L7986TA STMicroelectronics, L7986TA Datasheet
L7986TA
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L7986TA Summary of contents
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... LED driving August 2011 3 A step-down switching regulator HSOP8 exposed pad Description The L7986TA is a step-down switching regulator with 3.7 A (minimum) current limited embedded power MOSFET able to deliver current to the load depending on the application conditions. The input voltage can range from 4 while the output voltage can be set starting from 0 ...
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... Enable function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 5.6 Hysteretic thermal shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 6 Application informations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 6.1 Input capacitor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 6.2 Inductor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 6.3 Output capacitor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 6.4 Compensation network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 6.4.1 6.4.2 6.5 Thermal considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 6.6 Layout considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 6.7 Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 7 Application ideas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 7.1 Positive buck-boost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 7.2 Inverting buck-boost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 2/43 Type III compensation network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Type II compensation network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Doc ID 022098 Rev 1 L7986TA ...
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... L7986TA 8 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 9 Order codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 10 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Doc ID 022098 Rev 1 Contents 3/43 ...
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... Vout to FB pin. The switching frequency can be increased connecting an external resistor from FSW pin and ground. If this pin is left floating the device SW works at its free-running frequency of 250 kHz. Ground Unregulated DC input voltage CC Doc ID 022098 Rev 1 Description L7986TA ...
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... L7986TA 2 Maximum ratings Table 2. Absolute maximum ratings Symbol Vcc OUT F , COMP, SYNCH TOT stg 3 Thermal data Table 3. Thermal data Symbol R thJA 1. Package mounted on demonstration board. Parameter Input voltage Output DC voltage Analog pin Enable pin Feedback voltage Power dissipation ...
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... T =25° =33kΩ FSW 4.5V<V <38V CC Duty Cycle=0, V =0.8V FB Device OFF level Device ON level EN=V CC FSW pin floating F =1MHz =33kΩ FSW Doc ID 022098 Rev 1 L7986TA Values Unit Min Typ Max 4 4.5 0.1 0.4 200 400 mΩ 3.7 4.2 4.7 A 3.5 4.7 210 250 275 KHz 1.254 ...
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... L7986TA Table 4. Electrical characteristics (continued) Symbol Error amplifier V High level output voltage CH V Low level output voltage CL I Source COMP pin O SOURCE I Sink COMP pin O SINK G Open loop voltage gain V Synchronization function V High input voltage S_IN,HI V Low input voltage S_IN,LO t Input pulse width ...
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... Functional description 5 Functional description The L7986TA 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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... L7986TA 5.1 Oscillator and synchronization Figure 3 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 is left floating the frequency is 250 kHz; it can be increased as shown in ...
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... Functional description Figure 4. Sawtooth: voltage and frequency feed forward; external synchronization Figure 5. Oscillator frequency versus FSW pin resistor 10/43 Doc ID 022098 Rev 1 L7986TA ...
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... L7986TA 5.2 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 the non-inverting input (V Amplifier. So the output voltage slew rate is: ...
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... LC filter a type II compensation network can be used. Otherwise, a type III compensation network has to be used (see compensation network selection). Anyway the methodology to compensate the loop is to introduce zeros to obtain a safe phase margin. 12/43 GBWP Slew rate Chapter 6.4 Doc ID 022098 Rev 1 L7986TA 100dB 4.5MHz 7V/μ 3.3V 17mA/25mA for details about the ...
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... L7986TA 5.4 Overcurrent protection The L7986TA implements the overcurrent 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 “masking time” ...
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... Once the junction temperature goes back to about 130°C, the device restarts in normal operation. The sensing element is very close to the PDMOS area, so ensuring an accurate and fast temperature detection. 14/43 ⋅ ⁄ – --------------------------------------------------------------------------------------------------------------- - OUT ( ⁄ DRC ON_MIN DSON compatible. Doc ID 022098 Rev 1 T ON_MIN 4. ⋅ * DCR + SW L7986TA ...
