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| 型号： | LTC3732CG |
| 厂商： | Linear Technology |
| 文件页数： | 22/28页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 36-SSOP |
| 标准包装： | 37 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 750kHz |
| 占空比： | 98.5% |
| 电源电压： | 4.5 V ~ 7 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-SSOP（0.209"，5.30mm 宽） |
| 包装： | 管件 |
| 产品目录页面： | 1335 (CN2011-ZH PDF) |
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LTC3732
APPLICATIO S I FOR ATIO
Using L = 0.6 μ H, a commonly available value results in
34% ripple current. The worst-case output ripple for the
A short circuit to ground will result in a folded back current
of:
( ) ? ? = 7 . 5 A
?
+ ?
2 ? ?
?
threestagesoperatinginparallelwillbelessthan11%of
the peak output current.
R SENSE1, R SENSE2 and R SENSE3 can be calculated by using
a conservative maximum sense current threshold of 65mV
I SC ≈
25 mV
( 2 + 3 ) m ?
1 150 ns 20 V
0 . 6 μ H ?
and taking into account half of the ripple current:
with a typical value of R DS(ON) and d = (0.005/ ° C)(50 ° C) =
0.25. The resulting power dissipated in the bottom MOSFET
15 A ? 1 + ?
R SENSE =
65 mV
? 34 % ?
? 2 ?
= 0 . 0037 ?
is:
P SYNC = (7.5A) 2 (1.25)(0.007 ? ) ≈ 0.5W
which is less than one third of the normal, full load
Use a commonly available 0.003 ? sense resistor.
Next verify the minimum on-time is not violated. The
minimum on-time occurs at maximum V CC :
conditions. Incidentally, since the load no longer dissi-
pates any power, total system power is decreased by over
90%. Therefore, the system actually cools significantly
during a shorted condition!
()
(
t ON ( MIN ) =
V OUT
V IN ( MAX ) f
=
1 . 3 V
20 V 400 kHz
)
= 162 ns
PC Board Layout Checklist
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of the
The output voltage will be set by the VID code according
to Table 1.
The power dissipation on the topside MOSFET can be
estimated. Using a Fairchild FDS6688 for example, R DS(ON)
= 7m ? , C MILLER = 15nC/15V = 1000pF. At maximum input
voltage with T(estimated) = 50 ° C:
IC. These items are also illustrated graphically in the layout
diagram of Figure 11. Check the following in the PC layout:
1) Are the signal and power ground paths isolated? Keep the
SGND at one end of a printed circuit path thus preventing
MOSFET currents from traveling under the IC. The IC signal
ground pin should be used to hook up all control circuitry
on one side of the IC, routing the copper through SGND,
( ) [ ( ) ( ) ]
15 1 + 0 . 005 50 ° C ? 25 ° C
( ) ( )( ) ( )(
)
2 ? 45 A ?
? 2 3 ?
( )
? 400 kHz = 2 . 2 W
?
P MAIN ≈
1 . 8 V 2
20 V
0 . 007 ? + 20 ? ? 2 ? 1000 pF
? ?
? 1 1 ?
+
? 5 V – 1 . 8 V 1 . 8 V ?
under the IC covering the “shadow” of the package, connect-
ing to the PGND pin and then continuing on to the (–) plates
of C IN and C OUT . The V CC decoupling capacitor should be
placed immediately adjacent to the IC between the V CC pin
and PGND. A 1 μ F ceramic capacitor of the X7R or X5R type
is small enough to fit very close to the IC to minimize the ill
effects of the large current pulses drawn to drive the bottom
MOSFETs. An additional 5 μ F to 10uF of ceramic, tantalum
or other very low ESR capacitance is recommended in or-
The worst-case power dissipation by the synchronous
MOSFET under normal operating conditions at elevated
ambient temperature and estimated 50 ° C junction tem-
perature rise is:
der to keep the internal IC supply quiet. The power ground
returns to the sources of the bottom N-channel MOSFETs,
anodes of the Schottky diodes and (–) plates of C IN , which
should have as short lead lengths as possible.
( ) ( ) ( ) ? = 1 . 84 W
P SYNC =
20V ? 1 .3V
20 V
15 A 1 . 25 0 . 007
2
2) Does the IC IN + pin connect to the (+) plates of C OUT ?
A 30pF to 300pF feedforward capacitor between the
DIFFOUT and EAIN pins should be placed as close as
possible to the IC.
3732f
22
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| LTC3732CG#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:2,000 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:1MHz 占空比:50% 电源电压:9 V ~ 10 V 降压:无 升压:是 回扫:是 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 85°C 封装/外壳:8-TSSOP（0.173"，4.40mm 宽） 包装:带卷 (TR) |
| LTC3732CG#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 |
| LTC3732CG#TRPBF | 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 |
| LTC3732CUHF | 功能描述:IC REG CTRLR BUCK PWM CM 38-QFN 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 |
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