参数资料
型号: LTC3612IFE#TRPBF
厂商: Linear Technology
文件页数: 20/30页
文件大小: 0K
描述: IC REG BUCK SYNC ADJ 3A 20TSSOP
标准包装: 2,500
类型: 降压(降压)
输出类型: 可调式
输出数: 1
输出电压: 0.6 V ~ 5.5 V
输入电压: 2.25 V ~ 5.5 V
PWM 型: 电流模式,混合
频率 - 开关: 300kHz ~ 4MHz
电流 - 输出: 3A
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: 20-TSSOP(0.173",4.40mm 宽)裸露焊盘
包装: 带卷 (TR)
供应商设备封装: 20-TSSOP-EP
LTC3612
APPLICATIONS INFORMATION
t SS = R SS ?C SS ?ln ?
theRUNpinbyeitheraddinga1MΩresistorora100kΩ
resistor, plus a Schottky diode, to SV IN . After pulling the
RUN pin high, the chip enters a soft start-up state. This
type of soft start-up behavior is set by the TRACK/SS pin:
1. Tying TRACK/SS to SV IN selects the internal soft-start
circuit. This circuit ramps the output voltage to the final
value within 1ms.
2. If a longer soft-start period is desired, it can be set ex-
ternally with a resistor and capacitor on the TRACK/SS
pin, as shown in Figure 1. The TRACK/SS pin reduces
the value of the internal reference at V FB until TRACK/
SS is pulled above 0.6V. The external soft-start duration
can be calculated by using the following formula:
? SV IN ?
? SV IN – 0.6V ? ?
3. The TRACK/SS pin can be used to track the output
voltage of another supply.
Each time the RUN pin is tied high and the LTC3612 is
turned on, the TRACK/SS pin is internally pulled down
for ten microseconds in order to discharge the external
capacitor. This discharging time is typically adequate for
capacitors up to about 33nF. If a larger capacitor is required,
connect the external soft-start resistor to the RUN pin.
the TRACK/SS pin. The run state will resume if V TRACK/SS
again exceeds 0.6V and V OUT is referenced to the internal
precision reference (see Figure 7).
Through the TRACK/SS pin, the output voltage can be set
up for either coincident or ratiometric tracking, as shown
in Figure 5.
To implement the coincident tracking behavior in Fig-
ure 5a, connect an extra resistive divider to the output
of the master channel and connect its midpoint to the
TRACK/SS pin for the slave channel. The ratio of this
divider should be selected to be the same as that of the
slave channel’s feedback divider (Figure 6a). In this track-
ing mode, the master channel’s output must be set higher
than slave channel’s output. To implement the ratiometric
tracking behavior in Figure 5b, different resistor divider
values must be used as specified in Figure 6b.
V OUT1
V OUT2
Regardless of either internal or external soft-start state,
the MODE pin is ignored and soft-start will always be in
pulse-skipping mode. In addition, the PGOOD pin is kept
low and foldback of the switching frequency is disabled.
Output Voltage Tracking Input
TIME
(5a) Coincident Tracking
V OUT1
If the DDR pin is not tied to SV IN , once V TRACK/SS exceeds
0.6V, the run state is entered and the MODE selection,
power good and current foldback circuits are enabled.
In the run state, the TRACK/SS pin can be used for track-
ing down/up the output voltage of another supply. If the
V TRACK/SS drops below 0.6V, the LTC3612 enters the down
tracking state and V OUT is referenced to the TRACK/SS volt-
age. If the TRACK/SS pin drops below 0.2V, the switching
frequency is reduced to ensure that the minimum duty
cycle limit does not prevent the output from following
V OUT2
3612 F05
TIME
(5b) Ratiometric Tracking
Figure 5. Two Different Modes of Output Voltage Tracking
3612fb
20
For more information www.linear.com/LTC3612
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