Datasheet

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LT3433

3433f

High Voltage

Step-Up/Step-Down

DC/DC Converter

■

Automatic Step-Up and Step-Down Conversion

■

Uses a Single Inductor

■

Wide 4V to 60V Input Voltage Range

■

OUT

from 3.3V to 20V

■

Dual Internal 500mA Switches

■

100µA No-Load Quiescent Current

■

Low Current Shutdown

■

±1% Output Voltage Accuracy

■

200kHz Operating Frequency

■

Boosted Supply Pin to Saturate High Side Switch

■

Frequency Foldback Protection

■

Current Limit Foldback Protection

■

Current Limit Unaffected by Duty Cycle

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16-lead Thermally Enhanced TSSOP Package

■

12V Automotive Systems

■

Wall Adapter Powered Systems

■

Battery Power Voltage Buffering

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

Burst Mode is a registered trademark of Linear Technology Corporation.

U.S. patent number: 5731694

The LT

3433 is a 200kHz fixed-frequency current mode

switching regulator that provides both step-up and step-

down regulation using a single inductor. The IC operates

over a 4V to 60V input voltage range making it suitable for

use in various wide input voltage range applications such

as automotive electronics that must withstand both load

dump and cold crank conditions.

Internal control circuitry monitors system conditions and

converts from single switch buck operation to dual switch

bridged operation when required, seamlessly changing

between step-down and step-up voltage conversion.

Optional Burst Mode

operation reduces no-load quies-

cent current to 100µA and maintains high efficiencies with

light loads.

Current limit foldback and frequency foldback help pre-

vent inductor current runaway during start-up. Program-

mable soft-start helps prevent output overshoot at start-up.

The LT3433 is available in a 16-lead thermally enhanced

TSSOP package.

0.01µF

330pF

1nF

2.2µF

SHDN

BST

SWH

SGND

LT3433

SWL

OUT

0.1µF

1N4148

PGND

3433 TA01

100µH

47µF

309k

100k

OUT

B160A

B120A

68k

0.1µF

BIAS

BURST_EN

4V to 60V to 5V DC/DC Converter

with Burst Mode Operation

OUTPUT CURRENT (mA)

EFFICIENCY (%)

0.1 10 100 1000

3433 TA01b

= 13.8V

= 4V

Efficiency

(V)

MAXIMUM OUTPUT CURRENT (mA)

100

200

300

400

500

20 30 40

3433 TA01c

50 60

BRIDGED

BUCK

OUT

= 5V

Maximum Output

Current vs V

FEATURES

DESCRIPTIO

APPLICATIO S

TYPICAL APPLICATIO

Summary of content (16 pages)

