参数资料
型号: LT3688EFE#TRPBF
厂商: Linear Technology
文件页数: 18/28页
文件大小: 0K
描述: IC REG BUCK ADJ 0.8A DL 24TSSOP
标准包装: 2,500
类型: 降压(降压)
输出类型: 可调式
输出数: 2
输出电压: 0.8 V ~ 32.4 V
输入电压: 3.8 V ~ 36 V
PWM 型: 电流模式,Burst Mode?
频率 - 开关: 500kHz ~ 2.1MHz
电流 - 输出: 800mA
同步整流器:
工作温度: -40°C ~ 125°C
安装类型: 表面贴装
封装/外壳: 24-TSSOP(0.173",4.40mm)裸露焊盘
包装: 带卷 (TR)
供应商设备封装: 24-TSSOP
LT3688
APPLICATIONS INFORMATION
Low Ripple Burst Mode Operation
To enhance ef?ciency 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,
V IN 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
three ways to arrange the boost circuit. The BST pin must
be more than 2.3V above the SW pin for best ef?ciency.
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 ef?cient because the BST pin current
and BIAS pin quiescent current comes from a lower volt-
V OUT
BIAS
reduced, resulting in high ef?ciency even at very low loads
(see Figure 5). At higher output loads the LT3688 will be
running at the frequency programmed by the R T resistor,
and will be operating in standard PWM mode. The transi-
V IN
4.7μF
V IN LT3688
GND
BST
SW
C3
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.
(6a) For V OUT > 2.8V
V OUT
BIAS
BST
D2
I L
0.2A/DIV
V SW
5V/DIV
V IN
4.7μF
V IN LT3688
GND
SW
C3
V OUT
10mV/DIV
(6b) For 2.5V < V OUT < 2.8V
5μs/DIV
Figure 5. Burst Mode Operation
3688 F05
BIAS
BST
V OUT
BST and BIAS Pin Considerations
Capacitor C3 and the internal boost Schottky diodes (see
V IN
4.7μF
V IN LT3688
GND
SW
C3
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
3688 F06
(6c) For V OUT < 2.5V; V IN(MAX) = 30V
Figure 6. Three Circuits for Generating the Boost Voltage
3688f
18
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