LTC3520 Linear Technology, LTC3520 Datasheet
LTC3520
Available stocks
Related parts for LTC3520
LTC3520 Summary of contents
Page 1
... At light loads, use of Burst Mode operation will improve effi ciency. The LTC3520 provides a <1µA shutdown mode and over- temperature shutdown on both converters. The LTC3520 is available in a low profi le (0.75mm) 24-lead 4mm × ...
Page 2
... ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL LTC3520EUF#PBF LTC3520EUF#TRPBF Consult LTC Marketing for parts specifi ed with wider operating temperature ranges. Consult LTC Marketing for information on non-standard lead based fi nish parts. For more information on lead free part marking, go to: For more information on tape and reel specifi ...
Page 3
... Boost (% Switch C is On) Buck (% Switch 0.88V ⎯ S ⎯ D ⎯ 1 ⎯ S ⎯ D ⎯ 2 AIN V = 0.72V 1.8V AIN AOUT V = 0.88V 1.8V AIN AOUT V = 0.72V 1mA AIN AOUT LTC3520 = 3.6V 3.3V 54.9k, unless VIN3 OUT1 T MIN TYP MAX ● 0.771 0.790 0.809 1 50 ● 0.8 1.25 ● 100 ● ...
Page 4
... CONDITIONS A Falling OUT Note 4: The LTC3520 is tested in a proprietary non-switching test mode that internally connects the FB2 pin to the output of the buck converter error amplifi er. Note 5: This IC includes overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperature will exceed 125° ...
Page 5
... V IN 500mV/DIV LOAD CURRENT 500mA/DIV 3520 G05 50µs/DIV = 4.7µF BUCK V 100mV/DIV LOAD CURRENT 200mA/DIV (5mA TO 300mA STEP) 3520 G07 100µs/DIV LTC3520 Switching Frequency 10000 1000 100 10 100 1000 R (k) T 3520 G04 Buck-Boost Load Transient Response V OUT ...
Page 6
... LTC3520 TYPICAL PERFORMANCE CHARACTERISTICS Buck Burst Mode Threshold V = 1.8V OUT 4.7µ 274k 249k BURST www.DataSheet4U.com R = 301k BURST 5 0 2.2 2.7 3.2 3.7 4.2 4.7 V (V) IN Buck R DS(ON) 400 350 PMOS 300 250 NMOS 200 150 100 50 0 – 45 – 25 – TEMPERATURE (°C) Buck Feedback Voltage 1 ...
Page 7
... V (V) IN 3520 G16 100 L = 4.7µH COILCRAFT MSS7341 L = 2.2µH COILCRAFT 1812PS 1.2 1.4 1.6 1.8 2 3520 G18 BUCK V OUT 50mV/DIV INDUCTOR CURRENT 200mA/DIV 3520 G21 = 25mA LTC3520 Buck-Boost Maximum Output Current, Burst Mode Operation V = 3.3V OUT OUT 2.2 2.7 3.2 3.7 4.2 4.7 5.2 V (V) IN 3520 G17 Buck Effi ciency vs Frequency L = 4.7µ ...
Page 8
... PWM1 = Low: The buck-boost converter will operate in variable frequency mode to improve effi ciency at light loads. In this mode, the LTC3520 can only supply a reduced load current (typically 50mA). PWM1 = High: The buck-boost converter will remain in low noise, fi xed frequency PWM mode at all load currents. ⎯ ...
Page 9
... SV IN1 IN2 IN3 together in the application circuit. Exposed Pad (Pin 25): Ground. The Exposed Pad must be electrically connected to ground and soldered to the PCB. Pins PGND1, PGND2, SGND, and the Exposed Pad must be connected together in the application circuit. LTC3520 must be connected IN 3520f 9 ...
Page 10
... LTC3520 BLOCK DIAGRAM IN1 IN3 A www.DataSheet4U.com + Gm – PWM1 5 SD1 6 SD3 – 0.786V A OUT 2 INTERNAL SLOPE 1 COMPENSATION FB2 – 0.790V + SS2 + 13 5µA *PINS AND PV IN IN1 IN2 SW1A SW1B GATE DRIVERS ...
Page 11
... BUCK CONVERTER OPERATION PWM Mode Operation When the PWM2 pin is held high, the LTC3520 buck converter uses a constant-frequency, current mode control architec- ture. Both the main (P-channel MOSFET) and synchronous rectifi er (N-channel MOSFET) switches are internal. At ...
Page 12
... BUCK-BOOST CONVERTER OPERATION PWM Mode Operation When the PWM pin is held high, the LTC3520 buck-boost converter operates in a constant-frequency PWM mode us- ing voltage mode control. A proprietary switching algorithm allows the converter to switch between buck, buck-boost, and boost modes without discontinuity in inductor cur- rent or loop characteristics ...
