Power conversion chip TPS5430 and its application

1. Introduction

Earthquake precursor observation instruments are an important part of earthquake precursor observation. Only when the instruments are stable and reliable can they provide continuous raw data for earthquake precursor analysis. Continuously exploring and using high-performance components to replace relatively low-performance, old components is a way to improve instrument performance.

TPS5430 is a DC/DC switching power conversion chip with superior performance newly launched by TI. We have developed it and applied it to the data acquisition system of TJ-2 volumetric strain gauge.

2. Introduction to TPS5430

1.TPS5430 Features

TPS5430 has good characteristics, its performance and main parameters are as follows:

High current output: 3A (peak 4A);

Wide voltage input range: 5.5~36V;

High conversion efficiency: up to 95% under optimal conditions;

Wide voltage output range: the lowest voltage can be adjusted down to 1.221V;

Internal compensation minimizes external component count;

Fixed 500kHz conversion rate;

With over-current protection and thermal shutdown function;

With switch enable pin, the quiescent current is only 17uA in the off state;

Compared with other similar DC switching power conversion chips, the high conversion efficiency of TPS5430 is particularly noteworthy.

Figure 1 is a graph showing the relationship between the conversion efficiency and output current of the TPS5430 at a 12V input voltage and a 5V output voltage.

Figure 1 TPS5430 chip efficiency-current relationship curve

2. Function and structure

(1) Pin Description:

TPS5430 adopts 8-pin SO IC PowerPADTM package, as shown in Figure 2.

Figure 2 TPS5430 package

(2) Internal structure and function:

①Crystal oscillator (Oscillator) frequency.

The fixed 500kHz conversion rate allows for a smaller output inductor with the same output ripple requirement.

② Reference voltage.

The reference voltage system generates an accurate reference signal by scaling the output range of the temperature-stable bandgap circuit. Tests have shown that the bandgap and scaling circuits remain balanced at 1.221V output over the allowable temperature range.

③ ENA (enable pin) and (Slow Start) internal soft start.

When the voltage on the ENA pin exceeds the limit voltage, the converter and the internal soft start start working. When it is lower than the limit voltage, the converter stops working and the soft start starts to reset. When the ENA pin is grounded or the voltage is less than 0.15V, the converter stops working. The ENA pin can be left floating.

④ UVLO (Under Voltage Lockout).

TPS5430 has a UVLO circuit. Whether during power-on or power-off, as long as V IN (input voltage) is lower than the limit voltage, the conversion chip will not work. The typical hysteresis value of the UVLO comparator is 330mV.

⑤ Boost Capacitor (start capacitor).

Connect a 0.01μF ceramic capacitor between the BOOT pin and the PH pin to provide a gate voltage for the high side of the MOSFET.

⑥ VSENSE (External Feedback) and Internal Compensation (Internal Compensation).

The output voltage is fed back to the VSENSE pin through an external resistor divider. In a stable state, the voltage of the VSENSE pin is equal to the voltage reference value 1.221V. The TPS5430 has an internal compensation circuit, which simplifies the chip design.

⑦ Voltage Feed Forward (Voltage Positive Feedback).

The internal voltage positive feedback ensures that the power chip has a constant gain regardless of how the input voltage changes. This greatly simplifies stability analysis and improves transient response. The typical value of the positive feedback gain of TPS5430 is 25.

⑧ Pulse-Width-Modulation Control (Pulse Width Control).

The converter adopts fixed frequency control method.

⑨ Overcurrent Protection.

The overcurrent protection circuit ensures that when the current exceeds the limit value, the internal overcurrent indicator is set to true and the overcurrent protection is triggered.

⑩ Thermal Shutdown .

When the junction temperature exceeds the thermal shutdown point, the voltage parameter is set to ground and the high-side MOSFET is turned off. Under the control of the soft-start circuit, when the junction temperature drops to 14°C below the thermal shutdown point, the chip restarts.

3. Application of TPS5430 in earthquake precursor observation data acquisition system

The data acquisition system is an important part of earthquake precursor observation instruments. It converts the weak analog signals detected by sensors into digital signals and performs calculations to provide reliable data for subsequent earthquake analysis.

Initially, we used MAX1626 and other chip power supplies to power the TJ-2 volumetric strain gauge data acquisition system, but during the test we found that the system was unstable and the instrument would automatically restart. The reason was that the load capacity of MAX1626 and other chip power supplies was not large enough. Therefore, after many investigations, we finally selected the TPS5430 chip with strong load capacity, high efficiency and few peripheral devices as the power supply to power the A/D conversion module and data processing module of the data acquisition system. The principle is shown in Figure 3.

Figure 3 Schematic diagram of the data acquisition system.

1. Circuit design

In the process of designing the power supply for the TJ-2 volumetric strain gauge data acquisition system, the design parameters must first be determined according to the work requirements, and then the circuit must be designed and peripheral components must be selected based on the parameters.

(1) Design parameter requirements

Input voltage range: 10.8~19.8V; output voltage: 5V; input ripple voltage: 300mV; output ripple voltage: 30mV; output rated current: 3A.

(2) Application circuit

The power supply design of this system uses the classic circuit of TPS5430, as shown in Figure 4.

Figure 4 1018~1918V input to 5V output voltage application circuit diagram

(3) Component selection

① Input capacitance.

The TPS5430 requires a slightly larger decoupling capacitor. A 10μF (C1) high-performance ceramic capacitor is recommended. A smaller capacitor can also be selected, but it must meet the input voltage and rated current ripple requirements.

②Output filter components.

Output filter components, namely L1, C2.TPS5430 has internal compensation circuit. Output inductance is related to the maximum output current, and 15μH inductance is selected here.

Output capacitance is an important design factor that affects rated voltage, rated ripple current and equivalent impedance (ESR). In this application, a 220μF output capacitor is selected. At this time, the RMS ripple current generated in the circuit is 143mA, and the maximum ESR required is 40MΩ.

③Output voltage setting.

The output voltage is determined by the resistors (R1, R2) of the VSENSE pin. If the output voltage is 5.0V, the reference voltage is 1.221V, and R1 is 10kΩ, then R2 is determined to be 3.24kΩ.

④ BOOT (startup) capacitor.

The BOOT capacitor C2 is selected to be 0.01μF.

⑤Capture diode.

TPS5430 requires an external capture diode, select B340A, its reverse voltage is 40V, forward current is 3A, forward voltage is 0.5V.

2. Circuit board design

TI recommends the TPS5430 10.8~19.8V input to 5V output voltage circuit board wiring and component placement diagram, as shown in Figure 5.

The design process of TPS5430 circuit board should follow the design principles of general power conversion chip circuits to achieve the expected effect. There are two other points to note:

① PowerPAD is required to be connected to the ground. A pad can be placed directly under the chip and a hole can be punched to facilitate correct welding.

② If there is no special requirement for the ENA pin, it can be left floating, or a signal via can be reserved.

Figure 5 Circuit board design

4. Conclusion

At present, the data acquisition instrument of TJ22 volume strain gauge powered by TPS5430 power supply has been put into practical use in many seismic stations in Inner Mongolia, Yunnan, etc. It has been verified that the power supply works well and all performances can meet the working requirements, which can be extended to other hardware designs.