LTC3816 Single-Phase Wide VIN Range DC/DC Controller for Intel IMVP-6/IMVP-6.5 CPUs Description Features n n n n n n n n n n n n n Supports 7-Bit IMVP-6/IMVP-6.5 VID Code and Features Wide VIN Range: 4.
LTC3816 Absolute Maximum Ratings (Notes 1, 8) Input Supply Voltage (VIN).......................... –0.3V to 40V Topside Driver Voltage (BOOST)................. –0.3V to 46V Switch Voltage (SW)...................................... –5V to 40V INTVCC, EXTVCC, (BOOST-SW) . ................. –0.3V to 6V ISENN, ITCFB, PREIMON, IMON, RPTC, VRON, VCC(SEN), VFB, SS, VIDn, RFREQ, MODE/SYNC, LFF, ISENP, IMAX ..........................–0.3V to INTVCC + 0.3V PWRGD, CLKEN# . ....................................... –0.
LTC3816 Order Information LEAD FREE FINISH LTC3816EFE#PBF LTC3816IFE#PBF LTC3816EUHF#PBF TAPE AND REEL LTC3816EFE#TRPBF LTC3816IFE#TRPBF LTC3816EUHF#TRPBF PART MARKING* LTC3816FE LTC3816FE 3816 PACKAGE DESCRIPTION 38-Lead Plastic eTSSOP 38-Lead Plastic eTSSOP 38-Lead (5mm × 7mm) Plastic QFN LTC3816IUHF#PBF LTC3816IUHF#TRPBF 3816 38-Lead (5mm × 7mm) Plastic QFN Consult LTC Marketing for parts specified with wider operating junction temperature ranges.
LTC3816 Electrical Characteristics The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, BSOURCE = EXTVCC = 0V, VRON = 5V, unless otherwise noted. (Notes 2, 3) SYMBOL PARAMETER CONDITIONS MIN TYP MAX VBOOT Core Supply Start-Up Voltage VIMON = INTVCC (IMVP-6 Configuration) VIMON < 1.1V (IMVP-6.5 Configuration) VOVF Overvoltage Fault Threshold VIMON = INTVCC (IMVP-6 Configuration) VIMON < 1.1V (IMVP-6.
LTC3816 Electrical Characteristics The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, BSOURCE = EXTVCC = 0V, VRON = 5V, unless otherwise noted. (Notes 2, 3) SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS VID, DPRSLPVR, LFF Parameters VIL(VID) VID Input Low Threshold VIH(VID) VID Input High Threshold 0.3 0.
LTC3816 Typical Performance Characteristics Efficiency vs Load Current 90 80 100 VIN = 12V, fOSC = 400kHz VCC(CORE) = 0.75V, VEXTVCC = 0V LAST PAGE CIRCUIT 90 80 EFFICIENCY (%) EFFICIENCY (%) 70 60 PULSE-SKIPPING MODE 50 40 30 FORCED CONTINUOUS MODE 20 Efficiency vs VCC(CORE) VIN = 12V, fOSC = 400kHz, VEXTVCC = 0V FORCED CONTINOUS MODE LAST PAGE CIRCUIT 0.1 1 LOAD CURRENT (A) 50 40 30 VCC(CORE) = 0.50V VCC(CORE) = 0.75V VCC(CORE) = 1.00V VCC(CORE) = 1.20V 0 0.01 10 0.
LTC3816 Typical Performance Characteristics Line Regulation Load Regulation vs Temperature 0.7520 0 5A LOAD ∆VCC(CORE) (mV) –20 PTC CONFIGURATION (FIGURE 12) RLPTC = VISHAY TFPT1206L1002FV RVDCRP = 23.2k, CVDCRP = 10nF NTC CONFIGURATION, LAST PAGE CIRCUIT NO TEMPERATURE COMPENSATION LAST PAGE CIRCUIT, REPLACE NTC WITH 10k RESISTOR IDEAL VALUE 10A LOAD –30 –40 –50 20A LOAD –60 –70 –80 –90 VIN = 12V, fOSC = 400kHz VEXTVCC = 0V, AVP = –3mV/A L = VISHAY IHLP5050CE01 0.
