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| 型号： | LT1976EFE |
| 厂商： | Linear Technology |
| 文件页数： | 17/28页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK ADJ 1.5A 16TSSOP |
| 标准包装： | 95 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 1.2 V ~ 54 V |
| 输入电压： | 3.3 V ~ 60 V |
| PWM 型： | 电流模式，混合 |
| 频率 - 开关： | 200kHz |
| 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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LT1976/LT1976B
APPLICATIO S I FOR ATIO
Short-Circuit Considerations
The LT1976 is a current mode controller. It uses the V C
node voltage as an input to a current comparator which
turns off the output switch on a cycle-by-cycle basis as
this peak current is reached. The internal clamp on the V C
node, nominally 2.2V, then acts as an output switch peak
current limit. This action becomes the switch current limit
specification. The maximum available output power is
then determined by the switch current limit.
A potential controllability prod}m could occur under short-
circuit conditions. If the power supply output is short
circuited, the feedback amplifier responds to the low
output voltage by raising the control voltage, V C , to its
peak current limit value. Ideally, the output switch would
be turned on, and then turned off as its current exceeded
the value indicated by V C . However, there is finite response
time involved in both the current comparator and turn-off
of the output switch. These result in a minimum on time
t ON(MIN). When combined with the large ratio of V IN to
(V F + I ? R), the diode forward voltage plus inductor I ? R
voltage drop, the potential exists for a loss of control.
Expressed mathematically the requirement to maintain
control is:
The solution to this dilemma is to slow down the oscillator
to allow the current in the inductor to drop to a sufficiently
low value such that the current doesn’t continue to ratchet
higher. When the FB pin voltage is abnormally low thereby
indicating some sort of short-circuit condition, the oscil-
lator frequency will be reduced. Oscillator frequency is
reduced by a factor of 4 when the FB pin voltage is below
0.4V and increases linearly to its typical value of 200kHz at
a FB voltage of 0.95V (see Typical Performance Character-
istics). In addition, if the current in the switch exceeds 1.5
? I PK current demanded by the V C pin, the LT1976 will skip
the next on cycle effectively reducing the oscillator fre-
quency by a factor of 2. These oscillator frequency reduc-
tions during short-circuit conditions allow the LT1976 to
maintain current control.
SOFT-START
For applications where [V IN /(V OUT + V F )] ratios > 10 or
large input surge currents can’t be tolerated, the LT1976
soft-start feature 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. The soft-start function
f ? t ON ≤
V F + I ? R
V IN
limits the switch current via the V C pin to maintain a
constant voltage ramp rate (dV/dt) at the output capacitor.
A capacitor (C1 in Figure 2) from the C SS pin to the
where:
f = switching frequency
t ON = switch on time
V F = diode forward voltage
V IN = Input voltage
I ? R = inductor I ? R voltage drop
regulated output voltage determines the output voltage
ramp rate. When the current through the C SS capacitor
exceeds the C SS threshold (I CSS ), the voltage ramp of the
output capacitor is limited by reducing the V C pin voltage.
The C SS threshold is proportional to the FB voltage (see
Typical Performance Characteristics) and is defeated for
FB voltages greater than 0.9V (typical). The output dV/dt
can be approximated by:
= CSS
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 LT1976 clock frequency
dV
dt
I
C SS
of 200kHz, a V IN of 40V and a (V F + I ? R) of say 0.7V, the
maximum t ON to maintain control would be approximately
90ns, an unacceptably short time.
but actual values will vary due to start-up load conditions,
compensation values and output capacitor selection.
1976bfg
17
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相关代理商/技术参数 |
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| LT1976EFE#PBF | 功能描述:IC REG BUCK ADJ 1.5A 16TSSOP 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 |
| LT1976EFE#TR | 功能描述:IC REG BUCK ADJ 1.5A 16TSSOP 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 |
| LT1976EFE#TRPBF | 功能描述:IC REG BUCK ADJ 1.5A 16TSSOP 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 |
| LT1976EFEPBF | 制造商:Linear Technology 功能描述:LT1976 adj PWM 1.5A SD dc-dc converter 制造商:Linear Technology 功能描述:DC-DC Converter Step-Down 60V TSSOP16EP |
| LT1976HFE | 制造商:LINER 制造商全称:Linear Technology 功能描述:High Voltage 1.5A, 200kHz Step-Down Switching Regulator with 100μA Quiescent Current |
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