LTC1779 LINER [Linear Technology], LTC1779 Datasheet
LTC1779
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LTC1779 Summary of contents
Page 1
... Current mode control pro- vides excellent AC and DC load and line regulation. The device incorporates an accurate undervoltage lockout fea- ture that shuts down the LTC1779 when the input voltage falls below 2V. The LTC1779 boasts a 2.5% output voltage accuracy and consumes only 135 A of quiescent current. For applica- ...
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... Note 4: Dynamic supply current is higher due to the gate charge being delivered at the switching frequency. Note 5: The LTC1779 is tested in a feedback loop that servos V output of the error amplifier. Note 6: Peak current sense voltage is reduced dependent upon duty cycle to a percentage of value as given in Figure 2. ...
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... SENSE and V IN Applications Information for specifying resistor value.) V (Pin 5): Supply Pin. Must be closely decoupled to GND IN Pin 2. SW (Pin 6): Switching Node and Drain of Internal P-Channel Power MOSFET. Connects to external induc- tor and catch diode. LTC1779 Undervoltage Lockout Trip Voltage vs Temperature 2.20 V FALLING IN 2.16 2.12 2.08 2.04 2 ...
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... U OPERATIO (Refer to Functional Diagram) Main Control Loop The LTC1779 is a constant frequency current mode switch- ing regulator. During normal operation, the internal 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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... ITH RUN / SENSE when the LTC1779 is operating below 40% duty cycle. However, once the duty cycle exceeds 40%, slope com- pensation begins and effectively reduces the peak induc- tor current. The amount of reduction is given by the curves in Figure 2. 110 100 90 80 ...
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... The IN and then choose an appropriate L and recalculate the ripple current. In Burst Mode operation on the LTC1779, the ripple current is normally set such that the inductor current is continuous during the burst periods. Therefore, the peak- to-peak ripple current must not exceed: I RIPPLE ...
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... I . With the current comparator monitoring the CL voltage developed across R , the threshold of the SENSE comparator determines the inductor’s peak current. The maximum output current the LTC1779 can provide is CL given by ...
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... Nichicon PL series and Panasonic SP where I OUT RMS Low Supply Operation Although the LTC1779 can function down to approxi- mately 2.0V, the maximum allowable output current is reduced when V amount of change as the supply is reduced down to 2V. Also shown in Figure 4 is the effect of V goes below 2.3V. ...
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... W U Although all dissipative elements in the circuit produce losses, four main sources usually account for most of the losses in LTC1779 circuits: 1) LTC1779 DC bias current, 2) MOSFET gate charge current voltage drop of the output diode. 1. The V electrical characteristics, that excludes MOSFET driver and control currents ...
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... Figure 6. Foldback Current Limiting R ITH C ITH BOLD LINES INDICATE HIGH CURRENT PATHS Figure 7. LTC1779 Layout Diagram (See PC Board Layout Checklist Board Layout Checklist When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the LTC1779 ...
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... DWG # 05-08-1634) (LTC DWG # 05-08-1636) 2.60 – 3.00 1.50 – 1.75 (.102 – .118) (.059 – .069) (NOTE 3) .95 (.037) REF A2 A .09 – .20 (.004 – .008) (NOTE 2) LTC1779 2.80 – 3.10 (.110 – .118) (NOTE 3) PIN ONE ID .25 – .50 (.010 – .020) (6PLCS, NOTE 2) 1.90 (.074) A1 REF S6 SOT-23 0401 11 ...
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... LTC1779 U TYPICAL APPLICATIONS LTC1779 Minimal Component Count, Single Li-Ion to 1.8V/250mA Step-Down Converter /RUN SW TH LTC1779 20k 2 5 GND V IN 100pF 3 4 – V SENSE FB C1: TAIYO YUDEN CERAMIC EMK325BJ106MNT C2: SANYO POSCAP 6TPA47M D1: IR10BQ015 L1: COILTRONICS UP1B100 RELATED PARTS PART NUMBER DESCRIPTION ® ...