LTC3816 Typical Performance Characteristics Start-Up to VBOOT VBOOT to PWRGD Delay VRON Shutdown VCC(CORE) 200mV/DIV VCC(CORE) 200mV/DIV VCC(CORE) 200mV/DIV CLKEN# 5V/DIV CLKEN# 5V/DIV PWRGD 5V/DIV CLKEN# 5V/DIV PWRGD 5V/DIV VRON 5V/DIV VRON 5V/DIV PWRGD 5V/DIV VRON 5V/DIV 3816 G16 100µs/DIV VIN = 12V IMVP6 CONFIGURATION CSS = 470pF VID = 0.75V NO LOAD 3816 G17 2ms/DIV VIN = 12V IMVP6 CONFIGURATION CSS = 470pF VID = 0.75V NO LOAD Momentary Overcurrent, 45µs IMAX Pulse VIN = 12V VID = 0.
LTC3816 Typical Performance Characteristics Duty Cycle vs VCOMP without Line Feedforward 70 500 fOSC (kHz) 60 50 40 RFREQ FLOATS 400 300 30 20 VRFREQ = 0V 200 10 1.0 1.2 1.4 1.6 1.8 VCOMP (V) 2.0 2.2 100 –50 –25 2.4 50 25 75 0 TEMPERATURE (°C) 100 IIMAX, IRFREQ and IRPTC vs Temperature 105.0 1.4 11.25 102.5 1.3 IRFREQ, IIMAX (µA) 97.5 10.50 95.0 10.25 92.5 IRFREQ, IIMAX 10.00 90.0 9.75 87.5 50 25 75 0 TEMPERATURE (°C) 100 IRPTC (µA) 10.75 85.0 125 1.
LTC3816 Typical Performance Characteristics EXTVCC Switchover Voltage vs Temperature EXTVCC Voltage Drop vs Temperature 120 VEXTVCC – VINTVCC (mV) 100 4.6 EXTVCC RAMPS HIGH 4.5 4.4 4.3 4.2 EXTVCC RAMPS LOW 4.
LTC3816 Pin Functions (eTSSOP/QFN) ISENN (Pin 1/Pin 36): Current Sense Negative Input. Connect this pin to the negative terminal of the current sense resistor or the negative terminal of the inductor DCR lowpass filter. ITCFB (Pin 2/Pin 37): Inductor DCR Temperature Compensation Amplifer Feedback Input. To derive the temperature compensated voltage dropped across the inductor DCR, connect a resistor from the SW node to this pin.
LTC3816 Pin Functions (eTSSOP/QFN) CSLEW (Pin 15/Pin 12): VID DAC Slew Rate Control. CSLEW is internally pulled up by a current source. Add a capacitor to program the VID DAC transition slew rate. If slow slew rate is selected, a 100pF capacitor connected to CSLEW results in a VID DAC slew rate of 1.25mV/µs. When slow slew rate is disabled, a 100pF capacitor results in a VID DAC slew rate of 5mV/µs. Avoid coupling high frequency switching signals to this pin. For the IMVP-6.
LTC3816 Pin Functions (eTSSOP/QFN) SW (Pin 32/Pin 29): Switching Node. Connect SW to the source of the upper power MOSFET and to the negative terminal of the BOOST pin decoupling capacitor. PWRGD (Pin 33/Pin 30): Open-Drain Power Good Output/Power Bad Latchoff Input. PWRGD is an open-drain output pin and can be connected to other open-drain outputs to implement wire-ORing. PWRGD is externally pulled high 10ms after the output regulates.
