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参数资料
| 型号： | LTC1922IG-1#TR |
| 厂商： | Linear Technology |
| 文件页数： | 16/24页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR ISO PWM 20-SSOP |
| 标准包装： | 1,800 |
| PWM 型： | 电流/电压模式 |
| 输出数： | 1 |
| 频率 - 最大： | 1MHz |
| 占空比： | 99% |
| 电源电压： | 3.8 V ~ 10.3 V |
| 降压： | 无 |
| 升压： | 无 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 是 |
| 工作温度： | -40°C ~ 85°C |
| 封装/外壳： | 20-SSOP（0.209"，5.30mm 宽） |
| 包装： | 带卷 (TR) |
LTC1922-1
OPERATIO
V O = 3.3V
L O = 2.2 μ H
2.0
R S = 0.025
1.8 V IN = 48V
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
include, higher cost and complexity, lower accuracy, core
reset/max duty cycle limitations and lower speed. Never-
theless, for very high power applications, this method is
preferred. The sense transformer primary is placed in the
same location as the ground referenced sense resistor, or
between the upper MOSFET drains in the (MA, MC) and
V IN . The advantage of the high side location is a greater
immunity to leading edge noise spikes, since gate charge
current and reflected rectifier recovery current are largely
0
0
5
10 15 20 25 30
OUTPUT CURRENT (A)
35
40
eliminated. Figure 10 illustrates a typical current sense
transformer based sensing scheme. R S in this case is
1922 ? F09
Figure 9. R SENSE Power Loss vs I OUT
If RAMP and CS are connected together:
calculated the same as in the resistive case, only its value
is increased by the sense transformer turns ratio. At high
duty cycles, it may become difficult or impossible to reset
the current transformer. This is because the required
transformer reset voltage increases as the available time
R CS =
0 .4V – (125 μ A ? R SLOPE )
I P ( PEAK )
for reset decreases to equalize the (volt ? seconds) applied.
The interwinding capacitance and secondary inductance
of the current sense transformer form a resonant circuit
that limits the dV/dT on the secondary of the CS trans-
+
I P ( PEAK ) =
I O ( MAX ) V IN ( MAX ) ? 2 ? D MIN
2 ? N ? EFF L MAG ? f CLK
V O ( 1 – D MIN )
L OUT ? f CLK ? N
+
former. This in turn limits the maximum achievable duty
cycle for the CS transformer. Attempts to operate beyond
this limit will cause the transformer core to “walk” and
eventually saturate, opening up the current feedback loop.
Common methods to address this limitation include:
where: N = Transformer turns ratio
If RAMP and CS are separated
1. Reducing the maximum duty cycle by lowering the
power transformer turns ratio.
R CS
=
0 . 4 V
I P ( PEAK )
2. Reducing the switching frequency of the converter.
3. Employ external active reset circuitry.
4. Using two CS transformers summed together.
Current Transformer Sensing
A current sense transformer can be used in lieu of resistive
5. Choose a CS transformer optimized for high frequency
applications.
sensing with the LTC1922-1. Current sense transformers
are available in many styles from several manufacturers.
MB
SOURCE
MD
SOURCE
A typical sense transformer for this application will use a
1:50 turns ratio (N), so that the sense resistor value is N
times larger, and the secondary current N times smaller
than in the resistive sense case. Therefore, the sense
resistor power loss is about N times less with the trans-
former method, neglecting the transformers core and
RAMP
CS
R SLOPE
OPTIONAL
FILTERING
R S
N:1
CURRENT
TRANSFORMER
1922 F10
copper losses. The disadvantages of this approach
16
Figure 10. Current Transformer Sense Circuitry
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| LTC1923EGN | 功能描述:IC CONTROLLER TEC HI EFF 28SSOP RoHS:否 类别:集成电路 (IC) >> PMIC - 电源管理 - 专用 系列:- 标准包装:1 系列:- 应用:手持/移动设备 电流 - 电源:- 电源电压:3 V ~ 5.5 V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:14-WFDFN 裸露焊盘 供应商设备封装:14-LLP-EP（4x4） 包装:Digi-Reel® 配用:LP3905SD-30EV-ND - BOARD EVALUATION LP3905SD-30 其它名称:LP3905SD-30DKR |
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