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LT1533

Ultralow Noise

1A Switching Regulator

FEATURES

DESCRIPTION

The LT

1533 is a new class of switching regulator designed

to reduce conducted and radiated electromagnetic interfer-

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

user control of the output switch slew rates. Voltage and

current slew rates can be independently programmed to

optimize switcher harmonic content versus efficiency. The

LT1533 can reduce high frequency harmonic power by as

much as 40dB with only minor losses in efficiency.

The LT1533 utilizes a dual output switch current mode

architecture optimized for low noise topologies. The IC

includes two 1A power switches along with all necessary

oscillator, control and protection circuitry. Unique error amp

circuitry can regulate both positive and negative voltages.

The internal oscillator may be synchronized to an external

clock for more accurate placement of switching harmonics.

Protection features include cycle by cycle current limit pro-

tection, undervoltage lockout and thermal shutdown.

Low minimum supply voltage and low supply current during

shutdown make the LT1533 well suited for portable applica-

tions. The part may also be forced into a 50% duty cycle mode

for unregulated applications. The LT1533 is available in the

16-pin narrow SO package.

■

Greatly Reduced Conducted and Radiated EMI

(<100

P-P

in Typical Application)

■

Low Switching Harmonic Content

■

Independent Control of Switch Voltage and

Current Slew Rates

■

Two 1A Current Limited Power Switches

■

Regulates Positive and Negative Voltages

■

20kHz to 250kHz Oscillator Frequency

■

Easily Synchronized to External Clock

■

Wide Input Voltage Range: 2.7V to 23V

■

Low Shutdown Current: 12µA Typical

■

Easier Layout than with Conventional Switchers

■

Outputs Can Be Forced to 50% Duty Cycle for

Unregulated Applications

■

Precision Instrumentation Systems

■

Isolated Supplies for Industrial Automation

■

Medical Instruments

■

Wireless Communications

■

Single Board Data Acquisition Systems

APPLICATIONS

TYPICAL APPLICATION

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

SHDN

DUTY

SYNC



COL A

COL B

PGND

VSL



CSL



NFB

LT1533

GND

2

15

16

13

12

11

3

4



820pF

16.9k

0.015µF 1000pF

15k

Note 1

33µF

15k

1N4148

L1

300µH

L2

33µH

1N4148

2.49k

21.5k, 1%

C1

47µF

16V

C2

33µF

20V

 C1: SANYO OS-CON

 C2: AVX TPS TANTALUM

 L1: COILTRONICS CTX300-2

 L2: COILCRAFT DT1608C-333

 T1: COILTRONICS CTX02-13834

 NOTE 1: 25nH TRACE INDUCTANCE 

 OR COILCRAFT B07T

12V

150mA

1533 TA01



Low Noise 5V to 12V Forward Push-Pull DC/DC Converter

2mV/DIV

100µV/DIV

2µs/DIV

1533 TA02

12V Output Noise (BW = 100MHz)

<100µV

P-P

Summary of content (20 pages)

