Datasheet

ManualsBrandsLinear Technology ManualsDC / DC Adjustable Switching RegulatorsSwitching Regulator IC Step-Down SOT-23-1.2 ... 31.7V

LT1933

1933fe

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

600mA, 500kHz Step-Down

Switching Regulator in

SOT-23 and DFN Packages

The LT

1933 is a current mode PWM step-down DC/DC

converter with an internal 0.75A power switch, packaged

in a tiny 6-lead SOT-23. The wide input range of 3.6V

to 36V makes the LT1933 suitable for regulating power

from a wide variety of sources, including unregulated wall

transformers, 24V industrial supplies and automotive

batteries. Its high operating frequency allows the use of

tiny, low cost inductors and ceramic capacitors, resulting

in low, predictable output ripple.

Cycle-by-cycle current limit provides protection against

shorted outputs, and soft-start eliminates input current

surge during start up. The low current (<2µA) shutdown

provides output disconnect, enabling easy power manage-

ment in battery-powered systems.

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear

Technology Corporation. ThinSOT is a trademark of Linear Technology Corporation. All other

trademarks are the property of their respective owners.

3.3V Step-Down Converter

Wide Input Range: 3.6V to 36V

5V at 600mA from 16V to 36V Input

3.3V at 600mA from 12V to 36V Input

5V at 500mA from 6.3V to 36V Input

3.3V at 500mA from 4.5V to 36V Input

Fixed Frequency 500kHz Operation

Uses Tiny Capacitors and Inductors

Soft-Start

Internally Compensated

Low Shutdown Current: <2µA

Output Adjustable Down to 1.25V

Low Proﬁ le (1mm) SOT-23 (ThinSOT™) and

(2mm × 3mm × 0.75mm) 6-Pin DFN Packages

Automotive Battery Regulation

Industrial Control Supplies

Wall Transformer Regulation

Distributed Supply Regulation

Battery-Powered Equipment

Efﬁ ciency

4.5V TO 36V

OFF ON

0.1µF

22µH

1N4148

MBRM140

10k

16.5k

22µF

1933 TA01a

2.2µF

OUT

3.3V/500mA

BOOST

GND FB

SHDN SW

LT1933

LOAD CURRENT (mA)

300 400

1933 TA01b

100 200 600500

EFFICIENCY (%)

= 12V

OUT

= 5V

OUT

= 3.3V

Downloaded from Arrow.com.

Summary of content (20 pages)