LTC3816 Functional Diagram 3.3V 3.3V 1.9k 1.1V 1.9k PWRGD CINTVCC 56Ω CLKEN# VRTT# DPRSLPVR LFF PWRGD INTVCC EXTVCC EN CLK 10µA/40µA TSD 0.5V/1.6V TG SAW LFF VIN EN CLK 1µA 10µA PWRGD RFREQ DELAY AND LATCH + PWM – 1.2V OVF SS PPG 10µA IMAX 1x VAVP + – 2.4V INTVCC + – CC CC1 RSER 1.3V DAC – VAVP DAMP VSS(SEN) RPAR CVDCR ITC RPREIMON IMON RC CIDCR RAVPDCRN PREIMON VFB COMP RIMAX AITC ITCFB DA OUT + – RIDCR ISENP ISENN EA + GND –ILIM+ DAC + 0.
LTC3816 Operation (Refer to Funtional Diagram) Table 1. IMVP-6/IMVP-6.
LTC3816 OPERATION (Refer to Funtional Diagram) The LTC3816 is a constant frequency, voltage mode DC/DC step-down controller that complies with the Intel IMVP‑6/ IMVP-6.5 specifications. The 7-bit VID code programs the switcher output voltage as specified in Table 1. Figure 2 shows the timing diagram. Upon start-up, the switcher output soft-start ramps to the VBOOT voltage.
LTC3816 Applications Information LDO, INTVCC/EXTVCC Power Supply The LTC3816 is designed to operate with a wide range of VIN input voltages. The IC includes a 5.2V LDO to power the driver and control circuits. The LDO output, INTVCC should be bypassed with a minimum 4.7µF low ESR ceramic capacitor.
LTC3816 APPLICATIONS INFORMATION down mode by pulling the VRON pin below 0.65V. In the shutdown mode, the internal circuitry and the INTVCC regulator are off and the supply current drops well below 100µA. When the VRON pin voltage is between 0.65V and 1.2V, the INTVCC regulator and internal circuitry power up but the driver outputs remain low. Topside MOSFET Driver Supply An external bootstrap capacitor, CB, connected from the BOOST pin to the SW pin supplies the topside gate driver as shown in Figure 1.
LTC3816 APPLICATIONS INFORMATION achieve accurate current sensing. Figure 4 shows a real current sensing resistor, RSENSE, which can be modeled with an ideal resistance, RSEN, in series with its parasitic ESL. As shown in Figure 4, the voltage across the sense resistor includes the voltage across the parasitic inductor which is a strong function of inductor ripple current and the switching frequency. This effectively reduces the current limit threshold, typically by more than 30%.
LTC3816 APPLICATIONS INFORMATION Note that the value of RDCR must account for its temperature coefficient, which is approximately 0.39%/°C. The current limit architecture of the LTC3816 allows short durations of instantaneous overload. Upon power-up, the current limit threshold is set to 1×, equal to ILIMIT . The load is limited to ILIMIT until the switcher output reaches its VBOOT potential.
LTC3816 Active Voltage PositioNing (AVP) The AVP circuit obtains the load current information from the sense resistor or the inductor DCR as shown in Figure 8. The voltage drop across the sense resistor is extracted VOUT 50mV/DIV ILOAD 10A/DIV VSW 20V/DIV VIN = 12V VOUT = 1V ILOAD = 0A TO 20A 20µs/DIV 3816 F07a Figure 7a. Transient Waveform Without AVP. The Transient Peak-to-Peak Spike ≈ 130mV. The AITC Amplifier is Configured as a Unity-Gain Amplifier 3 1.00 0 PROGRAMMABLE AVP SLOPE 0.97 –3 0.
LTC3816 APPLICATIONS INFORMATION where AAVP(SR) is the AVP gain with sense resistor configuration and AG(SR) is the sense resistor gain: A AVP(SR) = A G(SR) • RSEN R and A G(SR) = VSR tt R AVPSR ESL R VSR • C VSR = RSEN Figure 9 shows the AVP configuration with current sense implemented using the inductor DCR. The AVP DC transfer function is: VIN IL QT TG L SW QB BG LTC3816 BSOURCE – AITC + ESL RSEN VOUT SENSE RESISTOR D + COUT RAVPSR ITCFB CVSR ITC RVSR ISENN 3916 F08 Figure 8.
