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Linear Technology LTC1624 Manual
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Linear Technology LTC1624 Manual

High efficiency so-8 n-channel switching regulator controller
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FEATURES
N-Channel MOSFET Drive
Implements Boost, Step-Down, SEPIC
and Inverting Regulators
Wide V
Range: 3.5V to 36V Operation
IN
Wide V
Range: 1.19V to 30V in Step-Down
OUT
Configuration
±
1% 1.19V Reference
Low Dropout Operation: 95% Duty Cycle
200kHz Fixed Frequency
Low Standby Current
Very High Efficiency
Remote Output Voltage Sense
Logic-Controlled Micropower Shutdown
Internal Diode for Bootstrapped Gate Drive
Current Mode Operation for Excellent Line and
Load Transient Response
Available in an 8-Lead SO Package
U
APPLICATIONS
Notebook and Palmtop Computers, PDAs
Cellular Telephones and Wireless Modems
Battery-Operated Digital Devices
DC Power Distribution Systems
Battery Chargers
TYPICAL
APPLICATION
470pF
–
SENSE
I
/RUN
TH
C
C
LTC1624
V
FB
R
C
100pF
6.8k
GND
Figure 1. High Efficiency Step-Down Converter
High Efficiency SO-8
N-Channel Switching
Regulator Controller
DESCRIPTION
®
The LTC
1624 is a current mode switching regulator
controller that drives an external N-channel power MOSFET
using a fixed frequency architecture. It can be operated in
all standard switching configurations including boost,
step-down, inverting and SEPIC. Burst Mode
provides high efficiency at low load currents. A maximum
high duty cycle limit of 95% provides low dropout operation
which extends operating time in battery-operated systems.
The operating frequency is internally set to 200kHz, allowing
small inductor values and minimizing PC board space. The
operating current level is user-programmable via an external
current sense resistor. Wide input supply range allows
operation from 3.5V to 36V (absolute maximum).
A multifunction pin (I
compensation for optimum load step response plus
shutdown. Soft start can also be implemented with the
I
/RUN pin to properly sequence supplies.
TH
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
V
IN
4.8V TO 28V
1000pF
V
IN
R
SENSE
0.05Ω
BOOST
M1
Si4412DY
TG
C
B
0.1µF
SW
D1
MBRS340T3
LTC1624
/ RUN) allows external
TH
C
+
IN
22µF
35V
× 2
L1
10µH
V
OUT
3.3V
2A
R2
35.7k
+
C
OUT
100µF
10V
R1
× 2
20k
1624 F01
TM
operation
1

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Summary of Contents for Linear Technology LTC1624

  • Page 1 Notebook and Palmtop Computers, PDAs Cellular Telephones and Wireless Modems Battery-Operated Digital Devices DC Power Distribution Systems , LTC and LT are registered trademarks of Linear Technology Corporation. Battery Chargers Burst Mode is a trademark of Linear Technology Corporation. TYPICAL APPLICATION 4.8V TO 28V...
  • Page 2 + (P • 110°C/W) temperature range. Note 2: The LTC1624 is tested in a feedback loop which servos V LTC1624CS: 0°C ≤ T ≤ 70°C the midpoint for the error amplifier (V = 1.8V).

  • Page 3: Typical Performance Characteristics

    LTC1624 TYPICAL PERFORMANCE CHARACTERISTICS Efficiency vs Input Voltage Efficiency vs Load Current Efficiency vs Load Current = 3.3V = 3.3V = 5V = 3.3V = 3.3V = 5V = 0.033Ω = 0.033Ω SENSE SENSE = 10V = 5V = 0.033Ω...
  • Page 4 LTC1624 TYPICAL PERFORMANCE CHARACTERISTICS /RUN Pin Source Current vs Temperature vs Output Current vs V /RUN = 1V /RUN = 0V ACTIVE MODE ACTIVE MODE SHUTDOWN SHUTDOWN –40 –15 OUT(MAX) OUT(MAX) TEMPERATURE (°C) 1624 G14 1624 G01 1624 G02 Operating Frequency vs...
  • Page 5 Low Current Operation described in the pin functions, allows EA to receive an The LTC1624 is capable of Burst Mode operation in which output feedback voltage from an external resistive divider. the external MOSFET operates intermittently based on When the load current increases, it causes a slight load demand.
  • Page 6 LTC1624 FUNCTIONAL DIAGRA (Shown in a step-down application)
  • Page 7 LTC1624 APPLICATIONS INFORMATION Accepting larger values of ∆I The LTC1624 can be used in a wide variety of switching allows the use of low regulator applications, the most common being the step- inductances, but results in higher output voltage ripple down converter.
  • Page 8 One external N-channel power MOSFET must be selected MAIN dissipation equation. for use with the LTC1624 for the top (main) switch. Step-Down Converter: Output Diode Selection (D1) The peak-to-peak gate drive levels are set by the INTV voltage. This voltage is typically 5V. Consequently, logic...
  • Page 9 (ESR). Typically, once the ESR require- are being driven at high frequencies may cause the maxi- ment is satisfied the capacitance is adequate for filtering. mum junction temperature rating for the LTC1624 to be The output ripple (∆V ) is determined by: exceeded.
  • Page 10 During normal operation the voltage on the I /RUN pin loop compensation and a means to shut down the LTC1624. will vary from 1.19V to 2.4V depending on the load current. Soft start can also be implemented with this pin. Soft start Pulling the I /RUN pin below 0.8V puts the LTC1624 into...
  • Page 11 3. Transition losses apply only to the topside MOSFET(s), losses, four main sources usually account for most of the and only when operating at high input voltages (typically losses in LTC1624 circuits: 20V or greater). Transition losses can be estimated from: 1.
  • Page 12 Using the circuit in Figure 5 can cause a positive spike as high as 60V which takes the LTC1624 will begin to skip cycles but stays in regula- several hundred milliseconds to decay. Reverse battery is...
  • Page 13 = 2A. R SENSE times of the internal circuitry the minimum recommended immediately be calculated: on-time is 450ns. Since the LTC1624’s frequency is inter- = 100mV/2A = 0.05Ω nally set to 200kHz a potential duty cycle limitation exists. SENSE When the duty cycle is less than 9%, cycle skipping may Assume a 10µH inductor.
  • Page 14 One external N-channel power MOSFET must be selected For most applications the inductor will fall in the range of for use with the LTC1624 for the switch. In boost applica- 10µH to 100µH. Higher values reduce the input ripple tions the source of the power MOSFET is grounded along voltage and reduce core loss.
  • Page 15 LTC1624 APPLICATIONS INFORMATION Allowing a margin for variations in the LTC1624 (without − ≈ )( )( ) considering variation in R ), assuming 30% ripple SENSE RIPPLE kHz L V current in the inductor, yields:   The input capacitor can see a very high surge current when IN MIN ...
  • Page 16 Step-Down Converter: Power MOSFET Selection in the Applications Information section. One external N-channel power MOSFET must be selected for use with the LTC1624 for the switch. As in boost SEPIC Converter: Inductor Selection applications the source of the power MOSFET is grounded along with the SW pin.
  • Page 17 The input capacitor can see a very high surge current when L1(PEAK) a battery is suddenly connected, and solid tantalum Allowing a margin for variations in the LTC1624 (without capacitors can fail under this condition. Be sure to specify considering variation in R...
  • Page 18 The maximum input voltage is (remem- MOSFET Selection ber not to exceed the absolute maximum limit of 36V): One external N-channel power MOSFET must be selected for use with the LTC1624 for the switch. As in step-down = 10.1V + 5V For DC > 9%...
  • Page 19 For additional informa- remainder divided by the duty cycle. tion refer to the Step-Down Converter: Power MOSFET Selection in the Applications Information section. Allowing a margin for variations in the LTC1624 (without considering variation in R ) and assuming 30% ripple SENSE...
  • Page 20 Positive-to-negative converters have high ripple current in /RUN pin below 0.8V relative to the LTC1624 ground pin. With the LTC1624 ground pin referenced to – V both the input and output capacitors. For long capacitor the nonimal range on the I /RUN pin is –...

