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參數(shù)資料
| 型號(hào)： | LT3412AIFE#TR |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 3 A SWITCHING REGULATOR, 4 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封裝： | 4.4 MM, PLASTIC, TSSOP-16 |
| 文件頁(yè)數(shù)： | 20/20頁(yè) |
| 文件大?。?/td> | 267K |
| 代理商： | LT3412AIFE#TR |
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LTC3412A
9
3412afb
The operating frequency is externally set by an external
resistor connected between the RT pin and ground. The
practical switching frequency can range from 300kHz to
4MHz.
Overvoltage and undervoltage comparators will pull the
PGOOD output low if the output voltage comes out of
regulation by
± 7.5%. In an overvoltage condition, the top
power MOSFET is turned off and the bottom power MOSFET
is switched on until either the overvoltage condition clears
or the bottom MOSFET’s current limit is reached.
Forced Continuous Mode
Connecting the SYNC/MODE pin to SVIN will disable Burst
Mode operation and force continuous current operation.
At light loads, forced continuous mode operation is less
efficient than Burst Mode operation, but may be desirable
in some applications where it is necessary to keep switch-
ing harmonics out of a signal band. The output voltage
ripple is minimized in this mode.
Burst Mode Operation
Connecting the SYNC/MODE pin to a voltage in the range
of 0V to 1V enables Burst Mode operation. In Burst Mode
operation, the internal power MOSFETs operate intermit-
tently at light loads. This increases efficiency by minimiz-
ing switching losses. During Burst Mode operation, the
minimum peak inductor current is externally set by the
voltage on the SYNC/MODE pin and the voltage on the ITH
pin is monitored by the burst comparator to determine
when sleep mode is enabled and disabled. When the
average inductor current is greater than the load current,
the voltage on the ITH pin drops. As the ITH voltage falls
below 150mV, the burst comparator trips and enables
sleep mode. During sleep mode, the top power MOSFET is
held off and the ITH pin is disconnected from the output of
the error amplifier. The majority of the internal circuitry is
also turned off to reduce the quiescent current to 64
μA
while the load current is solely supplied by the output
capacitor. When the output voltage drops, the ITH pin is
reconnected to the output of the error amplifier and the top
power MOSFET along with all the internal circuitry is
switched back on. This process repeats at a rate that is
dependent on the load demand.
Pulse Skipping operation is implemented by connecting
the SYNC/MODE pin to ground. This forces the burst
clamp level to be at 0V. As the load current decreases, the
peak inductor current will be determined by the voltage on
the ITH pin until the ITH voltage drops below 400mV. At this
point, the peak inductor current is determined by the
minimum on-time of the current comparator. If the load
demand is less than the average of the minimum on-time
inductor current, switching cycles will be skipped to keep
the output voltage in regulation.
Frequency Synchronization
The internal oscillator of the LTC3412A can be synchro-
nized to an external clock connected to the SYNC/MODE
pin. The frequency of the external clock can be in the range
of 300kHz to 4MHz. For this application, the oscillator
timing resistor should be chosen to correspond to a
frequency that is 25% lower than the synchronization
frequency. During synchronization, the burst clamp is set
to 0V, and each switching cycle begins at the falling edge
of the clock signal.
Dropout Operation
When the input supply voltage decreases toward the
output voltage, the duty cycle increases toward the maxi-
mum on-time. Further reduction of the supply voltage
forces the main switch to remain on for more than one
cycle eventually reaching 100% duty cycle. The output
voltage will then be determined by the input voltage minus
the voltage drop across the internal P-channel MOSFET
and the inductor.
Low Supply Operation
The LTC3412A is designed to operate down to an input
supply voltage of 2.25V. One important consideration
at low input supply voltages is that the RDS(ON) of the
P-channel and N-channel power switches increases. The
user should calculate the power dissipation when the
LTC3412A is used at 100% duty cycle with low input
voltages to ensure that thermal limits are not exceeded.
OPERATIO
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