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参数资料
| 型号： | LTC1149CS-5#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 11/20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 |
LTC1149
LTC1149-3.3/LTC1149-5
APPLICATIO S I FOR ATIO
output ripple at low frequencies will be large enough to trip
the voltage comparator. This causes the Burst Mode
operation to be activated when the LTC1149 series would
normally be in continuous operation. The effect is most
pronounced with low values of R SENSE and can be
improved by operating at higher frequencies with lower
values of L. The output remains in regulation at all times.
Checking Transient Response
Switching regulators take several cycles to respond to a
step in DC (resistive) load current. When a load step
occurs, V OUT shifts by an amount equal to ( ? I LOAD )(ESR),
where ESR is the effective series resistance of C OUT .
? I LOAD also begins to charge or discharge C OUT until the
1000
L = 50 μ H
R SENSE = 0.02 ?
regulator loop adapts to the current change and returns
V OUT to its steady state value. During this recovery time
V OUT can be monitored for overshoot or ringing which
would indicate a stability problem. The Pin 7 external
components shown in the Figure 1 circuit will prove
adequate compensation for most applications.
A second, more severe transient is caused by switching in
loads with large (>1 μ F) supply bypass capacitors. The
discharged bypass capacitors are effectively put in parallel
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 10 μ F capacitor would require a 250 μ s rise time,
limiting the charging current to about 200mA.
800
LTC1149 Adjustable Applications
600
L = 25 μ H
R SENSE = 0.02 ?
When an output voltage other than 3.3V or 5V is required,
the LTC1149 adjustable version is used with an external
) )
V OUT = 1.25 1 + R2
400
200
0
0
L = 50 μ H
R SENSE = 0.05 ?
1 2
3
4
5
resistive divider from V OUT to V FB Pin 10. The regulated
voltage is determined:
R1
(V IN – V OUT ) VOLTAGE (V)
1149 F04
In applications where V OUT is greater than the LTC1149
Figure 4. Minimum Suggested C OUT
V IN
internally regulated V CC voltage, R SENSE must be moved to
1N4148
0.068 μ F
+
1 μ F
0V = NORMAL
>2V = SHUTDOWN
CAP
V CC
V CC
SHDN2
V IN
PGATE
PDRIVE
NGATE
LTC1149
V FB
1N4148
0.047 μ F
100pF
IRF9Z34
IRFZ34
+
150 μ F
50V
100 μ H
1N5819
R2
215k
1%
R1
25k
+
150 μ F
16V
OS-CON
V OUT
LOAD
( )
V OUT = 1.25 1 + R2
3300pF
1k
C T
200pF
I TH
C T
GNDS
SENSE +
SENSE –
1000pF
R1
VALUES SHOWN FOR V OUT = 12V
1%
R SENSE
0.05 ?
OUTPUT
GROUND
CONNECTION
1149 F05
Figure 5. High Efficiency Step-Down Regulator with V OUT > V CC
11
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