LTC3521 LINER [Linear Technology], LTC3521 Datasheet
LTC3521
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LTC3521 Summary of contents
Page 1
... Burst Mode operation to improve efficiency and reduce no-load standby current. The LTC3521 provides a < 2μA shutdown mode, over- temperature shutdown and current limit protection on all converters. The LTC3521 is available in a 24-pin 0.75mm × 4mm × 4mm QFN package, and a 20-pin thermally enhanced TSSOP package. 4.7µH ...
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... TAPE AND REEL LTC3521EUF#PBF LTC3521EUF#TRPBF LTC3521EFE#PBF LTC3521EFE#TRPBF Consult LTC Marketing for parts specified with wider operating temperature ranges. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: For more information on tape and reel specifications, go to: ...
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... FB1 V Returning Good FB1 Note 4: The LTC3521 is tested in a proprietary test mode that connects each FB pin to the output of the respective error amplifier. Note 5: This IC includes overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperature will exceed 125°C when overtemperature protection is active. ...
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... LTC3521 Typical perForMance characTerisTics Buck-Boost Efficiency, Li-Ion to 3.3V 100 V = 2.7V PWM MODE 4. Burst Mode 40 OPERATION 0 LOAD CURRENT (mA) Buck Efficiency, Li-Ion to 1.8V 100 Burst Mode 80 OPERATION POWER LOSS 0 LOAD CURRENT (mA) Buck-Boost Switches R ...
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... V ( OUT 100mV/DIV INDUCTOR CURRENT 500mA/DIV 3.3 3.8 4.3 4.8 5.3 V (V) IN 3521 G14 LTC3521 T = 25°C, unless otherwise noted. A Buck Feedback Voltage vs Temperature 0.2 0.1 0 –0.1 –0.2 –0.3 –0.4 –0.5 –50 – 120 TEMPERATURE (°C) 3521 G09 Buck-Boost Maximum Load Current, PWM Mode L = 4.7µH ...
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... LTC3521 Typical perForMance characTerisTics Buck-Boost Burst to PWM Transition INDUCTOR CURRENT 200mA/DIV V OUT 20mV/DIV 3521 G16 50µs/DIV 4.7µ 3. 22µF OUT OUT Buck-Boost Current Limit vs Temperature 2150 2100 2050 2000 1950 –50 – 100 TEMPERATURE (°C) pin FuncTions ...
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... PWM mode. V (Pin 7/Pin 5): Low Current Power Supply Connection IN Used to Power the Internal Circuitry of the LTC3521. This pin should be bypassed by a 4.7µ larger, ceramic capacitor. The bypass capacitor should be placed as close to the pin as possible and should have a short return path to ground ...
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... LTC3521 pin FuncTions NC (Pin 19, UF Package Only): No Internal Connection. PV (Pin 20/Pin 22): High Current Power Supply Connec- IN2 tion Used to Supply the Buck Converter Power Switches. This pin should be bypassed by a 10µF or larger ceramic cap. The bypass capacitor should be placed as close to the pin as possible and should have a short return path to ground ...
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... All three converters are synchronized to the same internal 1.1MHz oscillator. BUCK CONVERTER OPERATION PWM Mode Operation When the PWM pin is held high, the LTC3521 buck con- verters use a constant-frequency, current mode control architecture. Both the main (P-channel MOSFET) and synchronous rectifier (N-channel MOSFET) switches are internal ...
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... BUCK-BOOST CONVERTER OPERATION PWM Mode Operation When the PWM pin is held high, the LTC3521 buck-boost converter operates in a constant-frequency PWM mode with voltage mode control. A proprietary switching algo- rithm allows the converter to switch between buck, buck- boost and boost modes without discontinuity in inductor current or loop characteristics ...
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... This provides additional protection in the case of an instantaneous hard output short. Reverse Current Limit The reverse current comparator on switch D monitors the inductor current entering PV exceeds 375mA (typical), switch D will be turned off for the remainder of the switching cycle. LTC3521 . When this current OUT 3521f ...
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... LTC3521 operaTion Burst Mode Operation With the PWM pin held low, the buck-boost converter operates utilizing a variable frequency switching algorithm designed to improve efficiency at light load and reduce the standby current at zero load. In Burst Mode operation, the inductor is charged with fixed peak amplitude current pulses ...
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... The basic LTC3521 application circuit is shown as the Typical Application on the front page of this data sheet. The external component selection is determined by the desired output voltages, output currents and ripple volt- age requirements of each particular application. Basic guidelines and considerations for the design process are provided in this section ...
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... The peak-to-peak 33pF inductor current ripple for each mode can be calculated 33pF 5.25V OUT3 R2 R1 3521 F03 Figure 4. Setting the Buck-Boost Output Voltage 1.8V V 5.25V OUT1 R2 FB1 LTC3521 R1 GND 3521 F04 3521f ...
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... The choice of inductor style depends upon the price, sizing, and EMI requirements of a particular application. Table 4 provides a sampling of inductors that are well suited to many LTC3521 application circuits. is the OUT ...
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... The LTC3521 switches large currents at high frequencies. Special care should be given to the PCB layout to ensure stable, noise-free operation. Figure 5 depicts the recom- mended PCB layout to be utilized for the LTC3521. A few key guidelines follow: 1. All circulating high current paths should be kept as short as possible ...
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... UNINTERRUPTED GROUND PLANE MUST EXIST UNDER ALL COMPONENTS SHOWN IN BOLD, AND UNDER TRACES CONNECTING TO THOSE COMPONENTS PGND2 (18) SW3 (17) V OUT1 (16) SW1A (15) SW1B (14) NC (13) Figure 5. LTC3521 Recommended PCB Layout LTC3521 KELVIN TO V PAD OUT BUCK V OUT VIA TO GROUND PLANE KELVIN TO V PAD OUT ...
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... V OUT3 2V/DIV 50µs/DIV 100mA Backup Power Supply C4 L1 4.7µF 4.7µ IN1 IN2 SW1A SW2 SW1B FB2 V OUT1 C1 R1 LTC3521 22µF 1.0M FB1 R2 SW3 SHDN1 ON 221k SHDN2 OFF SHDN3 FB3 PGOOD1 PWM PWM PGOOD2 BURST PGOOD3 PGND1 GND PGND2 3521 TA02a ...
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... DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.150mm (.006") PER SIDE UF Package 24-Lead Plastic QFN (4mm × 4mm) (Reference LTC DWG # 05-08-1697) 4.00 ± 0.10 (4 SIDES) PIN 1 TOP MARK (NOTE 6) 0.200 REF 0.00 – 0.05 LTC3521 6.40 – 6.60* (.252 – .260) 3.86 (.152 6.40 2.74 (.252) (.108) ...
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... Sequenced Start- 2. 4.2V L1 4.7µF Li-Ion 4.7µH PV IN1 SW1A SW1B L3 V OUT3 4.7µH 1.2V SW3 600mA C3 R5 LTC3521 10µF 100k FB3 R6 499k 100k PGOOD3 SHDN1 PGOOD1 PGOOD1 PWM PWM BURST PGND1 GND relaTeD parTs PART NUMBER DESCRIPTION LTC3100 700mA I , 1.5MHz, Synchronous Step-Up, 250mA SW ...