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参数资料
| 型号： | LTC1159IS-5#TR |
| 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： | 2,500 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 250kHz |
| 占空比： | 100% |
| 电源电压： | 4 V ~ 40 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 ~ 85°C |
| 封装/外壳： | 16-SOIC（0.154"，3.90mm 宽） |
| 包装： | 带卷 (TR) |
| 其它名称： | LTC1159IS-5TR LTC1159IS5TR |
LTC1159
LTC1159-3.3/LTC1159-5
APPLICATIO S I FOR ATIO
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.
Line Transient Response
The LTC1159 has better than 60dB line rejection and is
generally impervious to large positive or negative line
voltage transients. However, one rarely occurring condi-
tion can cause the output voltage to overshoot if the proper
precautions are not observed. This condition is a negative
V IN transition of several volts followed within 100 μ s by a
positive transition of greater than 0.5V/ μ s slew rate.
The reason this condition rarely occurs is because it takes
tens of amps to slew the regulator input capacitor at this
rate! The solution is to add a diode between the cap and V IN
pins of the LTC1159 as shown in several of the typical
application circuits. If you think your system could have
this problem, add the diode. Note that in surface mount
applications it can be combined with the P-gate diode by
using a low cost common cathode dual diode.
EXTV CC Pin Connection
The LTC1159 contains an internal PNP switch connected
between the EXTV CC and V CC pins. The switch closes and
supplies the V CC power whenever the EXTV CC pin is higher
in voltage than the 4.5V internal regulator. This allows the
V IN
MOSFET driver and control power to be derived from the
output during normal operation and from the internal
regulator when the output is out of regulation (start-up,
short circuit).
Significant efficiency gains can be realized by powering V CC
from the output, since the V IN current resulting from the
driver and control currents will be scaled by a factor of
(Duty Cycle)/(Efficiency). For 5V regulators this simply
means connecting the EXTV CC pin directly to V OUT . How-
ever, for 3.3V and other low voltage regulators, additional
circuitry is required to derive V CC power from the output.
The following list summarizes the four possible connec-
tions for EXTV CC :
1. EXTV CC Left Open. This will cause V CC to be powered
only from the internal 4.5V regulator resulting in reduced
MOSFET gate drive levels and an efficiency penalty of up to
10% at high input voltages.
2. EXTV CC Connected Directly to V OUT . This is the normal
connection for a 5V regulator and provides the highest
efficiency.
3. EXTV CC Connected to an Output-Derived Boost Net-
work. For 3.3V and other low voltage regulators, efficiency
gains can still be realized by connecting EXTV CC to an
output-derived voltage which has been boosted to greater
than 4.5V. This can be done either with the inductive boost
winding shown in Figure 5a or the capacitive charge pump
shown in Figure 5b. The charge pump has the advantage of
simple magnetics and generally provides the highest effi-
ciency at the expense of a slightly higher parts count.
V IN
V IN
P-GATE
+
P-CH
C IN
L
1:1
BAT85
?
1 μ F
+
V IN
P-GATE
P-DRIVE
P-CH
+
C IN
L
R SENSE
V OUT
R SENSE
P-DRIVE
LTC1159-3.3
N-GATE
P-GND
EXTV CC
N-CH
?
3
1
2
C OUT
4
+
LTC1159 ? F05a
V OUT
LTC1159-3.3
N-GATE
P-GND
EXTV CC
+
1 μ F
N-CH
BAT85
VN2222LL
0.22 μ F
LTC1159 ? F05b
BAT85
+
BAT85
C OUT
Figure 5a. Inductive Boost Circuit for EXTV CC
Figure 5b. Capacitive Charge Pump for EXTV CC
11
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|---|---|
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