参数资料
| 型号： | EL7585AILZ |
| 厂商： | Intersil |
| 文件页数： | 10/19页 |
| 文件大小： | 0K |
| 描述： | IC POWER SUPPLY TFT-LCD 20-QFN |
| 标准包装： | 90 |
| 应用： | 转换器，TFT，LCD |
| 输入电压： | 3 V ~ 5 V |
| 输出数： | 4 |
| 输出电压： | 5.5 V ~ 20 V |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 20-VFQFN 裸露焊盘 |
| 供应商设备封装： | 20-QFN 裸露焊盘（4x4） |
EL7585A
The following table gives typical values (margins are
considered 10%, 3%, 20%, 10%, and 15% on V IN , V O , L, f S ,
and I OMAX :
TABLE 2.
For low ESR ceramic capacitors, the output ripple is
dominated by the charging and discharging of the output
capacitor. The voltage rating of the output capacitor should
be greater than the maximum output voltage.
V IN (V)
3.3
3.3
3.3
5
5
5
V O (V)
9
12
15
9
12
15
L ( μH)
6.8
6.8
6.8
6.8
6.8
6.8
f S
(MHz)
1
1
1
1
1
1
I OMAX
1.040686
0.719853
0.527353
1.576797
1.090686
0.79902
NOTE: Capacitors have a voltage coefficient that makes their
effective capacitance drop as the voltage across them increases.
C OUT in the equation above assumes the effective value of the
capacitor at a particular voltage and not the manufacturer ’s stated
value, measured at zero volts.
Compensation
The EL7585A can operate in either P mode or PI mode.
Connecting the C INT pin directly to V IN will enable P mode;
For better load regulation, use PI mode with a 4.7nF
capacitor in series with a 10K resistor between C INT and
ground. This value may be reduced to improve transient
I LAVG = -------------
I LPK = I LAVG + -------- L
V RIPPLE = I LPK × ESR + ------------------------ × ---------------- × -----
Input Capacitor
An input capacitor is used to supply the peak charging
current to the converter. It is recommended that C IN be
larger than 10μF. The reflected ripple voltage will be smaller
with larger C IN . The voltage rating of input capacitor should
be larger than maximum input voltage.
Boost Inductor
The boost inductor is a critical part which influences the
output voltage ripple, transient response, and efficiency.
Values of 3.3μH to 10μH are to match the internal slope
compensation. The inductor must be able to handle the
following average and peak current:
I O
1 – D
? I
2
Rectifier Diode
A high-speed diode is necessary due to the high switching
frequency. Schottky diodes are recommended because of
their fast recovery time and low forward voltage. The rectifier
diode must meet the output current and peak inductor
current requirements.
Output Capacitor
The output capacitor supplies the load directly and reduces
the ripple voltage at the output. Output ripple voltage
consists of two components: the voltage drop due to the
inductor ripple current flowing through the ESR of output
capacitor, and the charging and discharging of the output
capacitor.
V O – V IN I O 1
V O C OUT f S
10
performance, however, very low values will reduce loop
stability.
Boost feedback resistors
As the boost output voltage, A VDD , is reduced below 12V the
effective voltage feedback in the IC increases the ratio of
voltage to current feedback at the summing comparator
because R 2 decreases relative to R 1 . To maintain stable
operation over the complete current range of the IC, the
voltage feedback to the FBB pin should be reduced
proportionally, as A VDD is reduced, by means of a series
resistor-capacitor network (R 7 and C 7 ) in parallel with R 1 ,
with a pole frequency (f p ) set to approximately 10kHz for C 2
effective = 10μF and 4kHz for C 2 (effective) = 30μF.
R 7 = ((1/0.1 x R 2 ) - 1/R 1 )^-1
C 7 = 1/(2 x 3.142 x f p x R 7 )
PI Mode C INT (C 23 ) and R INT (R 10 )
The IC is designed to operate with a minimum C 23 capacitor
of 4.7nF and a minimum C 2 (effective) = 10μF.
Note that, for high voltage A VDD , the voltage coefficient of
ceramic capacitors (C 2 ) reduces their effective capacitance
greatly; a 16V 10μF ceramic can drop to around 3μF at 15V.
To improve the transient load response of A VDD in PI mode,
a resistor may be added in series with the C 23 capacitor. The
larger the resistor the lower the overshoot but at the expense
of stability of the converter loop - especially at high currents.
With L = 10μH, A VDD = 15V, C 23 = 4.7nF, C 2 (effective)
should have a capacitance of greater than 10μF. R INT (R 7 )
can have values up to 5k ? for C 2 (effective) up to 20μF and
up to 10K for C 2 (effective) up to 30μF.
Larger values of R INT (R 7 ) may be possible if maximum
A VDD load currents less than the current limit are used. To
ensure A VDD stability, the IC should be operated at the
maximum desired current and then the transient load
response of A VDD should be used to determine the
maximum value of R INT .
FN7523.3
March 9, 2006
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