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参数资料
| 型号： | LT3837IFE#TRPBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING CONTROLLER, 110 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封装： | 4.40 MM, LEAD FREE, PLASTIC, TSSOP-16 |
| 文件页数： | 9/28页 |
| 文件大小： | 247K |
| 代理商： | LT3837IFE#TRPBF |
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LT3837
17
3837fc
APPLICATIONS INFORMATION
5. Verify this result by connecting a resistor of this value
from the RCMP pin to ground.
6. Disconnect the ground short to CCMP and connect the
requisite 0.1μF lter capacitor to ground. Measure
the output impedance RS(OUT) = ΔVOUT/ΔIOUT with the
new compensation in place. RS(OUT) should have
decreased signicantly. Fine tuning is accomplished
experimentally by slightly altering RCMP. A revised
estimate for RCMP is:
′
=+
RR
R
CMP
S OUT CMP
S OUT
()
1
where R
′CMPisthenewvaluefortheloadcompensation
resistor, RS(OUT)CMP is the output impedance with RCMP
in place and RS(OUT) is the output impedance with no
load compensation (from step 2).
Setting Frequency
The switching frequency of the LT3837 is set by an
external capacitor connected between the OSC pin and
ground. Recommended values are between 200pF and
33pF, yielding switching frequencies between 50kHz and
250kHz. Figure 3 shows the nominal relationship between
external capacitance and switching frequency. Place the
capacitor as close as possible to the IC and minimize OSC
trace length and area to minimize stray capacitance and
potential noise pickup.
You can synchronize the oscillator frequency to an external
frequency. This is done with a signal on the SYNC pin. Set
the LT3837 frequency 10% slower than the desired external
frequency using the OSC pin capacitor, then use a pulse
on the SYNC pin of amplitude greater than 2V and with the
desired period. The rising edge of the SYNC signal initiates
an OSC capacitor discharge forcing primary MOSFET off
(PG voltage goes low). If the oscillator frequency is much
different from the sync frequency, problems may occur
with slope compensation and system stability. Keep the
sync pulse width greater than 500ns.
Selecting Timing Resistors
There are three internal “one-shot” times that are pro-
grammed by external application resistors: minimum
on-time, enable delay time and primary MOSFET turn-on
delay. These are all part of the isolated yback control
technique, and their functions are previously outlined in
the Theory of Operation section.
The following information should help in selecting and/or
optimizing these timing values.
Minimum On-Time (tON(MIN))
Minimum on-time is the programmable period during
which current limit is blanked (ignored) after the turn
on of the primary side switch. This improves regulator
performance by eliminating false tripping on the leading
edge spike in the switch, especially at light loads. This
spike is due to both the gate/source charging current and
the discharge of drain capacitance. The isolated yback
sensing requires a pulse to sense the output. Minimum
on-time ensures that there is always a signal to close the
feedback loop. The LT3837 does not employ cycle skipping
at light loads. Therefore, minimum on-time along with
synchronous rectication sets the switch over in forced
continuous mode operation.
The tON(MIN) resistor is set with the following equation:
Rk
tns
tON MIN
ON MIN
()
() –
.
Ω=
104
1 063
Keep RtON(MIN) greater than 70k. A good starting value
is 160k.
Figure 3. fOSC vs OSC Capacitor Values
COSCAP (pF)
30
50
f OSC
(kHz)
100
200
300
100
200
3837 F03
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| LT3844EFE#PBF | 功能描述:IC REG CTRLR BST INV PWM 16TSSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 特色产品:LM3753/54 Scalable 2-Phase Synchronous Buck Controllers 标准包装:1 系列:PowerWise® PWM 型:电压模式 输出数:1 频率 - 最大:1MHz 占空比:81% 电源电压:4.5 V ~ 18 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:-5°C ~ 125°C 封装/外壳:32-WFQFN 裸露焊盘 包装:Digi-Reel® 产品目录页面:1303 (CN2011-ZH PDF) 其它名称:LM3754SQDKR |
| LT3844EFE#TRPBF | 功能描述:IC REG CTRLR BST INV PWM 16TSSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 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:24-WQFN 裸露焊盘 包装:带卷 (TR) |
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