L7986 STMicroelectronics, L7986 Datasheet
L7986
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L7986 Summary of contents
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... C1 November 2011 3 A step-down switching regulator VFQFPN10 Description The L7986 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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 5.6 Hysteretic thermal shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 6 Application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 6.1 Input capacitor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 6.2 Inductor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 6.3 Output capacitor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 6.4 Compensation network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 6.4.1 6.4.2 6.5 Thermal considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 6.6 Layout considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 6.7 Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 7 Application ideas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 7.1 Positive buck-boost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 7.2 Inverting buck-boost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 2/44 Type III compensation network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Type II compensation network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Doc ID 022450 Rev 1 L7986 ...
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... L7986 8 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 9 Order codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 10 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Doc ID 022450 Rev 1 Contents 3/44 ...
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... OUT OUT OUT SYNCH SYNCH SYNCH SYNCH SYNCH SYNCH GND GND GND GND GND GND FSW FSW FSW FSW FSW FSW COMP COMP COMP COMP COMP COMP HSOP8 HSOP8 Description L7986 ...
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... L7986 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 VFQFPN Power dissipation at T < ...
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... FSW pin floating F =1 MHz =33 kΩ FSW Doc ID 022450 Rev 1 Values Min. Typ. 4.5 0.1 200 3.7 4.2 210 250 1.254 0 1000 <38 V 0.593 0.6 0.607 (1) <38 V 0.582 0.6 0.618 =0 1.2 7.5 7.4 8.2 2 L7986 Unit Max 4.5 0.4 mΩ 400 4.7 A 275 KHz V 100 % KHz V 2.4 mA μA 30 0.3 V μA 10 9.1 ms ...
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... L7986 Table 4. Electrical characteristics Symbol 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 S_IN_PW I Slave sink current ...
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... Functional description 5 Functional description The L7986 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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... L7986 5.1 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 connected to the FSW pin. If 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 5. Sawtooth: voltage and frequency feed-forward; external synchronization Figure 6. Oscillator frequency vs. FSW pin resistor 10/44 Doc ID 022450 Rev 1 L7986 ...
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... L7986 5.2 Soft-start The soft-start is essential to assure correct and safe startup of the step-down converter. It avoids inrush current surge and makes the output voltage increase monothonically. The soft-start is performed by a staircase ramp on the non-inverting input (V amplifier. So the output voltage slew rate is: Equation 1 where SR ...
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... LC filter, a type II compensation network can be used. Otherwise, a type III compensation network must be used (see network selection). Anyway, the methodology to compensate the loop is to introduce zeroes to obtain a safe phase margin. 12/44 GBWP Slew rate Chapter 6.4 Doc ID 022450 Rev 1 100 dB 4.5 MHz 7 V/μ 3 mA/25 mA for details of the compensation L7986 ...
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... L7986 5.4 Overcurrent protection The L7986 implements overcurrent protection by 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 returns 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. 14/44 ⋅ ⁄ – --------------------------------------------------------------------------------------------------------------- - OUT ( ⁄ DRC ON_MIN DSON compatible. CC Doc ID 022450 Rev 1 T ON_MIN 4. ⋅ * DCR + SW L7986 ...
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... L7986 6 Application information 6.1 Input capacitor selection The capacitor connected to the input must be capable of supporting 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 022450 Rev 1 can be written as follows ⋅ --- - + 1 D – η ) value is: IN_MIN ⋅ Rated Voltage ( 4.7 50 L7986 ...
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... L7986 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 obtained at maximum T OUT calculate minimum duty). So, by 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 022450 Rev 1 ΔI MAX + ------------------------------------ - ⋅ ⋅ OUT SW Rated voltage (V) ESR (mΩ 6.3 6 6.3 L7986 < 5 < 5 < 5 < 5 ...
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... Compensation network The compensation network must assure stability and good dynamic performance. The loop of the L7986 is based on the voltage mode control. The error amplifier is a voltage operational amplifier with high bandwidth. So, by selecting the compensation network the E/A is considered as ideal, that is, its bandwidth is much larger than the system one. ...
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... ----------------------------------------------- - Z1 ⋅ ⋅ 2π Doc ID 022450 Rev 1 s ------------------------- - ⋅ 2π f zESR 2 ⎛ ⎞ s ------------------ - + ⎝ ⎠ ⋅ 2π ------------------------------------------- - zESR ⋅ ⋅ 2π ESR C OUT ) ESR V OUT , R = -------------- OUT I OUT ----------------------------- - Z2 ⋅ ⋅ 2π L7986 ...
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... L7986 Equation 23 Figure 10. Type III compensation network In Figure 11 the Bode diagram of the PWM and LC filter transfer function (G and the open-loop gain (G 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 follows: 1 ...
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... Doc ID 022450 Rev 1 ⋅ ⋅ ⋅ ⋅ ⋅ – ---------------------------------------- - ⋅ ⋅ ⋅ 3 2π set higher than 500 kHz. SW =22 μF, ESR < 1 mΩ, the OUT , , , C 3.3nF C 22nF = = 3 4 L7986 ): LC C 220pF = 5 ...
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... L7986 Figure 12. Open-loop gain Bode diagram with ceramic output capacitor Doc ID 022450 Rev 1 Application information 23/44 ...
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... Bode diagram of the PWM and LC filter transfer function (G and the open-loop gain (G 24/ ----------------------------- - = ⋅ ⋅ 2π (f)=G · G (f) · G LOOP PW0 LC Doc ID 022450 Rev ------------------------------------------- - ⋅ ⋅ ⋅ ------------------- - 2π · G PW0 (f)) are drawn. TYPEII L7986 (f)) LC ...
