LT3500 LINER [Linear Technology], LT3500 Datasheet
LT3500
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LT3500 Summary of contents
Page 1
... The LT 3500 is a current mode PWM step-down DC/DC converter with an internal 2.3A switch. The wide input range 40V makes the LT3500 suitable for regulating power from a wide variety of sources, including automo- tive batteries, 24V industrial supplies and unregulated wall adapters. Resistor-programmable 250kHz to 2.2MHz frequency range and synchronization capability enable optimization between effi ...
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... For more information on lead free part marking, go to: For more information on tape and reel specifi cations, go to: 2 (Note 1) Operating Junction Temperature Range LT3500EDD (Note 2) .......................... –40°C to 125°C IN LT3500IDD (Note 2) ........................... –40°C to 125°C LT3500HDD (Note 2).......................... –40°C to 150°C LT3500EMSE (Note 2)........................ –40°C to 125°C LT3500IMSE (Note 3) ........................ – ...
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... V = 0.7V 90.9k FB RT/SYNC 2A 18V 0.7V SW BST 18V 0.7V BST 18V 0.7V BST 2A 20V 0.7V SW BST 2A 0. LT3500 MIN TYP MAX UNITS l 710 760 780 mV 1.5 2.5 3.5 μA 1.25 2 3.25 μA l 2.4 2 μA 2.5 3 0.784 0.8 0.816 V l 0.776 0.8 0.824 ...
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... The LT3500IDD/LT3500IMSE is guaranteed over the full –40°C to 125°C operating junction temperature range. The LT3500HDD/LT3500HMSE is guaranteed over the full –40°C to 150°C operating junction temperature range. High junction temperatures degrade operating lifetimes. Operating lifetime is derated at junction temperatures greater than 125° ...
Page 5
... PG 800 700 600 PG 500 400 300 200 100 0 150 –50 – 100 TEMPERATURE (°C) LT3500 Error Amplifi Temperature m 400 350 300 250 200 150 100 75 125 150 –50 – TEMPERATURE (°C) 3500 G05 VC Switching Threshold vs Temperature 0 ...
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... LT3500 TYPICAL PERFORMANCE CHARACTERISTICS Peak Switch Current vs Temperature 3.5 3.4 3.3 MSE PACKAGE 3.2 3.1 3.0 DD PACKAGE 2.9 2.8 2.7 2.6 2.5 –50 – 100 125 TEMPERATURE (°C) 3500 G13 Minimum Switching Times 300 275 250 225 200 175 MINIMUM ON TIME 150 125 100 MINIMUM OFF TIME 75 50 –50 100 125 150 – ...
Page 7
... NPN switch and linear output NPN. The V dI/dt edges and must be decoupled to ground close to the pin of the device. SHDN: The SHDN pin is used to shut down the LT3500 and reduce quiescent current to a typical value of 12μA. The accurate 0.76V threshold and input current ...
Page 8
... For ideal operation all small-signal ground paths should connect to the GND pin at a single point, avoiding any high current ground returns. NC Pins (MSE Package Only): No Connection. The NC pins are electrically isolated from the LT3500. The NC pins may be connected to PCB traces to aid PCB layout. base drive to IN decoupling capacitor’ ...
Page 9
... BLOCK DIAGRAM LT3500 3500fb 9 ...
Page 10
... If the SHDN pin is taken below its 0.8V threshold, the LT3500 will be placed in a low quiescent current mode. In this mode the LT3500 typically draws 12μA from the V pin. IN When the SHDN pin is fl oated or driven above 0.76V, the internal bias circuits turn on generating an internal regu- lated voltage, 0 ...
Page 11
... R2 should be 10.0k or less to avoid bias current errors. Reference designators refer to the Block Diagram in Figure 1. Choosing the Switching Frequency The LT3500 switching frequency is set by resistor R5 in Figure 1. The R /SYNC pin is internally regulated at 1V. T Setting resistor R5 sets the current in the R which determines the oscillator frequency as illustrated in Figure 2 ...
Page 12
... Once the switching frequency has been determined, the input voltage range of the regulator can be determined. The minimum input voltage is determined by either the LT3500’s minimum operating voltage of ~2. its maximum duty cycle. The duty cycle is the fraction of time that the internal switch is on during a clock cycle. The ...
Page 13
... This gives the peak-to-peak ripple current in the inductor 1− OUT1 D Δ • f where f is the switching frequency of the LT3500 and L is the value of the inductor. The peak inductor and switch current is: Δ SW(PK) LPK OUT1 2 LT3500 3500fb ...
