參數(shù)資料
型號(hào)： LT3688IFE#PBF
廠商： LINEAR TECHNOLOGY CORP
元件分類： 穩(wěn)壓器
英文描述： SWITCHING REGULATOR, PDSO24
封裝： LEAD FREE, PLASTIC, TSSOP-24
文件頁(yè)數(shù)： 10/28頁(yè)
文件大小： 415K
代理商： LT3688IFE#PBF
LT3688
18
3688f
Low Ripple Burst Mode Operation
To enhance efciency at light loads, the LT3688 operates
in low ripple Burst Mode operation that keeps the output
capacitor charged to the proper voltage while minimizing
the input quiescent current. During Burst Mode opera-
tion, the LT3688 delivers single cycle bursts of current
to the output capacitor followed by sleep periods where
the output power is delivered to the load by the output
capacitor. Because the LT3688 delivers power to the
output with single, low current pulses, the output ripple
is kept below 25mV for a typical application. In addition,
VIN and BIAS quiescent currents are reduced to typically
65μA and 155μA, respectively, during the sleep time. As
the load current decreases towards a no-load condition,
the percentage of time that the LT3688 operates in sleep
mode increases and the average input current is greatly
reduced, resulting in high efciency even at very low loads
(see Figure 5). At higher output loads the LT3688 will be
running at the frequency programmed by the RT resistor,
and will be operating in standard PWM mode. The transi-
tion between PWM and low ripple Burst Mode operation
is seamless, and will not disturb the output voltage. The
front page application circuit will switch at full frequency
at output loads higher than about 60mA.
IL
0.2A/DIV
VSW
5V/DIV
VOUT
10mV/DIV
5μs/DIV
3688 F05
Figure 5. Burst Mode Operation
BST and BIAS Pin Considerations
Capacitor C3 and the internal boost Schottky diodes (see
the Block Diagram) are used to generate boost voltages
that are higher than the input voltage. In most cases, a
0.22μF capacitor will work well. For the best performance
in dropout, use a 1μF or larger capacitor. Figure 6 shows
VIN
BST
SW
BIAS
VIN
VOUT
4.7μF
C3
GND
LT3688
(6a) For VOUT > 2.8V
Figure 6. Three Circuits for Generating the Boost Voltage
VIN
BST
SW
BIAS
VIN
VOUT
4.7μF
C3
D2
GND
LT3688
(6b) For 2.5V < VOUT < 2.8V
VIN
BST
SW
BIAS
VIN
VOUT
4.7μF
C3
GND
LT3688
3688 F06
(6c) For VOUT < 2.5V; VIN(MAX) = 30V
APPLICATIONS INFORMATION
three ways to arrange the boost circuit. The BST pin must
be more than 2.3V above the SW pin for best efciency.
For outputs of 3V and above, the standard circuit (Figure
6a) is best. For outputs between 2.8V and 3V, use a 1μF
boost capacitor. A 2.5V output presents a special case
because it is marginally adequate to support the boosted
drive stage while using the internal boost diode. For reliable
BST pin operation with 2.5V outputs, use a good external
Schottky diode (such as the ON semi MBR0540), and a
1μF boost capacitor (see Figure 6b). For lower output
voltages, the boost diode can be tied to the input (Figure
6c), or to another supply greater than 2.8V. The circuit in
Figure 6a is more efcient because the BST pin current
and BIAS pin quiescent current comes from a lower volt-
相關(guān)PDF資料
PDF描述
LT3688HFE#PBF SWITCHING REGULATOR, PDSO24
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LT3689EMSE-5#TRPBF 1.95 A SWITCHING REGULATOR, 2160 kHz SWITCHING FREQ-MAX, PDSO16
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
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LT3688IUFPBF 制造商:LINER 制造商全稱:Linear Technology 功能描述:Dual 800mA Step-Down Switching Regulator with Power-On Reset
LT3689 制造商:LINER 制造商全稱:Linear Technology 功能描述:36V 500mA Step-Down Regulator and 200mA LDO
LT3689-5 制造商:LINER 制造商全稱:Linear Technology 功能描述:700mA Step-Down Regulator with Power-On Reset and Watchdog Timer
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