PAGE 1
LT1933 600mA, 500kHz Step-Down Switching Regulator in SOT-23 and DFN Packages FEATURES DESCRIPTION n The LT ®1933 is a current mode PWM step-down DC/DC converter with an internal 0.75A power switch, packaged in a tiny 6-lead SOT-23. The wide input range of 3.6V to 36V makes the LT1933 suitable for regulating power from a wide variety of sources, including unregulated wall transformers, 24V industrial supplies and automotive batteries.
PAGE 2
LT1933 ABSOLUTE MAXIMUM RATINGS (Note 1) Input Voltage (VIN) ..................................... –0.4V to 36V BOOST Pin Voltage ...................................................43V BOOST Pin Above SW Pin.........................................20V SHDN Pin ................................................... –0.4V to 36V FB Voltage .................................................... –0.4V to 6V Operating Temperature Range (Note 2) LT1933E ...................................................
PAGE 3
LT1933 ELECTRICAL CHARACTERISTICS The l denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. VIN = 12V, VBOOST = 17V, unless otherwise noted. (Note 2) PARAMETER CONDITIONS MIN TYP 3.35 3.6 V 1.225 1.245 1.265 V 40 120 nA Undervoltage Lockout l Feedback Voltage l MAX UNITS FB Pin Bias Current VFB = Measured VREF + 10mV (Note 4) Quiescent Current Not Switching 1.6 2.
PAGE 4
LT1933 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C VOUT = 5V 90 VIN = 24V 80 70 Switch Current Limit 1200 TA = 25°C VOUT = 3.3V 90 VIN = 12V EFFICIENCY (%) EFFICIENCY (%) Efﬁciency, VOUT = 3.
PAGE 5
LT1933 TYPICAL PERFORMANCE CHARACTERISTICS Frequency Foldback SHDN Pin Current Soft-Start 1.4 TA = 25°C TA = 25°C DC = 30% 1.2 500 400 300 200 100 200 SHDN PIN CURRENT (μA) 600 SWITCH CURRENT LIMIT (A) 1.0 0.8 0.6 0.4 0 0 1.0 0.5 FB PIN VOLTAGE (V) 0.0 150 100 50 0 1.5 0 2 3 1 SHDN PIN VOLTAGE (V) 1933 G10 4 VOUT = 3.3V TA = 25°C L = 22μH 5.5 7 TO START INPUT VOLTAGE (V) 6 TO RUN 5.0 4.5 4.0 5 TO RUN 3.5 4 10 100 LOAD CURRENT (mA) 1 1.2 1.0 0.8 0.6 0.
PAGE 6
LT1933 PIN FUNCTIONS (SOT-23/DFN) SHDN (Pin 4): The SHDN pin is used to put the LT1933 in shutdown mode. Tie to ground to shut down the LT1933. Tie to 2.3V or more for normal operation. If the shutdown feature is not used, tie this pin to the VIN pin. SHDN also provides a soft-start function; see the Applications Information section. BOOST (Pin 1): The BOOST pin is used to provide a drive voltage, higher than the input voltage, to the internal bipolar NPN power switch.
PAGE 7
LT1933 OPERATION (Refer to Block Diagram) The LT1933 is a constant frequency, current mode step down regulator. A 500kHz oscillator enables an RS ﬂipﬂop, turning on the internal 750mA power switch Q1. An ampliﬁer and comparator monitor the current ﬂowing between the VIN and SW pins, turning the switch off when this current reaches a level determined by the voltage at VC. An error ampliﬁer measures the output voltage through an external resistor divider tied to the FB pin and servos the VC node.
PAGE 8
LT1933 APPLICATIONS INFORMATION saturation current should be about 30% higher. For robust operation in fault conditions the saturation current should be ~1A. To keep efﬁciency high, the series resistance (DCR) should be less than 0.2Ω. Table 1 lists several vendors and types that are suitable. Of course, such a simple design guide will not always result in the optimum inductor for your application. A larger value provides a slightly higher maximum load current, and will reduce the output voltage ripple.
PAGE 9
LT1933 APPLICATIONS INFORMATION switching current into a tight local loop, minimizing EMI. A 2.2μF capacitor is capable of this task, but only if it is placed close to the LT1933 and the catch diode; see the PCB Layout section. A second precaution regarding the ceramic input capacitor concerns the maximum input voltage rating of the LT1933. A ceramic input capacitor combined with trace or cable inductance forms a high quality (under damped) tank circuit.
PAGE 10
LT1933 APPLICATIONS INFORMATION Figure 1 shows the transient response of the LT1933 with several output capacitor choices. The output is 3.3V. The load current is stepped from 100mA to 400mA and back to 100mA, and the oscilloscope traces show the output voltage. The upper photo shows the recommended value. The second photo shows the improved response (less voltage VOUT 16.5k FB drop) resulting from a larger output capacitor and a phase lead capacitor.
PAGE 11
