Compiled version: V1.0
DC/DC selection
1.DC/DC description
DC/DC refers to DC to DC power supply (Direct Current). It is a device that converts electrical energy of one voltage value into electrical energy of another voltage value in a DC circuit. For example, a DC voltage (5.0V) can be converted into another DC voltage (1.5V or 12.0V) through a converter. We call this converter a DC/DC converter, or switching power supply or switching adjustment Device. Strictly speaking, LDO is also a kind of DC/DC. In the selection of power supply chips, LDO and DC/DC are two completely different chips.
DC/DC achieves basically smooth voltage output through switching chopping, magnetoelectric energy conversion of inductance, and capacitor filtering. The output current of the power supply is large, the load capacity is strong, and the conversion efficiency is high, but because of the switching action, there will be high-frequency radiation.
The following are the filtering conditions for DC/DC purchase in the component mall:
Function type: Charge Pump, Isolated module, boost, step-down, etc.;
Output configuration: Positive, Negative and other combinations;
Power supply topology: Boost (boost), Buck (buck), etc.;
Output type: fixed, adjustable, programmable, etc.;
Number of output voltage channels: 1 to 8 channels;
Minimum input voltage: 0.3V to 85VAC (typical value);
Maximum input voltage: 1,5V to 265VAC (typical value);
Output voltage (minimum/fixed): 0.2 to 15V, Vin-39, Vin, etc.;
Output voltage (maximum value): 0.9Vin, 1.02V to 260V (typical value);
Output current: 200uA to 70A (typical value);
Switch operating frequency: 100HZ to 100KHZ, 180MHZ, etc.;
Whether synchronous rectification: yes, no.
Reference package: SOP-8, SOT-23-5, SOP-14, plug-in, etc.;
Brand/Place of Origin: ADI, AMS, TI, Jinshengyang, etc.
2. DC/DC key indicators and definitions
2.1 Power supply topology
The three common topologies of DC/DC are Buck (step-down DC/DC converter), Boost (boost DC/DC converter), and Buck-Boost (buck-boost DC/DC converter).
2.2 Input voltage/output voltage
Consider the actual input/output voltage fluctuation range, and select the recommended operating voltage range in accordance with the DC/DC device manual to ensure that the device specifications cannot be exceeded.
2.3 Output current
Continuous output current capability is an important parameter of DC/DC devices. Please refer to this parameter when selecting and keep a certain margin. At present, the maximum output current provided by the mall can reach 70A.
The selection of DC/DC output current parameters needs to evaluate the instantaneous peak current and heat generation of the subsequent circuit, and determine it comprehensively, and meet the derating requirements.
2.4 Ripple noise
DC/DC devices use switching power supplies to charge and discharge inductors and capacitors, which will cause EMI (electromagnetic radiation/interference) and large power supply ripple problems.
The switching action of DC/DC devices can also cause EMI (electromagnetic radiation/interference) or noise problems.
At the same time, it is required to pay attention to the ripple of light load and heavy load. Generally, the ripple of light load is too large. If the ripple of the DC/DC device is large, it will directly affect the conversion efficiency of the device, affect the unstable operation of the system, and cause high heat generation. The power consumption of the whole system is too large.
2.5 Switching frequency
The commonly used switching frequencies of DC/DC devices are mostly above 500kHz, such as TPS5430DDAR, and higher switching frequencies of 1.2M to 2M are also available, but every time the switching tube is turned on and off, a certain loss will be generated. The higher the switching frequency, the greater the switching loss. The switching loss at 5M switching frequency is 10 times larger than 500kHZ.
2.6 Efficiency
DC/DC devices have high conversion efficiency, which can generally reach more than 90%, and will not cause excessive heat loss and heat dissipation problems in high-power power conversion.
At the same time, we must pay attention to the light load and heavy load. Light load will affect the standby power, and heavy load will affect the temperature rise.
2.7 Enable level
The enable pin EN of the DC/DC device must meet the system control requirements, and the enable signal must not exceed the specific voltage range of the DC/DC device, and it must be satisfied within the maximum range of voltage fluctuations.