參數(shù)資料
型號(hào)： DS1227S
英文描述： KickStarter Chip
中文描述： Kickstarter的芯片
文件頁(yè)數(shù)： 11/20頁(yè)
文件大?。?/td> 156K
代理商： DS1227S
DS1227
022698 11/20
AUXILIARY BOOST SUPPLY CONFIGURATION
Figure 8
–
+
DS1227
KICKSTARTER
GND
+3V
OSCEXT
1N5418
BOOST
V
DCI
V
DCO
V
CC01
V
CC02
V
CC03
V
CCOAUX
270
μ
H (typ.)
200
μ
F (typ.)
100
μ
H (typ.)
The DC-DC converter’s output current is provided both
by the inductor and directly from the battery. If the load
draws less than the maximum current, the V
DCI
n-chan-
nel MOSFET is turned on only often enough to keep the
output voltage at the desired level.
If the selected inductor has too high a value, the DS1227
will not be able to deliver the desired output power, even
with the MOSFET turned on for every oscillator cycle.
The available output power can be increased by either
raising the input voltage or lowering the inductance.
This causes the current to rise at a faster rate, and re-
sults in a higher peak current at the end of each cycle.
The available output power increases since it is propor-
tional to the square of the peak inductor current. The
maximum inductance therefore is:
since : P
L
L I
PK
2 f
O
2
and : I
PK
V
IN
2
f
O
L
L
MAX
V
IN
8 f
O
P
L
2
The required output power must include what is dissi-
pated in the forward drop of the catch diode and each of
the V
CCO1
, V
CCO2
, and V
CCO3
pass transistors. This
can be expressed as follows:
P
OUT
= V
F
I
OUT
+ (I
OUT12
R
ON1
+ I
OUT22
R
ON2
+
I
OUT32
R
ON3
+ I
OUT42
R
ON4
) + V
OUT
I
OUT
where:
I
OUT
=
I
OUT1
+ I
OUT2
+ I
OUT3
+ I
OUT4
If the inductance value is too low, the current at V
DCI
may rise above the maximum rating. The minimum al-
lowed inductor value is expressed by:
L
MIN
V
IN
2 f
O
I
MAX
(I
MAX
450 mA)
TYPES OF INDUCTORS
The following is a brief discussion of various types of in-
ductors which may be typically used with the DS1227
Kickstarter to facilitate boost mode operation. Table 1
lists some typical manufacturers of these types of induc-
tors. Table 2 summarizes performance of the circuit for
various inductors.
Molded Inductors
These are cylindrically wound coils which look similar to
1-watt resistors. They have the advantages of low cost
and ease of handling, but have higher resistance, higher
losses, and lower power handling capability than other
types of inductors.
Potted Toroidal Inductors
A typical 1 mH, 0.82 ohm potted toroidal inductor (Dale
TE-3Q4TA) is 0.685 in diameter by 0.385 high and
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