 9A
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Vivian Gao：
1) Input capacitor use 1*10uF and 2*220nF
Looks good! Ensure the correct voltage rating as I had mentioned.
2) Output capacitor use 1*100uF Electrolytic Capacitor and 1*10uF and 1*4.7uF.
Again – looks good – however, since this is an adjustable output – check the performance on the board (especially at the max and min Vout).
3) FB consider add CFF=22pF and RFF=1K and
Keep provision for these on your board. If your loop response is good enough without these – you can keep these DNP. Otherwise, you can check the performance with the Cff and Rff.
4) inductor use 6.8uH, Saturation current is 9A
