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參數(shù)資料
| 型號： | LTC3809EMS#PBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 1 A SWITCHING CONTROLLER, 825 kHz SWITCHING FREQ-MAX, PDSO10 |
| 封裝： | PLASTIC, MSOP-10 |
| 文件頁數(shù)： | 23/24頁 |
| 文件大?。?/td> | 266K |
| 代理商： | LTC3809EMS#PBF |
8
LTC3809
3809f
OPERATIO
U
Main Control Loop
The LTC3809 uses a constant frequency, current mode
architecture. During normal operation, the top external
P-channel power MOSFET is turned on when the clock
sets the RS latch, and is turned off when the current
comparator (ICMP) resets the latch. The peak inductor
current at which ICMP resets the RS latch is determined by
the voltage on the ITH pin, which is driven by the output of
the error amplifier (EAMP). The VFB pin receives the output
voltage feedback signal from an external resistor divider.
This feedback signal is compared to the internal 0.6V
reference voltage by the EAMP. When the load current
increases, it causes a slight decrease in VFB relative to the
0.6V reference, which in turn causes the ITH voltage to
increase until the average inductor current matches the
new load current. While the top P-channel MOSFET is off,
the bottom N-channel MOSFET is turned on until either the
inductor current starts to reverse, as indicated by the
current reversal comparator IRCMP, or the beginning of
the next cycle.
Shutdown and Soft-Start (RUN Pin)
The LTC3809 is shut down by pulling the RUN pin low. In
shutdown, all controller functions are disabled and the
chip draws only 9
A. The TG output is held high (off) and
the BG output low (off) in shutdown. Releasing the RUN
pin allows an internal 0.7
A current source to pull up the
RUN pin to VIN. The controller is enabled when the RUN pin
reaches 1.1V.
The start-up of VOUT is controlled by the LTC3809’s
internal soft-start. During soft-start, the error amplifier
EAMP compares the feedback signal VFB to the internal
soft-start ramp (instead of the 0.6V reference), which
rises linearly from 0V to 0.6V in about 1ms. This allows
the output voltage to rise smoothly from 0V to its final
value while maintaining control of the inductor current.
Light Load Operation (Burst Mode Operation,
Continuous Conduction or Pulse Skipping Mode)
(SYNC/MODE Pin)
The LTC3809 can be programmed for either high effi-
ciency Burst Mode operation, forced continuous conduc-
tion mode or pulse skipping mode at low load currents. To
select Burst Mode operation, tie the SYNC/MODE pin to
VIN. To select forced continuous operation, tie the SYNC/
MODE pin to a DC voltage below 0.4V (e.g., GND). Tying
the SYNC/MODE to a DC voltage above 0.4V and below
1.2V (e.g., VFB) enables pulse skipping mode. The 0.4V
threshold between forced continuous operation and pulse
skipping mode can be used in secondary winding regula-
tion as described in the Auxiliary Winding Control Using
SYNC/MODE Pin discussion in the Applications Informa-
tion section.
When the LTC3809 is in Burst Mode operation, the peak
current in the inductor is set to approximately one-fourth
of the maximum sense voltage even though the voltage on
the ITH pin indicates a lower value. If the average inductor
current is higher than the load current, the EAMP will
decrease the voltage on the ITH pin. When the ITH voltage
drops below 0.85V, the internal SLEEP signal goes high
and the external MOSFET is turned off.
In sleep mode, much of the internal circuitry is turned off,
reducing the quiescent current that the LTC3809 draws.
The load current is supplied by the output capacitor. As the
output voltage decreases, the EAMP increases the ITH
voltage. When the ITH voltage reaches 0.925V, the SLEEP
signal goes low and the controller resumes normal opera-
tion by turning on the external P-channel MOSFET on the
next cycle of the internal oscillator.
When the controller is enabled for Burst Mode or pulse
skipping operation, the inductor current is not allowed to
reverse. Hence, the controller operates discontinuously.
(Refer to Functional Diagram)
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| LTC3809EMS | 1 A SWITCHING CONTROLLER, 825 kHz SWITCHING FREQ-MAX, PDSO10 |
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| LTC3816IUHF#PBF | SWITCHING CONTROLLER, PQCC38 |
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| LTC3816EFE#PBF | SWITCHING CONTROLLER, PDSO38 |
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