LT3508 LINER [Linear Technology], LT3508 Datasheet
LT3508
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LT3508 Summary of contents
Page 1
... PWM step-down DC/DC converter with internal power switches capable of generating two 1.4A outputs. The wide input voltage range of 3.7V to 36V makes the LT3508 suitable for regulating power from a wide variety of sources, including automo- tive batteries, 24V industrial supplies and unregulated wall adapters ...
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... BOOST Pin Voltage ...................................................60V BOOST Above SW Voltage ........................................30V SHDN, PG Voltage .....................................................40V TRACK/SS, FB, R /SYNC, V Voltage .......................... Operating Junction Temperature Range (Note 2) LT3508E ............................................. –40°C to 125°C LT3508I .............................................. –40°C to 125°C LT3508H ............................................ –40°C to 150°C PIN CONFIGURATION TOP VIEW 1 TRACK/SS1 2 BOOST1 SW1 ...
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... Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The LT3508E is guaranteed to meet performance specifi cations from 0°C to 125°C junction temperature. Specifi cations over the –40°C to 125°C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. The LT3508I is guaranteed over the full – ...
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... LT3508 TYPICAL PERFORMANCE CHARACTERISTICS Effi ciency OUT 25° 700kHz V = 12V 24V 32V 0.5 1 LOAD CURRENT (A) 3508 G01 Feedback Voltage 0.810 0.805 0.800 0.795 0.790 –50 – 100 125 150 TEMPERATURE (°C) 3508 G04 ...
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... G13 4 –45°C A 3.5 3 125° 25°C A 2.0 1.5 1.0 0 –50 –25 3508 G15 LT3508 Error Amp Output Current 35 30 SINKING SOURCING –50 – TEMPERATURE (°C) 3508 G11 T = 25° 1.5 0.5 SWITCH CURRENT (A) 3508 G14 ...
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... R with a logic-level signal with positive and negative pulse widths of at least 80ns. SHDN: The shutdown pin is used to put the LT3508 in shutdown mode. Pull the pin below 0.3V to shut down the LT3508. The 2.63V threshold can function as an accurate ...
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... SLOPE SLAVE OSC CLK + – 0.625V GND Figure 1. Block Diagram of the LT3508 with Associated External Components (One of Two Switching Regulators Shown) SHDN V IN1 CLK1 INT REG MASTER AND REF OSC CLK2 ERROR AMP – – ...
Page 8
... The LT3508 is a dual constant frequency, current mode regulator with internal power switches. Operation can be best understood by referring to the Block Diagram. If the SHDN pin is tied to ground, the LT3508 is shut down and draws minimal current from the input source tied to the pins. If the SHDN pin exceeds 1V, the internal bias ...
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... Unlike many fi xed frequency regulators, the LT3508 can extend its duty cycle by turning on for multiple cycles. The LT3508 will not switch off at the end of each clock cycle if there is suffi cient voltage across the boost capacitor (C3 in Figure 1). Eventually, the voltage on the boost capacitor falls and requires refreshing ...
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... LT3508 APPLICATIONS INFORMATION V OUT 100mV/DIV (AC 500mA/DIV 2μs/DIV Figure 2. Operation Below 10V, V IN(PS 1.5MHz SW V OUT 100mV/DIV (AC 500mA/DIV 2μs/DIV Figure 3. Operation Above IN(PS) IN and f = 1.5MHz. Output Ripple and Peak Inductor Current SW Increase Setting the Switching Frequency The switching frequency is programmed either by driving ...
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... Then use these equations to check that the LT3508 will be able to deliver the required output current. Note again that these equations assume that the inductor current is continuous. Discontinu- ...
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... Output Capacitor Selection The output capacitor has two essential functions. Along with the inductor, it fi lters the square wave generated by the LT3508 to produce the DC output. In this role it determines the output ripple, and low impedance at the switching frequency is important. The second function is to store ...
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... LT3508 GND – BOOST SW OUT BOOST IN OUT (4a BOOST LT3508 OUT IN GND – BOOST BOOST IN (4b) D2 BOOST C3 LT3508 OUT IN GND – BOOST SW IN2 3508 F04 BOOST IN2 IN 3V IN2 = (4c) OUT 3508fb 13 ...
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... OUT using a transient load. Figure 6 shows an equivalent circuit for the LT3508 control loop. The error amplifi transconductance amplifi er with fi nite output impedance. The power section, consisting of the modulator, power switch and inductor, is modeled as a transconductance amplifi ...
