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| 型号： | LTC1682IS8#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 8/12页 |
| 文件大小： | 0K |
| 描述： | IC REG MULTI CONFIG ADJ 8SOIC |
| 标准包装： | 100 |
| 类型： | 升压（升压），切换电容（充电泵），倍增器 |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 2.5 V ~ 5.5 V |
| 输入电压： | 1.8 V ~ 4.4 V |
| PWM 型： | Burst Mode? |
| 频率 - 开关： | 550kHz |
| 电流 - 输出： | 90mA |
| 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： | 管件 |
| 供应商设备封装： | 8-SOIC |
LTC1682/LTC1682-3.3/LTC1682-5
APPLICATIO N S I N FOR M ATIO N
Operation
The LTC1682 uses a switched-capacitor charge pump to
generate a CPO voltage of approximately 2(V IN ). CPO
powers an internal low dropout linear regulator that sup-
plies a regulated output at V OUT . Internal comparators are
used to sense CPO and V IN voltages for power-up condi-
tioning. The output current is sensed to determine the
charge pump operating mode. A trimmed internal bandgap
is used as the voltage reference and a trimmed internal
oscillator is used to control the charge pump switches.
The charge pump is a doubler configuration that uses one
external flying capacitor. When enabled, a 2-phase
nonoverlapping clock controls the charge pump switches.
At start-up, the LDO is disabled and the load is removed
from CPO. When CPO reaches 1.75(V IN ) the LDO is
enabled. If CPO falls below 1.45(V IN ) the LDO will be
disabled. Generally, the charge pump runs open loop with
continuous clocking for low noise. If CPO is greater than
1.95(V IN ) and I OUT is less than 100 μ A, the charge pump
will operate in Burst Mode operation for increased effi-
ciency but slightly higher output noise. In Burst Mode
operation, the clock is disabled when CPO reaches 1.95(V IN )
The LDO is used to filter the ripple on CPO and to set an
output voltage independent of CPO. V OUT is set by an
external or internal resistor divider. The LDO requires a
capacitor on V OUT for stability and improved load transient
response. A low ESR capacitor of ≥ 2 μ F should be used.
Output Voltage Selection
The LTC1682-3.3/LTC1682-5 versions have internal
resistor networks to set the regulated output voltage. The
LTC1682 output voltage is set using an external resistor
divider (see Figure 3). The output voltage is determined
using the following formula:
V OUT = 1.235V(1 + R1/R2)
The output voltage range is 2.5V to 5.5V.
Maximum V OUT and I OUT Calculations
The maximum available output voltage and current can be
calculated based on the open circuit CPO voltage, the
dropout voltage of the LDO and the effective output
resistance of the charge pump. The open circuit CPO
voltage is approximately 2(V IN ) (see Figure 4).
and enabled when CPO droops by about 100mV. The
switching frequency is precisely controlled to ensure that
the frequency is above 455kHz and at the optimum rate to
ensure maximum efficiency. The switch edge rates are
+
–
R CPO
2V IN
V CPO
C CPO
R DROPOUT
+ –
V DROPOUT
V OUT
I LOAD
also controlled to minimize noise. The effective output
resistance at CPO is dependent on the voltage at V IN , CPO
and the junction temperature. A low ESR capacitor of ≥ 2 μ F
should be used at CPO for minimum noise.
Figure 4. Equivalent Circuit
1682 F04
C5
3.3V
EXTERNAL LDO
IN
OUT
GND
V IN
3.6V
C4
4.7 μ F
C3
4.7 μ F
C1
0.22 μ F
8
7
6
5
C + SHDN
C – GND
CPO V OUT
LTC1682
V IN FB
1
2
3
4
R1
56k
R2
18k
5.1V
V RIPPLE = 800 μ V P-P
C2
4.7 μ F
V OUT = 1.235V(1 + R1/R2)
1682 F03
Figure 3. Powering an Auxiliary Regulator from CPO
8
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