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... L7986 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 follows: 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 is the ESR zero: ...
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... ------------------------------------------------------------- - ⋅ ⋅ 5 2π L=18 μ = OUT 1.1kΩ 150Ω Doc ID 022450 Rev 1 4 ⋅ ⋅ – 1 =330 μF, ESR=35 mΩ, the OUT , , 4.99kΩ 82nF C = 68pF 4 5 L7986 ...
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... L7986 Figure 15. Open-loop gain Bode diagram with electrolytic/tantalum output capacitor Doc ID 022450 Rev 1 Application information 27/44 ...
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... JA is the sum of the power losses just seen. TOT Doc ID 022450 Rev 1 of the power switch; these are DSON 2 ) ⋅ OUT overtemperature is DSON OUT ⋅ ⋅ ⋅ OUT SW SW ⋅ ⋅ P TOT L7986 and Figure 16. ...
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... L7986 of heat. The Rth JA paragraph, is about 60 °C/W for the VFQFPN package and about 40 °C/W for the HSOP package. Figure 16. Switching losses 6.6 Layout considerations The PC board layout of the switching the DC/DC regulator is very important to minimize the noise injected in high impedance nodes and interference generated by the high switching current loops ...
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... Application information Figure 17. Layout example 30/44 Doc ID 022450 Rev 1 L7986 ...
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... L7986 6.7 Application circuit In Figure 18 the demonstration board application circuit is shown. Figure 18. 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%, 0.1 W 0603 1.1 kΩ ...
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... Application information Figure 19. PCB layout: L7986 and L7986A (component side) Figure 20. PCB layout: L7986 and L7986A (bottom side) Figure 21. PCB layout: L7986 and L7986A (front side) 32/44 Doc ID 022450 Rev 1 L7986 ...
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... L7986 Figure 22. Junction temperature vs. output current VQFN HSOP V =5V OUT V =3.3V OUT V =1.8V OUT Figure 24. 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 26. Efficiency vs.output current ...
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... Doc ID 022450 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 L7986 Io=1A Io=2A Io=3A 40.0 1V/div 0.5V/div 1V/div 0.5V/div ...
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... Application ideas 7.1 Positive buck-boost The L7986 can implement the step-up/down converter with a positive output voltage. Figure 34. 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 35. Maximum output current according to max DC switch current (3.0 A 36/44 I OUT < ------------ - – OUT ⋅ < ------------ - 3.7A SW, – OUT ⋅ ----------------------------------- - – ⋅ ⋅ OUT SW Doc ID 022450 Rev 1 L7986 Equation 38, also the peak Equation 39, Equation ...
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... V D external power MOSFET. 7.2 Inverting buck-boost The L7986 can implement the step-up/down converter with a negative output voltage. Figure 34. 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 37. Maximum output current according to switch max. peak current (3.0 A 38/44 Figure 37. The dashed line considers a more accurate estimation of Equation 43, where power losses across diodes and the internal V – V OUT ---------------------------------------------------------------- - – – OUT Doc ID 022450 Rev 1 V – D L7986 ...
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... L7986 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. Doc ID 022450 Rev 1 Package mechanical data ...
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... Figure 38. Package dimensions 40/44 mm Min. Typ. Max. 0.80 0.90 1.00 0.02 0.05 0.70 0.20 0.18 0.23 0.30 2.95 3.00 3.05 2.21 2.26 2.31 2.95 3.00 3.05 1.49 1.64 1.74 0.50 0.3 0.40 0.5 0.75 0.25 Doc ID 022450 Rev 1 L7986 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 0.087 0.089 0.0906 0.1161 0.1181 0.1200 0.0587 0.0646 0.0685 0.0197 0.0118 0.0157 0.0197 0.0295 0.0098 7 ...
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... L7986 Table 11. HSOP8 mechanical data Dim Min ccc Figure 39. Package dimensions mm Typ. Max. 1.70 0.00 0.15 1.25 0.31 0.51 0.17 0.25 4.80 4.90 5.00 5.80 6.00 6.20 3.80 3.90 4.00 1.27 0.25 0.50 0.40 1. 0.10 Doc ID 022450 Rev 1 Package mechanical data inch Min. Typ. Max. 0.0669 0.00 0.0059 0.0492 0.0122 0.0201 0.0067 0.0098 0.1890 0.1929 0.1969 0.2283 ...
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... Order codes 9 Order codes Table 12. Order codes Order codes L7986 L7986A L7986TR L7986ATR 42/44 Package VFQFPN10 HSOP8 VFQFPN10 HSOP8 Doc ID 022450 Rev 1 L7986 Packaging Tube Tube Tape and reel Tape and reel ...
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... L7986 10 Revision history Table 13. Document revision history Date 07-Nov-2011 Revision 1 Initial release. Doc ID 022450 Rev 1 Revision history Changes 43/44 ...
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... Australia - Belgium - Brazil - Canada - China - Czech Republic - Finland - France - Germany - Hong Kong - India - Israel - Italy - Japan - Malaysia - Malta - Morocco - Philippines - Singapore - Spain - Sweden - Switzerland - United Kingdom - United States of America 44/44 Please Read Carefully: © 2011 STMicroelectronics - All rights reserved STMicroelectronics group of companies www.st.com Doc ID 022450 Rev 1 L7986 ...