PAGE 1
LT1533 Ultralow Noise 1A Switching Regulator U DESCRIPTION FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ The LT ®1533 is a new class of switching regulator designed to reduce conducted and radiated electromagnetic interference (EMI). Ultralow noise and EMI are achieved by providing user control of the output switch slew rates. Voltage and current slew rates can be independently programmed to optimize switcher harmonic content versus efficiency.
PAGE 2
LT1533 W U U U W W W ABSOLUTE MAXIMUM RATINGS PACKAGE/ORDER INFORMATION (Note 1) Input Voltage (VIN) .................................................. 30V Switch Voltage (COL A, COL B) ............................... 30V SHDN Pin Voltage .................................................... 30V Feedback Pin Current ............................................ 10mA Negative Feedback Pin Current ............................ ±10mA Storage Temperature Range .................
PAGE 3
LT1533 ELECTRICAL CHARACTERISTICS VIN = 5V, VC = 0.9V, VFB = VREF. COL A, COL B, SHDN, NFB, DUTY pins open, unless otherwise noted. SYMBOL PARAMETER CONDITIONS gm Error Amplifier Transconductance ∆IC = ±25µA MIN TYP MAX UNITS 1100 700 1500 ● 1900 2300 µmho µmho IESK Error Amplifier Sink Current VFB = VREF + 150mV, VC = 0.9V, VSHDN = 1V ● 120 200 350 µA IESRC Error Amplifier Source Current VFB = VREF – 150mV, VC = 0.
PAGE 4
LT1533 U W TYPICAL PERFORMANCE CHARACTERISTICS Minimum Input Voltage vs Temperature Change in ILIM vs DC 0.7 –50 0.6 25°C –100 2.60 ∆ILIM (mA) 2.55 125°C –150 –200 2.50 –300 25 50 75 100 125 150 0 JUNCTION TEMPERATURE (°C) 0 0 10 20 30 DUTY CYCLE (%) 40 50 1.8 –2.35 1.28 1.6 1.27 1.4 1.2 VFB 1.0 1.24 0.8 0.6 IFB 1.22 0.4 1.21 0.2 1.20 –50 –25 0 0 25 50 75 100 125 150 TEMPERATURE (°C) 30 VNFB –2.45 –2.50 25 –2.55 –2.60 20 INFB –2.65 –2.
PAGE 5
LT1533 U U U PIN FUNCTIONS COL A, COL B (Pins 2, 15): These are the output collectors of the power switches. Their emitters return to PGND through a common sense resistor. COL A and COL B are alternately turned on out of phase. Large currents flow into these pins so it is desirable to keep external trace lengths short to minimize radiation. The collectors can be tied together for simple boost applications. DUTY (Pin 3): Tying the DUTY pin to ground will force the outputs to switch with a 50% duty cycle.
PAGE 6
LT1533 W BLOCK DIAGRA SHDN VIN PGND COL A COL B VC LDO REGULATOR + NEGATIVE FEEDBACK AMP INTERNAL VCC – 100k + OUTPUT DRIVERS 50k NFB – – – FB RVSL SLEW CONTROL gm ERROR + AMP + RCSL COMP + S 1.25V Q FF R RT OSCILLATOR CT Q T SYNC FF BK QB GND DUTY 1533 BD U OPERATIO In noise sensitive applications, switching regulators tend to be ruled out as a power supply option due to their propensity for generating unwanted noise.
PAGE 7
LT1533 U OPERATIO Output regulation is obtained using the error amp to set the switch current trip point. The error amp is a transconductance amplifier that integrates the difference between the feedback output voltage and an internal 1.25V reference. The output of the error amp adjusts the switch current trip point to provide the required load current at the desired regulated output voltage.
PAGE 8
LT1533 U W U U APPLICATIONS INFORMATION It is beyond the scope of this data sheet to get into EMI fundamentals. AN70 contains much information concerning noise in switching regulators and should be consulted. them, 2) the oscillator will control the placement of output frequency harmonics which can aid in specific problems where you might be trying to avoid a certain frequency bandwidth that is used for detection elsewhere.
PAGE 9
LT1533 U W U U APPLICATIONS INFORMATION slower slewing waveforms will dissipate more power so that efficiency will drop. You can also monitor this as you make your slew adjustment by measuring input and output voltage and current. It is possible to use a single slew setting resistor. In this case the RVSL and RCSL pins are tied together. A resistor with a value of 2k to 34k (one half the individual resistors) can then be tied from these pins to ground. Emitter Inductance internal regulator voltage (2.
PAGE 10
LT1533 U U W U APPLICATIONS INFORMATION Thermal Considerations Computing power dissipation for this IC requires careful attention to detail. Reduced output slewing causes the part to dissipate more power than would occur with fast edges. However, much improvement in noise can be produced with modest decrease in supply efficiency. Power dissipation is a function of topology, input voltage, switch current and slew rates. It is impractical to come up with an all-encompassing formula.