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... L7986TA 6 Application informations 6.1 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 subject to a pulsed current, the RMS value of which is dissipated over its ESR, affecting the overall system efficiency ...
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... the minimum input capacitor (C PP_MAX ----------------------------------------------- - ⋅ IN_MIN 2 V PP_MAX Series Cap value (μF) UMK325BJ106MM-T GMK325BJ106MN-T GRM32ER71H475K Doc ID 022098 Rev 1 L7986TA can be written as follows ⋅ --- - + 1 D – η ) value is: IN_MIN ⋅ Rated voltage ( 4.7 50 ...
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... L7986TA Equation 12 Where T is the conduction time of the internal high side switch and T ON time of the external diode (in CCM, F fixed Vout, is obtained at maximum T to calculate minimum duty). So fixing ΔI minimum inductance value can be calculated: Equation 13 where F is the switching frequency, 1/(T SW For example for V value to have Δ ...
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... Cap value (μF) GRM32 22 to 100 GRM31 ECJ EEFCD TPA/B/C 100 to 470 C3225 22 to 100 Doc ID 022098 Rev 1 ΔI MAX + ------------------------------------ - ⋅ ⋅ OUT SW Rated voltage (V) ESR (mΩ 6.3 6 6.3 L7986TA < 5 < 5 < 5 < 5 ...
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... Compensation network The compensation network has to assure stability and good dynamic performance. The loop of the L7986TA 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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... ----------------------------------------------- - Z1 ⋅ ⋅ 2π Doc ID 022098 Rev 1 s ------------------------- - ⋅ 2π f zESR 2 ⎛ ⎞ s ------------------ - + ⎝ ⎠ ⋅ 2π ------------------------------------------- - zESR ⋅ ⋅ 2π ESR C OUT ) ESR V OUT , R = -------------- OUT I OUT ----------------------------- - Z2 ⋅ ⋅ 2π L7986TA ...
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... L7986TA Equation 23 Figure 9. Type III compensation network In Figure 10 the Bode diagram of the PWM and LC filter transfer function (G and the open loop gain (G Figure 10. 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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... Doc ID 022098 Rev 1 ⋅ ⋅ ⋅ ⋅ – ---------------------------------------- - ⋅ ⋅ ⋅ 3 2π set higher than 500 kHz. SW =22 μF, ESR<1 mΩ, the type OUT , , , C 3.3nF C 22nF = = 3 4 L7986TA ): LC C 220pF = 5 ...
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... L7986TA Figure 11. Open loop gain bode diagram with ceramic output capacitor Doc ID 022098 Rev 1 Application informations 23/43 ...
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... Bode diagram of the PWM and LC filter transfer function (G and the open loop gain (G 24/ ----------------------------- - = ⋅ ⋅ 2π ( · G (f) · G LOOP PW0 LC Doc ID 022098 Rev ------------------------------------------- - ⋅ ⋅ ⋅ ------------------- - 2π · G PW0 (f)) are drawn. TYPEII L7986TA (f)) LC ...
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... L7986TA Figure 13. 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 and C5 not comparable with parasitic capacitance of the board. 2. Choose a gain (R Equation 28 Where f ...
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... ------------------------------------------------------------- - ⋅ ⋅ 5 2π L=18 μ = OUT 1.1kΩ 150Ω Doc ID 022098 Rev 1 4 ⋅ ⋅ – 1 =330 μF, ESR=35 mΩ, the OUT , , 4.99kΩ 82nF C = 68pF 4 5 L7986TA ...
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... L7986TA Figure 14. Open loop gain bode diagram with electrolytic/tantalum output capacitor Doc ID 022098 Rev 1 Application informations 27/43 ...
