EVAL5985 STMicroelectronics, EVAL5985 Datasheet
EVAL5985
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EVAL5985
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EVAL5985 Summary of contents
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Features ■ output current ■ 2 input voltage ■ Output voltage adjustable from 0.6 V ■ 250 kHz switching frequency, programmable MHz ■ Internal soft-start and Inhibit ■ Low dropout ...
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Contents Contents 1 Pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...
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L5985 1 Pin settings 1.1 Pin connection Figure 2. Pin connection (top view) 1.2 Pin description Table 1. Pin description N° Type 1 OUT 2 SYNCH 3 INH 4 COMP GND 8 V OUT ...
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Maximum ratings 2 Maximum ratings 2.1 Absolute maximum ratings Table 2. Absolute maximum ratings Symbol Vcc Input voltage OUT Output DC voltage F , COMP, SW Analog pin SYNCH INH Inhibit pin FB Feedback voltage P Power dissipation at T ...
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L5985 3 Electrical characteristics ° unless otherwise specified Table 4. Electrical characteristics Symbol Operating input voltage V CC range V Turn on V CCON V V UVLO hysteresis CCHYS CC R ...
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Electrical characteristics Table 4. Electrical characteristics Symbol Error amplifier V High level output voltage CH V Low level output voltage CL I Bias source current FB I Source COMP pin O SOURCE I Sink COMP pin O SINK G Open ...
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L5985 4 Functional description The L5985 is based on a “voltage mode”, constant frequency control. The output voltage V is sensed by the feedback pin (FB) compared to an internal reference (0.6 V) providing OUT an error signal that, compared ...
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Functional description 4.1 Oscillator and synchronization Figure 4 shows the block diagram of the oscillator circuit. The internal oscillator provides a constant frequency clock. Its frequency depends on the resistor externally connect to FSW pin. In case the FSW pin ...
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L5985 Figure 5. Sawtooth: voltage and frequency feed forward; external synchronization Figure 6. Oscillator frequency versus FSW pin resistor Doc ID 13006 Rev 5 Functional description 9/37 ...
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Functional description 4.2 Soft-start The soft-start is essential to assure correct and safe start up of the step-down converter. It avoids inrush current surge and makes the output voltage increases monothonically. The soft-start is performed by a staircase ramp on ...
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L5985 4.3 Error amplifier and compensation The error amplifier (E/A) provides the error signal to be compared with the sawtooth to perform the pulse width modulation. Its non-inverting input is internally connected to a 0.6 V voltage reference, while its ...
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Functional description 4.4 Over-current protection The L5985 implements the over current protection sensing current flowing through the power MOSFET. Due to the noise created by the switching activity of the power MOSFET, the current sensing is disabled during the initial ...
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L5985 Figure 8. Overcurrent protection strategy 4.5 Inhibit function The inhibit feature allows to put in stand-by mode the device.With INH pin higher than 1.9 V the device is disabled and the power consumption is reduced to less than 30 ...
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Application information 5 Application information 5.1 Input capacitor selection The capacitor connected to the input has to be capable to support the maximum input operating voltage and the maximum RMS input current required by the device. The input capacitor is ...
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L5985 5.2 Inductor selection The inductance value fixes the current ripple flowing through the output capacitor. So the minimum inductance value in order to have the expected current ripple has to be selected. The rule to fix the current ripple ...
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Application information Table 7. Inductors (continued) Manufacturer BI SUMIDA 5.3 Output capacitor selection The current in the capacitor has a triangular waveform which generates a voltage ripple across it. This ripple is due to the capacitive component (charge or discharge ...
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L5985 Table 8. Output capacitors Manufacturer MURATA PANASONIC SANYO TDK 5.4 Compensation network The compensation network has to assure stability and good dynamic performance. The loop of the L5985 is based on the voltage mode control. The error amplifier is ...
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Application information The transfer function on the LC filter is given by: Equation 13 where: Equation 14 Equation 15 As seen in Chapter 4.3 following paragraph the guidelines to select the Type II and Type III compensation network are illustrated. ...
