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| 型号： | LTC1539CGW |
| 厂商： | Linear Technology |
| 文件页数： | 12/32页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 36-SSOP |
| 标准包装： | 32 |
| PWM 型： | 电流模式 |
| 输出数： | 2 |
| 频率 - 最大： | 138kHz |
| 占空比： | 99% |
| 电源电压： | 3.5 V ~ 30 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： | 0°C ~ 70°C |
| 封装/外壳： | 36-BSOP（0.295"，7.50mm 宽） |
| 包装： | 管件 |
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LTC1538-AUX/LTC1539
APPLICATIO N S I N FOR M ATIO N
R SENSE =
( )
Frequency ( )
C OSC ( pF ) = – 11
? I L =
V OUT ? 1 – OUT ?
Allowing some margin for variations in the LTC1538-AUX/
LTC1539 and external component values yield:
100mV
I MAX
The LTC1538-AUX/LTC1539 work well with values of
R SENSE from 0.005 ? to 0.2 ? .
C OSC Selection for Operating Frequency
The LTC1538-AUX/LTC1539 use a constant frequency
architecture with the frequency determined by an external
oscillator capacitor on C OSC . Each time the topside MOSFET
turns on, the voltage on C OSC is reset to ground. During the
on-time, C OSC is charged by a fixed current plus an
additional current which is proportional to the output
voltage of the phase detector (V PLLLPF )(LTC1539 only).
When the voltage on the capacitor reaches 1.19V, C OSC is
reset to ground. The process then repeats.
The value of C OSC is calculated from the desired operating
frequency. Assuming the phase-locked loop has no exter-
nal oscillator input (V PLLLPF = 0V):
1 . 37 10 4
kHz
A graph for selecting C OSC vs frequency is given in Figure
2. As the operating frequency is increased the gate charge
losses will be higher, reducing efficiency (see Efficiency
Considerations). The maximum recommended switching
frequency is 400kHz. When using Figure 2 for
300
synchronizable applications, choose C OSC corresponding
to a frequency approximately 30% below your center
frequency. (See Phase-Locked Loop and Frequency
Sychronization).
Inductor Value Calculation
The operating frequency and inductor selection are inter-
related in that higher operating frequencies allow the use
of smaller inductor and capacitor values. So why would
anyone ever choose to operate at lower frequencies with
larger components? The answer is efficiency. A higher
frequency generally results in lower efficiency because of
MOSFET gate charge losses. In addition to this basic trade
off, the effect of inductor value on ripple current and low
current operation must also be considered.
The inductor value has a direct effect on ripple current. The
inductor ripple current ? I L decreases with higher induc-
tance or frequency and generally increases with higher V IN
or V OUT :
1 ? V ?
( f )( L ) ? V IN ?
Accepting larger values of ? I L allows the use of low
inductances, but results in higher output voltage ripple
and greater core losses. A reasonable starting point for
setting ripple current is ? I L = 0.4(I MAX ). Remember, the
maximum ? I L occurs at the maximum input voltage.
The inductor value also has an effect on low current
operation. The transition to low current operation begins
60
250
200
150
100
50
V PLLLPF = 0V
50
40
30
20
10
V OUT = 5.0V
V OUT = 3.3V
V OUT = 2.5V
0
0
100 200 300 400
500
0
0
50
100 150 200
250
300
12
OPERATING FREQUENCY (kHz)
LTC1538 ? F02
Figure 2. Timing Capacitor Value
OPERATING FREQUENCY (kHz)
1538 F03
Figure 3. Recommended Inductor Values
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| LTC1539CGW#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 36-SSOP 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:4,500 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 |
| LTC1539CGW#TR | 功能描述:IC REG CTRLR BUCK PWM CM 36-SSOP 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 |
| LTC1539CGW#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 36-SSOP 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:4,500 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 |
| LTC1539IGW | 功能描述:IC REG CTRLR BUCK PWM CM 36-SSOP 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 |
| LTC1539IGW#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 36-SSOP 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:4,500 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 |
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