Datasheet LT3001 (Analog Devices) - 5
| Manufacturer | Analog Devices |
| Description | 36V 4W No-Opto Isolated Flyback Converter |
| Pages / Page | 10 / 5 — PIN FUNCTIONS. EN/UVLO (Pin 1):. SW (Pin 4):. GND (Pin 2):. IN (Pin 5):. … |
| File Format / Size | PDF / 626 Kb |
| Document Language | English |
PIN FUNCTIONS. EN/UVLO (Pin 1):. SW (Pin 4):. GND (Pin 2):. IN (Pin 5):. RFB (Pin 3):. OPERATION
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Text Version of Document
LT3001
PIN FUNCTIONS EN/UVLO (Pin 1):
Enable/Undervoltage Lockout. The SW pin. The ratio of the RFB resistor to an internal 10k EN/UVLO pin is used to enable the LT3001. Pull the pin resistor, times a trimmed 1.0V reference voltage, deter- below 0.2V to shut down the LT3001. This pin has an mines the output voltage (plus the effect of any non-unity accurate 1.228V threshold and can be used to program a transformer turns ratio). Minimize trace area at this pin. VIN undervoltage lockout (UVLO) threshold using a resis-
SW (Pin 4):
Drain of the 65V Internal DMOS Power tor divider from VIN to ground. A 2.5µA current hysteresis Switch. Minimize trace area at this pin to reduce EMI and al ows the programming of VIN UVLO hysteresis. If neither voltage spikes. function is used, tie this pin directly to VIN.
V GND (Pin 2):
Ground. Tie this pin directly to local ground
IN (Pin 5):
Input Supply. The VIN pin supplies current to internal circuitry and serves as a reference voltage for plane. the feedback circuitry connected to the RFB pin. Locally
RFB (Pin 3):
Input Pin for External Feedback Resistor. bypass this pin to ground with a capacitor. Connect a resistor from this pin to the transformer primary
OPERATION
The LT3001 is a current mode switching regulator IC The LT3001 samples the isolated output voltage through designed specially for the isolated flyback topology. The the primary-side flyback pulse waveform. In this man- key problem in isolated topologies is how to commu- ner, neither opto-isolator nor extra transformer winding nicate the output voltage information from the isolated is required for regulation. Since the LT3001 operates secondary side of the transformer to the primary side in either boundary conduction mode or discontinuous for regulation. Historically, opto-isolators or extra trans- conduction mode, the output voltage is always sampled former windings communicate this information across on the SW pin when the secondary current is zero. This the isolation boundary. Opto-isolator circuits waste output method improves load regulation without the need of power, and the extra components increase the cost and external load compensation components. physical size of the power supply. Opto-isolators can also cause system issues due to limited dynamic response, nonlinearity, unit-to-unit variation and aging over life- time. Circuits employing extra transformer windings also exhibit deficiencies, as using an extra winding adds to the transformer’s physical size and cost, and dynamic response is often mediocre. Rev. 0 For more information www.analog.com 5 Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Operation Applications Information Package Description
PIN FUNCTIONS EN/UVLO (Pin 1):
Enable/Undervoltage Lockout. The SW pin. The ratio of the RFB resistor to an internal 10k EN/UVLO pin is used to enable the LT3001. Pull the pin resistor, times a trimmed 1.0V reference voltage, deter- below 0.2V to shut down the LT3001. This pin has an mines the output voltage (plus the effect of any non-unity accurate 1.228V threshold and can be used to program a transformer turns ratio). Minimize trace area at this pin. VIN undervoltage lockout (UVLO) threshold using a resis-
SW (Pin 4):
Drain of the 65V Internal DMOS Power tor divider from VIN to ground. A 2.5µA current hysteresis Switch. Minimize trace area at this pin to reduce EMI and al ows the programming of VIN UVLO hysteresis. If neither voltage spikes. function is used, tie this pin directly to VIN.
V GND (Pin 2):
Ground. Tie this pin directly to local ground
IN (Pin 5):
Input Supply. The VIN pin supplies current to internal circuitry and serves as a reference voltage for plane. the feedback circuitry connected to the RFB pin. Locally
RFB (Pin 3):
Input Pin for External Feedback Resistor. bypass this pin to ground with a capacitor. Connect a resistor from this pin to the transformer primary
OPERATION
The LT3001 is a current mode switching regulator IC The LT3001 samples the isolated output voltage through designed specially for the isolated flyback topology. The the primary-side flyback pulse waveform. In this man- key problem in isolated topologies is how to commu- ner, neither opto-isolator nor extra transformer winding nicate the output voltage information from the isolated is required for regulation. Since the LT3001 operates secondary side of the transformer to the primary side in either boundary conduction mode or discontinuous for regulation. Historically, opto-isolators or extra trans- conduction mode, the output voltage is always sampled former windings communicate this information across on the SW pin when the secondary current is zero. This the isolation boundary. Opto-isolator circuits waste output method improves load regulation without the need of power, and the extra components increase the cost and external load compensation components. physical size of the power supply. Opto-isolators can also cause system issues due to limited dynamic response, nonlinearity, unit-to-unit variation and aging over life- time. Circuits employing extra transformer windings also exhibit deficiencies, as using an extra winding adds to the transformer’s physical size and cost, and dynamic response is often mediocre. Rev. 0 For more information www.analog.com 5 Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Operation Applications Information Package Description
