参数资料
| 型号： | LT3501IFE#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 12/30页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK ADJ 3A DL 20TSSOP |
| 标准包装： | 2,500 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 2 |
| 输出电压： | 0.8 V ~ 23.8 V |
| 输入电压： | 3.1 V ~ 25 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 250kHz ~ 1.5MHz |
| 电流 - 输出： | 3A |
| 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： | 20-TSSOP（0.173"，4.40mm 宽）裸露焊盘 |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 20-TSSOP-EP |
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LT3501
APPLICATIONS INFORMATION
Choosing the Output Voltage
1600
190
R1 = R2 ? ? OUT – 1 ?
Theoutputvoltageisprogrammedwitharesistordivider
between the output and the FB pin. Choose the 1% resis-
tors according to:
? V ?
? 0.8V ?
1400
1200
1000
800
600
400
FREQUENCY
PHASE
185
180
175
170
165
160
R2 should be 10k or less to avoid bias current errors. Refer-
ence designators refer to the Block Diagram in Figure 1.
200
100
0
20
40
60 80 100
120
140
155
150
Choosing the Switching Frequency
RESISTANCE (k )
3501 F02
V OUT + V D 1
V IN – V SW + V D t ON(MIN)
Max Frequency =
3.3 + 0.6 1
TheLT3501switchingfrequencyissetbyresistorR3in
Figure 1. The R T /SYNC pin is internally regulated at 0.975V.
Setting resistor R3 sets the current in the R T /SYNC pin
which determines the oscillator frequency as illustrated
in Figure 2.
The switching frequency is typically set as high as pos-
sible to reduce overall solution size. The LT3501 employs
techniques to enhance dropout at high frequencies but
efficiency and maximum input voltage decrease due to
switching losses and minimum switch on-times. The
maximum recommended frequency can be approximated
by the equation:
Frequency (Hz) = ?
where V D is the forward-voltage drop of the catch diode (D1
Figure 2), V SW is the voltage drop of the internal switch,
and t ON(MIN) in the minimum on-time of the switch, all at
maximum load current.
Figure 2. Frequency and Phase vs R T /SYNC Resistance
The following example along with the data in Table 1
illustrates the trade-offs of switch frequency selection.
Example:
V IN = 25V, V OUT = 3.3V, I OUT = 2.5A,
Temperature = 0°C to 85°C
t ON(MIN) = 200ns (85°C from Typical Characteristics
graph), V D = 0.6V, V SW = 0.4V (85°C)
? ~ 750 kHz
25 – 0.4 + 0.6 200e-9
R T /SYNC ~ 42k (Figure 2)
Input Voltage Range
Once the switching frequency has been determined, the
input voltage range of the regulator can be determined. The
minimum input voltage is determined by either the LT3501’s
minimum operating voltage of ~2.8V, or by its maximum
Table 1. Efficiency and Size Comparisons for Different R RT/SYNC Values. 3.3V Output
EFFICIENCY
FREQUENCY R T /SYNC V VIN1/2 = 12V V IN(MAX)? L* C* C+L
1.2MHz 20.5k 79.0% 16 1.5μH 22μH 63mm 2
1.0MHz 26.7k 80.9% 18 2.2μH 47μH 66mm 2
750kHz 38.3k 81.2% 22 3.3μH 47μF 66mm 2
500kHz 61.9k 82.0% 24 4.7μH 47μF 66mm 2
250kHz 133k 83.9% 24 10μH 100μF 172mm 2
? V IN(MAX) is defined as the highest input voltage that maintains constant output voltage ripple.
*Inductor and capacitor values chosen for stability and constant ripple current.
3501fd
12
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