L5985 STMicroelectronics, L5985 Datasheet
L5985
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L5985 Summary of contents
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... Figure 1. Application circuit June 2009 2 A step-down switching regulator VFQFPN8 Description The L5985 is a step-down switching regulator with 2.5 A (min) current limited embedded power MOSFET able to deliver current to the load depending on the application condition. The input voltage can range from 2 while the output voltage can be set starting from ...
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... Inductor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 5.3 Output capacitor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 5.4 Compensation network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 5.4.1 5.4.2 5.5 Thermal considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 5.6 Layout considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 5.7 Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 6 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 7 Order codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 8 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 2/37 Type III compensation network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Type II compensation network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Doc ID 13006 Rev 5 L5985 ...
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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 OUT SYNCH SYNCH INH INH COMP COMP Regulator output Master/slave synchronization. When it is left floating, a signal with a phase shift of half a period respect to the power turn on is present at the pin ...
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... Thermal data Table 3. Thermal data Symbol Maximum thermal resistance R thJA junction-ambient 1. Package mounted on demonstration board. 4/37 Parameter < 60 °C A Parameter VFQFPN (1) Doc ID 13006 Rev 5 L5985 Value Unit -0.3 to 1.5 1.5 W -40 to 150 °C -55 to 150 °C Value Unit 60 ° ...
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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 MOSFET on resistance DS(on) I Maximum limiting current LIM Oscillator F Switching frequency SW V FSW pin voltage FSW D Duty cycle ...
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... COMP ( 2.9 V SYNCH I = 4.5 mA SOURCE SYNCH floating from -40 to +125 °C. Specification in the -40 to +125 °C temperature range are J Doc ID 13006 Rev 5 Values Min Typ Max 3 0 COMP 25 100 2 3.3 0.7 0.9 2.0 110 70 1 150 30 L5985 Unit V μ μA °C ...
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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 to a fixed frequency sawtooth, controls the on and off time of the power switch ...
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... Figure Clock Clock Synchronization Synchronization Generator Generator Doc ID 13006 Rev 5 5.a). (Figure 5.b) in order to Section 5.4 for PWM gain Clock Clock Clock SYNCH SYNCH Ramp Ramp Sawtooth Sawtooth Generator Generator L5985 ...
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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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... Soft-start time results: Equation 2 For example with a switching frequency of 250 kHz the SS 10/37 ⎛ ⎞ R1 ⋅ ------- - ⎝ ⎠ OUT VREF R2 Figure 7). The soft-start stair case consists of 64 steps of ⋅ ----------------- TIME Fsw TIME Doc ID 13006 Rev 5 L5985 ) of the error REF is 8 ms. ...
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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 inverting input (FB) and output (COMP) are externally available for feedback and frequency compensation ...
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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 phase of the conduction time. This avoids an erroneous detection of a fault condition. This interval is generally known as “ ...
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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 μA. With INH pin lower than 0.6 V, the device is enabled. If the INH pin is left floating, an internal pull up ensures that the voltage at the pin reaches the inhibit threshold and the device is disabled ...
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... Table 6. Input capacitors Manufacturer MURATA TDK 14/ ⋅ ⋅ – -------------- - + ------ - RMS O η 2 η OUT ------------------------------------ - MAX V – V INMIN OUT ------------------------------------- - MIN V V – INMAX SW Series Cap value (μF) GRM31 10 GRM55 10 C3225 10 Doc ID 13006 Rev 5 L5985 is voltage drop across SW Rated voltage ( ...
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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 value is to have a ripple at 20%-40% of the output current. In ...
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... V, Δ 0.6 A (resulting by the inductor value), in OUT 0.01· the multi layer capacitor are adopted are OUT OUT Doc ID 13006 Rev 5 Saturation current ( 2.5 to 3.7 4 2 2.5 to 2.8 ΔI MAX + ------------------------------------ - ⋅ ⋅ OUT SW L5985 ...
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... 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 a voltage operational amplifier with high bandwidth. So selecting the compensation network the E/A will be considered as ideal, that is, its bandwidth is much larger than the system one. ...
