ltc1772b Linear Technology Corporation, ltc1772b Datasheet
ltc1772b
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ltc1772b Summary of contents
Page 1
... P-channel MOSFET is turned on continuously in dropout (100% duty cycle). High constant operating frequency of 550kHz allows the use of a small external inductor. The LTC1772B is available in a small footprint 6-lead SOT-23. For a Burst Mode operation enabled version of the LTC1772B, please refer to the LTC1772 data sheet. ...
Page 2
... J A Note 4: Dynamic supply current is higher due to the gate charge being delivered at the switching frequency. Note 5: The LTC1772B is tested in a feedback loop that servos V output of the error amplifier. Note 6: Peak current sense voltage is reduced dependent on duty cycle to and power a percentage of value as given in Figure 2. ...
Page 3
... G04 – SENSE (Pin 4): The Negative Input to the Current Com- parator. V (Pin 5): Supply Pin. Must be closely decoupled to GND IN Pin 2. PGATE (Pin 6): Gate Drive for the External P-Channel MOSFET. This pin swings from LTC1772B Undervoltage Lockout Trip Voltage vs Temperature 2.24 V FALLING IN 2.20 2.16 2.12 2.08 2 ...
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... U OPERATIO (Refer to Functional Diagram) Main Control Loop The LTC1772B is a constant frequency current mode switching regulator. During normal operation, the external P-channel power MOSFET is turned on each cycle when the oscillator sets the RS latch (RS1) and turned off when the current comparator (ICMP) resets the latch. The peak ...
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... At lower output current levels, the improve- P-P ment is even greater. This comes at a tradeoff of lower efficiency for the non-Burst Mode operation part (see Figure 1). Also notice the constant frequency operation of the LTC1772B, even maximum output current. V Ripple for Figure 1 Circuit Using OUT LTC1772 Burst Mode Operation. ...
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... OPERATIO (Refer to Functional Diagram) Overvoltage Protection As a further protection, the overvoltage comparator in the LTC1772B will turn the external MOSFET off when the feedback voltage has risen 7.5% above the reference voltage of 0.8V. This comparator has a typical hysteresis of 20mV. Slope Compensation and Inductor’s Peak Current The inductor’ ...
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... MOSFET (R guaranteed 2.5V) is required for applications that GS work close to this voltage. When these MOSFETs are used, make sure that the input supply to the LTC1772B is less than the absolute maximum V rating, typically 8V. GS The required minimum R of the MOSFET is gov- DS(ON) erned by its allowable power dissipation ...
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... RMS current rating generally far exceeds the RIPPLE(P-P) OUT D Low Supply Operation Although the LTC1772B can function down to approxi OUT mately 2.0V, the maximum allowable output current is V reduced when V IN amount of change as the supply is reduced down to 2V. ...
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... Although all dissipative elements in the circuit produce losses, four main sources usually account for most of the losses in LTC1772B circuits: 1) LTC1772B DC bias cur- rent, 2) MOSFET gate charge current voltage drop of the output diode ...
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... When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the R ITH C ITH BOLD LINES INDICATE HIGH CURRENT PATHS Figure 7. LTC1772B Layout Diagram (See PC Board Layout Checklist LTC1772B. These items are illustrated graphically in the layout diagram in Figure 7. Check the following in your layout: 1 ...
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... U TYPICAL APPLICATIO S LTC1772B High Efficiency, Small Footprint 3.3V to 1.8V/0.5A Regulator R4 10k C3 220pF R4 10k C3 220pF C1: TAIYO YUDEN CERAMIC LMK325BJ106K-T C2: AVXTPSE107M010R0100 D1: IR10BQ015 Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights. ...
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... DC/DC Controller in SOT-23 LTC1773 95% Efficient Synchronous Step-Down Controller LTC1872 SOT-23 Step-Up Controller trademark of Linear Technology Corporation. SENSE Linear Technology Corporation 12 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 www.linear-tech.com LTC1772B 3.3V to 5V/1A Boost Regulator R1 0.033 4.7 H 16V 2 D1 ...