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| 型号： | LT1952IGN-1#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 18/28页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR ISO PWM CM 16-SSOP |
| 标准包装： | 100 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 560kHz |
| 占空比： | 90% |
| 电源电压： | 6.82 V ~ 25 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 ~ 125°C |
| 封装/外壳： | 16-SSOP（0.154"，3.90mm 宽） |
| 包装： | 管件 |
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LT1952/LT1952-1
APPLICATIONS INFORMATION
(A) V IN > 14.25* (7.75V LT1952-1), and
(B) SD_V SEC > 1.32V, and
(C) OC < 107mV, and
(D) SS_MAXDC < 0.45V (SS_MAXDC reset threshold)
*V IN > 8.75V (6.5V LT1952-1) is ok for latch reset if the latch
was only set by overcurrent condition in (3) above.
SS_MAXDC Discharge Timing
It can be seen in Figure 10 that two types of discharge
can occur for the SS_MAXDC pin. In timing (A) the fault
that caused the soft-start event has been removed before
SS_MAXDC falls to 0.45V. This means the soft-start
latch will be reset when SS_MAXDC falls to 0.45V and
SS_MAXDC will begin charging. In timing (B), the fault that
caused the soft-start event is not removed until some time
after SS_MAXDC has fallen past 0.45V. The SS_MAXDC
pin continues to discharge to 0.2V and remains low until
all faults are removed.
The time for SS_MAXDC to fall to a given voltage can be
approximated as:
SS_MAXDC (t FALL ) =
(C SS /I DIS ) ? [SS_MAXDC(DC) – V SS(MIN) ]
where:
I DIS = net discharge current on C SS
C SS = capacitor value at SS_MAXDC pin
SS_MAXDC(DC) = programmed DC voltage
V SS(MIN) = minimum SS_MAXDC voltage before
recharge
I DIS ~ 8e –4 + (V REF – V SS(MIN) )[(1/2R B ) – (1/R T )]
For faults arising from (1) and (2),
V REF = 100mV.
For a fault arising from (3),
V REF = 2.5V.
SS_MAXDC(DC) = V REF [R B /(R T + R B )]
Example:
For an overcurrent fault (OC > 100mV), V REF = 2.5V,
R T = 35.7k, R B = 100k, C SS = 0.1μF and assume
V SS(MIN) = 0.45V,
I DIS ~ 8e –4 + (2.5 – 0.45)[(1/2 ? 100k) – (1/35.7k)]
= 8e –4 + (2.05)(–0.23e –4 ) = 7.5e –4
SS_MAXDC(DC) = 1.84V
SS_MAXDC (t FALL ) = (1e – 7/7.5e –4 ) ? (1.84 – 0.45)
= 1.85e–4 s
If the OC fault is not removed before 185μs then SS_MAXDC
will continue to fall past 0.45V towards a new V SS(MIN) .
The typical V OL for SS_MAXDC at 150μA is 0.2V.
SS_MAXDC Charge Timing
When all faults are removed and the SS_MAXDC pin
has fallen to its reset threshold of 0.45V or lower, the
SS_MAXDC pin will be released and allowed to charge.
SS_MAXDC will rise until it settles at its programmed DC
voltage —setting the maximum switch duty cycle clamp.
The calculation of charging time for the SS_MAXDC pin
between any two voltage levels can be approximated as
an RC charging waveform using the model shown in
Figure 11.
The ability to predict SS_MAXDC rise time between any two
voltages allows prediction of several key timing periods:
(1)No Switching Period
(time from SS_MAXDC(DC) to V SS(MIN) + time from
V SS(MIN) to V SS(ACTIVE) )
(2)Converter Output Rise Time
(time from V SS(ACTIVE) to V SS(REG) ; V SS(REG) is the
level of SS_MAXDC where maximum duty cycle
clamp equals the natural duty cycle of the switch)
(3)Time For Maximum Duty Cycle Clamp within X% of
Target Value
The time for SS_MAXDC to charge to a given voltage V SS
is found by re-arranging:
V SS(MIN) = SS_MAXDC reset threshold = 0.45V
(if fault removed before t FALL )
19521fe
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相关代理商/技术参数 |
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|---|---|
| LT1952IGN-1TR | 制造商:LINER 制造商全称:Linear Technology 功能描述:Single Switch Synchronous Forward Controller |
| LT1952IGN-1TRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Single Switch Synchronous Forward Controller |
| LT1952IGNPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Single Switch Synchronous Forward Controller |
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| LT1952IGNTRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Single Switch Synchronous Forward Controller |
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