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... In the two PWM PWM E/A E/A COMP COMP G G PW0 PW0 Doc ID 13006 Rev 5 s ------------------------- - ⋅ 2π f zESR 2 ⎛ ⎞ s ------------------ - + ⎝ ⎠ ⋅ 2π ------------------------------------------- - zESR ⋅ ⋅ 2π ESR C OUT ) ESR V OUT -------------- OUT I OUT OUT OUT ESR ESR OUT OUT L5985 ...
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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 the dc error on regulated output voltage; finally to place other poles far away the zero dB frequency ...
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... C = -------------------------- - π R ⋅ placing the second pole at four times the system bandwidth (BW ------------------------------------------------------------- - ⋅ ⋅ 5 2π -------------------------- - ⋅ ----------------- 1 – Doc ID 13006 Rev 5 ⋅ ⋅ ⋅ ⋅ – ---------------------------------------- - ⋅ ⋅ ⋅ 3 2π L5985 ): LC ...
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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 Figure 12 is shown the module and phase of the open loop gain. The bandwidth is about 75 kHz and the phase margin is 47° ...
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... Electrolytic capacitors show not negligible ESR (>30 mΩ), so with this kind of output capacitor the type II network combined with the zero of the ESR allows stabilizing the loop. In Figure 13 the type II network is shown. 22/37 Doc ID 13006 Rev 5 L5985 > 1/BW), this zero OUT ...
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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 Bode diagram The guidelines for positioning the poles and the zeroes and for calculating the component values can be summarized as follow: 1 ...
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... R in order to place the second pole at four times the system bandwidth ------------------------------------------------------------- - ⋅ ⋅ 5 2π μ 3 OUT 1.1kΩ 249Ω Doc ID 13006 Rev ⋅ ⋅ -------- - ⋅ OUT 10 ⋅ ⋅ ⋅ – 330 μF, OUT , , 10kΩ 68nF C = 68pF 4 5 L5985 ...
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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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... TOT measured on the application demonstration board described in the Doc ID 13006 Rev 5 of the power switch; these are DS(on ⋅ OUT is 220 mΩ. DS(on but actually OUT IN ⋅ ⋅ ⋅ OUT SW SW ⋅ ⋅ P TOT L5985 ) DS Figure 16. ...
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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 converter the input loop (including the input capacitor, the power MOSFET and the free wheeling diode) is the most critical one ...
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... Application information Figure 17. Layout example 28/37 Doc ID 13006 Rev 5 L5985 ...
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... VCC VCC VCC VCC OUT OUT OUT OUT SYNCH SYNCH SYNCH SYNCH INH INH INH INH L5985 L5983 L5985 L5983 GND GND GND GND 10nF C4 10nF C4 10nF C4 10nF COMP COMP COMP COMP COMP COMP COMP COMP FSW FSW FSW FSW R4 2.49K R4 2 ...
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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] Figure 23. Junction temperature vs output Figure 25. Efficiency vs output current 0.0 Figure 27. Efficiency vs output current 95 90 Vo=3.3V 85 Vo=2.5V 80 Vo=1. 1.5 2 Doc ID 13006 Rev 5 Application information current Vo=5 ...
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... OUT L=6.8uH L=6.8uH L=6.8uH L=6.8uH =500kHz =500kHz =500kHz =500kHz Timescale Timescale Timescale Timescale 100us/div 100us/div 100us/div 100us/div Time base 5ms/div Time base 5ms/div Doc ID 13006 Rev 5 Io=2A Io= VCC [ OUT OUT 500mV/div 500mV/div 200mV/div 200mV/div Time base 1ms/div Time base 1ms/div L5985 18 ...
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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 trademark. Doc ID 13006 Rev 5 Package mechanical data www.st.com. ECOPACK 33/37 ...
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... Doc ID 13006 Rev 5 L5985 inch Min Typ Max 0.0315 0.0354 0.0394 0.0008 0.0020 0.0276 0.0079 0.0071 0.0091 0.0118 0.1161 0.1181 0.1200 0.0878 0.0937 ...
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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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... Figure 8 on page 13 3 Figure 17 on page 28, Table 9 on page 29 4 Updated: Equation 18 5 Updated Table 4 on page 5 Doc ID 13006 Rev 5 Changes Figure 2 on page 3, Table 1 on page B, Table 7 on page Figure 18 on page 29, Table 9 on page and Figure 6 on page 9 L5985 3, 15, 29, ...
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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. ...