参数资料
型号: MAX8795AETJ+C7P
厂商: Maxim Integrated Products
文件页数: 22/31页
文件大小: 0K
描述: IC TFT-LCD DC/DC CONV 32-TQFN
产品培训模块: Lead (SnPb) Finish for COTS
Obsolescence Mitigation Program
标准包装: 60
应用: 转换器,TFT,LCD
输入电压: 2.5 V ~ 6 V
输出数: 8
输出电压: 2.5 V ~ 18 V
工作温度: -40°C ~ 85°C
安装类型: 表面贴装
封装/外壳: 32-WFQFN 裸露焊盘
供应商设备封装: 32-TQFN-EP(5x5)
包装: 管件
TFT-LCD DC-DC Converter with
Operational Amplifiers
n POS = GON DROPOUT MAIN
The number of positive charge-pump stages is given by:
V + V ? V
V MAIN ? 2 × V D
the forward-voltage drop of the charge-pump diode,
and V DROPOUT is the dropout margin for the linear reg-
ulator. Use V DROPOUT = 0.3V.
The number of negative charge-pump stages is given by:
where n POS is the number of positive charge-pump
stages, V GON is the gate-on linear-regulator REG P out-
put, V MAIN is the main step-up regulator output, V D is
n NEG =
? V GOFF + V DROPOUT
V MAIN ? 2 × V D
where n NEG is the number of negative charge-pump
V D = 0.3V TO 1V
60
50
40
30
20
10
POSITIVE CHARGE-PUMP
OUTPUT VOLTAGE vs. V MAIN
3-STAGE CHARGE PUMP
2-STAGE CHARGE PUMP
1-STAGE CHARGE PUMP
stages, V GOFF is the gate-off linear-regulator REG N
output, V MAIN is the main step-up regulator output, V D
is the forward-voltage drop of the charge-pump diode,
and V DROPOUT is the dropout margin for the linear reg-
ulator. Use V DROPOUT = 0.3V.
The above equations are derived based on the
assumption that the first stage of the positive charge
pump is connected to V MAIN and the first stage of the
negative charge pump is connected to ground.
Sometimes fractional stages are more desirable for bet-
ter efficiency. This can be done by connecting the first
stage to V IN or another available supply. If the first
charge-pump stage is powered from V IN , the above
equations become:
n POS = GON DROPOUT IN
0
2
4
6
8
V MAIN (V)
10
12
14
V + V + V
V MAIN ? 2 × V D
Figure 8. Positive Charge-Pump Output Voltage vs. V MAIN
n NEG =
? V GOFF + V DROPOUT + V IN
V MAIN ? 2 × V D
-0
NEGATIVE CHARGE-PUMP
OUTPUT VOLTAGE vs. V MAIN
Flying Capacitors
Increasing the flying-capacitor (C X ) value lowers the
effective source impedance and increases the output-
-5
-10
-15
-20
-25
-30
-35
-40
-45
2-STAGE
CHARGE PUMP
3-STAGE
CHARGE PUMP
V D = 0.3V TO 1V
1-STAGE
CHARGE PUMP
current capability. Increasing the capacitance indefinitely
has a negligible effect on output-current capability
because the internal switch resistance and the diode
impedance place a lower limit on the source imped-
ance. A 0.1μF ceramic capacitor works well in most
low-current applications. The flying capacitor’s voltage
rating must exceed the following:
V CX > n × V MAIN
where n is the stage number in which the flying capaci-
tor appears, and V MAIN is the output voltage of the
2
4
6
8
10
12
14
main step-up regulator.
V MAIN (V)
Figure 9. Negative Charge-Pump Output Voltage vs. V MAIN
22
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