POSCAP capacitors and their applications

POSCAP capacitors are new products developed by Sanyo after OS-CON capacitors. They are SMD tantalum polymer organic semiconductor solid electrolytic capacitors, hereinafter referred to as POSCAP tantalum capacitors. The main features of this series of capacitors are: low profile height; low impedance and equivalent series resistance (ESR) at high frequencies, large allowable ripple current; long life, up to 2000 hours at 105°C; excellent noise absorption capacity; good temperature characteristics, low temperature can reach -55°C; can withstand 20A impact current; allow 240°C, 10s reflow soldering; and superior performance in terms of safety compared to ordinary tantalum electrolytic capacitors.

Due to the above characteristics, POSCAP capacitors are particularly suitable for filter capacitors in power supply circuits
, such as DC/DC converters in personal computers, portable computers and base stations, video recorders, digital cameras, navigation systems (GPS), PDAs, mobile phones and DVDs. This article will introduce its structure, performance, application examples and precautions for use.
Table 1 Frequency characteristics of POSCAP capacitors

Performance and specifications of POSCAP tantalum capacitors
POSCAP tantalum capacitors are divided into three series: TPA, TPB and TPC. Their rated voltage, capacity and size are different. The performance is shown in Table 1.
The frequency characteristics of POSCAP tantalum capacitors are very good, especially in the range of 100 to 5000kHz, where their ESR and impedance are quite low (less than 0.1Ω). For example, the frequency characteristic curve of 16TPB47 is shown in Figure 1. This is extremely beneficial for DC/DC converters with current operating frequencies of 1 to 3MHz, which can reduce losses and can well reduce ripple voltage.
Compared with general tantalum electrolytic capacitors, as shown in Figure 2. Figure 2 is a comparison of POSCAP capacitors and standard tantalum electrolytic capacitors in terms of ESR and impedance, while Figure 3 is a frequency characteristic of POSCAP capacitors and standard tantalum electrolytic capacitors. It can be seen from Figure 3 that general tantalum capacitors are only suitable for frequencies below 1kHz. At 10 to 100kHz, the capacitance is much reduced, while POSCAP tantalum capacitors change less in the range of 10 to 100kHz.
The temperature characteristics of POSCAP tantalum capacitors are very good. For example, at 100kHz, the ESR and impedance values ​​of 10TPA100M remain basically unchanged in the temperature range from -55℃ to 105℃.

Application Examples
POSCAP tantalum capacitors are mainly used in high-efficiency DC/DC converter circuits as output filter capacitors COUT. Figure 4 is a low-voltage, high-efficiency step-down DC/DC converter. When 6TPC100M is used as COUT, the ripple voltage is 18.1mVp-p; if a general low-ESR tantalum electrolytic capacitor of 100μF/6.3V is used, the ripple voltage is 7.5mVp-p.
The following introduces an example of NS using POSCAP tantalum capacitors on the evaluation board of DC/DC converters. The NS LM3352 evaluation board circuit is shown in Figure 5, and its input and output capacitors both use 10TPA33M. This is a step-up/step-down charge pump DC/DC converter. The output voltage is 3.3V, 3.0V and 2.5V, the output current is 200mA, and the operating frequency is 1MHz.

Application Notes
1. POSCAP tantalum capacitors are polar electrolytic capacitors (the end with the "+" sign is the positive pole), and the polarity cannot be reversed when used. Reverse polarity will increase leakage or may cause a short circuit.
2. The circuits that cannot be used are as follows: high impedance voltage holding circuit; coupling circuit; time constant circuit; circuit with leakage current influence; circuit with series connection to increase withstand voltage.
3. Do not use it beyond the rated voltage, otherwise it may cause a short circuit.
4. Limit rapid charging or discharging. It is recommended to add a current limiting resistor in the charging and discharging circuit to make the impact current less than 20A.
5. When designing, the capacitance, withstand voltage, impedance, etc. of the capacitor should have a certain margin to make it safer and more reliable.
6. Make sure that the temperature range of use is within the operating temperature range of the capacitor. The power supply current does not exceed the allowable ripple current. When the ripple current exceeds the allowable ripple current, the heat inside the capacitor will increase and the service life will be reduced.
7. It is recommended that the voltage applied to the capacitor is 90% of the rated voltage. If the rated voltage is greater than 10V, 80% of the rated voltage is better. If a DC voltage is added to an alternating voltage, its peak voltage cannot exceed the rated voltage. If the total DC voltage is added to a negative peak alternating voltage, negative voltage is not allowed.