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I was reading through the datasheet of a boost converter, TPS61023 from TI. In the "Input Capacitor Selection section", they give the following advice: 8.2.2.5 Input Capacitor Selection Multil...
#2: Post edited
by
Nick Alexeev
·
2024-06-22T00:24:31Z (6 months ago)
Copy and paste datasheet excerpts instead of posting screenshots as images. Text is searheable, screenshots aren't.
I was reading through the datasheet of a boost converter, [TPS61023 ](https://www.ti.com/product/TPS61023?bm-verify=AAQAAAAJ_____6cbyRe2uJ2zoMEue49ianSG00JMgAfjo-dQkxuszVdF_g_GNNw7VOE38N6OJ9LuOQW0iGP5xtrguqt9RaXuI7WnQhGZ7__bNOKoGZ0QhedRCZTEjuJPUT1-3cyxyW3aB6oC3AReFvWYALEa9rKFxtMVdC2RYf9sFIVw-8MsqHCL6sA4V68bD9xfZn6yNpU-gbOxJMKzqyOyYXiTSMZhyQ_s37JaPfdrqb4ZquI6frEiejwJtq-bIL5IqWM50YcWoZy3BpfO0egmVcx-JMRVjyyB384zqHcNMQxY9yUjO9rocA)from TI.- In the "Input Capacitor Selection section", they give the following advice:
- Notably, TI advises against using only a ceramic capacitor at the input, citing that it could induce ringing when a load step is applied at the output. The recommended solution is to place an electrolytic bulk capacitor between the ceramic capacitor and the input pin of the boost converter.
- I am confused why this advice is given. The claim is that is reduces ringing caused by the inductance of the input power trace, but electrolytic capacitors usually have a worse ESL/ESR than ceramics. Nowadays, ceramics can have a comparable capacitance to the electrolytics as well. I know that ceramic capacitors can have a piezoelectric effect but I have not seen that cited as an issue for SMPS input capacitors.
- So, what is the reason for this manufacturer advice?
- I was reading through the datasheet of a boost converter, [TPS61023](https://www.ti.com/product/TPS61023) from TI.
- In the "Input Capacitor Selection section", they give the following advice:
- > **8.2.2.5 Input Capacitor Selection**
- >
- > Multilayer X5R or X7R ceramic capacitors are excellent choices for the input decoupling of the step-up converter
- as they have extremely low ESR and are available in small footprints. Input capacitors must be located as close
- as possible to the device. While a 10-μF input capacitor is sufficient for most applications, larger values may be
- used to reduce input current ripple without limitations. Take care when using only ceramic input capacitors.
- When a ceramic capacitor is used at the input and the power is being supplied through long wires, a load step at
- the output can induce ringing at the VIN pin. This ringing can couple to the output and be mistaken as loop
- instability or could even damage the part. In this circumstance, place additional bulk capacitance (tantalum or
- aluminum electrolytic capacitor) between ceramic input capacitor and the power source to reduce ringing that
- can occur between the inductance of the power source leads and ceramic input capacitor.
- Notably, TI advises against using only a ceramic capacitor at the input, citing that it could induce ringing when a load step is applied at the output. The recommended solution is to place an electrolytic bulk capacitor between the ceramic capacitor and the input pin of the boost converter.
- I am confused why this advice is given. The claim is that is reduces ringing caused by the inductance of the input power trace, but electrolytic capacitors usually have a worse ESL/ESR than ceramics. Nowadays, ceramics can have a comparable capacitance to the electrolytics as well. I know that ceramic capacitors can have a piezoelectric effect but I have not seen that cited as an issue for SMPS input capacitors.
- So, what is the reason for this manufacturer advice?
#1: Initial revision
by
Mu3
·
2024-06-21T18:30:02Z (6 months ago)
Using only ceramic capacitors on an input of an SMPS - unclear advice from manufacturer
I was reading through the datasheet of a boost converter, [TPS61023 ](https://www.ti.com/product/TPS61023?bm-verify=AAQAAAAJ_____6cbyRe2uJ2zoMEue49ianSG00JMgAfjo-dQkxuszVdF_g_GNNw7VOE38N6OJ9LuOQW0iGP5xtrguqt9RaXuI7WnQhGZ7__bNOKoGZ0QhedRCZTEjuJPUT1-3cyxyW3aB6oC3AReFvWYALEa9rKFxtMVdC2RYf9sFIVw-8MsqHCL6sA4V68bD9xfZn6yNpU-gbOxJMKzqyOyYXiTSMZhyQ_s37JaPfdrqb4ZquI6frEiejwJtq-bIL5IqWM50YcWoZy3BpfO0egmVcx-JMRVjyyB384zqHcNMQxY9yUjO9rocA)from TI. In the "Input Capacitor Selection section", they give the following advice:  Notably, TI advises against using only a ceramic capacitor at the input, citing that it could induce ringing when a load step is applied at the output. The recommended solution is to place an electrolytic bulk capacitor between the ceramic capacitor and the input pin of the boost converter. I am confused why this advice is given. The claim is that is reduces ringing caused by the inductance of the input power trace, but electrolytic capacitors usually have a worse ESL/ESR than ceramics. Nowadays, ceramics can have a comparable capacitance to the electrolytics as well. I know that ceramic capacitors can have a piezoelectric effect but I have not seen that cited as an issue for SMPS input capacitors. So, what is the reason for this manufacturer advice?