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参数资料
| 型号： | LTC1149CS#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 7/20页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 16-SOIC |
| 标准包装： | 50 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 250kHz |
| 占空比： | 100% |
| 电源电压： | 最高 48V |
| 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： | 16-SOIC（0.154"，3.90mm 宽） |
| 包装： | 管件 |
| 产品目录页面： | 1333 (CN2011-ZH PDF) |
LTC1149
LTC1149-3.3/LTC1149-5
TEST CIRCUIT
0.1 μ F
+
V IN
0.068 μ F
IRF9Z34
+
220 μ F
100V
MBR380
1
PGATE
CAP
16
+
IRFZ34
0.047 μ F
2
3
V IN
V CC
SHDN2
RGND
15
14
V 15
+
1 μ F
4
5
PDRIVE
V CC
LTC1149
NGATE
PGND
13
12
50 μ H
6
C T
SGND
11
+
SENSE +
390pF
3300pF
+
1k
V 8
7
8
I TH
SENSE –
V FB / 10
SHDN1
9
+
V 9 – V 8
25k
75k
220 μ F
0.05 ?
V 10
1000pF
V OUT
1149 TC
APPLICATIO S I FOR ATIO
Typical Application Circuit
The basic LTC1149 series application circuit is shown in
Figure 1. External component selection is driven by the
input voltage and output load requirement, and begins
with the selection of R SENSE . Once R SENSE is known, C T
and L can be chosen. Next, the power MOSFETs and D1
are selected. Finally, C IN and C OUT are selected and the
loop is compensated. The circuit shown in Figure 1 can be
configured for operation up to an input voltage of 48V. If
the application does not require greater than 15V opera-
tion, then the LTC1148 should be used.
R SENSE Selection for Output Current
R SENSE is chosen based on the required output current.
The LTC1149 series current comparator has a threshold
range which extends from a minimum of 25mV/R SENSE to
a maximum of 150mV/R SENSE . The current comparator
threshold sets the peak of the inductor ripple current,
yielding a maximum output current I MAX equal to the peak
value less half the peak-to-peak ripple current. For proper
Burst Mode operation, I RIPPLE(P-P) must be less than or
equal to the minimum current comparator threshold.
Since efficiency generally increases with ripple current,
the maximum allowable ripple current is assumed, i.e.,
I RIPPLE(P-P) = 25mV/R SENSE (see C T and L Selection for
Operating Frequency). Solving for R SENSE and allowing a
margin for variations in the LTC1149 series and external
component values yields:
R SENSE = 100mV
I MAX
A graph for selecting R SENSE versus maximum output
current is given in Figure 2. The LTC1149 series works well
with values of R SENSE from 0.02 ? to 0.2 ? .
The load current below which Burst Mode operation
commences, I BURST , and the peak short-circuit current,
I SC(PK) , both track I MAX . Once R SENSE has been chosen,
I BURST and I SC(PK) can be predicted from the following
equations:
I BURST ≈ 15mV
R SENSE
I SC(PK) = 150mV
R SENSE
7
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