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| 型号： | LT1956IFE-5#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 13/28页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK 5V 1.5A 16TSSOP |
| 标准包装： | 95 |
| 类型： | 降压（降压） |
| 输出类型： | 固定 |
| 输出数： | 1 |
| 输出电压： | 5V |
| 输入电压： | 5.5 V ~ 60 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 500kHz |
| 电流 - 输出： | 1.5A |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 16-TSSOP（0.173"，4.40mm）裸露焊盘 |
| 包装： | 管件 |
| 供应商设备封装： | 16-TSSOP-EP |
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LT1956/LT1956-5
APPLICATIO S I FOR ATIO
where:
f = switching frequency
t ON = switch minimum on time
V F = diode forward voltage
V IN = input voltage
I ? R = inductor I ? R voltage drop
If this condition is not observed, the current will not be
limited at I PK , but will cycle-by-cycle ratchet up to some
higher value. Using the nominal LT1956 clock frequency
of 500KHz, a V IN of 12V and a (V F + I ? R) of say 0.7V, the
maximum t ON to maintain control would be approximately
116ns, an unacceptably short time.
The solution to this dilemma is to slow down the oscillator
when the FB pin voltage is abnormally low thereby indicat-
ing some sort of short-circuit condition. Oscillator fre-
quency is unaffected until FB voltage drops to about 2/3 of
its normal value. Below this point the oscillator frequency
decreases roughly linearly down to a limit of about 100kHz.
This lower oscillator frequency during short-circuit condi-
tions can then maintain control with the effective mini-
mum on time. Even with frequency foldback, however, the
LT1956 will not survive a permanent output short at the
absolute maximum voltage rating of V IN = 60V; this is
defined solely by internal semiconductor junction break-
down effects.
For the maximum input voltage allowed during an output
short to ground, the previous equation defining minimum
on-time can be used. Assuming V F (D1 catch diode) =
0.63V at 1A (short-circuit current is folded back to typical
switch current limit ? 0.5), I (inductor) ? DCR = 1A ? 0.128
capacitor may potentially be starting from 0V. This re-
quires that the part obey the overall duty cycle demanded
by the loop, related to V IN and V OUT , as the output voltage
rises to its target value. It is recommended that for [V IN /
(V OUT + V F )] ratios > 4, a soft-start circuit should be used
to control the output capacitor charge rate during start-up
or during recovery from an output short circuit, thereby
adding additional control over peak inductor current. See
Buck Converter with Adjustable Soft-Start later in this
data sheet.
OUTPUT CAPACITOR
The LT1956 will operate with either ceramic or tantalum
output capacitors. The output capacitor is normally cho-
sen by its effective series resistance (ESR), because this
is what determines output ripple voltage. The ESR range
for typical LT1956 applications using a tantalum output
capacitor is 0.05 ? to 0.2 ? . A typical output capacitor is an
AVX type TPS, 100 μ F at 10V, with a guaranteed ESR less
than 0.1 ? . This is a “D” size surface mount solid tantalum
capacitor. TPS capacitors are specially constructed and
tested for low ESR, so they give the lowest ESR for a given
volume. The value in microfarads is not particularly criti-
cal, and values from 22 μ F to greater than 500 μ F work well,
but you cannot cheat mother nature on ESR. If you find a
tiny 22 μ F solid tantalum capacitor, it will have high ESR,
and output ripple voltage will be terrible. Table 3 shows
some typical solid tantalum surface mount capacitors.
Table 3. Surface Mount Solid Tantalum Capacitor ESR
and Ripple Current
E CASE SIZE ESR (MAX, ? ) RIPPLE CURRENT (A)
= 0.128V (L = CDRH6D28-22), typical f = 100kHz (folded
back) and typical minimum on-time = 300ns, the maxi-
mum allowable input voltage during an output short to
ground is typically:
V IN = (0.63V + 0.128V)/(100kHz ? 300ns)
AVX TPS, Sprague 593D
D CASE SIZE
AVX TPS, Sprague 593D
C CASE SIZE
AVX TPS
0.1 to 0.3
0.1 to 0.3
0.2 (typ)
0.7 to 1.1
0.7 to 1.1
0.5 (typ)
V IN(MAX) = 25V
Increasing the DCR of the inductor will increase the maxi-
mum V IN allowed during an output short to ground but will
also drop overall efficiency during normal operation.
Every time the converter wakes up from shutdown or
Unlike the input capacitor, RMS ripple current in the
output capacitor is normally low enough that ripple cur-
rent rating is not an issue. The current waveform is
triangular with a typical value of 125mA RMS . The formula
to calculate this is:
undervoltage lockout to begin switching, the output
1956f
13
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LT1956IGN | 功能描述:IC REG BUCK ADJ 1.5A 16SSOP RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 设计资源:Design Support Tool 标准包装:1 系列:- 类型:升压（升压） 输出类型:固定 输出数:1 输出电压:3V 输入电压:0.75 V ~ 2 V PWM 型:- 频率 - 开关:- 电流 - 输出:100mA 同步整流器:是 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:SOT-23-5 细型，TSOT-23-5 包装:剪切带 (CT) 供应商设备封装:TSOT-23-5 其它名称:AS1323-BTTT-30CT |
| LT1956IGN#PBF | 功能描述:IC REG BUCK ADJ 1.5A 16SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:250 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V 输入电压:2.05 V ~ 6 V PWM 型:电压模式 频率 - 开关:2MHz 电流 - 输出:500mA 同步整流器:是 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:6-UFDFN 包装:带卷 (TR) 供应商设备封装:6-SON（1.45x1） 产品目录页面:1032 (CN2011-ZH PDF) 其它名称:296-25628-2 |
| LT1956IGN#PBF | 制造商:Linear Technology 功能描述:IC STEP-DOWN REGULATOR SSOP-16 |
| LT1956IGN#TR | 功能描述:IC REG BUCK ADJ 1.5A 16SSOP RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 设计资源:Design Support Tool 标准包装:1 系列:- 类型:升压（升压） 输出类型:固定 输出数:1 输出电压:3V 输入电压:0.75 V ~ 2 V PWM 型:- 频率 - 开关:- 电流 - 输出:100mA 同步整流器:是 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:SOT-23-5 细型，TSOT-23-5 包装:剪切带 (CT) 供应商设备封装:TSOT-23-5 其它名称:AS1323-BTTT-30CT |
| LT1956IGN#TRPBF | 功能描述:IC REG BUCK ADJ 1.5A 16SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 设计资源:Design Support Tool 标准包装:1 系列:- 类型:升压（升压） 输出类型:固定 输出数:1 输出电压:3V 输入电压:0.75 V ~ 2 V PWM 型:- 频率 - 开关:- 电流 - 输出:100mA 同步整流器:是 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:SOT-23-5 细型，TSOT-23-5 包装:剪切带 (CT) 供应商设备封装:TSOT-23-5 其它名称:AS1323-BTTT-30CT |
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