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... If high resistor values are used, the SHDN pin should be bypassed with a 1nF capacitor to prevent coupling problems from the switch node. Soft-Start The output of the LT3508 regulates to the lowest voltage V present at either the TRACK/SS pin or an internal 0.8V C reference. A capacitor from the TRACK/SS pin to ground is charged by an internal 1.2μ ...
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... LT3508 APPLICATIONS INFORMATION Output Tracking and Sequencing Complex output tracking and sequencing between channels can be implemented using the LT3508’s TRACK/SS and PG pins. Figure 8 shows several confi gurations for output tracking and sequencing of 5V and 3.3V applications. Independent Start-Up V OUT1 V OUT2 ...
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... OUT2 operating. Shorted and Reverse Input Protection If the inductor is chosen so that it won’t saturate exces- sively, an LT3508 step-down regulator will tolerate a shorted output. There is another situation to consider in systems where the output will be held high when the input to the IN LT3508 is absent. This may occur in battery charging C1 4.7μ ...
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... To keep thermal resistance low, extend V OUT the ground plane as much as possible, and add thermal vias under and near the LT3508 to additional ground planes within the circuit board and on the bottom side. 3508 F10 (11b) Example Layout for QFN Package ...
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... APPLICATIONS INFORMATION High Temperature Considerations The die temperature of the LT3508 must be lower than the maximum rating of 125°C (150°C for the H grade). This is generally not a concern unless the ambient temperature is above 85°C. For higher temperatures, care should be taken in the layout of the circuit to ensure good heat sinking of the LT3508. The maximum load current should be derated as the ambient temperature approaches 125° ...
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... T 150pF R8 C8 100pF 52.3k 1nF f = 700kHz SW 1MHz, Wide Input Range 5V and 1.8V Outputs C1 4.7μ IN1 IN2 SHDN ON OFF BOOST1 BOOST2 C2 0.1μF SW1 SW2 D3 LT3508 FB1 FB2 TRACK/SS1 PG1 39k TRACK/SS2 PG2 C6 GND R /SYNC T 100pF 33.2k 330pF 1nF 3.3nF f = 1MHz ...
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... D1, D2: MMSD4148 D3: DIODES INC. B240A D4: DIODES INC. B140 R2: USE 0.25W RESISTOR. FOR CONTINUOUS OPERATION ABOVE 30V, USE TWO 2k, 0.25W RESISTORS IN PARALLEL *DERATE OUTPUT CURRENT AT HIGHER AMBIENT TEMPERATURES AND INPUT VOLTAGES TO MAINTAIN JUNCTION TEMPERATURE BELOW THE ABSOLUTE MAXIMUM LT3508 D2 OUT2 5V C3 1.4A* L2 6.8μH 0.1μF ...
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... LT3508 PACKAGE DESCRIPTION 6.60 ±0.10 4.50 ±0.10 SEE NOTE 4 RECOMMENDED SOLDER PAD LAYOUT 4.30 – 4.50* (.169 – .177) 0.09 – 0.20 (.0035 – .0079) (.020 – .030) NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS 2. DIMENSIONS ARE IN 3. DRAWING NOT TO SCALE 22 FE Package 16-Lead Plastic TSSOP (4.4mm) (Reference LTC DWG # 05-08-1663) Exposed Pad Variation BA 2 ...
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... Plastic QFN (4mm × 4mm) (Reference LTC DWG # 05-08-1697) 0.70 ±0.05 PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC BOTTOM VIEW—EXPOSED PAD 0.75 ± 0. 0.115 2.45 ± 0.10 (4-SIDES) 0.200 REF 0.00 – 0.05 LT3508 PIN 1 NOTCH R = 0.20 TYP OR 0.35 × 45° CHAMFER TYP 23 24 0.40 ± 0. (UF24) QFN 0105 0.25 ± 0.05 0.50 BSC ...
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... Linear Technology Corporation 24 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 ● 5V, 1.8V Output from PCI Express C1 4.7μ IN1 IN2 SHDN BOOST1 BOOST2 C3 0.1μF SW1 SW2 D3 LT3508 FB1 FB2 TRACK/SS1 PG1 43k C8 TRACK/SS2 PG2 0.047μF C9 GND R /SYNC T 100pF ...