L5980 0.7 A step-down switching regulator Features ■ 0.7 A DC output current ■ 2.9 V to 18 V input voltage ■ Output voltage adjustable from 0.6 V ■ 250 kHz switching frequency, programmable up to 1 MHz ■ Internal soft-start and inhibit ■ Low dropout operation: 100% duty cycle Description ■ Voltage feed-forward ■ Zero-load current operation ■ Overcurrent and thermal protection ■ VFQFPN8 3 x 3 mm package The L5980 is step-down switching regulator with 1 A (min.
Contents L5980 Contents 1 2 Pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1 Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.1 Absolute maximum ratings .
L5980 Contents 8 Order codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 9 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pin settings L5980 1 Pin settings 1.1 Pin connection Figure 2. Pin connection (top view) OUT SYNCH GND INH FSW COMP 1.2 FB Pin description Table 1. 4/42 VCC Pin description Pin n° Type 1 OUT Description Regulator output 2 SYNCH 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.
L5980 Maximum ratings 2 Maximum ratings 2.1 Absolute maximum ratings Table 2. Absolute maximum ratings Symbol Parameter Vcc Input voltage OUT Output DC voltage -0.3 to VCC -0.3 to 4 INH Inhibit pin -0.3 to VCC FB Feedback voltage -0.3 to 1.5 PTOT Unit 20 FSW, COMP, SYNCH Analog pin 2.2 Value Power dissipation at TA < 60 °C V 1.5. W TJ Junction temperature range -40 to 150 °C Tstg Storage temperature range -55 to 150 °C Thermal data Table 3.
Electrical characteristics 3 L5980 Electrical characteristics TJ = 25 °C, VCC = 12 V, unless otherwise specified. Table 4. Electrical characteristics Values Symbol Parameter Test condition Unit Min VCC Operating input voltage range (1) VCCON Turn on VCC threshold (1) VCCHYS VCC UVLO hysteresis (1) RDS(on) MOSFET on resistance ILIM 2.9 Max 18 2.9 0.175 V 0.3 140 170 140 220 1.0 1.3 1.
L5980 Electrical characteristics Table 4. Electrical characteristics (continued) Values Symbol Parameter Test condition Unit Min Typ Max VCH High level output voltage VFB < 0.6 V VCL Low level output voltage VFB > 0.6 V IFB Bias source current VFB = 0 V to 0.8 V 1 μA VFB = 0.5 V, VCOMP = 1 V 20 mA Sink COMP pin VFB = 0.7 V, VCOMP = 1 V 25 mA Open loop voltage gain (2) 100 dB IO SOURCE Source COMP pin IO SINK GV 3 V 0.1 Synchronization function High input voltage 2 3.
Functional description 4 L5980 Functional description The L5980 is based on a “voltage mode”, constant frequency control. The output voltage VOUT is sensed by the feedback pin (FB) compared to an internal reference (0.6 V) providing an error signal that, compared to a fixed frequency sawtooth, controls the on and off time of the power switch. The main internal blocks are shown in the block diagram in Figure 3.
L5980 4.1 Functional description 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 is left floating the frequency is 250 kHz; it can be increased as shown in Figure 6 by external resistor connected to ground.
Functional description 10/42 L5980 Figure 5. Sawtooth: voltage and frequency feed forward; external synchronization Figure 6.
L5980 4.2 Functional description 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 (VREF) of the error amplifier.
Functional description 4.3 L5980 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. In this device the error amplifier is a voltage mode operational amplifier so with high DC gain and low output impedance.
L5980 4.4 Functional description Overcurrent protection The L5980 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” or “blanking time”. The masking time is about 200 ns.
Functional description Figure 8. 4.5 L5980 Overcurrent protection strategy 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. The pin is also VCC compatible. 4.
L5980 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 subject to a pulsed current, the RMS value of which is dissipated over its ESR, affecting the overall system efficiency.
Application information 5.2 L5980 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.
