参数资料
型号: LTC3612IUDC#PBF
厂商: Linear Technology
文件页数: 19/30页
文件大小: 0K
描述: IC REG BUCK SYNC ADJ 3A 20QFN
标准包装: 91
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-WFQFN 裸露焊盘
包装: 管件
供应商设备封装: 20-QFN(3x4)
LTC3612
APPLICATIONS INFORMATION
AVP Mode
Fast load transient response, limited board space and low
cost are typical requirements of microprocessor power
supplies. A microprocessor has typical full load step with
very fast slew rate. The voltage at the microprocessor must
be held to about ±0.1V of nominal in spite of these load
current steps. Since the control loop cannot respond this
fast, the output capacitors must supply the load current
until the control loop can respond.
Normally, several capacitors in parallel are required to
meet microprocessor transient requirements. Capacitor
ESR and ESL primarily determine the amount of droop or
overshoot in the output voltage.
Consider the LTC3612 without AVP with a bank of tantalum
output capacitors. If a load step with very fast slew rate
occurs, the voltage excursion will be seen in both direc-
tions, for full load to minimum load transient and for the
minimum load to full load transient.
If the ITH pin is tied to SV IN , the active voltage position-
ing (AVP) mode and internal compensation are selected.
AVP mode intentionally compromises load regulation by
reducing the gain of the feedback circuit, resulting in an
output voltage that varies with load current. When the load
current suddenly increases, the output voltage starts from
a level slightly higher than nominal so the output voltage
can droop more and stay within the specified voltage
range. When the load current suddenly decreases the
output voltage starts at a level lower than nominal so the
output voltage can have more overshoot and stay within
the specified voltage range (see Figures 3 and 4).
V OUT
200mV/DIV
I L
1A/DIV
The benefit is a lower peak-to-peak output voltage deviation
for a given load step without having to increase the output
filter capacitance. Alternatively, the output voltage filter
capacitance can be reduced while maintaining the same
peak to peak transient response. Due to the reduced loop
gain in AVP mode, no external compensation is required.
DDR Mode
The LTC3612 can both source and sink current if the MODE
pin is configured to forced continuous mode.
Current sinking is typically limited to 1.5A, for 1MHz
frequency and a 1μH inductor, but can be lower at higher
frequencies and low output voltages. If higher ripple current
can be tolerated, smaller inductor values can increase the
sink current limit. See the Typical Performance Charac-
teristics curves for more information.
In addition, tying the DDR pin to SV IN , lower external
reference voltage and tracking output voltage between
channels are possible. See the Output Voltage Tracking
and External Reference Input sections.
Soft-Start
The RUN pin provides a means to shut down the LTC3612.
Tying the RUN pin to SGND places the LTC3612 in a low
quiescent current shutdown state (I Q < 1μA).
The LTC3612 is enabled by pulling the RUN pin high. How-
ever, the applied voltage must not exceed SV IN . In some
applications, the RUN signal is generated within another
power domain and is driven high while the SV IN and PV IN
is still 0V. In this case, it’s required to limit the current into
V OUT
100mV/DIV
I L
1A/DIV
V IN = 3.3V 50μs/DIV
V OUT = 1.8V
I LOAD = 100mA TO 3A
V MODE = 1.5V
COMPENSATION FIGURE 1
3612 F03
V IN = 3.3V 50μs/DIV
V OUT = 1.8V
I LOAD = 100mA TO 3A
V MODE = 1.5V
V ITH = 3.3V
OUTPUT CAPACITOR VALUE FIGURE 1
3612 F04
Figure 3. Load Step Transient Forced Continuous Mode
(AVP Inactive)
Figure 4. Load Step Transient Forced Continuous Mode
with AVP Mode
3612fb
For more information www.linear.com/LTC3612
19
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