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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)： | 24/24頁 |
| 文件大?。?/td> | 266K |
| 代理商： | LTC3809EMS#PBF |
9
LTC3809
3809f
The reverse current comparator RICMP senses the drain-
to-source voltage of the bottom external N-channel
MOSFET. This MOSFET is turned off just before the
inductor current reaches zero, preventing it from going
negative.
In forced continuous operation, the inductor current is
allowed to reverse at light loads or under large transient
conditions. The peak inductor current is determined by the
voltage on the ITH pin. The P-channel MOSFET is turned on
every cycle (constant frequency) regardless of the ITH pin
voltage. In this mode, the efficiency at light loads is lower
than in Burst Mode operation. However, continuous mode
has the advantages of lower output ripple and no noise at
audio frequencies.
When the SYNC/MODE pin is clocked by an external clock
source to use the phase-locked loop (see Frequency
Selection and Phase-Locked Loop), or is set to a DC
voltage between 0.4V and several hundred mV below VIN,
the LTC3809 operates in PWM pulse skipping mode at
light loads. In this mode, the current comparator ICMP
may remain tripped for several cycles and force the
external P-channel MOSFET to stay off for the same
number of cycles. The inductor current is not allowed to
reverse (discontinuous operation). This mode, like forced
continuous operation, exhibits low output ripple as well as
low audio noise and reduced RF interference as compared
to Burst Mode operation. However, it provides low current
efficiency higher than forced continuous mode, but not
nearly as high as Burst Mode operation. During start-up or
an undervoltage condition (VFB ≤ 0.54V), the LTC3809
operates in pulse skipping mode (no current reversal
allowed), regardless of the state of the SYNC/MODE pin.
Short-Circuit and Current Limit Protection
The LTC3809 monitors the voltage drop
VSC (between
the GND and SW pins) across the external N-channel
MOSFET with the short-circuit current limit comparator.
The allowed voltage is determined by:
VSC(MAX) = A 90mV
where A is a constant determined by the state of the IPRG
pin. Floating the IPRG pin selects A = 1; tying IPRG to VIN
selects A = 5/3; tying IPRG to GND selects A = 2/3.
The inductor current limit for short-circuit protection is
determined by
VSC(MAX) and the on-resistance of the
external N-channel MOSFET:
I
V
R
SC
SC MAX
DS ON
=
()
Once the inductor current exceeds ISC, the short current
comparator will shut off the external P-channel MOSFET
until the inductor current drops below ISC.
Output Overvoltage Protection
As further protection, the overvoltage comparator (OVP)
guards against transient overshoots, as well as other more
serious conditions that may overvoltage the output. When
the feedback voltage on the VFB pin has risen 13.33%
above the reference voltage of 0.6V, the external P-chan-
nel MOSFET is turned off and the N-channel MOSFET is
turned on until the overvoltage is cleared.
OPERATIO
U
(Refer to Functional Diagram)
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| LTC3809EMS | 1 A SWITCHING CONTROLLER, 825 kHz SWITCHING FREQ-MAX, PDSO10 |
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| LTC3816IUHF#PBF | SWITCHING CONTROLLER, PQCC38 |
| LTC3816IFE#TRPBF | SWITCHING CONTROLLER, PDSO38 |
| LTC3816EFE#PBF | SWITCHING CONTROLLER, PDSO38 |
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參數(shù)描述 |
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