Page 13
... If this current OUT1 returning to the fi xed frequency mode of operation. To prevent this from happening, the LTC3520 employs an active clamp circuit that holds the voltage on the V to the optimal level during Burst Mode operation. This minimizes any output transient when returning to fi xed frequency operation ...
Page 14
... T Gain Block The LTC3520 contains a gain block (pins A that can be used as a low battery indicator or power-good comparator for either the buck or buck-boost output volt- age. Typical circuits for these applications are shown in Figure 2. A small-valued capacitor can be added from A to GND to provide fi ...
Page 15
... APPLICATIONS INFORMATION The basic LTC3520 application circuit is shown as the Typical Application on the front page of this datasheet. The external component selection is determined by the desired output voltages, output currents, and ripple volt- age requirements of each particular application. However, basic guidelines and considerations for the design process are provided in this section ...
Page 16
... 782 . V 1 ⎝ ⎜ ⎠ ⎟ − OUT IN OUT = − − OUT IN = − OUT 2.2V ≤ V ≤ 5.25V OUT LTC3520 R2 FB1 R1 GND 3520 F05 Figure 5. Setting the Buck-Boost Output Voltage 3520f ...
Page 17
... ESR to provide acceptable effi ciency and must be able to carry the highest current required by the application without saturating. Table 3 − provides a list of several manufacturers of inductors that f OUT are well suited to LTC3520 applications. − OUT OUT Table 3. Inductor Vendor Information ...
Page 18
... Capacitor Vendor Information Both the input and output capacitors used with the LTC3520 must be low ESR and designed to handle the large AC cur- rents generated by switching converters. The vendors in Table 4 provide capacitors that are well suited to LTC3520 application circuits. Table 4. Capacitor Vendor Information MANU- ...
Page 19
... The LTC3520 switches large currents at high frequencies. Special care should be given to the PCB layout to ensure stable, noise-free operation. Figure 8 depicts the recom- mended PCB layout to be utilized for the LTC3520. A few key guidelines follow: 1. All circulating current paths should be kept as short as possible. This can be accomplished by keeping the routes ≅ ...
Page 20
... SGND FB2 PWM1 5 14 SS2 SD1 VIA TO GROUND PLANE Figure 8. LTC3520 Recommended PCB Layout BUCK-BOOST V OUT C SS1 KELVIN DIRECTLY TO PIN 16 KELVIN DIRECTLY C1 TO PIN 16 C SS2 BURST BUCK V OUT 3520 F08 3520f ...
Page 21
... THE BUCK CONVERTER IS ENABLED WHEN THE BUCK-BOOST OUTPUT VOLTAGE REACHES 3.0V. Typical Waveforms During Power-Up SD1, SD3 5V/DIV BUCK-BOOST V OUT 2V/DIV A OUT 5V/DIV BUCK V OUT 1V/DIV 1ms/DIV LTC3520 L1 4.7µH V OUT 3.3V 500mA C3 56pF 1A FOR V 22µF 1M 15k 10k 309k 442k 158k 3520 TA02a 3520 TA02b ≥ ...
Page 22
... SW1A IN1 IN2 IN3 IN 3.3µH SW1B SW2 V OUT1 470pF V C1 FB2 0.022µF FB1 SS2 0.022µF LTC3520 54.9k SS1 PWM1 301k A PWM2 OUT SD3 SD2 SD1 PGND1 SGND PGND2 Typical Waveforms During Power-Up SD1, SD2, SD3 5V/DIV BUCK-BOOST V OUT 1 ...
Page 23
... Plastic QFN (4mm × 4mm) (Reference LTC DWG # 05-08-1697) 0.70 ±0.05 PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC 0.75 ± 0.05 4.00 ± 0.10 (4 SIDES) 2.45 ± 0.10 (4-SIDES) 0.200 REF 0.00 – 0.05 LTC3520 BOTTOM VIEW—EXPOSED PAD PIN 1 NOTCH R = 0.20 TYP 0.115 0.35 × 45° CHAMFER TYP 23 24 0.40 ± 0. (UF24) QFN 0105 0.25 ± ...
Page 24
... Low Battery Detection C1 22µ SW1A IN1 IN2 IN3 IN 3.3µH SW1B SW2 V OUT1 27pF V C1 FB2 3.3nF FB1 SS2 LTC3520 SS1 54. PWM1 301k A PWM2 OUT SD3 SD2 ON SD1 PGND1 SGND PGND2 3520 TA04 COMMENTS V : 2.5V to 5.5V OUT(RANGE ...