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| 型号： | MC34704BEPR2 |
| 厂商： | Freescale Semiconductor |
| 文件页数： | 45/54页 |
| 文件大小： | 0K |
| 描述： | IC PWR MNGMT DC-DC MULT 56-QFN |
| 特色产品： | MC34704 Multi-channel Power Management IC (PMIC) |
| 标准包装： | 1 |
| 应用： | 处理器 |
| 电流 - 电源： | 86mA |
| 电源电压： | 2.7 V ~ 5.5 V |
| 工作温度： | -20°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 56-VFQFN 裸露焊盘 |
| 供应商设备封装： | 56-QFN-EP（7x7） |
| 包装： | 标准包装 |
| 产品目录页面： | 809 (CN2011-ZH PDF) |
| 其它名称： | MC34704BEPR2DKR |
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FUNCTIONAL DEVICE OPERATION
COMPONENT CALCULATION
feedback using the standard voltage divider configuration, or
can be programmed to work with a current feedback
configuration to control the current flowing through a LED
string. It does not need external compensation network, thus
the only components that need to be calculated are:
? L : A boost power stage can be designed to operate in
CCM for load currents above a certain level usually 5 to
15% of full load. The minimum value of inductor to
maintain CCM can be determined by using the following
procedure:
? Define I OB between 60 to 80% of the maximum current
rating to maintain CCM as 15% of full load:
controls the amount of current flowing through it. To
calculate this resistor, set the maximum current you want
to flow though the string and use the following formula:
V ref [ Ω ]
RS = ----------
Io
Where V REF =230 mV is the maximum internal reference
voltage in current mode control that is reflected on the FB8
pin.
When Input voltage is equal to or higher than VOUT8, a
reverse bias diode is needed from the switching node to the
output in order to cause a drop from the Input to the output,
see Figure 9 below:
Vo ( D ) ( 1 – D ) T
L min ≥ ------------------------------------------
2
[H]
2I OB
However the worst case condition for the boost power
BT8
CBOOT
VIN
stage is when the input voltage is equal to one half of the
output voltage, which results in the Maximum ?I L , then:
SW8
L8
L min ≥ ----------------
Vo ( T ) [H]
16I OB
? C OUT : The three elements of output capacitor that
contribute to its impedance and output voltage ripple are
VOUT8
FB8
D8
R1
RB
VOUT8
the ESR, the ESL and the capacitance C. The minimum
capacitor value is approximately:
Figure 9. Reverse Bias Diode
C OUT ≥ ----------------------------
Io max D max
Fsw Δ Vo r
[F]
Regulator 7 (Inverter controller - external compensation
needed)
Δ Vo r [ Ω ]
? ---------------------- + I
? 1 – D max
– ( Io + I OB )
I Q ≥ I Lpeak = ----------------------------
? Where Δ VO r is the desired output voltage ripple.
? Now calculate Δ VO r the maximum allowed ESR to
reach the desired.
ESR ≤ -------------------------------------------
Io max ?
OB ?
? R1 and RB (for Voltage feedback control): These two
resistors help to set the output voltage to the desire value
using a V REF =0.6 V, select R1 between 10k and 100K and
then calculate RB as follows:
REG7 is a non-synchronous buck/boost inverting PWM
voltage-mode control DC-DC regulator that drive an external
P-MOSFET to supply a typical voltage of -7.0 V at a
maximum current of 60 mA.
? P-MOSFET: The peak current of the MOSFET is assumed
to be I D , which is obtained by the following formula, define
I OB between 60 to 80% of the maximum current rating.
1 – D
And the voltage rating is given by:
V Q = Vin – Vo
RB = ---------------------
------------ – 1
R1
Vo
Vref
[ Ω ]
? Diode D7: The peak value of the diode current is I FSM
which should also be higher than I Lpeak . The average
current rating should be higher than the output current low
and the repetition reverse voltage V RRM is given by:
? RS (For current feedback control with LED string):
This resistor is attached at the end of the LED string and it
34704
Analog Integrated Circuit Device Data
Freescale Semiconductor
45
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