  • Page 21: Typical Applications

    SENSE SENSE BOOST /RUN – LTC1624 100pF 0.1µF – BOLD LINES INDICATE HIGH CURRENT PATHS 1624 F09 Figure 9. LTC1624 Layout Diagram (See Board Layout Checklist) 5.3V TO 28V 1000pF 22µF SENSE – SENSE 0.033Ω × 2 0.1µF /RUN BOOST...
  • Page 22 LTC1624 TYPICAL APPLICATIONS 4.8V TO 22V 1000pF – SENSE 22µF 0.1µF SENSE 0.068Ω /RUN BOOST × 2 470pF LTC1624 Si6436DY 6.8k 100pF 10µH 0.1µF 1.8V 1.5A MBRS340T3 35.7k 100µF × 2 *SUMIDA CDR105B-100 69.8k Figure 11. Wide Input Range 1.8V/1.5A Converter 1624 F11 12.3V TO 28V...
  • Page 23 LTC1624 TYPICAL APPLICATIONS 5V TO 15V 1000pF – SENSE 22µF 22µF SENSE 0.1µF 0.068Ω MBRS130LT3 L1a* BOOST /RUN LTC1624 330pF Si4412DY L1b* 0.5A 4.7k 100pF 0.1µF 35.7k 100µF × 2 *COILTRONICS CTX20-4 3.92k Figure 14. 12V/0.4A SEPIC Converter 1624 F14...
  • Page 24 LTC1624 TYPICAL APPLICATIONS 3.6V TO 18V 1000pF 22µF SENSE – SENSE 0.05Ω × 2 22µF 0.1µF MBRS130LT3 L1a* CMDSH-3 BOOST /RUN LTC1624 330pF Si6426DQ L1b* 100pF 6.8k 0.1µF 35.7k 100µF × 2 * COILTRONICS CTX20-4 1624 F17 Figure 17. 5V/1A SEPIC Converter with Output Derived Boost Voltage 13V TO 1000µF...
  • Page 25 LTC1624 TYPICAL APPLICATIONS 20V TO SENSE 0.025Ω 22µF 47µH 0.1µF LTC1624 0.5A – SENSE 820pF BOOST /RUN 100µF 0.1µF 100V 100pF 13.3k 6.8k R2, 1M, 1% 1624 F19 = KEMET T495X226M035AS L1 = COILCRAFT D05022P-473 = SANYO 100MV100GX M1 = INTERNATIONAL RECTIFIER IRL 540NS...
  • Page 26 LTC1624 TYPICAL APPLICATIONS 13V TO 22µF × 2 SENSE C5, 0.1µF 0.033Ω LTC1624 – SENSE 330pF BOOST /RUN 0.1µF 27µH 0.025Ω 100pF 3.92k 100µF MBRS340 35.7k 100pF × 2 0.1µF 0.1µF SENSE PROG 1µF NC/ADJ LTC1620 LT1121-5 0.1µF –IN SHDN CURRENT C14, 0.01µF...
  • Page 27 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 represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

  • Page 28: Related Parts

    Ultralow Quiesent Current Step-Down Monolithic Switching Regulators 100% DC, 8-Pin MSOP, V < 20V Adaptive Power is a trademark of Linear Technology Corporation. 1624f LT/TP 0198 4K • PRINTED IN USA Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 TELEX: 499-3977 www.linear-tech.com...