L5980 5.3 Application information 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 and discharge of the output capacitor) and the resistive component (due to the voltage drop across its ESR). So the output capacitor has to be selected in order to have a voltage ripple compliant with the application requirements.
Application information 5.4 L5980 Compensation network The compensation network has to assure stability and good dynamic performance. The loop of the L5980 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. The transfer functions of PWM modulator and the output LC filter are studied (see).
L5980 Application information Equation 13 s 1 + ------------------------2π ⋅ f zESR G LC ( s ) = ------------------------------------------------------------------------2 s s 1 + ---------------------------+ ⎛⎝ -------------------⎞⎠ 2π ⋅ f LC 2π ⋅ Q ⋅ f LC where: Equation 14 1 f LC = -----------------------------------------------------------------------, ESR 2π ⋅ L ⋅ C OUT ⋅ 1 + --------------R OUT 1 f zESR = ------------------------------------------2π ⋅ ESR ⋅ C OUT Equation 15 R OUT ⋅ L ⋅ C OUT ⋅ ( R
Application information L5980 Equation 17 f P0 = 0, 1 -, f P1 = ----------------------------2π ⋅ R 3 ⋅ C 3 1 f P2 = ------------------------------------------C4 ⋅ C5 ------------------2π ⋅ R 4 ⋅ C4 + C5 Figure 10. Type III compensation network In Figure 11 the Bode diagram of the PWM and LC filter transfer function (GPW0 · GLC(f)) and the open loop gain (GLOOP(f) = GPW0 · GLC(f) · GTYPEIII(f)) are drawn. Figure 11.
L5980 Application information Equation 18 BW ⋅ K R 4 = ------------------ ⋅ R 1 f LC where K is the feed forward constant and 1/K is equals to 9. 3. Calculate C4 by placing the zero at 50% of the output filter double pole frequency (fLC): Equation 19 1 C 4 = --------------------------π ⋅ R 4 ⋅ f LC 4. Calculate C5 by placing the second pole at four times the system bandwidth (BW): Equation 20 C4 C 5 = ------------------------------------------------------------2π ⋅ R 4 ⋅ C 4 ⋅ 4 ⋅ BW – 1 5.
Application information L5980 Figure 12.
L5980 5.4.2 Application information 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 is: 2π * ESR * COUT > 1/BW), this zero helps stabilize the loop. 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. Figure 13.
Application information L5980 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. Choose a value for R1, usually between 1 kΩ and 5 kΩ, in order to have values of C4 and C5 not comparable with parasitic capacitance of the board. 2.
L5980 Application information Equation 25 C4 C 5 = ------------------------------------------------------------2π ⋅ R 4 ⋅ C 4 ⋅ 4 ⋅ BW – 1 For example with VOUT = 1.2 V, VIN = 12 V, IO = 0.7 A, L = 22 μH, COUT = 220 μF, ESR = 50 mΩ, the type II compensation network is: R 1 = 1.1kΩ, R 2 = 249Ω, R 4 = 12kΩ, C 4 = 47nF, C 5 = 68pF In Figure 15 is shown the module and phase of the open loop gain. The bandwidth is about 35 kHz and the phase margin is 49°.
Application information L5980 Figure 15.
L5980 5.5 Application information 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 not negligible RDS(on) of the power switch; these are equal to: Equation 26 2 P ON = R DS ( on ) ⋅ ( I OUT ) ⋅ D Where D is the duty cycle of the application and the maximum RDS(on) is 300 mΩ.
Application information L5980 of heat. The RthJA measured on the demonstration board described in the following paragraph is about 60 °C/W. 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.
L5980 Application information Figure 17.
Application information 5.7 L5980 Application circuit In Figure 18 the demonstration board application circuit is shown. Figure 18. Demonstration board application circuit VIN=3.3V to 18V INH GND C1 C6 10uF 68nF L1 15uH OUT VCC 8 1 3 2 SYNCH D1 STPS2L25U L5985 L5980 7 Vout=3.3V C2 R1 4.99K FB 22uF 5 6 FSW 4 C4 10nF COMP R5 100K R3 180 R4 3.9K C3 3.3nF R2 1.1K C5 150pF Table 9.
