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参数资料
| 型号： | LTC3728IG |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 3 A DUAL SWITCHING CONTROLLER, 590 kHz SWITCHING FREQ-MAX, PDSO28 |
| 封装： | 0.209 INCH, PLASTIC, SSOP-28 |
| 文件页数： | 7/36页 |
| 文件大小： | 1661K |
| 代理商： | LTC3728IG |
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LTC3728
15
3728fg
Figure 1 on the rst page is a basic LTC3728 application
circuit. External component selection is driven by the
load requirement, and begins with the selection of RSENSE
and the inductor value. Next, the power MOSFETs and
D1 are selected. Finally, CIN and COUT are selected. The
circuit shown in Figure 1 can be congured for operation
up to an input voltage of 28V (limited by the external
MOSFETs).
RSENSE Selection for Output Current
RSENSE ischosenbasedontherequiredoutputcurrent.The
LTC3728 current comparator has a maximum threshold
of 75mV/RSENSE and an input common mode range of
SGND to 1.1(INTVCC). The current comparator threshold
sets the peak of the inductor current, yielding a maximum
average output current IMAX equal to the peak value less
half the peak-to-peak ripple current, ΔIL.
Allowing a margin for variations in the LTC3728 and external
component values yields:
RSENSE =
50mV
IMAX
Because of possible PCB noise in the current sensing loop,
the AC current sensing ripple of ΔVSENSE = ΔI RSENSE
also needs to be checked in the design to get good sig-
nal-to-noise ratio. In general, for a reasonable good PCB
layout, a 15mV ΔVSENSE voltage is recommended as a
conservative number to start with.
When using the controller in very low dropout conditions,
the maximum output current level will be reduced due to the
internal compensation required to meet stability criterion
for buck regulators operating at greater than 50% duty
factor. A curve is provided to estimate this reduction in
peak output current level depending upon the operating
duty factor.
Operating Frequency
The LTC3728 uses a constant-frequency, phase-lockable
architecture with the frequency determined by an internal
capacitor. This capacitor is charged by a xed current plus
an additional current which is proportional to the voltage
applied to the PLLFLTR pin. Refer to Phase-Locked Loop
APPLICATIONS INFORMATION
and Frequency Synchronization in the Applications Infor-
mation section for additional information.
A graph for the voltage applied to the PLLFLTR pin vs
frequency is given in Figure 5. As the operating frequency
is increased the gate charge losses will be higher, reducing
efciency (see Efciency Considerations). The maximum
switching frequency is approximately 550kHz.
Inductor Value Calculation
The operating frequency and inductor selection are inter-
related in that higher operating frequencies allow the use
of smaller inductor and capacitor values. So why would
anyone ever choose to operate at lower frequencies with
larger components? The answer is efciency. A higher
frequency generally results in lower efciency because
of MOSFET gate charge losses. In addition to this basic
trade-off, the effect of inductor value on ripple current and
low current operation must also be considered.
The inductor value has a direct effect on ripple current.
The inductor ripple current ΔIL decreases with higher
inductance or frequency and increases with higher VIN:
IL =
1
(f)(L)
VOUT 1–
VOUT
VIN
Accepting larger values of ΔIL allows the use of low
inductances, but results in higher output voltage ripple
and greater core losses. A reasonable starting point for
setting ripple current is ΔIL=0.3(IMAX) or higher for good
Figure 5. PPLFLTR Pin Voltage vs Frequency
OPERATING FREQUENCY (kHz)
200
250
300
350
550
400
450
500
PLLFLTR
PIN
VOLTAGE
(V)
3728 F05
2.5
2.0
1.5
1.0
0.5
0
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相关代理商/技术参数 |
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| LTC3728IG#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 28-SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:PolyPhase® 标准包装:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 V 降压:是 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
| LTC3728IG#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 28-SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:PolyPhase® 标准包装:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 V 降压:是 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
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