PAGE 1
LT3433 High Voltage Step-Up/Step-Down DC/DC Converter U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO The LT®3433 is a 200kHz fixed-frequency current mode switching regulator that provides both step-up and stepdown regulation using a single inductor. The IC operates over a 4V to 60V input voltage range making it suitable for use in various wide input voltage range applications such as automotive electronics that must withstand both load dump and cold crank conditions.
PAGE 2
LT3433 U U W W W Input Supply (VIN) .................................... –0.3V to 60V Boosted Supply (VBST) .............. –0.3V to VSW_H + 30V (VBST(MAX) = 80V) Internal Supply (VBIAS) ............................. – 0.3V to 30V SW_H Switch Voltage .................................. – 2V to 60V SW_L Switch Voltage ............................... – 0.3V to 30V Feedback Voltage (VFB) ............................... – 0.3V to 5V Burst Enable Pin (VBURST_EN) ................... – 0.
PAGE 3
LT3433 ELECTRICAL CHARACTERISTICS The ● denotes specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 13.8V, VFB = 1.25V, VOUT = 5V, VBURST_EN = 0V, VBST – VIN = 5V, unless otherwise noted. SYMBOL PARAMETER CONDITIONS VFB Feedback Reference Voltage ● ∆VFB Feedback Reference Line Regulation 5.
PAGE 4
LT3433 U W TYPICAL PERFOR A CE CHARACTERISTICS Error Amp Reference vs Temperature Soft-Start Current vs Temperature 7.0 Switch Current Limit vs VFB 1.232 700 ERROR AMP REFERENCE (V) ISS (µA) 6.0 5.5 5.0 SWITCH CURRENT LIMIT (mA) TA = 25°C 6.5 1.231 1.230 1.229 4.5 4.0 –50 0 50 TEMPERATURE (°C) 100 125 1.228 –50 600 500 400 300 0 50 TEMPERATURE (°C) 100 3433 G03 125 0.2 0 0.6 0.4 VFB (V) 0.
PAGE 5
LT3433 U W TYPICAL PERFOR A CE CHARACTERISTICS VBST Supply Switch Drive Current vs Temperature (ISW = 500mA) Switch Resistance vs Temperature (ISW = 500mA) 1.1 VOUT Supply Switch Drive Current vs Temperature (ISW = 500mA) 40 40 37 37 RSWH 0.8 0.7 RSWL IVOUT/ISW (mA/A) 0.9 IBST/ISW (mA/A) SWITCH ON RESISTANCE (Ω) 1.0 34 31 34 31 0.6 28 0.5 0.
PAGE 6
LT3433 U U U PI FU CTIO S VFB (Pin 7): Error Amplifier Inverting Input. The noninverting input of the error amplifier is connected to an internal 1.231V reference. The VFB pin is connected to a resistor divider from the converter output. Values for the resistor connected from VOUT to VFB (RFB1) and the resistor connected from VFB to ground (RFB2) can be calculated to program converter output voltage (VOUT) via the following relation: VOUT = 1.
PAGE 7
LT3433 W BLOCK DIAGRA VBIAS 1.25V BURST CONTROL CIRCUITS BIAS 12 BURST_EN 5 VIN 4 SENSE AMPLIFIER VBST 2 COMPARATOR BOOSTED DRIVER SW_H 3 SLOPE COMP OSCILLATOR 200kHz FREQUENCY CONTROL MODE CONTROL SWITCH CONTROL LOGIC SW_L 15 DRIVER GND VFB 14 7 ERROR AMPLIFIER 30% LOAD 1.231V VC + Burst Mode CONTROL SHDN 6 11 SHUTDOWN – 15% LOAD 0.
PAGE 8
LT3433 U W U U APPLICATIO S I FOR ATIO Overview The LT3433 is a high input voltage range, step-up/stepdown DC/DC converter IC using a 200kHz constant frequency, current mode architecture. Dual internal switches allow the full input voltage to be imposed across the switched inductor, such that both step-up and step-down modes of operation can be realized using the same single inductor topology. The LT3433 has provisions for high efficiency, low load operation for battery-powered applications.
PAGE 9
LT3433 U W U U APPLICATIO S I FOR ATIO Antislope Compensation Most current mode switching controllers use slope compensation to prevent current mode instability. The LT3433 is no exception. A slope compensation circuit imposes an artificial ramp on the sensed current to increase the rising slope as duty cycle increases. Unfortunately, this additional ramp corrupts the sensed current value, reducing the achievable current limit value by the same amount as the added ramp represents.
PAGE 10
LT3433 U W U U APPLICATIO S I FOR ATIO The requirement for avoiding current mode instability is that the rising slope of sensed inductor ripple current (S1) is greater than the falling slope (S2). At duty cycles greater than 50% this is not true. To avoid the instability condition, a false signal is added to the sensed current with a slope (SX) that is sufficient to prevent current mode instability, or S1 + SX ≥ S2.
PAGE 11
LT3433 U W U U APPLICATIO S I FOR ATIO RL = Inductor series resistance ∆BST = Boosted switch drive currents IVBST/ISW (in A/A) ∆OUT = Grounded switch drive currents IVOUT/ISW (in A/A) VF1 = Switch node catch diode forward voltage VF2 = Pass diode forward voltage IVIN = VIN quiescent input current IIN = VIN switched current IBIAS = VBIAS quiescent input current RCESR = Output capacitor ESR Operational duty cycle is a function of voltage imposed across the switched inductance and switch on/off times.
PAGE 12
LT3433 U W U U APPLICATIO S I FOR ATIO Design Example CALCULATED VALUES 4V-60V to 5V DC/DC converter (the application on the front page of this data sheet), load capability for TA = 85°C. Application Specific Constants: VIN = 4V VOUT = 5V L = 100µH RL = 0.28Ω VF1 = 0.45V VF2 = 0.4V RCESR = 0.01Ω LT3433 W/C Constants: IMAX = 0.55A RSWH = 1.2Ω RSWL = 1Ω fO = 190kHz ∆BST = 0.05 ∆OUT = 0.
PAGE 13
LT3433 U W U U APPLICATIO S I FOR ATIO Input Voltage Transient Suppression 4V-50V to 5V Converter Input Transient Response 1ms 13.8V to 4V Input Transition Not only does a LT3433 converter operate across a large range of DC input voltages, it also maintains tight output regulation during significant input voltage transients. The LT3433 automatic transitioning between buck and buck/ boost modes of operation provides seamless output regulation over these input voltage transients.
PAGE 14
LT3433 U TYPICAL APPLICATIO S 8V-60V to 12V Converter L1 200µH TDK SLF12565T-221M1R0 DS1 B160A D2 1N4148 C7 0.47µF 20V VIN 8V TO 60V C6 2.2µF 100V C3 330pF DS2 B120A VBST + C5 47µF 25V SW_L SW_H PWRGND LT3433 VOUT VIN D1 1N4148 (BURST) BURST_EN VBIAS VC SHDN VOUT 12V 8V < VIN < 18V: 125mA 18V < VIN < 60V: 380mA C6 0.1µF 20V R1 68k C2 1nF SS VFB R2 20k 1% R3 174k 1% SGND C4 0.01µF MODE SWITCH: VIN H-L: 16.
PAGE 15
LT3433 U PACKAGE DESCRIPTIO FE Package 16-Lead Plastic TSSOP (4.4mm) (Reference LTC DWG # 05-08-1663) Exposed Pad Variation BB 4.90 – 5.10* (.193 – .201) 3.58 (.141) 3.58 (.141) 16 1514 13 12 1110 6.60 ±0.10 9 2.94 (.116) 4.50 ±0.10 2.94 6.40 (.116) (.252) BSC SEE NOTE 4 0.45 ±0.05 1.05 ±0.10 0.65 BSC 1 2 3 4 5 6 7 8 RECOMMENDED SOLDER PAD LAYOUT 4.30 – 4.50* (.169 – .177) 0.09 – 0.20 (.0035 – .0079) 0.50 – 0.75 (.020 – .030) NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS MILLIMETERS 2.
PAGE 16
LT3433 U TYPICAL APPLICATIO Burst Only Low Noise 5V Maintenance Supply L1 33µH COILCRAFT LPO1704-333 DS1 B160A DS2 B120A D1 1N4148 C1 0.1µF VBST SW_L SW_H PWRGND LT3433 VIN VOUT VIN 4V TO 60V 2.2µF C6 100pF R2 510k 5% BURST_EN VBIAS VC SHDN VFB R1 2.2M 5% D2 1N4148 C2 0.1µF SS SGND IN OUT LT1761-5 SHDN GND BYP C4 0.01µF VOUT 5V C5 10mA 2.2µF C3 10µF 3433 TA02 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1076/LT1076HV 1.