LT3437 LINER [Linear Technology], LT3437 Datasheet
LT3437
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LT3437 Summary of contents
Page 1
... SYNC pin with logic-level inputs. A single capacitor from the C controlled output voltage ramp (soft-start). The LT3437 is available in a low profile (0.75mm) 3mm × 3mm 10-pin DFN package or a 16-Pin TSSOP Package both with exposed pad leadframes for low thermal resistance ...
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... Minimum BIAS Voltage (Note Operating Junction Temperature Range LT3437EDD (Note 2) ....................... – 40°C to 125°C LT3437IDD (Note 2) ........................ – 40°C to 125°C LT3437EFE (Note 2) ........................ – 40°C to 125°C LT3437IFE (Note 2) ......................... – 40°C to 125°C Storage Temperature Range ................. – 65°C to 125° ...
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... Note 4: Supply input current is the quiescent current drawn by the input pin. Its typical value depends on the voltage on the BIAS pin and operating state of the LT3437. With the BIAS pin at 0V, all of the quiescent current required to operate the LT3437 will be provided by the V BIAS voltage above its minimum input voltage, a portion of the total quiescent current will be supplied by the BIAS pin ...
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... LT3437 W U TYPICAL PERFOR A CE CHARACTERISTICS Efficiency and Power Loss vs Load Current 100 V = 12V 3.3V 90 OUT T = 25° EFFICIENCY POWER LOSS 0 100 1000 LOAD CURRENT (mA) 3437 G01 SHDN Threshold 1.50 1.45 1.40 1.35 1.30 1.25 1.20 1.15 1.10 –50 – 100 125 TEMPERATURE (°C) ...
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... LOAD CURRENT (mA) Boost Current vs Load Current 100 200 300 400 LOAD CURRENT (mA) LT3437 Switch On Voltage (V CESAT 600 500 400 T = 25°C J 300 T J 200 100 0 1.25 100 200 300 LOAD CURRENT (mA) 3437 G11 Burst Mode Threshold ...
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... LT3437 W U TYPICAL PERFOR A CE CHARACTERISTICS Dropout Operation OUT I = 250mA LOAD BOOST DIODE = DIODES INC B1100 2.0 2.5 3.0 3.5 4.5 5.5 4.0 5.0 INPUT VOLTAGE (V) 3437 G19 Maximum Sync Frequency vs Temperature 1600 V = 12V IN 1500 V = 3.3V OUT I = 100mA 1400 OUT 1300 1200 1100 1000 900 800 ...
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... CSS source current of 5µA to take the IC out of the shutdown threshold is SS state. Exposed Pad (Pin 11/Pin 17): Ground. Must be soldered to the PCB. LT3437 pin is the output of the error C pin is held at a voltage slightly below the C pin. See the Feedback section in SS ...
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... DETECT ERROR AMP Figure 1. LT3437 Block Diagram Most of the circuitry of the LT3437 operates from an internal 2.4V bias line. The bias regulator normally draws power from the V an external voltage higher than 3V, bias power will be drawn from the external source (typically the regulated output voltage) ...
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... U U APPLICATIO S I FOR ATIO FEEDBACK PIN FUNCTIONS The feedback (FB) pin on the LT3437 is used to set output voltage and provide several overload protection features. The first part of this section deals with selecting resistors to set output voltage, and the remaining part talks about frequency foldback and soft-start features ...
Page 10
... If opera- tion is required close to the minimum input required by the LT3437, a larger value may be required. This is to prevent excessive ripple causing dips below the minimum operat- ing voltage resulting in erratic operation. ...
Page 11
... C =27pF. FB 0.5 OUTPUT RIPPLE VOLTAGE Figure 3 shows a typical output ripple voltage waveform for the LT3437. Ripple voltage is determined by the impedance of the output capacitor and ripple current through the inductor. Peak-to-peak ripple current through the inductor into the output capacitor is P-P For high frequency switchers the ripple current slew rate is also relevant and can be calculated from: ...
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... Application Note 19.) The LT3437 is able to maintain peak switch current limit over the full duty cycle range by using patented circuitry to cancel the effects of slope compensation on peak switch current without affecting the frequency compensation it provides ...