LTC3816 APPLICATIONS INFORMATION 1.02 1.00 ) With the NTC resistor network, the temperature compensated AVP transfer function becomes: VOUT = VDAC – AAVP(DCRN) • IL = VDAC – AG(DCRN) • IL • RDCR where AAVP(DCRN) and AG(DCRN) are the AVP and DCR gain using the inductor DCR current sense with NTC temperature compensation configuration.
LTC3816 APPLICATIONS INFORMATION resistance (0.39%/°C) and produces a near perfect AVP slope across temperature. VOUT = VDAC – AAVP(DCRP) • IL = VDAC – AG(DCRP) • IL • RDCR where: A AVP(DCRP) = A G(DCRP) • RDCR and A G(DCRP) = C VDCRP = R VDCRP RLPTC L R VDCRP • RDCR CIMON = IMON To facilitate CPU monitoring of load current in an IMVP‑6.5 application, the LTC3816 forces the IMON pin voltage to be proportional to the average load current.
LTC3816 APPLICATIONS INFORMATION LC Filter where: The external inductor and output capacitor combination causes a second order LC roll-off at the output with 180° of phase shift. At higher frequencies, the reactance of the output capacitor approaches its ESR, and the roll-off due to the capacitor stops, leaving –20dB/decade and 90° of phase shift. Beyond the ESR zero, the ceramic capacitor creates a high frequency pole.
LTC3816 APPLICATIONS INFORMATION CFF CC RC CC1 R1 VIN – +EA SERVO VFB COMP 1.3V IL TG SW SW ESL L RSEN VOUT SENSE RESISTOR BG + RAVPSR LTC3816 RESR BSOURCE + DAMP – CCER CBULK ITCFB – +AITC CVSR ITC RVSR ISENN VSS(SEN) VCC(SEN) 3816 F14a Figure 14a. LTC3816 Frequency Compensation with Sense Resistor Configuration CFF CC RC CC1 R1 VIN – +EA SERVO VFB COMP 1.
LTC3816 APPLICATIONS INFORMATION 1. Select fC = feedback crossover frequency = where N is between 5 and 10. fOSC N 2. At the feedback loop crossover frequency, fC, the loop gain is unity, therefore the error amplifier gain is: VCOMP = VSERVO 1 AMOD • ALC • VSERVO VOUT 3. Place the error amplifier zero near the LC filter doublepole frequency: fEA(ZERO) = 1 1 ≈ 2π • RC • CC 2π LLCOUT 4.
LTC3816 APPLICATIONS INFORMATION drops, which further improves efficiency by minimizing gate charge losses. VOUT 100mV/DIV VID5 1V/DIV DPRSLPVR 5V/DIV 0.1ms/DIV VIN = 12V VOUT = 0.75V TO 1.15V CSLEW = 47pF IMVP-6 CONFIGURATION 3816 F15 Figure 15. Programmable VID Slew Rate the controller reduces the ICSLEW pull-up current from 40µA to 10µA (deeper sleep mode). This effectively reduces the VID DAC slew rate to 1/4 of its original value. If IMVP-6.5 is selected, the slow slew rate function is disabled.
LTC3816 APPLICATIONS INFORMATION 10µA current source pull-up. Placing a resistor between RFREQ and GND creates a potential given by the following equation: VRFREQ = IRFREQ • RRFREQ where IRFREQ = 10µA and allows the oscillator free-running frequency to be programmed between 210kHz to 580kHz as shown in Figure 16. An internal phase-locked loop (PLL) allows the LTC3816 to synchronize the internal oscillator to an external clock.
LTC3816 APPLICATIONS INFORMATION output voltage is ramped down, the controller continues to hold the regulator output and PWRGD low until the VRON pin toggles or the input supply resets. During a VID transition, the power good comparators are masked for 100µs.
LTC3816 APPLICATIONS INFORMATION Power MOSFET and Schottky Diode Selection The LTC3816 requires two external N-channel power MOSFETs: One for the top (main) switch and one (or more) for the bottom (synchronous) switch. The peak-to-peak MOSFET gate drive levels are set by the 5.2V INTVCC supply, requiring the use of logic-level threshold MOSFETs in most applications. Pay close attention to the BVDSS specification for the MOSFETs as well; many logic-level MOSFETs are limited to 30V or less.