PAGE 11
LT1533 U U W U APPLICATIONS INFORMATION VC PIN RVC 2k turns ratio of the transformer. The turns ratio must be large enough to ensure that the transformer can put out a voltage equal to the output voltage plus the diode under minimum input conditions. CVC2 4.7nF CVC 0.01µF 1533 F03 Figure 3 N= To prevent irregular switching, VC pin ripple should be kept below 50mVP-P.
PAGE 12
LT1533 U U W U APPLICATIONS INFORMATION For continuous operation the inductor ripple current must be less than twice the output current. The worst case for this is at maximum input (lowest DC) but we will evaluate at nominal input since the IOUT/4 is somewhat arbitrary. Note when both inputs are off, inductor current splits between outputs and the diode common goes to 0V.
PAGE 13
LT1533 U U W U APPLICATIONS INFORMATION Output ripple current at maximum input (DC = 34.7%) is: ∆IOUT = ( ) = 92mA 12 1 − 2 • 34.7% 800µH • 50kHz The maximum inductor current is: ILMAX = 150mA + 92mA = 196mA 2 Primary inductance should be greater than: LPRI = 5 • 800µH 3.62 = 309µH The magnetizing ripple current is approximately: 12 + 0.5 ∆IMAG = = 225mA 3.6 • 309µH • 50kHz Peak switch current is: ISW(PEAK) = 3.6 • 196mA + 225mA = 930mA which is less than the 1A maximum switch current.
PAGE 14
LT1533 U W U U APPLICATIONS INFORMATION Ceramic: Generally used for high frequency and high voltage bypass. If all ceramic capacitors are used, they can have such a low ESR as to cause loop stability problems. Often they can resonate with their ESL before ESR becomes effective. Table 1 CAPACITOR E CASE AVX TPS, Sprague 593D AVX TAJ 0.7 to 0.9 D CASE AVX TPS, Sprague 593D 0.1 to 0.3 AVX TAJ 0.9 to 2.0 Input Capacitor The requirements for the input capacitor are less stringent for this part.
PAGE 15
LT1533 U U W U APPLICATIONS INFORMATION The slew rate adjustment should be made by putting a 3.9k resistor in series with a 50k pot on the RVSL and RCSL pins (or a 2k resistor in series with a 25k pot with both pins tied together). Monitor output noise or other system signal while increasing the resistance until desired noise performance is reached. System efficiency can also be monitored.
PAGE 16
LT1533 U TYPICAL APPLICATIONS Low Noise 5V to –12V Forward Push-Pull Converter. Output Noise Is Below 100µV. Noise Performance Is Identical to Positive Output Version. See AN70 for Details 5V + T1 14 4.7µF 11 3 3300pF 4 5 18k 6 VIN SHDN COL A DUTY COL B SYNC PGND CT LT1533 RVSL RT RCSL 10 VC NFB FB GND 0.01µF 9 L2 100µH 1N4148 ( L3 OPTIONAL FOR 100µH LOWEST RIPPLE –12V 2 1N4148 47µF + 15 + 47µF L1 16 13 15k 12 15k 9.6k 1% 8 1533 TA03 2.4k 1% 7 L1: 22nH INDUCTOR.
PAGE 17
LT1533 U TYPICAL APPLICATIONS Hysteretic Loop Lowers Quiescent Current to 100µA While Maintaining Low Output Noise. See AN70 for Details 2.7V TO 4V (3 Ni-Cd BATTERIES) 11 3 3300pF 4 5 18k 6 VIN SHDN COL A DUTY COL B SYNC PGND CT LT1533 RVSL RT RCSL 10 VC GND NFB 9 8 0.01µF FB 2 1N4148 ( OPTIONAL FOR L3 100µH LOWEST RIPPLE ) + + 47µF 47µF 15 L2 16 5V 21.5k 1% 13 15k 12 15k C1 LTC1440 7 2.32k 1% + 4.7µF L1 100µH 12V 1N4148 T1 14 – + 150k 10pF 1.
PAGE 18
LT1533 U TYPICAL APPLICATIONS A 10W Low Noise 5V to 12V Converter. Q1-Q2 Provide 5A Output Capacity While Preserving LT1533’s Voltage Current Slew Control. Efficiency Is 68%. Higher Input Voltages Minimize Follower Loss, Boosting Efficiency Above 71%. See AN70 for Details 1N4148 330Ω 5V 1N5817 0.05Ω T1 Q1 + 4.7µF 14 11 3 1500pF 4 5 18k 6 VIN SHDN COL A DUTY COL B SYNC CT PGND LT1533 RVSL RT RCSL 10 0.01µF 18 VC L1 300µH 0.003µF GND NFB 9 8 FB 2 FB1 15 FB2 + 4.7µF 0.
PAGE 19
LT1533 U PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. S Package 16-Lead Plastic Small Outline (Narrow 0.150) (LTC DWG # 05-08-1610) 0.386 – 0.394* (9.804 – 10.008) 16 15 14 13 12 11 10 9 0.150 – 0.157** (3.810 – 3.988) 0.228 – 0.244 (5.791 – 6.197) 1 0.010 – 0.020 × 45° (0.254 – 0.508) 0.008 – 0.010 (0.203 – 0.254) 2 3 4 5 6 0.053 – 0.069 (1.346 – 1.752) 0.014 – 0.019 (0.355 – 0.483) 8 0.004 – 0.010 (0.101 – 0.254) 0° – 8° TYP 0.016 – 0.050 0.
PAGE 20
LT1533 U TYPICAL APPLICATION 10W Off-Line Power Supply Passes FCC Emission Requirements Without Filter Components T1 !! GER !! DAN LTAGE O HV HIG 0.1µF AC LINE + HV 100µF 400V 1N4005 1.6k 1W 0.001µF 250V 0.001µF 250V 1.6k 1W HV HV + 10µF 5k 0.5W 360k Q1 MPSA42 Q2 12V 12V D Q5 Q6 IRF840 IRF840 S 1N5818 1N5818 S Q3 10k 1N759A 12V D 1k 1k 0.