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參數(shù)資料
| 型號： | RM4391D |
| 廠商： | RAYTHEON SEMICONDUCTOR |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Inverting and Step-Down Switching Regulator |
| 中文描述： | 0.375 A SWITCHING REGULATOR, CDIP8 |
| 文件頁數(shù)： | 9/22頁 |
| 文件大?。?/td> | 153K |
| 代理商： | RM4391D |
RC4391
PRODUCT SPECIFICATION
9
The oscillator creates a squarewave using a method similar
to the 555 timer IC, with a current steering flip-flop con-
trolled by two voltage sensing comparators. The oscillator
frequency is set by the timing capacitor (C
X
) according to
the following equation.
The squarewave output of the oscillator is internal and
cannot be directly measured, but is equal in frequency to the
triangle waveform measurable at pin 3. The switch transistor
is normally on when the triangle waveform is ramping up
and off when ramping down. Capacitor selection depends on
the application; higher operating frequencies will reduce the
output voltage ripple and will allow the use of an inductor
with a physically smaller inductor core, but excessively
high frequencies will reduce load driving capability and
efficiency.
Inverting Design Procedure
1. Select an operating frequency and timing capacitor value
as shown above (frequencies from 10kHz to 50kHz are
typical).
2. Find the maximum on time T
ON
(add 3
m
S for the turn off
base recombination delay of Q1):
3. Calculate the peak inductor current IMAX (if this value
is greater than 375mA then an external power transistor
must be used in place of Q1):
Where:
V
S
= Supply Voltage
V
SW
= Saturation Voltage of Q1 (typically 0.5V)
V
D
= Diode Forward Voltage (typically 0.7V)
I
L
= DC Load Current
4. Find an inductance value for LX:
The inductor chosen must exhibit this value of inductance
and have a current rating equal to I
MAX
.
FOHz
(
)
(
–
)
CxpF
=
T
ON
2F
O
---1
3
m
S
+
=
I
MAX
V
)
T
ON
(
D
)
V
S
(
)
2I
L
V
SW
–
F
O
(
)
-------------------------+
=
L
X
Henries
(
)
V
------------------------
V
–
I
MAX
è
T
ON
(
)
=
Figure 12. Step-Down Regulator Waveforms
65-2474
A
B
C
D
E
F
V
L
V - V
L
BAT
X
BAT
X
1.78V
0.62V
(Internal)
I
0 mA
+V
(Internal)
+V - 0.7V
I
0 mA
+V - V
V
OUT
V ( -0.7V)
C
OSC
I
V
I
V
L
S
MAX
SW
X
LOAD
BEQ1
LX
LX
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