Manufacturer Part NumberLM2642MTC
DescriptionVoltage Regulator IC
ManufacturerNational Semiconductor
LM2642MTC datasheet

Specifications of LM2642MTC

No. Of Pins28Peak Reflow Compatible (260 C)No
Leaded Process CompatibleNoPackage / Case28-TSSOP
Lead Free Status / RoHS StatusContains lead / RoHS non-compliant  
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Two-Phase Synchronous Step-Down Switching
General Description
The LM2642 consists of two current mode synchronous
buck regulator controllers with a switching frequency of
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 single output regulator.
The output of each channel can be independently adjusted
• maximum duty cycle. An internal 5V rail is
from 1.3 to V
also available externally for driving bootstrap circuitry.
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 current-
sense resistor connected in series with the drain of the top
FET. Current limit is independently adjustable for each chan-
The LM2642 features analog soft-start circuitry that is inde-
pendent of the output load and output capacitance. This
makes the soft-start behavior more predictable and control-
lable than traditional soft-start circuits.
A PGOOD1 pin is provided to monitor the dc output of
channel 1. Over-voltage protection is available for both out-
puts. A UV-Delay pin is also available to allow delayed shut
off time for the IC during an output under-voltage event.
Block Diagram
© 2003 National Semiconductor Corporation
n Two synchronous buck regulators
n 180˚ out of phase operation
n 4.5V to 30V input range
n Power good function monitors Ch.1
n 37µA Shutdown current
n 0.04% (typical) line and load regulation error
n Current mode control with or without a sense resistor
n Independent enable/soft-start pins allow simple
sequential startup configuration.
n Configurable for single output parallel operation. (See
Figure 2).
n Adjustable cycle-by-cycle current limit
n Input under-voltage lockout
n Output over-voltage latch protection
n Output under-voltage protection with delay
n Thermal shutdown
n Self discharge of output capacitors when the regulator is
n TSSOP package
n Embedded computer systems
n High end gaming systems
n Set-top boxes
n WebPAD
May 2003

LM2642MTC Summary of contents

  • Page 1

    ... Over-voltage protection is available for both out- puts. A UV-Delay pin is also available to allow delayed shut off time for the IC during an output under-voltage event. Block Diagram © 2003 National Semiconductor Corporation Features n Two synchronous buck regulators n 180˚ out of phase operation n 4.5V to 30V input range n Power good function monitors Ch.1 n 37µ ...

  • Page 2

    ... TOP VIEW 20046202 28-Lead TSSOP (MTC) Order Number LM2642MTC See NS Package Number MTC28 VLIN5 (Pin 7): The output of an internal 5V LDO regulator derived from VIN. It supplies the internal bias for the chip and supplies the bootstrap circuitry for gate drive. Bypass this pin to signal ground with a minimum of 4.7µ ...

  • Page 3

    Pin Descriptions (Continued) SW2 (Pin 16): Switch-node connection for Channel 2, which is connected to the source of the top MOSFET of Channel 2. It serves as the negative supply rail for the top-side gate driver, HDRV2. HDRV2 (Pin 17): ...

  • Page 4

    ... 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 SW1, SW2, RSNS1, RSNS2 FB1, FB2, VDD1, VDD2 PGOOD, COMP1, COMP2, UV ...

  • Page 5

    Electrical Characteristics Unless otherwise specified 15V, GND = PGND = 0V, VLIN5 = VDD1 = VDD2. Limits appearing in boldface type apply IN over the specified operating junction temperature range, (-20˚C to +125˚C, if not otherwise specified). Specifications ...

  • Page 6

    ... Note 4: For detailed information on soldering plastic small-outline packages, refer to the Packaging Databook available from National Semiconductor Corporation. Note 5: For testing purposes, ESD was applied using the human-body model, a 100pF capacitor discharged through a 1.5kΩ resistor. ...

  • Page 7

    FIGURE 1. Typical 2 Channel Application Circuit 7 20046203 www.national.com ...

  • Page 8

    FIGURE 2. Typical Single Channel Application Circuit www.national.com 8 20046204 ...

  • Page 9

    9 www.national.com ...

  • Page 10

    Typical Performance Characteristics Softstart Waveforms ( LOAD1 LOAD2 UVP Startup Waveforms Shutdown Waveforms ( LOAD1 LOAD2 www.national.com = 0A) 20046223 20046268 = 0A) 20046222 10 Power On and PGOOD1 Waveforms ( 0A) LOAD1 ...

  • Page 11

    Typical Performance Characteristics Ch.2 Load Transient Response 3.3V , 12V OUT IN Input Supply Current vs Temperature (Shutdown Mode V IN VLIN5 vs Temperature (Continued) 20046229 = 15V) 20046224 20046226 11 Load Transient Response Parallel Operation 1.8V , 12V OUT ...

  • Page 12

    Typical Performance Characteristics FB Reference Voltage vs Temperature Error Amplifier Gain vs Temperature Efficiency vs Load Current Ch.2 = 2.5V, Ch.1 = Off www.national.com (Continued) Operating Frequency vs Temperature 20046266 Efficiency vs Load Current Ch.1 = 5V, Ch.2 = Off ...

  • Page 13

    Operation Descriptions SOFT START The ON/SS1 pin has dual functionality as both channel enable and soft start control. The soft start block diagram is shown in Figure 3. The LM2642 will remain in shutdown mode while both soft start pins ...

  • Page 14

    Operation Descriptions typical) both channels will latch off. Also, UV_DELAY will be disabled and the UV_DELAY pin will return to 0V. During UVP, both the high side and low side FET drivers will be turned off capacitor is ...

  • Page 15

    Operation Descriptions FIGURE 7. Current Sense and Current Limit Current limit is activated when the inductor current is high enough to cause the voltage at the RSNSx pin to be lower than that of the ILIMx pin. This toggles the ...

  • Page 16

    Component Selection Choose 60K The output voltage is limited by the maximum duty cycle as well as the minimum on time. Figure 9 shows the limits for input and output voltages. The recommended maximum out- put voltage is approximately 1V ...

  • Page 17

    Inductor Selection The size of the output inductor can be determined from the desired output ripple voltage, Vrip, and the impedance of the output capacitors at the switching frequency. The equation to determine the minimum inductance value is as follows: ...

  • Page 18

    MOSFET Selection (Continued) where Tj_max is the maximum allowed junction temperature in the FET, Ta_max is the maximum ambient temperature the junction-to-ambient thermal resistance of the FET, θja and TC is the temperature coefficient of the on resistance ...

  • Page 19

    Loop Compensation (Continued) FIGURE 11. Output-Control Transfer Function The control-output corner frequencies, and thus the desired compensation corner frequencies, can be determined ap- proximately by the following equations: Since fp is determined by the output network, it will shift with ...

  • Page 20

    ... National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications. inches (millimeters) 28-Lead TSSOP Package Order Number LM2642MTC NS Package Number MTC28 2. A critical component is any component of a life ...