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参数资料
| 型号： | LTC3417AIFE-2#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 16/20页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK SYNC ADJ 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 ~ 5 V |
| 输入电压： | 2.25 V ~ 5.5 V |
| PWM 型： | 电流模式，混合 |
| 频率 - 开关： | 1.5MHz，600kHz ~ 4MHz |
| 电流 - 输出： | 1A，1.5A |
| 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： | 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 |
LTC3417A-2
APPLICATIONS INFORMATION
The power dissipated by the part is:
PD = I 12 ? R DS(ON)1 + I 22 ? R DS(ON)2
Using the 1.5MHz frequency setting (FREQ = V IN ), we get
the following equations for L1 and L2:
PD = 1.5 2 ? 0.09 + 1 2 ? 0.163
PD = 366mW
L1 =
1.8V
1.5MHz ? 525mA
1–
1.8V
4.2V
= 1.3 μ H
The DFN package junction-to-ambient thermal resistance,
Use 1.5 μ H.
L2 =
θ JA ,isabout43°C/W.Therefore,thejunctiontemperature
of the regulator operating in a 70°C ambient temperature
is approximately:
T J = 0.366 ? 43 + 70
2.5V
1.5MHz ? 350mA
Use 2.2 μ H.
1–
2.5V
4.2V
= 1.9 μ H
T J = 85.7°C
Remembering that the above junction temperature is
C OUT selection is based on load step droop instead of ESR
requirements. For a 2.5% output droop:
obtained from an R DS(ON) at 25°C, we might recalculate
the junction temperature based on a higher R DS(ON) since
it increases with temperature. However, we can safely as-
sume that the actual junction temperature will not exceed
the absolute maximum junction temperature of 125°C.
C OUT1 = 2.5 ?
C OUT2 = 2.5 ?
1.5A
1.5MHz ( 5% ? 1.8V )
1A
1.5MHz ( 5% ? 2.5V )
= 28 μ F
= 13 μ F
Design Example
As a design example, consider using the LTC3417A-2 in
a portable application with a Li-Ion battery. The battery
provides a V IN from 2.8V to 4.2V. One load requires 1.8V
at 1.5A in active mode, and 1mA in standby mode. The
other load requires 2.5V at 1A in active mode, and 500μA
in standby mode. Since both loads still need power in
standby, Burst Mode operation is selected for good low
load ef?ciency (SYNC/MODE = V IN ).
First, determine what frequency should be used. Higher
frequency results in a lower inductor value for a given Δ I L
( Δ I L is estimated as 0.35I LOAD(MAX) ). Reasonable values
for wire wound surface mount inductors are usually in the
range of 1μH to 10μH.
The closest standard values are 47μF and 22μF.
The output voltages can now be programmed by choos-
ing the values of R1, R2, R3, and R4. To maintain high
ef?ciency, the current in these resistors should be kept
small. Choosing 2μA with the 0.8V feedback voltages makes
R2 and R4 equal to 400k. A close standard 1% resistor is
412k. This then makes R1 = 515k. A close standard 1%
is 511k. Similarily, with R4 at 412k, R3 is equal to 875k.
A close 1% resistor is 866k.
The compensation should be optimized for these compo-
nents by examining the load step response, but a good
place to start for the LTC3417A-2 is with a 5.9kΩ and
2200pF ?lter on I TH1 and 2.87k and 6800pF on I TH2 . The
output capacitor may need to be increased depending on
the actual undershoot during a load step.
CONVERTER OUTPUT
SW1
SW2
I LOAD(MAX)
1.5A
1A
Δ I L
525mA
350mA
The PGOOD pin is a common drain output and requires a
pull-up resistor. A 100k resistor is used for adequate speed.
Figure 4 shows a complete schematic for this design.
3417a2fa
16
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