lt1941 Linear Technology Corporation, lt1941 Datasheet

Page 1

... The constant switching frequency, combined with low impedance ceramic capacitors, result in low, predictable output ripple. With its wide input voltage range of 3.5V to 25V, the LT1941 regulates a broad array of power sources from 4-cell batteries and 5V logic rails to unregulated wall transformers, lead acid batteries and distributed-power supplies ...

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... SW1 to SW2 SW1 to SW3 Rising 125µ 5GOOD 5GOOD V Rising TOP VIEW ORDER PART NUMBER 1 28 BIAS2 2 27 SW3 LT1941EFE 3 26 PGND BOOST2 6 23 SW2 PGOOD3 9 20 FB3 19 NFB ...

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... PGOOD V Rising 12V 15V IN BOOST1 BOOST2 Rising 12V 15V IN BOOST1 BOOST2 1.5A SW LT1941 = 25°C. A MIN TYP MAX UNITS 0.2 0.4 10 400 nA 0.2 0.4 10 400 nA 618 628 638 mV ● 613 638 mV ● 50 500 0.35 1700 µMhos 500 V/V 0 ...

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... Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LT1941E is guaranteed to meet performance specifications from 0°C to 70°C. Specifications over the –40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls ...

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... DUTY CYCLE (%) 1941 G06 V vs Temperature FB3 1.280 1.265 1.250 1.235 1.220 –50 – 100 125 TEMPERATURE (°C) 1941 G05 LT1941 SW3 V CESAT 500 T = 25°C A 400 300 200 100 0 0 0.5 0.75 1 1.25 1.5 0.25 SWITCH CURRENT (A) 1941 G10 BOOST2 Pin Current ...

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... LT1941 W U TYPICAL PERFOR A CE CHARACTERISTICS Frequency vs Temperature 1.3 1.2 1.1 1.0 0.9 –50 – 100 125 TEMPERATURE (°C) 1941 G13 RUN/SS Thresholds vs Temperature 1.4 1.2 1.0 TO SWITCH 0.8 0.6 TO RUN 0.4 0.2 0 – 100 125 –25 0 TEMPERATURE (°C) 1941 G16 6 Switching Frequency Feedback Voltage 1 25°C A 1.0 0.8 0.6 0.4 0 ...

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... Each switching regulator can be shut down by pulling its respective V to ground with an NMOS or NPN transistor. FB1, FB2, FB3 (Pins 8, 11, 20): The LT1941 regulates each feedback pin to either 0.628V (FB1, FB2) or 1.25V (FB3). Connect the feedback resistor divider taps to these pins. ...

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... Operation can be best understood by referring to the Block Diagram. If the RUN/SS pins are tied to ground, the LT1941 is shut down and draws 50µA from the input source tied to V Internal 2µA current sources charge external soft-start capacitors, generating voltage ramps at these pins ...

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... POSITIVE FB3 OUTPUTS NFB R4 (EXTERNAL) FB3 R3 (EXTERNAL) FOR NFB NEGATIVE R4 OUTPUTS (EXTERNAL) NFB – –V OUT3 + Figure 2. Block Diagram of the LT1941 with Associated External Components V IN CLK1 INT REG MASTER CLK2 AND REF OSC CLK3 0.9V + ∑ SLOPE R – SLAVE OSC + – ...

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... R2 should be 10k or less to avoid bias current errors. Input Voltage Range The minimum operating voltage is determined either by the LT1941’s undervoltage lockout of ~3. its maximum duty cycle. The duty cycle is the fraction of time that the internal switch is on and is determined by the input ...

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... This gives the peak-to-peak ripple current in the inductor – DC)( )/(L • f) ∆I L OUT F where f is the switching frequency of the LT1941 and L is the value of the inductor. The peak inductor and switch current is ∆I /2 SWPK ...

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... LIM OUT The low ESR and small size of ceramic capacitors make them the preferred type for LT1941 applications. Not all ceramic capacitors are the same, however. Many of the higher value capacitors use poor dielectrics with high temperature and voltage coefficients. In particular, Y5V and Z5U types lose a large fraction of their capacitance with applied voltage and at temperature extremes ...