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... U U APPLICATIO S I FOR ATIO more output current because they reduce peak current seen by the LT3437 switch, which has a 0.5A limit. Higher values also reduce output ripple voltage and reduce core loss. When choosing an inductor you might have to consider maximum load current, core and copper losses, allow- able component height, output voltage ripple, EMI, fault current in the inductor, saturation and of course cost ...
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... V OUT 1V/DIV Burst Mode OPERATION To enhance efficiency at light loads, the LT3437 automati- cally switches to Burst Mode operation which keeps the output capacitor charged to the proper voltage while minimizing the input quiescent current. During Burst Mode operation, the LT3437 delivers short bursts of ...
Page 15
... As the load current decreases towards a no load condition, the percentage of time that the LT3437 operates in sleep mode increases and the average input current is greatly reduced, resulting in higher efficiency. ...
Page 16
... SHUTDOWN FUNCTION AND UNDERVOLTAGE LOCKOUT The SHDN pin on the LT3437 controls the operation of the IC. When the voltage on the SHDN pin is below the 1.2V shutdown threshold, the LT3437 is placed in a “zero” supply current state. Driving the SHDN pin above the shutdown threshold enables normal operation. The SHDN pin has an internal sink current with a typical value of 5µ ...
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... See the Typical Performance Characteristics section for graphs of SHDN and V SYNCHRONIZING Oscillator synchronization to an external input is achieved by connecting a TTL logic-compatible square wave with a duty cycle between 25% and 75% to the LT3437 SYNC pin. The synchronizing range is equal to initial operating ⎞ ⎟ + frequency up to 700kHz. This means that minimum ...
Page 18
... Pin 4/Pin 10 and the exposed die pad, Pin 11/ Pin 17, are connected by a continuous copper plate that V OUT runs under the LT3437 die. This is the best thermal path for heat out of the package. Reducing the thermal resis- tance from Pin 4 and the exposed pad onto the board will C1 ...
Page 19
... V = Schottky diode forward drop switching frequency OSC A potential controllability problem arises if the LT3437 is called upon to produce an on time shorter than it is able to produce. Feedback loop action will lower, then reduce, the V control voltage to the point where some sort of cycle- C skipping or Burst Mode behavior is exhibited. ...
Page 20
... V C unstable duty cycle switching, similar to subharmonic oscillations. If needed, an additional capacitor (C added across the R to further suppress V With a tantalum output capacitor, the LT3437 already includes a resistor (R pin (see Figures 10 and 11) to compensate the loop over the entire V blocks, the error high V ...
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... OUT 330pF 25k 1500pF 250mA LOAD –20 –40 10 100 1k 10k 100k FREQUENCY (Hz) Figure 11. Overall Loop Response LT3437 OUTPUT ESR R2 C OUT 3437 F13 0 –20 –40 –60 –80 –100 –120 –140 –160 –180 1M 3437 F12 3437f 21 ...
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... LT3437 PACKAGE DESCRIPTIO 3.50 ±0.05 1.65 ±0.05 2.15 ±0.05 (2 SIDES) 0.25 ± 0.05 RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS PIN 1 TOP MARK (SEE NOTE Package 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699) 0.675 ±0.05 PACKAGE OUTLINE 0.50 BSC 2.38 ±0.05 (2 SIDES) 1.65 ± 0.10 3.00 ±0.10 ...
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... REF 0° – 8° 0.65 (.0256) BSC 4. RECOMMENDED MINIMUM PCB METAL SIZE FOR EXPOSED PAD ATTACHMENT MILLIMETERS (INCHES) *DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.150mm (.006") PER SIDE LT3437 4.90 – 5.10* (.193 – .201) 3.58 (.141) 16 1514 6.40 2.94 (.252) ( ...
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... Step-Down Converter with 100µA No Load Quiescent Current V BOOST 2.2µF 100µH BAS21 0.1µF 4.5V TO SHDN 100V SW 80V* CER LT3437 0.1µF 10MQ100N 1500pF 330pF BIAS 27pF 25k SYNC FB GND *FOR INPUT VOLTAGES ABOVE 60V SOME RESTRICTIONS MAY APPLY ...