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LM3678
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SNVS464C – APRIL 2008 – REVISED MAY 2013
High-Performance Miniature 1.5-A Step-Down DC-DC Converter for Handheld Applications
Check for Samples: LM3678
FEATURES
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•2 VOUT = 0.8 V or 1.2 V • VIN = 2.5 V to 5.5 V • 1.5-A Maximum Load Capability • 3.3-MHz (Typical) PWM Fixed Switching
Frequency Allows Use of 1-µH Inductor • ±3% DC Output Voltage Precision • 0.01-µA (Typical) Shutdown Current • Internal Synchronous Rectification for High
Efficiency • Internal Soft Start • Current Overload and Thermal Shutdown
Protection
APPLICATIONS
• PDAs and Smart Phones • Personal Media Players • W-LAN • USB Modem Applications • Digital Still Cameras • Portable Hard Disk Drives
DESCRIPTION
The LM3678 step-down DC-DC converter is optimized for powering low-voltage circuits from a single Li-Ion cell battery and input voltage rails from 2.5 V to 5.5 V. It provides up to 1.5-A load current, over the entire input voltage range. LM3678 offers a 0.8V or 1.2V option. One of the pair of voltages is set through the VSELECT pin.
LM3678 operates in PWM mode with a fixed frequency of 3.3 MHz. Internal synchronous rectification provides high efficiency during PWM mode operation. In shutdown mode, the device turns off and reduces battery consumption to 0.01 µA (typical).
The LM3678 is available in a 3mm x 3mm DSC-10 package. A high switching frequency of 3.3 MHz (typical) allows use of tiny surface-mount components. Only three external surface-mount components, an inductor and two ceramic capacitors, are required (solution size less than 33 mm2). For voltages other than the voltage shown, contact TI or your distributor.
VIN = 2.5V to 5.5V CIN 10 PF
Typical Application Circuit
VDD VDD
1 PH SW
FB COUT
EN PWM
LM3678
0.8V/1.2V VSELECT
GND
PGOOD GND
VOUT 22 PF
NOTE: VSEL H = 1.2V, VSEL L = 0.8V
EFFICIENCY (%)
Efficiency vs. Output Current ( VOUT = 1.2V)
VIN = 2.5V, 2.7V
90
80
70
60 VIN = 3.6V
50
40 30
VIN = 4.5V
20
10 0 VIN = 5.5V
Figure 1.
0.010
0.100
1.000
LOAD (A)
Figure 2.
10.000
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Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. All trademarks are the property of their respective owners.
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PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of the Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters.
Copyright © 2008–2013, Texas Instruments Incorporated
LM3678
SNVS464C – APRIL 2008 – REVISED MAY 2013
Functional Block Diagram
EN
VIN
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SW
Undervoltage Lockout
Ramp Generator
Soft Start
Thermal Shutdown
Bandgap
2 MHz Oscillator
Current Limit Comparator
+ - Ref1
PFM Current Comparator
+ - Ref2
+
Error Amp
PWM Comparator
Control Logic
Driver
VREF + 0.5V -
VCOMP + 1.0V -
Frequency Compensation
+ -
Zero Crossing Comparator
Fixed Ver
FB VSELECT
PGOOD PWM
Figure 3. LM3678 Block Diagram
GND
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Product Folder Links: LM3678
Copyright © 2008–2013, Texas Instruments Incorporated
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Connection Diagram and Package Mark Information
LM3678
SNVS464C – APRIL 2008 – REVISED MAY 2013
GND GND
SW VDD VDD
1 2 3 4 5
10 FB
D 9 EN A 8 PWM P
7 PGOOD
6 VSELECT
FB 10
EN 9
PWM PGOOD VSELECT
8 7 6
D A P
1 GND 2 GND 3 SW 4 VDD 5 VDD
Figure 4. Top View
Figure 5. Bottom View
Pin No.
1 2 3 4 5 6
7
8 9
10 DAP
Name GND GND SW VDD VDD VSELECT
PGOOD
PWM EN
FB DAP
Table 1. Pin Descriptions
Description
Power Ground pin. Analog Ground Pin Switching node connection to the internal PFET switch and NFET synchronous rectifier Analog supply input. Connect to the input filter capacitor (see Figure 1). Power supply Input. Connect to the input filter capacitor (see Figure 1). Output voltage select (For example) VSELECT = LOW, VOUT = 0.8V VSELECT = HIGH , VOUT = 1.2V Power Good Flag. This common drain logic output is pulled to ground when the output voltage is not within ±7.5% of regulation. Connect PWM pin to VIN. Enable pin. The device is in shutdown mode when voltage to this pin is <0.4V and enabled when >1.0V. Do not leave this pin floating. Feedback analog input. Connect directly to the output filter capacitor for fixed voltage versions. Die Attach Pad, connect the DAP to GND on PCB layout to enhance thermal performance. It should not be used as a primary ground connection.
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam during storage or handling to prevent electrostatic damage to the MOS gates.
Absolute Maximum Ratings(1)
VIN Pin: Voltage to GND EN Pin FB, SW Pin Continuous Power Dissipation(2) Junction Temperature (TJ-MAX) Storage Temperature Range Maximum Lead Temperature (Soldering, 10 seconds)
−0.2V to 6.0V −0.2.