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LM27222 Folha de dados(PDF) 6 Page - Texas Instruments

Nome de Peças LM27222
Descrição Electrónicos  LM27222 High-Speed 4.5A Synchronous MOSFET Driver
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Fabricante Electrônico  TI [Texas Instruments]
Página de início  http://www.ti.com
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LM27222 Folha de dados(HTML) 6 Page - Texas Instruments

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tON (ns)
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20 ns/DIV
IN
HG-SW
LM27222
SNVS306B – SEPTEMBER 2004 – REVISED MARCH 2013
www.ti.com
APPLICATION INFORMATION
GENERAL
The LM27222 is designed for high speed and high operating reliability. The driver can handle very narrow, down
to zero, PWM pulses in a specified, deterministic way. Therefore, the HG and LG outputs are always in
predictable states. No latches are used in the HG and LG control logic so the drivers cannot get "stuck" in the
wrong state. The driver design allows for powering up with a pre-biasing voltage being present at the regulator
output. To reduce conduction losses in DC-DC converters with low duty factors the LM27222 driver can be
powered from a 6.5V ±5% power rail.
It is recommended to use the same power rail for both the controller and driver. If two different power rails are
used, never allow the PWM pulse magnitude at the IN input or the control voltage at the LEN input to be above
the driver VCC voltage or unpredictable HG and LG outputs pulse widths may result.
MINIMUM PULSE WIDTH
As the input pulse width to the IN pin is decreased, the pulse width of the high-side gate drive (HG-SW) also
decreases. However, for input pulse widths 60ns and smaller, the HG-SW remains constant at 30ns. Thus the
minimum pulse width of the driver output is 30ns. Figure 5 shows an input pulse at the IN pin 20ns wide, and the
output of the driver, as measured between the nodes HG and SW is a 30ns wide pulse. Figure 6 shows the
variation of the SW node pulse width vs IN pulse width. At the IN pin, if a falling edge is followed by a rising edge
within 5ns, the HG may ignore the rising edge and remain low until the IN pin toggles again. If a rising edge is
followed by a falling edge within 5ns, the pulse may be completely ignored.
Figure 5. Min On Time
Figure 6.
ADAPTIVE SHOOT-THROUGH PROTECTION
The LM27222 prevents shoot-through power loss by ensuring that both the high- and low-side MOSFETs are not
conducting at the same time. When the IN signal rises, LG is first pulled down. The adaptive shoot-through
protection circuit waits for LG to reach 0.9V before turning on HG. Similarly, when IN goes low, HG is pulled
down first, and the circuit turns LG on only after the voltage difference between the high-side gate and the switch
node, i.e., HG-SW, has fallen to 0.9V.
It is possible in some applications that at power-up the driver's SW pin is above 3V in either buck or boost
comverter applications. For instance, in a buck configuration a pre-biasing voltage can be either a voltage from
anothert power rail connected to the load, or a leakage voltage through the load, or it can be an output capacitor
pre-charged above 3V while no significant load is present. In a boost application it can be an input voltage rail
above 3V.
6
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