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Linear Technology LTC1872 Manual

Constant frequency current mode step-up dc/dc controller in sot-23
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FeaTures
High Efficiency: Over 90%
n
High Output Currents Easily Achieved
n
Wide V
Range: 2.5V to 9.8V
n
IN
V
Limited Only by External Components
n
OUT
Constant Frequency 550kHz Operation
n
Burst Mode™ Operation at Light Load
n
Current Mode Operation for Excellent Line and Load
n
Transient Response
Low Quiescent Current: 270µA
n
Shutdown Mode Draws Only 8µA Supply Current
n
±2.5% Reference Accuracy
n
Tiny 6-Lead SOT-23 Package
n
applicaTions
Lithium-Ion-Powered Applications
n
Cellular Telephones
n
Wireless Modems
n
Portable Computers
n
Scanners
n
Typical applicaTion
147k
1
I
/RUN
V
TH
IN
LTC1872
220pF
2
–
GND
SENSE
80.6k
3
V
NGATE
FB
422k
C1: TAIYO YUDEN CERAMIC EMK325BJ106MNT
C2: MURATA GRM42-2X5R226K6.3
D1: IR10BQ015
L1: MURATA LQN6C4R7M04
M1: IRLMS2002
R1: DALE 0.25W
Figure 1. LTC1872 High Output Current 3.3V to 5V Boost Converter
C1
R1
10µF
0.03
10V
5
L1
4.7µH
4
+
C2
6
D1
M1
2× 22F
6.3V
For more information
Constant Frequency
Current Mode Step-Up
DC/DC Controller in SOT-23
DescripTion
The
LTC
1872
is a constant frequency current mode step-
®
up DC/DC controller providing excellent AC and DC load
and line regulation. The device incorporates an accurate
undervoltage lockout feature that shuts down the LTC1872
when the input voltage falls below 2.0V.
The LTC1872 boasts a ±2.5% output voltage accuracy
and consumes only 270µA of quiescent current. For ap-
plications where efficiency is a prime consideration, the
LTC1872 is configured for Burst Mode operation, which
enhances efficiency at low output current.
In shutdown, the device draws a mere 8µA. The high
550kHz constant operating frequency allows the use of a
small external inductor.
The LTC1872 is available in a small footprint 6-lead
SOT-23.
L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
V
IN
3.3V
100
95
90
V
OUT
85
5V
1A
80
75
70
65
1
1872 TA01
www.linear.com/LTC1872
LTC1872
Efficiency vs Load Current
V
= 3.3V
IN
V
= 5V
OUT
10
100
LOAD CURRENT (mA)
1872 TA01b
1000
1872fa
1

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Summary of Contents for Linear Technology LTC1872

  • Page 1 The LTC1872 is available in a small footprint 6-lead Lithium-Ion-Powered Applications SOT-23. Cellular Telephones L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks Wireless Modems of Linear Technology Corporation. All other trademarks are the property of their respective owners.

  • Page 2: Absolute Maximum Ratings

    Note 2: The LTC1872E is guaranteed to meet performance specifications Note 5: The LTC1872 is tested in a feedback loop that servos V to the from 0°C to 70°C. Specifications over the – 40°C to 85°C operating output of the error amplifier.

  • Page 3: Typical Performance Characteristics

    LTC1872 Typical perForMance characTerisTics Undervoltage Lockout Trip Reference Voltage Normalized Oscillator Frequency Voltage vs Temperature vs Temperature vs Temperature 2.24 = 4.2V = 4.2V FALLING 2.20 2.16 2.12 2.08 2.04 –2 2.00 –4 1.96 –6 1.92 –8 1.88 –10 1.84 –55...

  • Page 4: Functional Diagram

    Main Control Loop relative to the 0.8V reference, which in turn causes the /RUN voltage to increase until the average inductor The LTC1872 is a constant frequency current mode current matches the new load current. switching regulator. During normal operation, the external...
  • Page 5 Comparator OVP guards against transient overshoots Overvoltage Protection > 7.5% by turning off the external N-channel power The overvoltage comparator in the LTC1872 will turn the MOSFET and keeping it off until the fault is removed. external MOSFET off when the feedback voltage has risen 7.5% above the reference voltage of 0.8V.

  • Page 6: Applications Information

    LTC1872 applicaTions inForMaTion The basic LTC1872 application circuit is shown in Inductor Value Calculation Figure 1. External component selection is driven by the The operating frequency and inductor selection are inter- load requirement and begins with the selection of L1 and related in that higher operating frequencies permit the use (= R1).
  • Page 7 When these MOSFETs are where I is as defined in the Inductor Value Calcula- used, make sure that the input supply to the LTC1872 is RIPPLE tion section. less than the absolute maximum V rating, typically 8V.
  • Page 8 I is the ripple current in the inductor. RIPPLE The LTC1872 develops a 0.8V reference voltage between Manufacturers such as Nichicon, United Chemicon and the feedback (Pin 3) terminal and ground (see Figure 4). Sanyo should be considered for high performance through- By selecting resistor R1, a constant current is caused to hole capacitors.
  • Page 9 LTC1872 circuits: 1) LTC1872 DC bias current, 2) 5. Transition losses apply to the external MOSFET and MOSFET gate charge current, 3) I...
  • Page 10 3. The input decoupling capacitor (0.1µF) should be connected closely between V (Pin 5) and ground (Pin 2). /RUN NGATE LTC1872 0.1µF – SENSE BOLD LINES INDICATE HIGH CURRENT PATHS 1872 F05 Figure 5. LTC1872 Layout Diagram (See PC Board Layout Checklist) 1872fa For more information www.linear.com/LTC1872...

  • Page 11: Typical Application

    1872 TA02 78.7k C1: TAIYO YUDEN CERAMIC EMK325BJ106MNT L1: COILTRONICS UP2B-100 C2: AVX TPSE476M016R0150 M1: Si9804DV D1: IR10BQ015 R1: DALE 0.25W LTC1872 Three-Cell White LED Driver = 3 AA CELLS ≈ 2.7V TO 4.8V 10µF 0.27 /RUN 150µH ≈ 28.8V LTC1872 (WITH 8 LEDs) –...

  • Page 12: Package Description

    LTC1872 package DescripTion Dimensions in inches (millimeters) unless otherwise noted. S6 Package 6-Lead Plastic TSOT-23 (Reference LTC DWG # 05-08-1636) 2.90 BSC 0.62 0.95 (NOTE 4) 1.22 REF 1.50 – 1.75 2.80 BSC 3.85 MAX 2.62 REF 1.4 MIN (NOTE 4)

  • Page 13: Revision History

    Revised package drawing 1872fa Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa- For more information www.linear.com/LTC1872 tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.

  • Page 14: Related Parts

    LTC1872 Typical applicaTion LTC1872 – 2.5V to 3.3V/0.5A Boost Converter LTC1872 2.7V to 9.8V Input to 3.3V/1.2A Output SEPIC Converter 0.034 2¥ 100F 2.7V TO 9.8V 10µF 0.03 /RUN 4.7µH 10V, X5R 220pF LTC1872 – 3.3V /RUN SENSE 3.3V/1.2A 0.5A...

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