Page 14
... The input capacitor is required to reduce the resulting voltage ripple at the LT3500 and to force this very high frequency switching current into a tight local loop, minimizing EMI. The input capacitor must have low impedance at the switching frequency to do this effectively, and it must have an adequate ripple current rating ...
Page 15
... LT3500. The solution is to either clamp the input voltage or dampen the tank circuit by adding a lossy capacitor in parallel with the ceramic capacitor ...
Page 16
... The high performance (low ESR), small size and robust- ness of ceramic capacitors make them the preferred type for LT3500 applications. However, all ceramic capacitors are not the same. As mentioned above, many of the high value capacitors use poor dielectrics with high tempera- ture and voltage coeffi ...
Page 17
... With a shorted condition, diode current will increase to a typical value of 3A, determined by the peak switch current limit of the LT3500. This is safe for short periods of time, but it would be prudent to check with the diode manu- facturer if continuous operation under these conditions can be tolerated ...
Page 18
... For proper start-up, the minimum input voltage is also limited by the boost circuit. If the input voltage is ramped slowly, or the LT3500 is turned on with its SS pin when the output is already in regulation, then the boost capacitor may not be fully charged. Because the boost capacitor is charged ...
Page 19
... C If the synchronization signal powers undetermined state ( the LT3500 as shown in Figure 7. The circuit as shown will isolate the synchronization signal when the output voltage is below 90% of the regulated output. The LT3500 will start-up with a switching frequency determined by the resistor from the R ...
Page 20
... SHDN pin should be bypassed with a 1nF capacitor to prevent coupling problems from the switch node. Soft-Start The outputs of the LT3500 regulate to either the SS pin voltage minus 100mV or an internally regulated 800mV, whichever is lowest. A capacitor from the SS pin to ground is charged by an internal 2.75μA current source resulting ...
Page 21
... The PG pull-up resistor should be sized in the same manner as the PG pull-up resistor. Linear Regulator The LT3500 contains an error amplifi er and a NPN output device which can be confi gured as a linear regulator linear regulator controller. With the LFB and LDRV pins confi gured as shown in Figure 1, the LDRV pin outputs a regulated voltage with a typical current limit of 13mA ...
Page 22
... The output current capability of Figure 10’s circuit is a product of the LDRV current limit and beta of the external NPN which is normally less than the current capability of the LT3500. The dropout voltage for the circuit is set by the saturation voltage of the external NPN, which is typically 300mV. The minimum V ...
Page 23
... The topside metal from the DC1069A demonstration board in Figure 12 illustrates proper component placement and trace routing. Thermal Considerations The PCB must also provide heat sinking to keep the LT3500 cool. The exposed metal on the bottom of the package must be soldered to a ground plane. This ground LT3500 ...
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... LT3500 TYPICAL APPLICATIONS 4.5V TO 36V C1 2.2μF C2 0.47μF C3 220pF R6 40.2k 24 High Effi ciency Linear Regulator D2 BAT54 V BST LT3500 3.3μH 0.47μ SHDN B240A R2 25.5k SS 8.06k FB R SYNC LDRV 10k 24.9k LFB GND R5 R4 49.9k 8.06k Effi ciency vs Load Current ...
Page 25
... Step-Down with Power Good LED D2 BAT54 V BST LT3500 4.7μH 0.47μ SHDN B240A 42. SYNC LDRV 8.06k C 42.2k LFB PG GND R6 49.9k LT3500 V OUT1 5V 1. 22μF 100k Q1 ZXTCM322 V OUT2 3.3V 0.5A I89 C6 ZXMP3A17E6 22μF 3500 TA03 V OUT1 22μF 8.06k R8 8.06k C8 1μF R5 100k M1 ...
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... LT3500 PACKAGE DESCRIPTION 3.50 ±0.05 2.10 ±0.05 0.25 ± 0.05 RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED PIN 1 TOP MARK (SEE NOTE 6) 0.200 REF NOTE: 1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH ...
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... MAX SEATING PLANE 0.17 – 0.27 (.007 – .011) 0.50 TYP (.0197) BSC LT3500 8 0.35 REF 1.651 0.102 0.12 REF (.065 .004) DETAIL “B” CORNER TAIL IS PART OF THE LEADFRAME FEATURE. DETAIL “B” FOR REFERENCE ONLY 9 NO MEASUREMENT PURPOSE ...
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... High Effi ciency Step-Down DC/DC OUT Converter ThinSOT 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 ● 1.8V/2A Step-Down Regulator V LDRV LT3500 2.2μF 24.9k 1μF 8.06k LFB SHDN SS BST 0.47μF 0.47μF D1 40.2k R /SYNC ...