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L5985 5.4.1 Type III compensation network The methodology to stabilize the loop consists of placing two zeros to compensate the effect of the LC double pole, so increasing phase margin; then to place one pole in the origin to minimize ...
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Application information Figure 11. Open loop gain: module Bode diagram The guidelines for positioning the poles and the zeroes and for calculating the component values can be summarized as follow: 1. Choose a value for R 2. Choose a gain ...
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L5985 The suggested maximum system bandwidth is equals to the switching frequency divided by 3.5 (F /3.5), anyway lower than 100 kHz if the F SW For example with V the type III compensation network is 4.99kΩ R ...
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Application information Figure 12. Open loop gain Bode diagram with ceramic output capacitor 5.4.2 Type II compensation network If the equivalent series resistance (ESR) of the output capacitor introduces a zero with a frequency lower than the desired bandwidth (that ...
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L5985 Figure 13. Type II compensation network The singularities of the network are: In Figure 14 the Bode diagram of the PWM and LC filter transfer function (G and the open loop gain (G Figure 14. Open loop gain: module ...
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Application information Equation 22 Where f is the ESR zero: ESR Equation 23 and Vs is the saw-tooth amplitude. The voltage feed forward keeps the ratio Vs/Vin constant. 3. Calculate C 4 Equation 24 4. Then calculate C (BW): Equation ...
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L5985 Figure 15. Open loop gain Bode diagram with electrolytic/tantalum output capacitor Doc ID 13006 Rev 5 Application information 25/37 ...
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Application information 5.5 Thermal considerations The thermal design is important to prevent the thermal shutdown of device if junction temperature goes above 150 °C. The three different sources of losses within the device are: a) conduction losses due to the ...
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L5985 Figure 16. Switching losses 5.6 Layout considerations The PC board layout of switching DC/DC regulator is very important to minimize the noise injected in high impedance nodes and interferences generated by the high switching current loops step-down ...
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Application information Figure 17. Layout example 28/37 Doc ID 13006 Rev 5 L5985 ...
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... Vout=3.3V Vout=3. STPS2L25U STPS2L25U STPS2L25U STPS2L25U 4.99K R1 4.99K R1 4.99K R1 4.99K 22uF 22uF 22uF 22uF R3 330 R3 330 R3 330 R3 330 C3 2.2nF C3 2.2nF C3 2.2nF C3 2.2nF R2 1.1K R2 1.1K R2 1.1K R2 1.1K Description Manufacturer 10 µ MURATA 22 µ MURATA 2.2 nF nF, 50V 220 pF nF Wurth elektronik STMicroelectronics 29/37 ...
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Application information Figure 19. PCB layout (component side) Figure 20. PCB layout (bottom side) Figure 21. PCB layout (front side) 30/37 Doc ID 13006 Rev 5 L5985 ...
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L5985 Figure 22. Junction temperature vs output current Figure 24. Junction temperature vs output current Figure 26. Efficiency vs output current VCC=5V =250kHz 0 [A] ...
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Application information Figure 28. Load regulation 0.6 F =250KHz SW 0.5 0.4 0.3 V =12V CC 0 [A] Figure 30. Load transient form 0 1 OUT OUT ...
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L5985 6 Package mechanical data In order to meet environmental requirements, ST offers these devices in different grades of ECOPACK® packages, depending on their level of environmental compliance. ECOPACK® specifications, grade definitions and product status are available at ...
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Package mechanical data Table 9. VFQFPN8 ( 1.08 mm) mechanical data Dim ddd Figure 33. Package dimensions 34/37 mm Min Typ Max 0.80 0.90 1.00 0.02 ...
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L5985 7 Order codes Table 10. Order codes Order codes L5985 L5985TR Package VFQFPN8 1.08 mm Doc ID 13006 Rev 5 Order codes Packaging Tube Tube and reel 35/37 ...
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Revision history 8 Revision history Table 11. Document revision history Date 21-Dec-2006 16-Oct-2007 16-Sep-2008 28-Jan-2009 17-Jun-2009 36/37 Revision 1 Initial release 2 Document status promoted from preliminary data to datasheet Updated: Cover Page, Table 4 on page 5, Figure 8 ...
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... L5985 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. ...