L5980 Application information Figure 19. PCB layout (component side) Figure 20. PCB layout (bottom side) Figure 21.
Application information L5980 Figure 22. Junction temperature vs output current Figure 23. Junction temperature vs output current Figure 24. Junction temperature vs output current Figure 25. Efficiency vs output current 95 E fficiency [% ] 90 Vo=5.0V 85 Vo=3.3 80 Vo=2.5V VCC=12V FSW =250KHz 75 70 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Io [A] Figure 26. Efficiency vs output current Figure 27. Efficiency vs output current 94 95 92 E ffic ie n c y [% ] E ffic ie n c y [% ] 88 Vo=2.
L5980 Application information Figure 28. Load regulation Figure 29. Line regulation 0.4 0.14 FSW=250KHz 0.35 Δ V F B /V F B [% ] ΔVFB/VFB [%] 0.12 0.1 0.08 VCC=3.3V 0.06 VCC=5.0V 0.04 0.3 0.25 0.2 0.15 0.1 Io=0.7A 0.05 VCC=12V 0.02 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0 -0.05 2 8 10 12 14 16 18 Figure 31. Load transient: from 0.1 A to 0.7 A OUT VOUT 50mV/div AC coupled 10V/div OUTPUT SHORTED 6 VCC [V] Io [A] Figure 30.
Application ideas 6 Application ideas 6.1 Positive buck-boost L5980 The L5980 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 2.9 V to 18 V. Figure 33.
L5980 Application ideas Equation 32 I OUT I SW = ------------- < 0.7 A 1–D where ISW is the average current in the embedded power MOSFET in the ON time. To chose the right value of the inductor and to manage transient output current, that for short time can exceed the maximum output current calculated by Equation 32, also the peak current in the power MOSFET has to be calculated. The peak current, showed in Equation 33, must be lower than the minimum current limit (1.
Application ideas L5980 Figure 34. Maximum output current according to max DC switch current (0.7 A): VO=12V Equation 34 V OUT + 2 ⋅ V D D = ------------------------------------------------------------------------------------------V IN – V SW – V SWE + V OUT + 2 ⋅ V D where VD is the voltage drop across diodes, VSW and VSWE across the internal and external power MOSFET. 6.2 Inverting buck-boost The L5980 can implement the step up/down converter with a negative output voltage.
L5980 Application ideas As in the positive one, in the inverting buck-boost the current flowing through the power MOSFET is transferred to the load only during the OFF time. So according to the maximum DC switch current (0.7 A), the maximum output current can be calculated from the Equation 32, where the duty cycle is given by Equation 36. Figure 35.
Package mechanical data 7 L5980 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® is an ST trademark.
L5980 Package mechanical data Table 10. VFQFPN8 (3 x 3 x 1.08 mm) mechanical data mm inch Dim. Min Typ Max Min Typ Max 0.80 0.90 1.00 0.0315 0.0354 0.0394 A1 0.02 0.05 0.0008 0.0020 A2 0.70 0.0276 A3 0.20 0.0079 A b 0.18 0.23 0.30 0.0071 0.0091 0.0118 D 2.95 3.00 3.05 0.1161 0.1181 0.1200 D2 2.23 2.38 2.48 0.0878 0.0937 0.0976 E 2.95 3.00 3.05 0.1161 0.1181 0.1200 E2 1.49 1.64 1.74 0.0587 0.0646 0.0685 e L 0.50 0.30 0.40 ddd 0.0197 0.50 0.
Order codes 8 L5980 Order codes Table 11. Order codes Order codes Package L5980 Packaging Tube VFQFPN8 (3 x 3 x 1.
L5980 9 Revision history Revision history Table 12.
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