Datasheet

ManualsBrandsLINEAR TECHNOLOGY ManualsPMICsPMIC - DC/DC voltage regulator Push-pull TSSOP 16 EP

LT3439

sn3439 3439fs

Slew Rate Controlled

Ultralow Noise1A Isolated

DC/DC Transformer Driver

■

Reduced Conducted and Radiated EMI

■

Single Resistor Control of Output Switch Voltage

and Current Slew Rates

■

Cross Conduction Prevention Circuitry

■

Two 1A Current Limited Power Switches

■

Low Minimum Supply Voltage: 2.8V

■

Low Shutdown Current: <20µA

■

50% Duty Cycle

■

20kHz to 250kHz Oscillator Frequency

■

Synchronizable to 300kHz

■

Overcurrent and Overtemperature Protected

■

Low Noise Isolated Supplies

■

Radio and Telecom Supplies

■

Distributed Supplies

■

Medical Instruments

■

Precision Instruments

■

Low Noise Filament Supplies

, LTC and LT are registered trademarks of Linear Technology Corporation.

Low Noise 5V to 5V Push-Pull DC/DC Transformer

The LT

3439 is a push-pull DC/DC transformer driver that

reduces conducted and radiated electromagnetic interfer-

ence (EMI). Ultralow noise and EMI are achieved by

controlling the output switch voltage and current slew

rates. Slew rates are user adjustable to optimize output

noise versus efficiency. The LT3439 can reduce high

frequency harmonic content by as much as 40dB with only

a minor decrease in efficiency.

The LT3439 includes two 1A current limited power switches

to ensure start-up under heavy loads. It also includes an

oscillator that can be synchronized to an external clock for

more accurate placement of switcher harmonics. Protec-

tion features include current limiting, undervoltage lock-

out, thermal shutdown and cross conduction prevention

circuitry.

The LT3439 is available in a thermally enhanced 16-pin

TSSOP with an exposed backside.

SHDN

1, 16

22µF

10V

L1 33µH

OPTIONAL

OUT

500mA

680pF

LT3439

SYNC

16.9k

34k

47µF

6.3V

: MURATA GRM235Y5V226Z10

C1, C2: TDK C4532X5R0J476M

D1, D2: MBR0520

L1: TDK SLF6028T-330MR69

T1: COILTRONICS 15835

47µF

6.3V

3439 TA01

COL A

COL B

GND PGND

•

200µV/DIV

20mV/DIV

5V Output Noise

5µs/DIV 3439 TA01b

DESCRIPTIO

FEATURES

APPLICATIO S

TYPICAL APPLICATIO

Summary of content (12 pages)

