Datasheet LT3439 (Analog Devices) - 5
| Manufacturer | Analog Devices |
| Description | Slew Rate Controlled Ultralow Noise 1A Isolated DC/DC Transformer Driver |
| Pages / Page | 12 / 5 — BLOCK DIAGRA. OPERATIO. Push-Pull Topology. Slew Control. Internal … |
| File Format / Size | PDF / 196 Kb |
| Document Language | English |
BLOCK DIAGRA. OPERATIO. Push-Pull Topology. Slew Control. Internal Regulator
Model Line for this Datasheet
Text Version of Document
LT3439
W BLOCK DIAGRA
D1 T1 VOUT • • VIN COUT D2 • • 11 13 3 14 SHDN V LT3439 COLA COLB IN LDO REGULATOR OUTPUT Q DRIVERS SLEW T FF CONTROL INTERNAL VCC QB RT RT 7 CT OSCILLATOR + CT 6 R 16 SENSE PGND 1 SYNC – 5 GND RSL 10 4 3439 BD RSL
U OPERATIO Push-Pull Topology
eventually cause the transformer to saturate. Also, dur- ing the turn-off of the switches, the leakage inductance The push-pull DC transformer topology is a very straight- causes a large undesirable voltage spike. The LT3439 forward switching power supply. The two switches are slew control feature addresses both of these concerns turned on out of phase at 50% duty cycles. During the and is discussed in the Applications Information section. switch on time, VIN is applied across the primary side of the transformer. The voltage on the secondary side of the
Slew Control
transformer is simply VIN times the turns ratio. The diodes rectify the secondary voltage and generate the output Control of voltage and current slew rate is maintained via voltage. The output capacitor is for hold-up and filtering. two feedback loops. One loop controls the output switch collector voltage dV/dt and the other loop controls the Some of the topology’s advantages are: 1) Stepping up or emitter current dI/dt. Output slew control is achieved by down the input voltage can easily be done by setting the comparing the two currents generated by these slewing turns ratio. 2) The transformer provides isolation between events to a current set by the external resistor R the input and output. 3) Each switch cycle applies V SL. The two IN control loops work together to provide a smooth transition across the transformer in opposite polarities. Therefore, from voltage slew control to current slew control. the transformer core never saturates and a separate reset circuit is not necessary.
Internal Regulator
The push-pull topology is not without its concerns. An Most of the control circuitry operates from an internal 2.4V imbalance in the two sides of the transformer can low dropout regulator that is powered from VIN. VIN can sn3439 3439fs 5
W BLOCK DIAGRA
D1 T1 VOUT • • VIN COUT D2 • • 11 13 3 14 SHDN V LT3439 COLA COLB IN LDO REGULATOR OUTPUT Q DRIVERS SLEW T FF CONTROL INTERNAL VCC QB RT RT 7 CT OSCILLATOR + CT 6 R 16 SENSE PGND 1 SYNC – 5 GND RSL 10 4 3439 BD RSL
U OPERATIO Push-Pull Topology
eventually cause the transformer to saturate. Also, dur- ing the turn-off of the switches, the leakage inductance The push-pull DC transformer topology is a very straight- causes a large undesirable voltage spike. The LT3439 forward switching power supply. The two switches are slew control feature addresses both of these concerns turned on out of phase at 50% duty cycles. During the and is discussed in the Applications Information section. switch on time, VIN is applied across the primary side of the transformer. The voltage on the secondary side of the
Slew Control
transformer is simply VIN times the turns ratio. The diodes rectify the secondary voltage and generate the output Control of voltage and current slew rate is maintained via voltage. The output capacitor is for hold-up and filtering. two feedback loops. One loop controls the output switch collector voltage dV/dt and the other loop controls the Some of the topology’s advantages are: 1) Stepping up or emitter current dI/dt. Output slew control is achieved by down the input voltage can easily be done by setting the comparing the two currents generated by these slewing turns ratio. 2) The transformer provides isolation between events to a current set by the external resistor R the input and output. 3) Each switch cycle applies V SL. The two IN control loops work together to provide a smooth transition across the transformer in opposite polarities. Therefore, from voltage slew control to current slew control. the transformer core never saturates and a separate reset circuit is not necessary.
Internal Regulator
The push-pull topology is not without its concerns. An Most of the control circuitry operates from an internal 2.4V imbalance in the two sides of the transformer can low dropout regulator that is powered from VIN. VIN can sn3439 3439fs 5
