LM2642

Manufacturer Part NumberLM2642
ManufacturerTexas Instruments
LM2642 datasheet
 


Specifications of LM2642

Switching Frequency(max)(khz)300Regulated Outputs(#)2
Frequency(min)(khz)300Vin(min)(v)4.5
Vin(max)(v)30Iout(max)(a)20
Vout(min)(v)1.238Vout(max)(v)27
TopologyBuckPin/package28TSSOP
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LM2642
LM2642 Two-Phase Synchronous Step-Down Switching Controller
Literature Number: SNVS203H

LM2642 Summary of contents

  • Page 1

    ... LM2642 LM2642 Two-Phase Synchronous Step-Down Switching Controller Literature Number: SNVS203H ...

  • Page 2

    ... FET. Current limit is independently adjustable for each chan- nel. 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 ...

  • Page 3

    ... 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 4

    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 5

    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, ...

  • Page 6

    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 7

    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 8

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

  • Page 9

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

  • Page 10

    9 www.national.com ...

  • Page 11

    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 12

    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 13

    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 14

    ... 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 are grounded.In a normal application (with a soft start capacitor connected between the ON/SS1 pin and SGND) soft start functions as follows. As the input voltage rises (note: Iss starts to flow when VIN ≥ ...

  • Page 15

    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 16

    Operation Descriptions where Imax is the maximum expected load current, including overload multiplier (ie:120%), and Irip is the inductor ripple current (See equation 7). The above equation gives the maximum allowable value for Rsns. Switching losses will increase with Rsns, ...

  • Page 17

    Component Selection Where 200nA is the maximum current drawn by FBx pin. FIGURE 8. Output Voltage Setting Example: Vnom=5V, Vfb=1.238V, Ifbmax=200nA. Choose 60K The output voltage is limited by the maximum duty cycle as well as the minimum on time. ...

  • Page 18

    ... RMS current rating should be higher than the maximum load current. Input Capacitor Selection The fact that the two switching channels of the LM2642 are 180˚ out of phase will reduce the RMS value of the ripple current seen by the input capacitors. This will help extend input capacitor life span and result in a more efficient sys- tem ...

  • Page 19

    ... The crossover frequency should not exceed one-fifth of the switching frequency, i.e. 60kHz in the case of LM2642. The higher the bandwidth is, the faster the load transient response speed will potentially be. However, if the duty cycle saturates during a load tran- sient, further increasing the small signal bandwidth will not help ...

  • Page 20

    Loop Compensation (Continued) FIGURE 10. Control-Output Transfer Function As shown in Figure 10, the control-output transfer function consists of one pole (fp), one zero (fz), and a double pole at fn (half the switching frequency). The following can be done ...

  • Page 21

    Loop Compensation A second zero can also be added with a resistor in series with Cc2. If used, this zero should be placed at fn, where the control to output gain rolls off at -40dB/dec. Generally, fn will be well ...

  • Page 22

    ... Deutsch Tel: +49 (0) 69 9508 6208 English www.national.com Français Tel: +33 ( 8790 28-Lead TSSOP Package Order Number LM2642MTC NS Package Number MTC28 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 ...

  • Page 23

    ... Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, modifications, enhancements, improvements, and other changes to its products and services at any time and to discontinue any product or service without notice. Customers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. All products are sold subject to TI’ ...