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参数资料
| 型号： | LT3759IMSE#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 13/32页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BST INV PWM 12-MSOP |
| 标准包装： | 37 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 1MHz |
| 电源电压： | 1.6 V ~ 42 V |
| 降压： | 无 |
| 升压： | 是 |
| 回扫： | 无 |
| 反相： | 是 |
| 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： | 12-TSSOP （0.118"，3.00mm 宽）裸露焊盘 |
| 包装： | 管件 |
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LT3759
APPLICATIONS INFORMATION
D V SENSE
40mV - 0.5 ? D V SENSE
C FLT
R SENSE
DuetothecurrentlimitfunctionoftheSENSEpin,R SENSE
should be selected to guarantee that the peak current sense
voltage V SENSE(PEAK) during steady state normal opera-
tion is lower than the SENSE current limit threshold (see
the Electrical Characteristics table). Given a 20% margin,
V SENSE(PEAK) is set to be 40mV. Then, the maximum switch
ripple current percentage can be calculated using the fol-
lowing equation:
c=
χ is used in subsequent design examples to calculate
inductor value. ΔV SENSE is the ripple voltage across R SENSE .
The LT3759 has internal slope compensation to stabilize
the control loop against sub-harmonic oscillation. When
the LT3759 operates at a high duty cycle in continuous
conduction mode, the SENSE voltage ripple ΔV SENSE (re-
fer to Figure 2) needs to be limited to ensure the internal
slope compensation is sufficient to stabilize the control
loop. Figure 3 shows the maximum allowed ΔV SENSE over
the duty cycle. It is recommended to check and ensure
ΔV SENSE is below the curve at the highest duty cycle.
60
50
40
30
20
10
0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
DUTY CYCLE
3759 F03
Figure 3. The Maximum Allowed SENSE Voltage Ripple vs
Duty Cycle
The LT3759 switching controller incorporates 100ns timing
interval to blank the ringing on the current sense signal
immediately after M1 is turned on. This ringing is caused
by the parasitic inductance and capacitance of the PCB
trace, the sense resistor, the diode, and the MOSFET. The
100ns timing interval is adequate for most of the LT3759
applications. In the applications that have very large and
long ringing on the current sense signal, a small RC filter
can be added to filter out the excess ringing. Figure 4
shows the RC filter on SENSE pin. It is usually sufficient
to choose 22Ω for R FLT and 2.2nF to 10nF for C FLT . Keep
R FLT’s resistance low. Remember that there is 50μA (typi-
cal) flowing out of the SENSE pin. Adding R FLT will affect
the SENSE current limit threshold:
V SENSE _ILIM = 50mV ? 50μA ? R FLT
GATE M 1
LT3759
R FLT
SENSE
GND
3759 F04
Figure 4. The RC Filter on SENSE pin
APPLICATION CIRCUITS
The LT3759 can be configured as different topologies.
The design procedure for component selection differs
somewhat between these topologies. The first topology
to be analyzed will be the boost converter, followed by the
flyback SEPIC and inverting converters.
Boost Converter: Switch Duty Cycle and Frequency
The LT3759 can be configured as a boost converter for
the applications where the converter output voltage is
higher than the input voltage. Remember that boost con-
verters are not short-circuit protected. Under a shorted
output condition, the inductor current is limited only by
the input supply capability. For applications requiring a
step-up converter that is short-circuit protected, please
refer to the Applications Information section covering
SEPIC converters.
3759fc
For more information www.linear.com/3759
13
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