參數資料
型號: LTC3835IGN-1
廠商: LINEAR TECHNOLOGY CORP
元件分類: 穩(wěn)壓器
英文描述: 3 A SWITCHING CONTROLLER, 580 kHz SWITCHING FREQ-MAX, PDSO16
封裝: 0.150 INCH, PLASTIC, SSOP-16
文件頁數: 10/28頁
文件大?。?/td> 303K
代理商: LTC3835IGN-1
LTC3835-1
18
38351fc
APPLICATIONS INFORMATION
If the external clock frequency is greater than the internal
oscillator’s frequency, fOSC, then current is sourced con-
tinuously from the phase detector output, pulling up the
PLLLPF pin. When the external clock frequency is less
than fOSC, current is sunk continuously, pulling down
the PLLLPF pin. If the external and internal frequencies
are the same but exhibit a phase difference, the current
sources turn on for an amount of time corresponding to
the phase difference. The voltage on the PLLLPF pin is
adjusted until the phase and frequency of the internal and
external oscillators are identical. At the stable operating
point, the phase detector output is high impedance and
the lter capacitor CLP holds the voltage.
The loop lter components, CLP and RLP, smooth out the
current pulses from the phase detector and provide a stable
input to the voltage-controlled oscillator. The lter compo-
nents CLP and RLP determine how fast the loop acquires
lock. Typically RLP = 10k and CLP is 2200pF to 0.01μF.
Typically, the external clock (on PLLIN/MODE pin) input high
threshold is 1.6V, while the input low threshold is 1.2V.
Table 1 summarizes the different states in which the
PLLLPF pin can be used.
Table 1
PLLLPF PIN
PLLIN/MODE PIN
FREQUENCY
0V
DC Voltage
250kHz
Floating
DC Voltage
400kHz
INTVCC
DC Voltage
530kHz
RC Loop Filter
Clock Signal
Phase-Locked to External Clock
Minimum On-Time Considerations
Minimum on-time tON(MIN)isthesmallesttimedurationthat
the LTC3835-1 is capable of turning on the top MOSFET.
It is determined by internal timing delays and the gate
charge required to turn on the top MOSFET. Low duty
cycle applications may approach this minimum on-time
limit and care should be taken to ensure that:
t
V
Vf
ON MIN
OUT
IN
()
<
If the duty cycle falls below what can be accommodated
by the minimum on-time, the controller will begin to skip
cycles. The output voltage will continue to be regulated,
but the ripple voltage and current will increase.
The minimum on-time for the LTC3835-1 is approximately
180ns. However, as the peak sense voltage decreases the
minimum on-time gradually increases up to about 200ns.
This is of particular concern in forced continuous applica-
tions with low ripple current at light loads. If the duty cycle
drops below the minimum on-time limit in this situation,
a signicant amount of cycle skipping can occur with cor-
respondingly larger current and voltage ripple.
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