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... The boost circuit also limits the minimum input voltage for proper start-up. If the input voltage ramps slowly, or the LT1941 turns on when the output is already in regulation, the boost capacitor may not be fully charged. Because the boost capacitor charges ...

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... U APPLICATIO S I FOR ATIO Converter with Backup Output Regulator There is another situation to consider in systems where the output will be held high when the input to the LT1941 is absent. If the V and one of the RUN/SS pins are allowed IN to float, then the LT1941’s internal circuitry will pull its quiescent current through its SW pin ...

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... INPUT CAPACITOR SELECTION 0.095 3.0 Bypass the input of the LT1941 circuit with a 10µF or higher ceramic capacitor of X7R or X5R type. A lower value or a 0.520 1.4 less expensive Y5V type will work if there is additional 0.920 2.8 bypassing provided by bulk electrolytic capacitors the input source impedance is low ...

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... This simplifies loop compensation. In particular, the LT1941 does not depend on the ESR of the output capaci- tor for stability so you are free to use ceramic capacitors to achieve low output ripple and small circuit size. The components tied to the V compensation. Generally, a capacitor and a resistor in series to ground determine loop gain ...

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... Tie the PGOOD to any TANTALUM supply with a pull-up resistor that will supply less than 200µA. Note that this pin will be open when the LT1941 is in shutdown mode (all three RUN/SS pins at ground) 1941 F05 regardless of the voltage at the FB pin. PGOOD is valid ...

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... For independent control of channel 2, use the circuit in Figure 6c. The capacitor on RUN/SS1 is smaller than the capacitor on RUN/SS2. This allows the LT1941 to start up and enable its power good comparator before RUN/SS2 gets high enough to allow channel 2 to start switching. ...

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... Further increases in airflow will lead to lower thermal resistance. Because of the large output current capability of the LT1941 possible to dissipate enough heat to raise the junction temperature beyond the absolute maximum of 125°C. If two of the channels are running at full output current, the third channel may have reduced output ...

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... DISS θ DISS P 3 – • – • – η Example: LT1941 2.5V 2A 3.3V 12V, η 75° 25°C/W: 125 C – ° ° DISS ° – . ...

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... FB3 RUNSS3 PGND GND NOTE: TOTAL OUTPUT POWER OF V OUT3 C1 TO C11: X5R OR X7R D1, D2: CMDSH-3 D3: B220A D4: MBRM120L D5 TO D7: BAV99 OR EQUIVALENT C8 1µF 35V C10 1µF 35V LT1941 V OUT2 R8 R9 100k 100k PGOOD1 PGOOD2 PGOOD3 3.3µH 0.22µF R12 10.7k V OUT2 3.3V 1 ...

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... C1 TO C9: X5R OR X7R D1, D2: CMDSH-3 D3: B220A D4: MBRM120L D5 TO D8: MBR0540 Triple Output Power Supply: 3.3V, 1.8V and –12V V OUT1 130k 100k V IN PGOOD1 5GOOD PGOOD2 12GOOD PGOOD3 BOOST1 BOOST2 C1 LT1941 0.22µF SW1 SW2 13.7k FB1 FB2 C8 3300pF 7.32k 3.3k 1.5nF RUNSS1 RUNSS2 SW3 BIAS1 ...

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... BSC 0.195 – 0.30 (.0077 – .0118) 4. RECOMMENDED MINIMUM PCB METAL SIZE FOR EXPOSED PAD ATTACHMENT *DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.150mm (.006") PER SIDE LT1941 9.60 – 9.80* (.378 – .386) 4.75 (.187 ...

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... LT1941 RELATED PARTS PART NUMBER DESCRIPTION LT1613 550mA (I ), 1.4MHz, High Efficiency Step-Up DC/DC Converter V SW LT1615/LT1615-1 300mA/80mA (I ), High Efficiency Step-Up DC/DC Converter SW LT1617/LT1617-1 300mA/100mA (I ), 1.2MHz/2.2MHz, High Efficiency Inverting SW DC/DC Converter LT1618 1. 1.25MHz, High Efficiency Step-Up DC/DC Converter SW LT1930/LT1930A 1.2MHz/2.2MHz, High Efficiency Step-Up ...