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... JA is the sum of the power losses just seen. TOT Doc ID 022098 Rev 1 of the power switch; these are DSon 2 ) ⋅ OUT over temperature is DSon OUT ⋅ ⋅ ⋅ OUT ⋅ P TOT L7986TA and Figure 15. ...
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... L7986TA of heat. The Rth JA paragraph is about 40°C/W for the HSOP package. Figure 15. Switching losses 6.6 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 informations Figure 16. Layout example 30/43 Doc ID 022098 Rev 1 L7986TA ...
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... L7986TA 6.7 Application circuit In Figure 17 the demonstration board application circuit is shown. Figure 17. Demonstration board application circuit Table 9. Component list Reference Part number 10 μF, 50V UMK325BJ106MM-T 22 μF, 25V GRM32ER61E226KE15 3.3 nF, 50V 33 nF, 50V 100 pF, 50V 470 nF, 50V 4.99 kΩ, 1%, 0.1W 0603 1.1 kΩ ...
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... Application informations Figure 18. PCB layout: L7986TA (component side) Figure 19. PCB layout: L7986TA (bottom side) Figure 20. PCB layout: L7986TA (front side) 32/43 Doc ID 022098 Rev 1 L7986TA ...
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... L7986TA Figure 21. Junction temperature vs. output current VQFN HSOP V =5V OUT V =3.3V OUT V =1.8V OUT Figure 23. Junction temperature vs. output current VQFN HSOP V =3.3V OUT V =1.8V OUT V =1.2V OUT V = =250KHz SW T =25 C AMB Figure 25. Efficiency vs.output current 0.100 0.600 1.100 1.600 Io [A] Figure 22 ...
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... Doc ID 022098 Rev 1 10.0 15.0 20.0 25.0 30.0 35 1A/div 0.5A/div 1A/div 0.5A/div OUT OUT OUT OUT Time base 1ms/div Time base 1ms/div Time base 1ms/div Time base 1ms/div = Timebase 10us/div Timebase 10us/div L7986TA Io=1A Io=2A Io=3A 40.0 1V/div 0.5V/div 0.5V/div 1V/div ...
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... Application ideas 7.1 Positive buck-boost The L7986TA can implement the step-up/down converter with a positive output voltage. Figure 33. shows the schematic: one power MOSFET and one Schottky diode are added to the standard buck topology to provide 12 V output voltage with input voltage from 4 ...
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... Figure 34. Maximum output current according to max DC switch current (3.0 A 36/43 I OUT < ------------ - – OUT ⋅ < ------------ - 3.7A SW, – OUT ⋅ ----------------------------------- - – ⋅ ⋅ OUT SW Doc ID 022098 Rev 1 L7986TA Equation 38, also the peak Equation Equation ...
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... V D external power MOSFET. 7.2 Inverting buck-boost The L7986TA can implement the step-up/down converter with a negative output voltage. Figure 33. shows the schematic to regulate - further external components are added to the standard buck topology. The relationship between input and output voltage is: ...
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... Figure 36. Maximum output current according to switch max peak current (3.0 A 38/43 Figure 36. The dashed line considers a more accurate estimation of Equation 43, where power losses across diodes and the internal V – V OUT ---------------------------------------------------------------- - – V – OUT Doc ID 022098 Rev 1 L7986TA – ...
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... L7986TA 8 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: www.st.com. ® ECOPACK trademark. Table 10. HSOP8 mechanical data Dim ...
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... Package mechanical data Figure 37. Package dimensions 40/43 Doc ID 022098 Rev 1 L7986TA ...
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... L7986TA 9 Order codes Table 11. Order codes Order codes L7986TA L7986TATR Package HSOP8 HSOP8 Doc ID 022098 Rev 1 Order codes Packaging Tube Tape and reel 41/43 ...
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... Revision history 10 Revision history Table 12. Document revision history Date 11-Aug-2011 42/43 Revision 1 Initial release. Doc ID 022098 Rev 1 L7986TA Changes ...
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... L7986TA 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. ...