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| 型号： | LT3437HFE#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 16/28页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK ADJ 0.5A 16TSSOP |
| 标准包装： | 2,500 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 1.25 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： | 500mA |
| 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： | 带卷 (TR) |
| 供应商设备封装： | 16-TSSOP-EP |
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LT3437
APPLICATIO S I FOR ATIO
Short-Circuit Considerations
The LT3437 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 1.5V, 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 problem 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. This results 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:
thereby indicating some sort of short-circuit condition,
the oscillator frequency will be reduced. Oscillator fre-
quency is reduced by a factor of 10 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
Characteristics). These oscillator frequency reductions
during short-circuit conditions allow the LT3437 to main-
tain current control
SOFT-START
For applications where [V IN /(V OUT + V F )] >10 or large input
surge currents cannot be tolerated, the LT3437 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 limits
the switch current via the V C pin to maintain a constant
voltage ramp rate (dV/dt) at the output capacitor. A capaci-
tor (C1 in Figure 2) from the C SS pin to the 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
f ? t ON ≤
V F + I ? R
V IN
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 approxi-
= CSS
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
If this condition is not observed, the current will not be
mated by:
dV I
dt C SS
but actual values will vary due to start-up load conditions,
compensation values and output capacitor selection.
C SS = GND
limited at I PK but will cycle-by-cycle ratchet up to some
higher value. Using the nominal LT3437 clock frequency
of 200kHz, a V IN of 40V and a (V F + I ? R) of say 0.7V, the
V OUT
1V/DIV
C SS = 0.01μF
C SS = 0.1μF
maximum t ON to maintain control would be approximately
90ns, an unacceptably short time.
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 does not continue to
V IN = 12V
C OUT = 100 μ F
I LOAD = 200mA
1ms/DIV
3437 F04
ratchet higher. When the FB pin voltage is abnormally low,
Figure 4. V OUT dV/dt
3437fc
16
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| LT3437IDD | 制造商:Linear Technology 功能描述:SP-SWREG/Monolithic, 60V, 500mA, 200kHz Step-down Converter w/ BurstMode |
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| LT3437IDD#PBF | 制造商:Linear Technology 功能描述:DC-DC CONVERTER BUCK 200KHZ 制造商:Linear Technology 功能描述:DC-DC CONVERTER, BUCK, 200KHZ, DFN-10 |
| LT3437IDD#TRPBF | 功能描述:IC REG BUCK ADJ 0.5A 10DFN 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:2,500 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V，1.5V，1.8V，2.5V 输入电压:2.7 V ~ 20 V PWM 型:- 频率 - 开关:- 电流 - 输出:50mA 同步整流器:是 工作温度:-40°C ~ 125°C 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽）裸露焊盘 包装:带卷 (TR) 供应商设备封装:10-MSOP 裸露焊盘 |
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