LT1933 Linear Technology, LT1933 Datasheet

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LT1933

Manufacturer Part Number
LT1933
Description
600mA 500kHz Step-Down Switching Regulator in SOT-23
Manufacturer
Linear Technology
Datasheet

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FEATURES
APPLICATIO S
TYPICAL APPLICATIO
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 Profile (1mm) SOT-23 (ThinSOT™) Package
Automotive Battery Regulation
Industrial Control Supplies
Wall Transformer Regulation
Distributed Supply Regulation
Battery-Powered Equipment
4.5V TO 36V
OFF ON
V
IN
2.2µF
U
V
SHDN
IN
GND
3.3V Step-Down Converter
LT1933
BOOST
FB
SW
10k
16.5k
U
0.1µF
MBRM140
1N4148
22µH
1933 TA01a
22µF
V
3.3V/500mA
OUT
600mA, 500kHz Step-Down
DESCRIPTIO
The LT
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 man-
agement in battery-powered systems.
ThinSOT is a trademark of Linear Technology Corporation.
, LTC and LT are registered trademarks of Linear Technology Corporation.
®
1933 is a current mode PWM step-down DC/DC
Switching Regulator
95
90
85
80
70
65
75
0
U
V
IN
= 12V
100
LOAD CURRENT (mA)
200
Efficiency
V
OUT
www.DataSheet4U.com
V
300
OUT
= 5V
= 3.3V
in SOT-23
400
500
LT1933
1933 TA01b
600
1
1933f

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LT1933 Summary of contents

Page 1

... 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

... Note 1: Absolute Maximum Ratings are those values beyond which the life of the device may be impaired. Note 2: The LT1933E is guaranteed to meet performance specifications from 0°C to 70°C. Specifications over the –40°C to 85°C operating temperature range are assured by design, characterization and correlation ...

Page 3

... T = 85°C A 300 200 100 0 0 0.1 0.2 0 SWITCH CURRENT (A) 1933 G05 Switching Frequency 600 550 500 450 400 100 125 –50 – TEMPERATURE (°C) 1933 G08 LT1933 80 100 1933 G03 T = –40°C A 0.4 0.5 0.6 1933 G06 75 100 125 1933 G09 1933f 3 ...

Page 4

... LT1933 W U TYPICAL PERFOR A CE CHARACTERISTICS Frequency Foldback 700 T = 25°C A 600 500 400 300 200 100 0 0.0 0.5 1.0 FB PIN VOLTAGE (V) 1933 G10 Typical Minimum Input Voltage OUT T = 25° 33µ START 6 TO RUN 100 LOAD CURRENT (mA) ...

Page 5

... C4 OSC FREQUENCY FOLDBACK 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 V provides a soft-start function; see the Applications Infor- mation section ...

Page 6

... An internal regulator provides power to the control cir- cuitry. This regulator includes an undervoltage lockout to prevent switching when V pin is used to place the LT1933 in shutdown, disconnect- ing the output and reducing the input current to less than 2µA. The switch driver operates from either the input or from the BOOST pin ...

Page 7

... The MBRM140 provides better efficiency, and will handle extended overload conditions. Input Capacitor Bypass the input of the LT1933 circuit with a 2.2µF or higher value ceramic capacitor of X7R or X5R type. Y5V types have poor performance over temperature and ap- plied voltage, and should not be used. A 2.2µF ceramic is adequate to bypass the LT1933 and will easily handle the ripple current ...

Page 8

... Output Capacitor The output capacitor has two essential functions. Along with the inductor, it filters the square wave generated by the LT1933 to produce the DC output. In this role it determines the output ripple, and low impedance at the switching frequency is important. The second function is to store energy in order to satisfy transient loads and stabilize the LT1933’ ...

Page 9

... U U APPLICATIO S I FOR ATIO 16.5k FB 10k 470pF 16.5k FB 10k 16. 10k Figure 1. Transient Load Response of the LT1933 with Different Output Capacitors as the Load Current is Stepped from 100mA OUT OUT 50mV/DIV 22µF I OUT 200mA/DIV 1933 F01a V OUT V OUT 50mV/DIV 22µ OUT ...

Page 10

... For proper startup, the minimum input voltage is also limited by the boost circuit. If the input voltage is ramped slowly, or the LT1933 is turned on with its SHDN pin when the output is already in regulation, then the boost capacitor may not be fully charged ...

Page 11

... SHDN pin reaches 2.3V. RUN RUN 15k 0.1µF Figure 4. To Soft-Start the LT1933, Add a Resistor and Capacitor to the SHDN Pin Shorted and Reversed Input Protection If the inductor is chosen so that it won’t saturate exces- sively, an LT1933 buck regulator will tolerate a shorted output ...

Page 12

... AI.EI. + 0.1µF Figure 6. A Well Chosen Input Network Prevents Input Voltage Overshoot and Ensures Reliable Operation When the LT1933 is Connected to a Live Supply Hot Plugging Safely The small size, robustness and low impedance of ceramic capacitors make them an attractive option for the input bypass capacitor of LT1933 circuits ...

Page 13

... Frequency Compensation The LT1933 uses current mode control to regulate the output. This simplifies loop compensation. In particular, the LT1933 does not require the ESR of the output capacitor for stability allowing the use of ceramic capaci- tors to achieve low output ripple and small circuit size. ...

Page 14

... 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. High Temperature Considerations The die temperature of the LT1933 must be lower than the maximum rating of 125° ...

Page 15

... MIN (NOTE 4) 0.95 BSC 0.90 – 1.30 0.90 – 1.45 0.09 – 0.20 (NOTE 3) ATTENTION: ORIGINAL SOT23-6L PACKAGE. MOST SOT23-6L PRODUCTS CONVERTED TO THIN SOT23 PACKAGE, DRAWING # 05-08-1636 AFTER APPROXIMATELY APRIL 2001 SHIP DATE LT1933 www.DataSheet4U.com 2.80 – 3.10 (NOTE 4) PIN ONE ID 0.25 – 0.50 TYP 6 PLCS NOTE 3 1.90 BSC 0.09 – 0.15 NOTE 3 S6 SOT-23 0502 ...

Page 16

... OUT DC/DC Converter Burst Mode is a registered trademark of Linear Technology Corporation. Linear Technology Corporation 16 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 ● 2.5V Step-Down Converter BOOST IN C3 LT1933 0.47µ SHDN SW GND 10. 2.2µF 10k COMMENTS ...

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