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| 型号： | LTC3545EUD-1#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 15/20页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK SYNC ADJ 0.8A 16QFN |
| 标准包装： | 2,500 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 3 |
| 输出电压： | 0.6 V ~ 5.5 V |
| 输入电压： | 2.25 V ~ 5.5 V |
| PWM 型： | 电流模式，混合 |
| 频率 - 开关： | 2.25MHz |
| 电流 - 输出： | 800mA |
| 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： | 16-WFQFN 裸露焊盘 |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 16-QFN-EP（3x3） |
LTC3545/LTC3545-1
APPLICATIONS INFORMATION
Loss = P O ?
= 1 . 4 W ? 0 . 17 = 0 . 25 W
Similar situations can occur when all three channels are
operating at maximum loads at high ambient temperature.
As an example, consider a channel supplying 800mA at
1.8V output and 85% ef?ciency. The dissipated power can
be calculated using
? 1– E ?
? E ? ?
Design Example
As a design example, consider using the LTC3545/LTC3545-
1 in a portable application with a Li-Ion battery. The battery
provides V IN ranging from 2.8V to 4.2V. The demand on
one channel at 2.5V is 600mA. Using this channel as an
example, ?rst calculate the inductor value for 40% ripple
current (240mA in this example) at maximum V IN . Using
a form of Equation 1:
? ? 1 – 3 . 6 V ? ? = 1 . 4 1 μH
where P O is the output power and E is the ef?ciency.
In this case the temperature rise is 17°C, similar to the
dropout scenario described above. Whereas one channel
L 1 =
2 . 5 V
( 2 . 25 MHz )( 240 mA )
? 2 .5 V ?
operating at these levels will safely fall within the tem-
perature limitations of the part, three channels operating
simultaneously at these levels will place limits on the peak
ambient temperature.
Note that at higher supply voltages, the junction tempera-
ture is lower due to reduced switch resistance R DS(ON) .
Checking Transient Response
The regulator loop response can be checked by looking
at the load transient response. Switching regulators take
several cycles to respond to a step in load current. When
a load step occurs, V OUT immediately shifts by an amount
equal to ( Δ I LOAD ? ESR), where ESR is the effective series
resistance of C OUT . Δ I LOAD also begins to charge or dis-
charge C OUT , which generates a feedback error signal. The
regulator loop then acts to return V OUT to its steady-state
value. During this recovery time V OUT can be monitored
for overshoot or ringing that would indicate a stability
problem. For a detailed explanation of switching control
loop theory, see Application Note 76.
Use the closest standard value of 1.5μH. For low ripple
applications, 10μF is a good choice for the output capacitor.
A smaller output capacitor will shorten transient response
settling time, but also increase the load transient ripple. A
value for C5 = 4.7μF should suf?ce as the source imped-
ance of a Li-Ion battery is very low. C5 and C1 both provide
switching current to the output power switches. They
should be placed as close a possible to the chip between
V IN /GNDA and PV IN /PGND respectively. PV IN and PGND
are the supply and return power paths for both channels
2 and 3, so a value of 10μF for C1 is appropriate. The
feedback resistors program the output voltage. Minimiz-
ing the current in these resistors will maximize ef?ciency
at very light loads, but totals on the order of 200k are a
good compromise between ef?ciency and immunity to
any adverse effects of PCB parasitic capacitance on the
feedback pins. Choosing 10μA as the feedback current with
0.6V feedback voltage makes R4 = 60k. A close standard
1% resistor is 60.4k. Using:
R 3 = ?
– 1 ? ? R 4 = 191 . 1 k
A second, more severe transient is caused by switching
in loads with large (>1μF) supply bypass capacitors. The
? 2 .5 V
? 0 . 6 V
?
?
discharged bypass capacitors are effectively put in paral-
lel with C OUT , causing a rapid drop in V OUT . No regulator
can deliver enough current to prevent this problem if the
load switch resistance is low and it is driven quickly. The
only solution is to limit the rise time of the switch drive
so that the load rise time is limited to approximately (25
? C LOAD ). Thus, a 10μF capacitor charging to 3.3V would
require a 250μs rise time, limiting the charging current
The closest standard 1% resistor is 191k. A 20pF feed-
forward capacitor is recommended to improve transient
response. The component values for the other channels
are chosen in a similar fashion. Figure 4 shows the com-
plete schematic for this example, along with the ef?ciency
curve and burst mode ripple at an output current for the
2.5V output.
to about 130mA.
35451fb
15
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相关代理商/技术参数 |
参数描述 |
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| LTC3545EUDPBF | 制造商:Linear Technology 功能描述:Conv DC-DC Triple Step-Down 5.5V QFN16EP |
| LTC3545EUD-PBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Triple 800mA Synchronous Step-Down Regulator-2.25MHz |
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| LTC3545IUD#PBF | 功能描述:IC REG BUCK SYNC ADJ 0.8A 16QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 设计资源:Design Support Tool 标准包装:1 系列:- 类型:升压（升压） 输出类型:固定 输出数:1 输出电压:3V 输入电压:0.75 V ~ 2 V PWM 型:- 频率 - 开关:- 电流 - 输出:100mA 同步整流器:是 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:SOT-23-5 细型，TSOT-23-5 包装:剪切带 (CT) 供应商设备封装:TSOT-23-5 其它名称:AS1323-BTTT-30CT |
| LTC3545IUD#TRPBF | 功能描述:IC REG BUCK SYNC ADJ 0.8A 16QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 设计资源:Design Support Tool 标准包装:1 系列:- 类型:升压（升压） 输出类型:固定 输出数:1 输出电压:3V 输入电压:0.75 V ~ 2 V PWM 型:- 频率 - 开关:- 电流 - 输出:100mA 同步整流器:是 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:SOT-23-5 细型，TSOT-23-5 包装:剪切带 (CT) 供应商设备封装:TSOT-23-5 其它名称:AS1323-BTTT-30CT |
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