LM2645MTD National Semiconductor, LM2645MTD Datasheet

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LM2645MTD

Manufacturer Part Number
LM2645MTD
Description
Advanced Two-Phase Switching Controller With Two Linear Outputs
Manufacturer
National Semiconductor
Datasheet

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© 2005 National Semiconductor Corporation
LM2645
Advanced Two-Phase Switching Controller With Two
Linear Outputs
General Description
The LM2645 is a feature-rich IC that combines two current
mode synchronous buck regulator controllers, an adjustable
linear regulator controller and a fixed 3.3V standby output
rail.
The two switching regulator controllers operate 180˚ out of
phase. This feature reduces the input ripple RMS current,
thereby significantly reducing the required input capacitance.
The two switching regulator outputs can also be paralleled to
operate as a dual-phase regulator.
The use of synchronous rectification and pulse-skip opera-
tion at light load achieves high efficiency over a wide load
range. Fixed-frequency operation can be obtained by dis-
abling the pulse-skip mode. The switching frequency of the
LM2645 is user selectable between 200 kHz or 300 kHz.
The first switching controller (Channel 1) features a fixed 5V
output, and the second switching controller controller (Chan-
nel 2) features a fixed 3.3V output. Both channels can also
be independently adjusted from 1.3 to 5.5V. The adjustable
linear regulator can be adjusted from 3.3V to 15V. An internal
5V rail is also available externally for driving bootstrap cir-
cuitry. This rail also serves as the input for an internal LDO
that provides the fixed 3.3V/50mA output rail.
Current-mode feedback control assures excellent line and
load regulation and a wide loop bandwidth for excellent
response to fast load transients. Current is sensed across
either the Vds of the top FET or across an external sense
resistor connected in series with the drain of the top FET.
Current limit is independently adjustable for each channel.
The analog soft-start for the switching controllers uses an
innovative new approach. It is independent of the input
voltage which makes the soft-start behavior more predict-
able and controllable.
Independant PGOOD signals monitor each of the switching
regulator outputs. The switching outputs have under-voltage
and over-voltage latch protection, while the output of the
external linear regulator has undervoltage latch protection.
The undervoltage latch can be disabled or adjustably de-
layed.
DS200159
Features
GENERAL
n 4.5V to 30V input range
n Power good function
n Input under-voltage lockout
n 10 µA Shutdown/Recycle for entire chip
n Thermal shutdown
n TSSOP package
SWITCHING SECTION
n Two synchronous buck regulators for fixed 5V/3.3V or
n Outputs adjustable from 1.3V to 5.5V
n 0.04% (typical) line and load regulation error
n Selectable switching frequency 200/300 kHz
n Two channels operating 180˚ out of phase
n Separate on/off for each channel
n Separate Power Good signals
n Current mode control with or without sense resistor
n Adjustable cycle-by-cycle current limit
n Skip-mode operation available
n Negative current limit
n Separate soft start for each channel
n Output UVP and OVP
n Programmable output UVP delay
n Self discharge of output capacitors when turned off
LINEAR SECTION
n Adjustable (3.3V to 15V) linear regulator with external
n
n Output UVP for adjustable linear regulator
n Fixed 3.3V/50mA output rail
n Fixed 5V reference rail
Applications
n Notebook and sub-notebook computers
n Embedded computer systems
n Battery-powered instruments
n High end gaming systems
n Set-top boxes
n WebPAD
adjustable outputs
PNP pass transistor
±
2% initial tolerance of set voltage
www.national.com
April 2005

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LM2645MTD Summary of contents

Page 1

... The switching outputs have under-voltage and over-voltage latch protection, while the output of the external linear regulator has undervoltage latch protection. The undervoltage latch can be disabled or adjustably de- layed. © 2005 National Semiconductor Corporation Features GENERAL n 4.5V to 30V input range n Power good function n Input under-voltage lockout n 10 µ ...

Page 2

... Connection Diagram TOP VIEW 48-Lead TSSOP (MTD) Order Number LM2645MTD See NS Package Number MTD48 Pin Descriptions VO1 (Pin 1):The feedback input for Channel 1. Always con- nect directly to the output. Fixed or adjustable output voltage is selected by FB1_FIX. FB1_FIX (Pin 2): The feedback input for setting the output voltage of Channel 1 ...

