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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)： | 10/24頁 |
| 文件大?。?/td> | 266K |
| 代理商： | LTC3809EMS#PBF |
18
LTC3809
3809f
Table 2 summarizes the different states in which the
SYNC/MODE Pin can be used.
Table 2. The States of the SYNC/MODE Pin
SYNC/MODE PIN
CONDITION
GND (0V to 0.35V)
Forced Continuous Mode
Current Reversal Allowed
VFB (0.45V to 1.2V)
Pulse Skipping Mode
No Current Reversal Allowed
Resistor to VIN
Spread Spectrum Modulation
(1.35V to VIN – 0.5V)
Pulse Skipping at Light Loads
No Current Reversal Allowed
VIN
Burst Mode Operation
No Current Reversal Allowed
Feedback Resistors
Regulate an Auxiliary Winding
External Clock Signal
Enable Phase-Locked Loop
(Synchronize to External Clock)
Pulse Skipping at Light Load
No Current Reversal Allowed
Fault Condition: Short-Circuit and Current Limit
If the LTC3809’s load current exceeds the short-circuit cur-
rent limit (ISC),whichissetbytheshort-circuitsensethresh-
old (
VSC) and the on resistance (RDS(ON)) of bottom
N-channel MOSFET, the top P-channel MOSFET is turned
off and will not be turned on at the next clock cycle unless
the load current decreases below ISC. In this case, the
controller’s switching frequency is decreased and
the output is regulated by short-circuit (current limit)
protection.
In a hard short (VOUT = 0V), the top P-channel MOSFET is
turned off and kept off until the short-circuit condition is
cleared. In this case, there is no current path from input
supply (VIN) to either VOUT or GND, which prevents
excessive MOSFET and inductor heating.
Low Input Supply Voltage
Although the LTC3809 can function down to below 2.4V,
the maximum allowable output current is reduced as VIN
decreases below 3V. Figure 9 shows the amount of change
as the supply is reduced down to 2.4V. Also shown is the
effect on VREF.
can be lowered and distributed to other frequencies and
their harmonics by modulating the PWM frequency. The
LTC3809’s switching noise (at 550kHz) is spread between
460kHz and 635kHz in spread spectrum modulation op-
eration. Figure 8 shows the spectral plots of the output
(VOUT) noise with/without spread spectrum modulation.
Note the significant reduction in peak output noise
(>20dBm).
The spread spectrum modulation operation of the LTC3809
is enabled by setting SYNC/MODE pin to a DC voltage
between 1.35V and several hundred mV below VIN by tying
a resistor between SYNC/MODE and VIN.
APPLICATIO S I FOR ATIO
WU
UU
Figure 8. Spectral Response of Spread Spectrum Modulation
VOUT Spectrum with Spread Spectrum Modulation
(CSSM = 2200pF)
VOUT Spectrum without Spread Spectrum Modulation
START FREQ: 400kHz
RBW: 100Hz
STOP FREQ: 700kHz
NOISE (dBm)
–10dBm/DIV
3809 F08a
START FREQ: 400kHz
RBW: 100Hz
STOP FREQ: 700kHz
NOISE (dBm)
–10dBm/DIV
3809 F08b
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