LTC3816 APPLICATIONS INFORMATION Both MOSFETs have I2R losses while the topside N-channel equation includes an additional term for transition losses, which are highest at the highest input voltage. The number, type and on-resistance of all MOSFETs selected take into account the voltage step-down ratio as well as the actual position (main or synchronous) in which the MOSFET is used. A much smaller, lower input capacitance MOSFET should be used for the top MOSFET in applications where VIN >> VOUT .
LTC3816 APPLICATIONS INFORMATION The resistive component of the bulk capacitor ESR must be small enough that under a load release, ESR multiplied by the change in load current must meet the following criteria: ∆VOUT(LOAD) > ∆ILOAD • RESR The ceramic capacitors at the regulator output help to absorb some of the change in the load current and reduce the ESR voltage step predicted by the above equation.
LTC3816 APPLICATIONS INFORMATION and operating frequency. Given a specified limit for ripple current, the inductor value can be obtained using the following equation: VOUT VOUT L= 1 – fOSC • ∆IL(MAX ) VIN(MAX ) Once the value for L is known, the type of inductor must be selected. High efficiency converters generally cannot afford the core loss found in low cost powdered iron cores, forcing the use of more expensive ferrite cores.
LTC3816 APPLICATIONS INFORMATION A Design Example Conveniently, the typical probe tip ground clip is spaced just right to span the leads of a typical output capacitor. In general, it is best to take this measurement with the 20MHz bandwidth limit on the oscilloscope turned on to limit high frequency noise.
LTC3816 APPLICATIONS INFORMATION For this example, a Vishay IHLP-5050CE-01 0.33µH inductor is chosen. According to the inductor data sheet, it has a maximum DC current rating of 36.5A and a saturation current of 62A. At room temperature, the typical DCR is 1.3mΩ and the maximum DCR is 1.5mΩ. At 125°C, the DCR increases to approximately 2.085mΩ. The RIMAX resistor value can be calculated. To derive the voltage drop across the inductor DCR (typically 1.3mΩ), place a 0.
LTC3816 APPLICATIONS INFORMATION Therefore RSER is calculated to be 13.99k and standard value RSER = 14k is used. Next, the resistor RAVPDCRN value is obtained from the AVP slope requirement: RSER + (RPAR || RNTC ) • RDCR A AVP= = 3mV/A = R AVPDCRN 14k + (10k || 10k ) ⇒ R AVPDCRN = • 1.3mΩ = 8.233k 3mV/A Select the standard value 8.25k. The capacitor value CVDCRN is given by the following equation: C VDCRN = = L RSER + (RPAR || RNTC ) • RDCR 0.33µH = 13.36nF 14k + (10kk || 10k ) • 1.
LTC3816 APPLICATIONS INFORMATION For the synchronous MOSFETs, assume that the two bottom MOSFETs share the inductor current equally. The power dissipation for one MOSFET is: ( ) 2 V –V PSYNC = IN OUT ILOAD(MAX ) (1+ δ )RDS(ON) VIN 12V – 0.75V 2 PSYNC = 13.5A ) (1+ 0.25) 2.8mΩ ( 12V = 0.598 W Most regulator designs allow a slight transient overshoot for a short duration. If this is limited to 40mV, we have: ( ∆VOUT( AVP) = AVP • ILOAD(MAX ) – ILOAD(MIN) ) mV • ( 27 A – 1.5A ) = 76.
LTC3816 APPLICATIONS INFORMATION As can be seen from the above equation, the biggest portion of the output ripple comes from the ESR of the capacitor. This is why low ESR capacitors are so important in low voltage, high current applications. PC Board Layout Checklist When laying out the printed circuit board, start with the power devices. Be sure to orient the power circuitry so that a clean flow of the power path is achieved. Conductor widths should be maximized and lengths minimized.
