Texas Instruments LM3242 6MHz, 750mA Miniature, Adjustable, Step-Down DC-DC EVM LM3242TM-EV/NOPB LM3242TM-EV/NOPB 데이터 시트
제품 코드
LM3242TM-EV/NOPB
High ECO Threshold
ECO Mode at Light Load
PWM Mode at Heavy Load
Load current increases
Low ECO Threshold
Target Output Voltage
SNOSB48D – OCTOBER 2011 – REVISED MARCH 2013
Bypass Mode Operation
The LM3242 contains an internal BPFET switch for bypassing the PWM DC-DC converter during Bypass mode.
In Bypass mode, this BPFET is turned on to power the PA directly from the battery for maximum RF output
power. When the part operates in the Bypass mode, the output voltage will be the input voltage less the voltage
drop across the resistance of the BPFET in parallel with the PFET + Switch Inductor. Bypass mode is more
efficient than operating in PWM mode at 100% duty cycle because the combined resistance is significantly less
than the series resistance of the PWM PFET and inductor. This translates into higher voltage available on the
output in Bypass mode, for a given battery voltage. The part can be set to bypass mode by sending BPEN pin
high. This is called Forced Bypass Mode and it remains in bypass mode until BPEN pin goes low. Alternatively
the part can go into Bypass mode automatically. This is called Auto-Bypass mode or Automatic Bypass mode.
The bypass switch turns on when the difference between the input voltage and programmed output voltage is
less than 200 mV (typ.) for longer than 10 µs (typ.). The bypass switch turns off when the input voltage is higher
than the programmed output voltage by 250 mV (typ.) for longer than 0.1 µs (typ.). This method is very system
resource friendly in that the Bypass PFET is turned on automatically when the input voltage gets close to the
output voltage, a typical scenario of a discharging battery. It is also turned off automatically when the input
voltage rises, a typical scenario when connecting a charger. When V
In Bypass mode, this BPFET is turned on to power the PA directly from the battery for maximum RF output
power. When the part operates in the Bypass mode, the output voltage will be the input voltage less the voltage
drop across the resistance of the BPFET in parallel with the PFET + Switch Inductor. Bypass mode is more
efficient than operating in PWM mode at 100% duty cycle because the combined resistance is significantly less
than the series resistance of the PWM PFET and inductor. This translates into higher voltage available on the
output in Bypass mode, for a given battery voltage. The part can be set to bypass mode by sending BPEN pin
high. This is called Forced Bypass Mode and it remains in bypass mode until BPEN pin goes low. Alternatively
the part can go into Bypass mode automatically. This is called Auto-Bypass mode or Automatic Bypass mode.
The bypass switch turns on when the difference between the input voltage and programmed output voltage is
less than 200 mV (typ.) for longer than 10 µs (typ.). The bypass switch turns off when the input voltage is higher
than the programmed output voltage by 250 mV (typ.) for longer than 0.1 µs (typ.). This method is very system
resource friendly in that the Bypass PFET is turned on automatically when the input voltage gets close to the
output voltage, a typical scenario of a discharging battery. It is also turned off automatically when the input
voltage rises, a typical scenario when connecting a charger. When V
OUT
< 300 mV, BPEN will be ignored.
ECO Mode Operation
At very light loads (50 mA to 100 mA), the LM3242 enters ECO mode operation with reduced switching
frequency and supply current to maintain high efficiency. During ECO mode operation, the LM3242 positions the
output voltage slightly higher (+7mV typ.) than the normal output voltage during PWM mode operation, allowing
additional headroom for voltage drop during a load transient from light to heavy load.
frequency and supply current to maintain high efficiency. During ECO mode operation, the LM3242 positions the
output voltage slightly higher (+7mV typ.) than the normal output voltage during PWM mode operation, allowing
additional headroom for voltage drop during a load transient from light to heavy load.
Figure 31. Operation in ECO Mode and Transfer to PWM Mode
Sleep Mode Operation
When VCON is less than 80 mV in 10 µs, the LM3242 will go into SLEEP mode — the SW pin will be in Tri-state
(floating), which will operate like ECO mode with no switching. LM3242 will return to normal operation
immediately when VCON
(floating), which will operate like ECO mode with no switching. LM3242 will return to normal operation
immediately when VCON
≥
130 mV in PWM mode or ECO mode, depending on load detection.
Shutdown Mode
Setting the EN digital pin low (<0.4V) places the LM3242 in Shutdown mode (0.1 µA typ.). During shutdown, the
PFET switch, the NFET synchronous rectifier, reference voltage source, control and bias circuitry of the LM3242
are turned off. Setting EN high (>1.2V) enables normal operation. EN should be set low to turn off the LM3242
during power-up and under voltage conditions when the power supply is less than the 2.7V minimum operating
voltage. The LM3242 has an UVLO (Under Voltage Lock Out) comparator to turn the power device off in the
case the input voltage or battery voltage is too low. The typical UVLO threshold is around 2.0V for lock and 2.1V
for release.
PFET switch, the NFET synchronous rectifier, reference voltage source, control and bias circuitry of the LM3242
are turned off. Setting EN high (>1.2V) enables normal operation. EN should be set low to turn off the LM3242
during power-up and under voltage conditions when the power supply is less than the 2.7V minimum operating
voltage. The LM3242 has an UVLO (Under Voltage Lock Out) comparator to turn the power device off in the
case the input voltage or battery voltage is too low. The typical UVLO threshold is around 2.0V for lock and 2.1V
for release.
Copyright © 2011–2013, Texas Instruments Incorporated
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