l6997 STMicroelectronics, l6997 Datasheet
l6997
Available stocks
Related parts for l6997
l6997 Summary of contents
Page 1
... Drivers current capability allows output currents in excess of 20A. Rin2 Rin1 Cin OSC Dboot BOOT HGATE HS Cboot PHASE PGOOD LGATE OVP LS DS L6997 PGND ILIM GND GNDSENSE VSENSE SS INT VFB Vref SHDN Cvref L6997 TSSOP20 Package L6997D TSSOP20 Tape & Reel 3.3V L 0.6V Ro1 Cout Ro2 REV. 4 1/30 ...
Page 2
... L6997 Table 2. Absolute Maximum Ratings Symbol GND GND DR DR HGATE and BOOT, to PHASE HGATE and BOOT, to PGND V PHASE PHASE LGATE to PGND ILIM, VFB, VSENSE, NOSKIP, SHDN, PGOOD, OVP, VREF, INT, GND to GND SENSE P Power dissipation at T tot T Storage temperature range stg Table 3 ...
Page 3
... Input bias current LIM Zero Crossing Comparator offset Phase-gnd K Current limit factor ILIM Description Test Condition Vout=Vref Fsw=110Khz Iout=1A VFB > VREF VFB > VREF SHDN to GND SHDN to GND 200K ILIM L6997 Min. Typ. Max. Unit 5.5 V 2.86 2.97 V 2.75 2 ...
Page 4
... L6997 Table 5. Electrical Characteristics (continued 3.3V 0°C to 85°C unless otherwise specified amb Symbol Parameter ON TIME Ton On time duration OFF TIME T Minimum off time OFFMIN K /T OSC OFFMIN VOLTAGE REFERENCE VREF Voltage Accuracy PWM COMPARATOR Input voltage offset I Input Bias Current ...
Page 5
... Figure 4. Functional & Block Diagram VCC OSC VSENSE OSC VSENSE L6997 5/30 ...
Page 6
... L6997 4 DEVICE DESCRIPTION 4.1 Constant On Time PWM topology Figure 5. Loop block schematic diagram Vin R1 One-shot generator OSC R2 Vsense Vref R4 The device implements a Constant On Time control scheme, where the Ton is the high side MOSFET on time duration forced by the one-shot generator. The On Time is directly proportional to VSENSE pin voltage and in- ...
Page 7
... DC pole in the control loop. C INT1 DC Error Offset Vref INT2 g INT OUT = ------------------------------ - the output divider ratio given from Eq4 and F OUT is connected between INT pin and ground. C INT2 also provides INT1 <Vout> Time can be connected between INT pin and (5) INT2 L6997 given 7/30 ...
Page 8
... On Time and Off Time fixed On Time topology , the increase of the losses generates only a variation on the Off Time, changing the switching frequency. In L6997 is implemented the voltage feed-forward circuit that allows constant switching frequency during steady-sate operation and withinthe input range variation. ...
Page 9
... In order to calculate the output voltage chargin time it should be considered that the inductor current function can be supposed linear function of the time the NOSKIP pin. CC Vss Soft-start active range Maximum current limit 1V ------- - Iss ilim dson ILIM SS = -------------------------------------------------------------------------- - and V . Note that the higher IN OUT Time Time (7) t (8) L6997 ). SS 9/30 ...
Page 10
... L6997 so considering zero the output load the output voltage is given by: Q t,C V t,C = ------------------------ - out SS indicating with V the final value, the output charging time can be estimated as: out out SS the minimum C value is given imposing this condition: SS 4.5 Current limit The current limit comparator senses the inductor current through the low side MOSFET RDS pares this value with the ILIM pin voltage value ...
Page 11
... When the 3.3V bus is used to supply the drivers, ULTRA LOGIC LEVEL MOSFETs should be selected , to be sure that the MOSFETs work in properly way (14 gTOT SW f SW0 ------------ - 75nC (15 SW0 ------------ - 125nC (16 150°C. If the system temperature is lower the 125nC. MAXLS L6997 G 11/30 ...
Page 12
... NOINT are closed and the jumpers named with INT are open the NON INTEGRATOR configuration is selected. Refer to the Table 1 and 2 for the jumpers connection. Figure 10. Demoboard Schematic Diagram R7 C11 C10 R5 R10 TP1 PGOOD OVP TP2 L6997 ILIM R8 C12 SHDN SD 12/30 from 3. ...
Page 13
... DEMOBOARD LAYOUT Real dimensions: 4 2,7 cm (1.85 inch X 1. 063 inch) Figure 11. Top side components placement Figure 12. Bottom side Jumpers distribution Connection C1 Mounted C2 Mounted * INT Close Open Connection C1 Not mounted C2 Not Mounted INT Open Close Figure 13. Top side layout Figure 14. Bottom side layout L6997 13/30 ...
Page 14
... L6997 Table 8. PCB Layout guidelines Goal To minimize radiation and magnetic coupling with the adjacent circuitry. To maximize the efficiency. To ensure high accuracy in the current sense system. To reduce the noise effect on the IC. Table 9. Component list The component list is shared in two sections: the first for the general-purpose component, the second for ...
Page 15
... All capacitors are intended ceramic type otherwise specified. 5.4 EFFICIENCY CURVES Source mode 1.25V F = 270kHz IN OUT SW Figure 15. Efficiency vs output current Eff [%] 100,0 90,0 80,0 70,0 60,0 50,0 40,0 30,0 20,0 10,0 0,0 0,0 Dimension 2R5TPE220M POSCAP DO3316P-272HC COILCRAFT STMicroelectronics Double mosfet in sigle package STMicroelectronics 3 = 1.25V, F OUT SW 1,0 2,0 3,0 4,0 Current [A] PFM mode Notes = 270kHz with an input voltage around V 5,0 6,0 PWM mode L6997 = 15/30 ...