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Pin Descriptions (Continued) of the top MOSFET or the voltage across an external current sense resistor to determine if an over-current condition has occurred in Channel 2. RSNS2 (Pin 26): The negative (−) Kelvin sense for the internal current limit ...

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www.national.com 4 ...

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5 www.national.com ...

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www.national.com 6 ...

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Notes: 1. "fault" is the logic OR of UVLO and thermal shutdown. 2. "cap" means the pin has a capacitor of appropriate value between it and ground. 3. ...

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... Absolute Maximum Ratings If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Voltages from the indicated pins to SGND/PGND: VIN, ILIM1, ILIM2, KS1, KS2, LDODRV SW1, SW2, RSNS1, RSNS2 VO1, VO2, FB1_FIX, FB2_FIX, VDD1, VDD2, EXT ...

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Electrical Characteristics Unless otherwise specified 15V, SGND = PGND = 0V, VLIN5 = VDD1 = VDD2. Limits appearing in boldface type apply IN over the entire operating junction temperature range, 0˚C to +125˚C. Specifications appearing in plain type ...

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Electrical Characteristics Unless otherwise specified 15V, SGND = PGND = 0V, VLIN5 = VDD1 = VDD2. Limits appearing in boldface type apply IN over the entire operating junction temperature range, 0˚C to +125˚C. Specifications appearing in plain type ...

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... Note 3: For detailed information on soldering plastic small-outline packages, refer to the Packaging Databook available from National Semiconductor Corporation. Note 4: Except for SW1, SW2, CBOOT1 and CBOOT2 pins which are 1.5kV. For testing purposes, ESD was applied using the human-body model, a 100pF capacitor discharged through a 1.5kΩ ...

Page 12

Typical Performance Characteristics Efficiency vs Load Current (FPWM/2NDFB = VLIN5) Efficiency vs Load Current (FPWM/2NDFB = VLIN5) Reference Voltage vs Temperature (Bandgap + Error Amplifier Offset) www.national.com Efficiency vs Load Current (FPWM/2NDFB = VLIN5) 20015906 Quiescent Current vs Supply Voltage ...

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Typical Performance Characteristics Switching Frequency vs Load Current (FPWM/2NDFB = VLIN5) VLIN5 Output vs Temperature Shutdown Waveforms (V = 3.3V 0A) OUT OUT (Continued) Normalized Switching Frequency vs Temperature 20015909 (V = 15V, EXT = Vo1 = 5V, ...

Page 14

Typical Performance Characteristics Load Transient Response (V = 10V 3.3V 6.0 µ OUT Overcurrent and Undervoltage Protection (V = 5V, V OUT1 OUT2 Soft Start (V = 10V to 28V 5V, I ...

Page 15

Operation Descriptions GENERAL The LM2645 integrates two synchronous switching control- lers, one adjustable linear regulator controller and one fixed 3.3V output into a single package. It solves the need within many portable systems for 5V, 3.3V, 3.3V stand-by and 12V ...

Page 16

Operation Descriptions The force-PWM mode is good for applications where fixed switching frequency is required. In force-PWM mode, the top FET has to be turned on for a minimum of typically 220ns each cycle. However, when the required duty cycle ...

Page 17

Operation Descriptions NEGATIVE CURRENT LIMIT The purpose of negative current limit is to ensure that the inductor will not saturate during negative current flow caus- ing excessive current to flow through the bottom FET. The negative current limit is realized ...

Page 18

Operation Descriptions FIGURE 3. Connecting OUT3 to VLIN5 when not in use Likewise, if the LDODRV pin is not used, connect the LD- OFB pin to VLIN5 as shown in Figure 4 to disable this channel and the under voltage ...

Page 19

Operation Descriptions (Continued) FIGURE 7. Dual-Phase parallel operation 19 20015904 www.national.com ...

Page 20

... Deutsch Tel: +49 (0) 69 9508 6208 English www.national.com Français Tel: +33 ( 8790 48-Lead TSSOP Package Order Number LM2645MTD NS Package Number MTD48 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system affect its safety or effectiveness ...

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