EVAL5970D STMicroelectronics, EVAL5970D Datasheet

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Designing with the L5970D 1A high efficiency DC-DC converter Introduction The L5970D is a step-down monolithic power switching regulator capable of delivering output voltages from 1.235 The operating input voltage ranges ...

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Contents Contents 1 Pin functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...

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AN1330 6.1 Positive buck-boost regulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 ...

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List of figures List of figures Figure 1. Demonstration board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...

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AN1330 1 Pin functions 1.1 Pin description Table 1. Pin description N. Name 1 OUT Regulator output Master/slave synchronization. When open, a signal synchronous with the turn-OFF of the internal power is present. When connected to an external signal at ...

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Functional description 2 Functional description The main internal blocks are shown in the device block diagram in ● A voltage regulator supplying the internal circuitry. From this regulator, a 3.3 V reference voltage is externally available. ● A voltage monitor ...

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AN1330 Figure 5. Internal regulator circuit 2.3 Oscillator and synchronizer Figure 6 shows the block diagram of the oscillator circuit. The Clock Generator provides the switching frequency of the device, which is internally fixed at 250 kHz. The Frequency Shifter ...

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Functional description Figure 6. Oscillator circuit block diagram 2.4 Current protection The L5970D has two types of current limit protection: pulse-by-pulse and frequency foldback. The schematic of the current limitation circuitry for the pulse-by-pulse protection is shown in Figure 7. ...

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AN1330 reference (1.235 V), while the inverting input (FB) is connected to the external divider or directly to the output voltage. The output (COMP) is connected to the external compensation network. The uncompensated error amplifier has the following characteristics: Table ...

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Functional description Figure 8. Driving circuitry 2.7 Inhibit function The inhibit feature is used to put the device in standby mode. With the INH pin higher than 2.2 V the device is disabled and the power consumption is reduced to ...

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AN1330 3 Additional features and protection 3.1 Feedback disconnection If the feedback is disconnected, the duty cycle increases towards the maximum allowed value, bringing the output voltage close to the input supply. This condition could destroy the load. To avoid ...

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Closing the loop 4 Closing the loop Figure 9. Block diagram of the loop 4.1 Error amplifier and compensation network The output L-C filter of a step-down converter contributes with 180 degrees phase shift in the control loop. For this ...

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AN1330 Figure 10. Error amplifier equivalent circuit and compensation network The poles of this transfer function are (if C Equation 3 Equation 4 where the zero is defined as: Equation the low frequency which sets the bandwidth, ...

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Closing the loop Equation 7 The zero of this transfer function is given by: Equation the zero introduced by the ESR of the output capacitor and it is very important to 0 increase the phase margin of ...

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AN1330 This means that even if the input voltage changes, the error amplifier does not change its value to keep the loop in regulation, thus ensuring a better line regulation and line transient response. To sum up the Open Loop ...

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Closing the loop Figure 12. Phase plot The cut-off frequency and the phase margin are: Equation 16 16/ 22.8kHz Phase margin = 39.8° C AN1330 ...

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AN1330 5 Application information 5.1 Component selection ● Input capacitor The input capacitor must be able to withstand the maximum input operating voltage and the maximum RMS input current. Since step-down converters draw current from the input in pulses, the ...

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Application information Nevertheless, the ESR of the output capacitor introduces a zero in the open loop gain, which helps to increase the phase margin of the system. If the zero goes to a very high frequency, its effect is negligible. ...

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AN1330 Table 4. Inductor selection (continued) Manufacturer Coiltronics BI Murata Panasonic Sumida Epcos Wurth Elektronik 5.2 Layout considerations The layout of switching DC-DC converters is very important to minimize noise and interference. Power-generating portions of the layout are the main ...

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Application information 5.3 Thermal considerations The dissipated power of the device is tied to three different sources: ● switching losses due to the not negligible R Equation 21 Where D is the duty cycle of the application. Note that the ...

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AN1330 Considering the device in an SO-8 package mounted on the board with a good groundplane, that it has a thermal resistance-junction to-ambient (Rth ambient temperature of about 70 °C. Equation 26 5.4 Short-circuit protection In overcurrent protection mode, when ...

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Application information Figure 14. Short-circuit current (V Figure 15. Short-circuit current (V In Figure 14 and increases for a given component list, the current peak increases also. The current limit is immediately triggered but the current peak increases until the ...

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... EVAL.BOARD R2 R3 REF VIN U1 VOUT C1 D1 GND C2 www.st.com Application information L1 33∝H VOUT=3.3V OUT D1 R1 STPS2L25U 5. 100∝F 10V R2 3.3K AM00017v1 Description Manufacturer 10 µ Murata 100 µ Sanyo KEMET KEMET Neohm Neohm Neohm STMicroelectronics 33 µ Coilcraft R INH SYN GND. AM00018v1 23/31 ...

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Application information Figure 18. PCB layout (bottom side) Figure 19. PCB layout (front side) Below, some graphs are provided which show the T and output voltage conditions, as well as some efficiency measurements. Figure 20. Junction temperature vs. output current ...

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AN1330 Figure 22. Junction temperature vs. output current ( Tj(°C) 140 Vo=18V 120 100 Vcc=24V Tamb=25° 0.2 0.4 0.6 0.8 Io(A) Figure 24. Junction temperature vs. output current (V Figure 23. ...

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Application ideas 6 Application ideas 6.1 Positive buck-boost regulator The device can be used to implement a step-up/down converter with a positive output voltage. Figure The input voltage can range from 5 V and 35 V. ...

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AN1330 6.3 Dual output voltage with auxiliary winding When two output voltages are required possible to create a dual output voltage converter by using a coupled inductor. During the ON phase, the current is delivered to V while ...

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Compensation network with MLCC (multiple layer ceramic capacitor) at the output 7 Compensation network with MLCC (multiple layer ceramic capacitor) at the output MLCCs with values in the range of 10 µF-22 µF and rated voltages in the range of ...

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AN1330 Compensation network with MLCC (multiple layer ceramic capacitor) at the output Figure 30. Soft start network example VIN=4.4V to 25V VIN=4.4V to 25V VREF VREF VREF R=4K7 R=4K7 R=4K7 C1 C1 10uF 10uF 25V 25V Css=2.7nF Css=2.7nF CERAMIC CERAMIC ...

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Revision history 8 Revision history Table 6. Document revision history Date 22-May-2007 19-May-2008 30/31 Revision – the document has been reformatted 2 – Section 4: Closing the loop – Minor text changes – Restructured document sections 3 – Minor text ...

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... AN1330 Information in this document is provided solely in connection with ST products. STMicroelectronics NV and its subsidiaries (“ST”) reserve the right to make changes, corrections, modifications or improvements, to this document, and the products and services described herein at any time, without notice. All ST products are sold pursuant to ST’s terms and conditions of sale. ...