ltc1709-7 Linear Technology Corporation, ltc1709-7 Datasheet
ltc1709-7
Related parts for ltc1709-7
ltc1709-7 Summary of contents
Page 1
... SENSE1 TG2 BOOST2 0. SW2 BG2 INTV SENSE2 – SENSE2 Figure 1. High Current Dual Phase Step-Down Converter LTC1709-7 2-Phase, 5-Bit VID, U 1709 2-phase, VID programmable, synchro- TM operation for highest efficiency 28V 10 F 35V 4 0.002 1 H 0.002 V OUT 0 ...
Page 2
... LTC1709 ABSOLUTE AXI U RATI GS (Note 1) Input Supply Voltage (V ).........................36V to – 0.3V IN Topside Driver Voltages (BOOST1,2) .........42V to – 0.3V Switch Voltage (SW1, 2) .............................36V to – – SENSE1 , SENSE2 , SENSE1 , – SENSE2 Voltages ................... (1.1)INTV + – EAIN EXTV , INTV ATTENIN, ATTENOUT, PGOOD, BIAS VID0– ...
Page 3
... Ramping Positive 20mA, EXTV Ramping Negative CC CC (Note 8) V < VID0–VID4 < 7V BIAS V = 1.2V PLLFLTR PLLFLTR V 2.4V PLLFLTR f < f PLLIN OSC f > f PLLIN OSC LTC1709 unless otherwise noted. MIN TYP MAX UNITS 470 20 40 – 0.5 –1.2 1.0 1.5 1.9 4.1 4.5 0 1.6 5 – 85 – 99 ...
Page 4
... T J dissipation P according to the following formula: D LTC1709EG- • Note 4: The LTC1709-7 is tested in a feedback loop that servos V specified voltage and measures the resultant TYPICAL PERFOR A CE CHARACTERISTICS Efficiency vs Load Current (3 Operating Modes) (Figure 12) 100 Burst Mode 90 OPERATION 80 ...
Page 5
... Maximum Current Sense Threshold vs Duty Factor DUTY FACTOR (%) Maximum Current Sense Threshold vs Sense Common Mode Voltage COMMON MODE VOLTAGE (V) LTC1709-7 INTV and EXTV Switch CC CC Voltage vs Temperature 5.05 INTV VOLTAGE CC 5.00 4.95 4.90 4.85 4.80 EXTV SWITCHOVER THRESHOLD CC 4.75 4. – 50 – ...
Page 6
... LTC1709 TYPICAL PERFOR A CE CHARACTERISTICS Load Regulation 0.0 FCB = 15V IN FIGURE 1 –0.1 –0.2 –0.3 –0 LOAD CURRENT (A) 17097 G13 Maximum Current Sense Threshold vs Temperature –50 – 125 100 TEMPERATURE ( C) 17097 G16 Load Step (Figure 12) ...
Page 7
... EAIN (Pin 4): Input to the error amplifier that compares the feedback voltage to the internal 0.8V reference voltage. This pin is normally connected to a resistive divider from the output of the differential amplifier (DIFFOUT). pin voltage and TH + and SENSE pins in LTC1709-7 Oscillator Frequency vs Temperature 350 V FREQSET 300 250 V ...
Page 8
... LTC1709 CTIO S PLLFLTR (Pin 5): The phase-locked loop’s lowpass filter is tied to this pin. Alternatively, this pin can be driven with voltage source to vary the frequency of the internal oscillator. PLLIN (Pin 6): External Synchronization Input to Phase Detector. This pin is internally terminated to SGND with 50k ...
Page 9
... COMP 2.4V – – 1.2 A SHDN RUN RST SOFT 6V 4(V ) START FB 5-BIT VID DECODER TYPICAL ALL VID PINS 40k VID1 VID2 VID3 VID4 V BIAS LTC1709-7 INTV BOOST TOP D1 SW INTV CC LOGIC BG BOT PGND R SENSE • • INTV CC + SENSE D ...
Page 10
... U OPERATIO (Refer to Functional Diagram) Main Control Loop The LTC1709-7 uses a constant frequency, current mode step-down architecture with the two output stages oper- ating 180 degrees out of phase. During normal operation, each top MOSFET is turned on when the clock for that channel sets the RS latch, and turned off when the main current comparator resets the RS latch ...
Page 11
... RUN/SS capacitor during a severe overcurrent and/or short-circuit condition. Foldback current limiting is acti- vated when the output voltage falls below 70% of its nominal level whether or not the short-circuit latchoff – benefits regula- OUT circuit is enabled. LTC1709-7 11 ...
Page 12
... LTC1709 APPLICATIO S I FOR ATIO The basic LTC1709-7 application circuit is shown in Figure 1 on the first page. External component selection begins with the selection of the inductor(s) based on ripple current requirements and continues with the R resistor selection using the calculated peak SENSE1, 2 inductor current and/or maximum current limit ...
Page 13
... Power MOSFET, D1 and D2 Selection Two external power MOSFETs must be selected for each output stage with the LTC1709-7: one N-channel MOSFET for the top (main) switch, and one N-channel MOSFET for the bottom (synchronous) switch. The peak-to-peak drive levels are set by the INTV voltage ...
