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参数资料
| 型号： | LTC1148HVCS-3.3#TR |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING CONTROLLER, 250 kHz SWITCHING FREQ-MAX, PDSO14 |
| 封装： | 0.150 INCH, PLASTIC, SOP-14 |
| 文件页数： | 6/20页 |
| 文件大小： | 237K |
| 代理商： | LTC1148HVCS-3.3#TR |
14
LTC1148
LTC1148-3.3/LTC1148-5
114835fd
APPLICATIO S I FOR ATIO
W
UU
U
With the addition of R3, a current is generated through R1
causing an offset of:
VOFFSET = VOUT
)
) R1
R1 + R3
If VOFFSET > 25mV, the minimum threshold will be can-
celled and Burst Modeoperation is prevented from occur-
ring. Since VOFFSET is constant, the maximum load current
is also decreased by the same offset. Thus, to get back to
the same IMAX, the value of the sense resistor must be
lower:
RSENSE ≈
75mV
IMAX
To prevent noise spikes from erroneously tripping the
current comparator, a 1000pF capacitor is needed across
Pins 7 and 8.
Output Crowbar
An added feature to using an N-channel MOSFET as the
synchronous switch is the ability to crowbar the output
with the same MOSFET. Pulling the timing capacitor Pin
4 above 1.5V when the output voltage is greater than the
desired regulated value will turn “on” the N-channel
MOSFET.
A fault condition which causes the output voltage to go
above a maximum allowable value can be detected by
external circuitry. Turning on the N-channel MOSFET
when this fault is detected will cause large currents to flow
and blow the system fuse.
The N-channel MOSFET needs to be sized so it will safely
handle this overcurrent condition. The typical delay from
pulling the CT pin high and the N drive Pin 14 going high
is 250ns. Note: Under shutdown conditions, the N-chan-
nel is held OFF and pulling the CT pin high will not cause
the N-channel MOSFET to crowbar the output.
A simple N-channel FET can be used as an interface
between the overvoltage detect circuitry and the LTC1148
as shown in Figure 7.
Figure 7. Output Crowbar Interface
LTC1148
INTVCC
CT
VN2222LL
5
4
FROM CROWBAR DETECT CIRCUIT
(ACTIVE WHEN VGATE = VIN
OFF WHEN VGATE = GROUND)
LTC1148 F07
Troubleshooting Hints
Since efficiency is critical to LTC1148 series applications,
it is very important to verify that the circuit is functioning
correctly in both continuous and Burst Mode operation.
The waveform to monitor is the voltage on the timing
capacitor Pin 4.
In continuous mode (ILOAD > IBURST) the voltage on the CT
pin should be a sawtooth with a 0.9VP-P swing. This
voltage should never dip below 2V as shown in Figure 8a.
When load currents are low (ILOAD < IBURST) Burst Mode
operation should occur with the CT pin waveform periodi-
cally falling to ground as shown in Figure 8b.
3.3V
0V
(a) CONTINUOUS MODE OPERATION
3.3V
0V
(b) Burst Mode OPERATION
LTC1148 F08
Figure 8. CT Waveforms
If Pin 4 is observed falling to ground at high output
currents, it indicates poor decoupling or improper ground-
ing. Refer to the Board Layout Checklist.
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| LTC1148HVCS5 | 制造商:LT 功能描述:REREALED |
| LTC1148HVCS-5 | 功能描述:IC REG CTRLR BUCK PWM CM 14-SOIC RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 V 降压:是 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
| LTC1148HVCS-5#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 14-SOIC RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:4,000 系列:- PWM 型:电压模式 输出数:1 频率 - 最大:1.5MHz 占空比:66.7% 电源电压:4.75 V ~ 5.25 V 降压:是 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 85°C 封装/外壳:40-VFQFN 裸露焊盘 包装:带卷 (TR) |
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