LTC3816 Typical Applications An IMVP-6 Converter Using Current Sense Resistor with –5.7mV/A AVP Slope 4.75k 3.32k 33pF 2.37k 1000pF 124Ω 1.1V INTVCC GND ITC ITCFB SGND ISENN VRON IMON CLKEN# RPTC PWRGD VRON SW VSS(SEN) LTC3816 10k 1500pF VFB 8 + 1 0.1µF 5 6, 7 VIN CIN L 1µF DB INTVCC 4.7µF RSEN CBULK 330µF s2 4 BG 2, 3 Si4816BDY + CCER 10µF s6 100Ω VCC(CORE) ILOAD(MAX) 4A VSS(CORE) 100Ω BSOURCE MODE/SYNC DPRSLPVR RFREQ CSLEW 22pF PTC 4.
VRON 22pF 10k VID6 VID5 VID4 VID3 VID2 VID1 VID0 22pF 10.2k 10pF LT3816 VRTT# VID5 VID4 VID2 VID3 GND VID6 BSOURCE MODE/SYNC RFREQ BG INTVCC VIN EXTVCC BOOST TG SW PWRGD CLKEN# VID1 VID0 CSLEW DPRSLPVR SS COMP VFB SERVO VCC(SEN) VSS(SEN) VRON RPTC IMON LFF ISENP ITC PREIMON IMAX ISENN ITCFB 2.43k CBULK: 4 s SANYO 2TPF330M6 (330µF) CCER: 32 s 10µF + 2 s 1µF CIN: 3 s SANYO OS-CON 35SVPD47M + 2 s 10µF DB: CMDSH-4E L: IHLP-5050CE-01 (0.33µH, DCR = 1.
LTC3816 Package Description FE Package 38-Lead Plastic eTSSOP (4.4mm) (Reference LTC DWG # 05-08-1772 Rev B) Exposed Pad Variation AA 4.75 REF 38 9.60 – 9.80* (.378 – .386) 4.75 REF (.187) 20 6.60 ±0.10 4.50 REF 2.74 REF SEE NOTE 4 6.40 2.74 REF (.252) (.108) BSC 0.315 ±0.05 1.05 ±0.10 0.50 BSC RECOMMENDED SOLDER PAD LAYOUT 4.30 – 4.50* (.169 – .177) 0.09 – 0.20 (.0035 – .0079) 0.50 – 0.75 (.020 – .030) NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS 2. DIMENSIONS ARE IN MILLIMETERS (INCHES) 3.
LTC3816 Package Description UHF Package 38-Lead Plastic QFN (5mm × 7mm) (Reference LTC DWG # 05-08-1701 Rev C) 0.70 p 0.05 5.50 p 0.05 5.15 ± 0.05 4.10 p 0.05 3.00 REF 3.15 ± 0.05 PACKAGE OUTLINE 0.25 p 0.05 0.50 BSC 5.5 REF 6.10 p 0.05 7.50 p 0.05 RECOMMENDED SOLDER PAD LAYOUT APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 5.00 p 0.10 0.75 p 0.05 PIN 1 NOTCH R = 0.30 TYP OR 0.35 s 45o CHAMFER 3.00 REF 37 0.00 – 0.05 38 0.40 p0.10 PIN 1 TOP MARK (SEE NOTE 6) 1 2 5.15 ± 0.10 5.50 REF 7.
LTC3816 Typical Application An IMVP-6.5 Converter Using Temperature Compensated Inductor DCR Sensing with –3mV/A AVP Slope 10k 14k 8.25k ISENN 15nF 15nF 5.1k 21k ITCFB IMAX ITC ISENP LT3816 RPTC 1000pF VRON LFF PREIMON IMON IMON VRON 22pF 2.2nF 470pF 22pF VID0 VID1 VID2 VID3 VID4 VID5 VID6 CLKEN# PWRGD 1.9k COMP VIN EXTVCC SS INTVCC DPRSLPVR 0.1µF DB 5V BG VID0 BSOURCE MODE/SYNC RFREQ VID1 VID6 VID2 VID5 VID3 1.1V GND VIN 4.5V TO 24V 3.