Page 14
... LTC1709 APPLICATIO S I FOR ATIO factors for the top and bottom MOSFETs of each output stage are given by: V OUT Main Switch Duty Cycle V IN Synchronous Switch Duty Cycle The MOSFET power dissipations at maximum output current are given by OUT ...
Page 15
... L INTV Regulator CC /2 assuming: An internal P-channel low dropout regulator produces 5V at the INTV regulator powers the drivers and internal circuitry of the LTC1709-7. The INTV LTC1709-7 pin from the V supply pin. The INTV CC IN pin regulator can supply ...
Page 16
... MOSFET gate drivers. High input voltage applications in which large MOSFETs are being driven at high frequencies may cause the maxi- mum junction temperature rating for the LTC1709 exceeded. The supply current is dominated by the gate charge supply current, in addition to the current drawn from the differential amplifier output ...
Page 17
... If the input current does not change then the efficiency has not changed either. Output Voltage The LTC1709-7 has a true remote voltage sense capablity. The sensing connections should be returned from the load back to the differential amplifier’s inputs through a com- mon, tightly coupled pair of PC traces. The differential amplifier corrects for DC drops in both the power and ground paths ...
Page 18
... Intel specifications. The LTC1709-7 interprets these codes as a valid input and produces an output voltage as follows: (11111) = 0.900V (01111) = 1.250V Soft-Start/Run Function VID0 LTC1709-7 The RUN/SS pin provides three functions: 1) Run/Shut ...
Page 19
... F will be sufficient for most applications. SS Phase-Locked Loop and Frequency Synchronization The LTC1709-7 has a phase-locked loop comprised of an internal voltage controlled oscillator and phase detector. This allows the top MOSFET turn- locked to the rising edge of an external source. The frequency range of ...
Page 20
... At this stable operating point the phase comparator output is open and the filter capacitor C holds the voltage. The LP LTC1709-7 PLLIN pin must be driven from a low imped- ance source such as a logic gate located close to the pin. The loop filter components ( current pulses from the phase detector and provide a stable input to the voltage controlled oscillator ...
Page 21
... normally set as : SEC(MIN) Figure 8. Active Voltage Positioning Applied to the LTC1709-7 midpoint operating voltage of the error amplifier, or 1.2V (see Figure 8). The resistive load reduces the DC loop gain while main- taining the linear control range of the error amplifier. The worst-case peak-to-peak output voltage deviation due to ...
Page 22
... A 50W supply will typically require a minimum of 200 F to 300 F of output capaci- tance having a maximum of 10m to 20m of ESR. The LTC1709-7 2-phase architecture typically halves the input and output capacitance requirements over compet- ing solutions. Other losses including Schottky conduc- tion losses during dead-time and inductor core losses generally account for less than 2% total additional loss ...
Page 23
... INTV inductance for 30% ripple current is: V OUT 300 LTC1709-7 . DSS 50A I RATING 12V LTC1709-7 TRANSIENT VOLTAGE SUPPRESSOR GENERAL INSTRUMENT 1.5KA24A 17097 F09 = 5V (nominal 1.8V 20A and f = 300kHz. MAX A pin for 300kHz operation. The minimum CC V OUT 1 ...
Page 24
... LTC1709 APPLICATIO S I FOR ATIO A 1.5 H inductor will produce 27% ripple current. The peak inductor current will be the maximum DC value plus one half the ripple current, or 11.5A. The minimum on- time occurs at maximum OUT t ON MIN 300 kHz ...
Page 25
... LTC1709-7. These items are also illustrated graphically in the layout diagram of Figure 12. Check the following in your layout: 1) Are the signal and power grounds segregated? The LTC1709-7 signal ground pin should return to the (–) plate of C separately. The power ground returns to the OUT sources of the bottom N-channel MOSFETs, anodes of the Schottky diodes, and (– ...
Page 26
... LTC1709 APPLICATIO S I FOR ATIO BOLD LINES INDICATE HIGH, SWITCHING CURRENT LINES. KEEP LINES TO A MINIMUM LENGTH. Figure 10. Instantaneous Current Path Flow in a Multiple Phase Switching Regulator SINGLE PHASE SW V SW1 V SW2 V I CIN COUT I L2 ...
Page 27
... Dimensions in inches (millimeters) unless otherwise noted. G Package 36-Lead Plastic SSOP (0.209) (LTC DWG # 05-08-1640 – 8 0.65 (0.0256) BSC 0.25 – 0.38 (0.010 – 0.015) LTC1709 OUT approximately equal to 2(V IN 12.67 – 12.93* (0.499 – 0.509) 30 ...
Page 28
... LTC1735 High Efficiency Synchronous Step-Down Controller LTC1736 High Efficiency Synchronous Step-Down Controller with 5-Bit VID Adaptive Power is a trademark of Linear Technology Corporation. Linear Technology Corporation 28 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 www.linear-tech.com LTC1709 RUN/ SENSE1 ...