PAGE 1
LT3439 Slew Rate Controlled Ultralow Noise1A Isolated DC/DC Transformer Driver U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO The LT®3439 is a push-pull DC/DC transformer driver that reduces conducted and radiated electromagnetic interference (EMI). Ultralow noise and EMI are achieved by controlling the output switch voltage and current slew rates. Slew rates are user adjustable to optimize output noise versus efficiency.
PAGE 2
LT3439 W W W AXI U U ABSOLUTE RATI GS U U W PACKAGE/ORDER I FOR ATIO (Note 1) VIN Voltage ............................................................. 20V COL A, COL B Voltage ............................................. 35V SHDN, SYNC Voltage .............................................. 20V Maximum Junction Temperature ......................... 150°C Operating Junction Temperature Range (Note 2) ............................................ – 40°C to 125°C Storage Temperature Range ............
PAGE 3
LT3439 U W TYPICAL PERFOR A CE CHARACTERISTICS Supply Current in Shutdown Mode vs Temperature 2.750 16 2.700 14 SUPPLY CURRENT (µA) INPUT VOLTAGE (V) 2.650 2.600 2.550 2.500 2.450 2.400 120 12 17.5V 10 8 5V 6 4 2.7V 2 2.350 2.
PAGE 4
LT3439 U U U PI FU CTIO S PGND (Pins 1, 16): Power ground is connected to the emitter of the power switches via an internal sense resistor. It has large currents flowing through it and should be connected to a good quality ground plane. RT (Pin 7): The oscillator resistor pin is used to set the charge and discharge currents of the oscillator capacitor. The nominal value is 16.9k. The resistance can be adjusted between ±25% of nominal for better frequency accuracy.
PAGE 5
LT3439 W BLOCK DIAGRA D1 T1 • VIN • • 11 13 3 LT3439 SHDN VIN LDO REGULATOR INTERNAL VCC 7 CT 6 5 SLEW CONTROL FF • COUT D2 14 COLB OUTPUT DRIVERS Q T RT COLA VOUT QB RT CT + OSCILLATOR 16 RSENSE – SYNC 10 GND 4 PGND 1 RSL 3439 BD RSL U OPERATIO Push-Pull Topology The push-pull DC transformer topology is a very straightforward switching power supply. The two switches are turned on out of phase at 50% duty cycles.
PAGE 6
LT3439 U OPERATIO vary from 2.8V to 17.5V with very little change in device performance. When the part is in shutdown mode, the internal regulator is turned off, drawing less than 20µA of current from VIN. Overtemperature Protection Overcurrent Protection Undervoltage Lockout Protection A linearly controlled current limit circuit is provided to protect the circuit from excessive currents and to facilitate start-up into a highly capacitive load.
PAGE 7
LT3439 U W U U APPLICATIO S I FOR ATIO Oscillator SYNC The oscillator can be synchronized to an external clock. Set the RC timing components for an oscillator frequency 10% below the desired sync frequency. It is recommended that the SYNC pin be driven with a square wave that has an amplitude greater than 2V, a pulse width greater than 1µs and a rise time less than 500ns. The rising edge of the sync waveform triggers the change in the state of the outputs.
PAGE 8
LT3439 U W U U APPLICATIO S I FOR ATIO mean greater switching losses in the internal output switches. However, efficiency is only modestly reduced for a large improvement in EMI. Care should be taken to ensure that the worst-case input voltage and load current conditions do not cause an excessive die temperature. The total power dissipation of the IC is dominated by three loss terms, regulator losses, saturation losses and switching losses.
PAGE 9
LT3439 U W U U APPLICATIO S I FOR ATIO current. This can be accomplished by adding more turns onto a given core or selecting a new core with a higher inductance per turn squared characteristic (AL). The following equation can be used to set the transformer primary inductance: LPRI = VIN tON ∆I tON can be calculated by 1/fOSC.
PAGE 10
LT3439 U W U U APPLICATIO S I FOR ATIO The primary inductance is then calculated: 1 1 fOSC LPRI = VIN = 5 100kHz = 467µH ∆IPRI 0.107 A ∆I = 15% of IPRI = 0.15 • 0.714A = 0.107 A Next, build a transformer with the calculated values of turns ratio and primary inductance. Minimize resistance in the windings. The turns ratio can be tweaked to get the specified output voltage. Capacitors The DC transformer topology runs effectively at 100% duty cycle (50% each side).
PAGE 11
LT3439 U TYPICAL APPLICATIO Low Noise 5V to ±12V Push-Pull DC Transformer OPTIONAL D1 + D2 C3 47µF T1 13 C1 4.7µF SHDN COLA 7 CT 820pF RT 16.9k SYNC • • 14 COLB RT 4 RSL GND R8 10k D4 PGND 10 R1 442k + C9 39µF D3 OPTIONAL CT ADJ VOUT 12V 80mA R2 49.9k RSI 16.9k 1, 16 C11 2.
PAGE 12
LT3439 U TYPICAL APPLICATIO Low Noise 12V to –12V, 6W Push-Pull DC Transformer OPTIONAL VIN 12V T1 C1 4.7µF C2 0.1µF 11 13 • VIN SHDN COLA LT3439 5 6 7 CT 680pF RT 16.9k SYNC COLB CT RT RSL GND PGND 10 1, 16 L2 33µH D1 • C3 15µF 3 • • 14 4 RSI 16.9k C4 15µF LT1175 IN ILIM2 ILIM4 OUT GND SENSE VOUT –12V 500mA C5 4.