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参数资料
| 型号： | LTC1144IS8#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 6/8页 |
| 文件大小： | 0K |
| 描述： | IC REG SWITCHED CAP INV 8SOIC |
| 标准包装： | 2,500 |
| 类型： | 切换式电容器（充电泵），反相 |
| 输出数： | 1 |
| 输入电压： | 2 V ~ 18 V |
| 频率 - 开关： | 4kHz ~ 10kHz |
| 电流 - 输出： | 50mA |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm 宽） |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 8-SOIC |
LTC1144
A PPLICATI
S I FOR ATIO
and hence the efficiency, is set by the output impedance.
As frequency is decreased, the output impedance will
V +
eventually be dominated by the 1/(f × C1) term and power
efficiency will drop.
BOOST
9I
I
(1)
Note also that power efficiency decreases as frequency
goes up. This is caused by internal switching losses which
occur due to some finite charge being lost on each
switching cycle. This charge loss per unit cycle, when
OSC
(7)
SCHMITT
TRIGGER
multiplied by the switching frequency, becomes a current
loss. At high frequency this loss becomes significant and
the power efficiency starts to decrease.
GND
(3)
9I
I
1144 F06
≈ 20pF
100
95
V + = 15V, C1 = C2 = 10 μ F
I L = 20mA, T A = 25°C
600
500
Figure 6. Oscillator
POWER
90
CONVERSION
EFFICIENCY
400
REQUIRED FOR
TTL LOGIC
V +
85
300
NC
1
8
100k
80
75
OUTPUT
RESISTANCE
200
100
C1
+
2
3
4
LTC1144
7
6
5
–(V + )
OSC INPUT
C2
70
0.1
1 10
0
100
1144 F07
OSCILLATOR FREQUENCY (kHz)
1144 F05
Figure 7. External Clocking
Figure 5. Power Conversion Efficiency and Output
Resistance vs Oscillator Frequency
SHDN (Pin 6)
The LTC1144 has a SHDN pin that will disable the internal
oscillator when it is pulled low. The supply current will also
drop to 8 μ A.
OSC (Pin 7) and Boost (Pin 1)
The switching frequency can be raised, lowered or driven
from an external source. Figure 6 shows a functional
diagram of the oscillator circuit.
By connecting the boost pin (pin 1) to V + , the charge and
discharge current is increased, and hence the frequency is
increased by approximately 10 times. Increasing the fre-
quency will decrease output impedance and ripple for
higher load currents.
Loading pin 7 with more capacitance will lower the fre-
quency. Using the boost (pin 1) in conjunction with exter-
6
nal capacitance on pin 7 allows user selection of the
frequency over a wide range.
Driving the LTC1144 from an external frequency source
can be easily achieved by driving pin 7 and leaving the
boost pin open as shown in Figure 7. The output current
from pin 7 is small, typically 4 μ A, so a logic gate is capable
of driving this current. The choice of using a CMOS logic
gate is best because it can operate over a wide supply
voltage range (3V to 15V) and has enough voltage swing
to drive the internal Schmitt trigger shown in Figure 6. For
5V applications, a TTL logic gate can be used by simply
adding an external pull-up resistor (see Figure 7).
Capacitor Selection
External capacitors C1 and C2 are not critical. Matching is
not required, nor do they have to be high quality or tight
tolerance. Aluminum or tantalum electrolytics are excellent
choices, with cost and size being the only consideration.
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