LT1933 APPLICATIONS INFORMATION BOOST Pin Considerations Capacitor C3 and diode D2 are used to generate a boost voltage that is higher than the input voltage. In most cases a 0.1μF capacitor and fast switching diode (such as the 1N4148 or 1N914) will work well. Figure 2 shows two ways to arrange the boost circuit. The BOOST pin must be at least 2.3V above the SW pin for best efﬁciency. For outputs of 3V and above, the standard circuit (Figure 2a) is best. For outputs between 2.5V and 3V, use a 0.
PAGE 12
LT1933 APPLICATIONS INFORMATION cases the discharged output capacitor will present a load to the switcher which will allow it to start. The plots show the worst-case situation where VIN is ramping very slowly. For lower start-up voltage, the boost diode can be tied to VIN; however, this restricts the input range to one-half of the absolute maximum rating of the BOOST pin. At light loads, the inductor current becomes discontinuous and the effective duty cycle can be very high.
PAGE 13
LT1933 APPLICATIONS INFORMATION Shorted and Reversed Input Protection If the inductor is chosen so that it won’t saturate excessively, an LT1933 buck regulator will tolerate a shorted output. There is another situation to consider in systems where the output will be held high when the input to the LT1933 is absent. This may occur in battery charging applications or in battery backup systems where a battery or some other supply is diode OR-ed with the LT1933’s output.
PAGE 14
LT1933 APPLICATIONS INFORMATION CLOSING SWITCH SIMULATES HOT PLUG IIN VIN DANGER! LT1933 + VIN 20V/DIV 2.2μF LOW IMPEDANCE ENERGIZED 24V SUPPLY RINGING VIN MAY EXCEED ABSOLUTE MAXIMUM RATING OF THE LT1933 IIN 5A/DIV STRAY INDUCTANCE DUE TO 6 FEET (2 METERS) OF TWISTED PAIR 20μs/DIV (6a) LT1933 + 10μF 35V AI.EI. + VIN 20V/DIV 2.2μF IIN 5A/DIV 20μs/DIV (6b) 1Ω LT1933 + 0.1μF VIN 20V/DIV 2.2μF IIN 5A/DIV 20μs/DIV 1933 F06 (6c) Figure 6.
PAGE 15
LT1933 APPLICATIONS INFORMATION Figure 6 shows the waveforms that result when an LT1933 circuit is connected to a 24V supply through six feet of 24-gauge twisted pair. The ﬁrst plot is the response with a 2.2μF ceramic capacitor at the input. The input voltage rings as high as 35V and the input current peaks at 20A. One method of damping the tank circuit is to add another capacitor with a series resistor to the circuit. In Figure 6b an aluminum electrolytic capacitor has been added.
PAGE 16
LT1933 APPLICATIONS INFORMATION PCB Layout unbroken ground plane below these components, and tie this ground plane to system ground at one location, ideally at the ground terminal of the output capacitor C1. The SW and BOOST nodes should be as small as possible. Finally, keep the FB node small so that the ground pin and ground traces will shield it from the SW and BOOST nodes. Include two vias near the GND pin of the LT1933 to help remove heat from the LT1933 to the ground plane.
PAGE 17
LT1933 TYPICAL APPLICATIONS 3.3V Step-Down Converter VIN 4.5V TO 36V OFF ON D2 VIN BOOST C3 0.1μF LT1933 SHDN L1 22μH SW GND FB C2 2.2μF R1 16.5k VOUT 3.3V/ 500mA D1 C1 22μF 6.3V R2 10k 1933 TA02b 12V Step-Down Converter VIN 14.5V TO 36V D3, 6V VIN C3 0.1μF LT1933 OFF ON SHDN GND C2 2.2μF D2 BOOST SW FB R1 86.6k R2 10k L1 47μH VOUT 12V/ 450mA D1 C1 10μF 1933 TA02d 1933fe 17 Downloaded from Arrow.com.
PAGE 18
LT1933 PACKAGE DESCRIPTION DCB Package 6-Lead Plastic DFN (2mm × 3mm) (Reference LTC DWG # 05-08-1715) 0.70 ±0.05 3.55 ±0.05 1.65 ±0.05 (2 SIDES) 2.15 ±0.05 PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 1.35 ±0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS R = 0.115 TYP 2.00 ±0.10 (2 SIDES) R = 0.05 TYP 3.00 ±0.10 (2 SIDES) 0.40 ± 0.10 4 6 1.65 ± 0.10 (2 SIDES) PIN 1 NOTCH R0.20 OR 0.25 × 45° CHAMFER PIN 1 BAR TOP MARK (SEE NOTE 6) 3 0.200 REF 0.75 ±0.05 1 (DCB6) DFN 0405 0.25 ± 0.05 0.
PAGE 19
LT1933 PACKAGE DESCRIPTION S6 Package 6-Lead Plastic SOT-23 (Reference LTC DWG # 05-08-1634) 0.62 MAX 2.80 – 3.10 (NOTE 4) 0.95 REF 1.22 REF 1.4 MIN 3.85 MAX 2.62 REF 2.60 – 3.00 1.50 – 1.75 (NOTE 4) PIN ONE ID RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR 0.25 – 0.50 TYP 6 PLCS NOTE 3 0.95 BSC 0.90 – 1.30 0.20 BSC 0.90 – 1.45 DATUM ‘A’ 0.35 – 0.55 REF 0.09 – 0.20 (NOTE 3) NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DRAWING NOT TO SCALE 3. DIMENSIONS ARE INCLUSIVE OF PLATING 4.
PAGE 20
LT1933 TYPICAL APPLICATION 2.5V Step-Down Converter D2 VIN 3.6V TO 36V VIN BOOST C3 L1 0.47μF 15μH LT1933 SHDN OFF ON GND SW FB C2 2.2μF R1 10.5k VOUT 2.5V/500mA D1 C1 22μF R2 10k 1933 TA03 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1074/LT1074HV 4.4A IOUT, 100kHz, High Efﬁciency Step-Down DC/DC Converter VIN: 7.3V to 45V/64V, VOUT(MIN) = 2.21V, IQ = 8.5mA, ISD = 10μA, DD-5/DD-7, TO220-5/TO220-7 Packages LT1076/LT1076HV 1.