Page 16
... L6997 6 STEP BY STEP DESIGN Application conditions 3.3V, ±10 6.1 Input capacitor. A pulsed current (with zero average value) flows through the input capacitor of a buck converter. The AC com- ponent of this current is quite high and dissipates a considerable amount of power on the ESR of the capacitor CIN ...
Page 17
... By selecting identical ON Lmin 2 H Vin Vo – Vo ---------------------- - -------- - T (21 Vin V 25mV ripple -------------------- - = = --------------- - = 20m I 1.25 ---- - 2 1 ---------- - I = (23) rms 330 F EEFUE0D331R PANASONIC 220 F 2R5TPE220M POSCAP (22) and its ESR, ESRC OUT must be greater than VINMAX BRDSS L6997 , OUT 17/30 ...
Page 18
... Once output divider and frequency divider have been designed as to obtain OUT the required output voltage and switching frequency, the following equation gives the smallest input voltage, which allows L6997 to regulate (which corresponds 6.6 Voltage Feedforward From the equations 1,2 and 3, choosing the switching frequency of 270kHz the resistor divider can be selected. ...
Page 19
... In this way, changing the pow MOSFETs possible evaluate the device performance in differ- IN OUT and V are both present; the other one, near to R11 is used CC IN 4,0 5 OUT OUT . On the top side CC can be applied too. If the correct sequence CC L6997 = 15A [from 19/30 ...
Page 20
... ESR capacitor. See the integrator section. Table 11. Jumper connection without integrator Component C4 C7 INT NOINT 20/30 R5 C22 C3 D1 VDR VCC OSC BOOT SS C20 HGATE R8 C19 PHASE L6997 Q4, Q5, Q6 SHDN LGATE NOSKIP OVP PGOOD PGND GND VSENSE GNDSENSE NOINT INT INT FB VREF C6 Connection Mounted Mounted* Close Open ...
Page 21
... Put the feedback component (like output divider, integrator network, etc) as close as possible to the IC. 2) Keep the feedback traces parallel and as close as possible. Moreover they must be routed as far as possible from the switching current loops. 3) Make the controller ground connection like the figure 8. L6997 , High Side IN 21/30 ...
Page 22
... F C15 C18 47 F INDUCTOR L1 1.8 H POWER MOS Q1,Q2 SI4442DY Q5,Q6 SI4442DY INTEGRATED CIRCUIT U1 L6997 22/30 Dimension GENERAL-PURPOSE SECTION 0603 Output resistor divider for the linear regulator. 0603 0603 Input resistor divider (To set switching frequency) 0603 0603 0603 0603 Current limit resistor (To set current limit) ...
Page 23
... Output resistor divider (To set output voltage) 0603 0603 0805 KEMET-16V 0805 0603 First integrator capacitor 0603 0603 0603 Second integrator capacitor 0805 0603 Softstart capacitor 0603 0805 0603 N.M. Vout=2.5V Vout=1.8V Vout=1.5V Vout=1.2V Vout=0. 25V) IN Notes L6997 23/30 ...
Page 24
... C17, C15 C18 INDUCTOR POWER MOS Q1,Q2 STS11NF3LL Q5,Q6 STS11NH3LL DIODES D2 STPS2L25U INTEGRATED CIRCUIT U1 L6997 NOTE: For the 25V to 12V conversion the inductor used is: 77120A core 7T. 7.4 EFFICIENCY CURVES Figure 23. Efficiency vs output Current 100 Vin = Vcc = 5V 70 Fsw = 200KHz ...
Page 25
... Supply is 2.5V and the Termination voltage is 1.25Vwhile for the DDRII the Memory Supply is 1.8V and the Ter- mination voltage is 0.9V. Figure 27 shows a complete DDRII Memory and Termination Supply realized by using 2 x L6997. The 1.8V section is powering the memory, while the 0.9V section is providing the termination voltage. Figure 27. Application Idea: DDRII Memory Supply ...
Page 26
... L6997 The current required by the Memory and Termina- tion supply, depends on the memory type and size. The figures 28 and 29 show the efficiency of the L6997 for the termination section of the appli- cation shown in fig.27 Figure 28. Eff. vs. Output Current Source Mode 100 95 90 ...
Page 27
... Figure 33. Normal functionality in PFM mode. Ch1-> Inductor current Ch2-> Phase Node Ch3-> Output voltage Figure 34. Start up waveform with 0A load. Ch1-> Inductor current Ch2-> Soft start Voltage Ch3-> Output voltage Figure 35. Start up waveform with 5A load.. Ch1-> Inductor current Ch2-> Soft start Voltage Ch3-> Output voltage L6997 27/30 ...
Page 28
... L6997 Figure 36. TSSOP20 Mechanical Data & Package Dimensions mm DIM. MIN. TYP. MAX. A 1.20 A1 0.050 0.150 A2 0.800 1.000 1.050 b 0.190 0.300 c 0.090 0.200 D (1) 6.400 6.500 6.600 E 6.200 6.400 6.600 E1 (1) 4.300 4.400 4.500 e 0.650 L 0.450 0.600 0.750 L1 1.000 k 0˚ (min.) 8˚ (max.) aaa 0 ...
Page 29
... Table 15. Revision History Date Revision November 2003 May 2004 3 First Issue in the DMS EDOCS database. 4 Data values changed on the pages section 6.4 last two paragraph on the page 18; section 6.9 on the page 19 Description of Changes L6997 29/30 ...
Page 30
... L6997 Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publication are subject to change without notice ...