Datasheet LT8301 (Analog Devices) - 10
| Fabricante | Analog Devices |
| Descripción | 42VIN Micropower No-Opto Isolated Flyback Converter with 65V/1.2A Switch |
| Páginas / Página | 24 / 10 — APPLICATIONS INFORMATION. Figure 1. Output Power for 3.3V Output. … |
| Revisión | B |
| Formato / tamaño de archivo | PDF / 1.4 Mb |
| Idioma del documento | Inglés |
APPLICATIONS INFORMATION. Figure 1. Output Power for 3.3V Output. Figure 2. Output Power for 5V Output
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LT8301
APPLICATIONS INFORMATION
7 7 MAXIMUM MAXIMUM 6 OUTPUT 6 N = 5:1 OUTPUT CURRENT CURRENT N = 4:1 5 5 N = 3:1 N = 3:1 4 4 N = 2:1 N = 2:1 3 3 N = 1:1 OUTPUT POWER (W) 2 N = 1:1 OUTPUT POWER (W) 2 1 1 0 0 0 10 20 30 40 0 10 20 30 40 INPUT VOLTAGE (V) INPUT VOLTAGE (V) 8301 F01 8301 F02
Figure 1. Output Power for 3.3V Output Figure 2. Output Power for 5V Output
7 7 MAXIMUM MAXIMUM 6 OUTPUT N = 3:2 6 OUTPUT CURRENT CURRENT N = 4:5 5 5 N = 1:1 N = 1:2 4 4 N = 2:3 N = 1:3 3 3 N = 1:5 OUTPUT POWER (W) 2 N = 1:3 OUTPUT POWER (W) 2 1 1 0 0 0 10 20 30 40 0 10 20 30 40 INPUT VOLTAGE (V) INPUT VOLTAGE (V) 8301 F03 8301 F04
Figure 3. Output Power for 12V Output Figure 4. Output Power for 24V Output Primary Inductance Requirement
In addition to the primary inductance requirement for The LT8301 obtains output voltage information from the the minimum switch-off time, the LT8301 has minimum reflected output voltage on the SW pin. The conduction of switch-on time that prevents the chip from turning on secondary current reflects the output voltage on the pri- the power switch shorter than approximately 170ns. mary SW pin. The sample-and-hold error amplifier needs This minimum switch-on time is mainly for leading-edge a minimum 450ns to settle and sample the reflected out- blanking the initial switch turn-on current spike. If the put voltage. In order to ensure proper sampling, the sec- inductor current exceeds the desired current limit during ondary winding needs to conduct current for a minimum that time, oscillation may occur at the output as the cur- of 450ns. The following equation gives the minimum rent control loop will lose its ability to regulate. Therefore, value for primary-side magnetizing inductance: the following equation relating to maximum input voltage must also be followed in selecting primary-side magnetiz- t ( ) ing inductance: L OFF(MIN) •NPS • VOUT + VF PRI ≥ t ISW(MIN) L ON(MIN) • VIN(MAX) PRI ≥ I t SW(MIN) OFF(MIN) = Minimum switch-off time = 450ns ISW(MIN) = Minimum switch current limit = 290mA (typ) tON(MIN) = Minimum switch-on time = 170ns Rev. B 10 For more information www.analog.com Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Applications Package Description Revision History Typical Application Related Parts
APPLICATIONS INFORMATION
7 7 MAXIMUM MAXIMUM 6 OUTPUT 6 N = 5:1 OUTPUT CURRENT CURRENT N = 4:1 5 5 N = 3:1 N = 3:1 4 4 N = 2:1 N = 2:1 3 3 N = 1:1 OUTPUT POWER (W) 2 N = 1:1 OUTPUT POWER (W) 2 1 1 0 0 0 10 20 30 40 0 10 20 30 40 INPUT VOLTAGE (V) INPUT VOLTAGE (V) 8301 F01 8301 F02
Figure 1. Output Power for 3.3V Output Figure 2. Output Power for 5V Output
7 7 MAXIMUM MAXIMUM 6 OUTPUT N = 3:2 6 OUTPUT CURRENT CURRENT N = 4:5 5 5 N = 1:1 N = 1:2 4 4 N = 2:3 N = 1:3 3 3 N = 1:5 OUTPUT POWER (W) 2 N = 1:3 OUTPUT POWER (W) 2 1 1 0 0 0 10 20 30 40 0 10 20 30 40 INPUT VOLTAGE (V) INPUT VOLTAGE (V) 8301 F03 8301 F04
Figure 3. Output Power for 12V Output Figure 4. Output Power for 24V Output Primary Inductance Requirement
In addition to the primary inductance requirement for The LT8301 obtains output voltage information from the the minimum switch-off time, the LT8301 has minimum reflected output voltage on the SW pin. The conduction of switch-on time that prevents the chip from turning on secondary current reflects the output voltage on the pri- the power switch shorter than approximately 170ns. mary SW pin. The sample-and-hold error amplifier needs This minimum switch-on time is mainly for leading-edge a minimum 450ns to settle and sample the reflected out- blanking the initial switch turn-on current spike. If the put voltage. In order to ensure proper sampling, the sec- inductor current exceeds the desired current limit during ondary winding needs to conduct current for a minimum that time, oscillation may occur at the output as the cur- of 450ns. The following equation gives the minimum rent control loop will lose its ability to regulate. Therefore, value for primary-side magnetizing inductance: the following equation relating to maximum input voltage must also be followed in selecting primary-side magnetiz- t ( ) ing inductance: L OFF(MIN) •NPS • VOUT + VF PRI ≥ t ISW(MIN) L ON(MIN) • VIN(MAX) PRI ≥ I t SW(MIN) OFF(MIN) = Minimum switch-off time = 450ns ISW(MIN) = Minimum switch current limit = 290mA (typ) tON(MIN) = Minimum switch-on time = 170ns Rev. B 10 For more information www.analog.com Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Applications Package Description Revision History Typical Application Related Parts