參數(shù)資料
型號: LT3585EDDB-1#PBF
廠商: LINEAR TECHNOLOGY CORP
元件分類: 穩(wěn)壓器
英文描述: 0.65 A BATTERY CHARGE CONTROLLER, PDSO10
封裝: 3 X 2 MM, LEAD FREE, PLASTIC, MO-229WECD-1, DFN-10
文件頁數(shù): 3/20頁
文件大?。?/td> 423K
代理商: LT3585EDDB-1#PBF
LT3585-0/LT3585-1
LT3585-2/LT3585-3
11
3585f
APPLICATIO S I FOR ATIO
WU
UU
Choosing the Right Device
(LT3585-0/LT3585-1/LT3585-2/LT3585-3)
The only difference between the four versions of the
LT3585 series is the peak current level. For the fastest
possible charge time, use the LT3585-3. The LT3585-1
has the lowest peak current capability, and is designed
for applications that need a more limited drain on the
batteries. Due to the lower peak current, the LT3585-1
can use a physically smaller transformer. The LT3585-0
and LT3585-2 have a current limit in between that of the
LT3585-1 and the LT3585-3.
Transformer Design
The yback transformer is a key element for any LT3585-0/
LT3585-1/LT3585-2/LT3585-3 design. It must be designed
carefully and checked that it does not cause excessive cur-
rent or voltage on any pin of the part. The main parameters
that need to be designed are shown in Table 1. The rst
transformer parameter that needs to be set is the turns
ratio, N. The LT3585-0/LT3585-1/LT3585-2/LT3585-3
accomplish output voltage detection by monitoring the
yback waveform on the SW pin. When the SW voltage
reaches 31.5V higher than the VBAT voltage, the part halts
power delivery. Thus, the choice of N sets the target output
voltage and changes the amplitude gain of the reected
voltage from the output to the SW pin. Choose N according
to the following equation:
N
VOUT
=
+ 2
31 5
.
where VOUT is the desired output voltage. The number 2
in the numerator is used to include the forward voltage
drop across the output diode(s). Thus, for a 320V output,
N should be 322/31.5 or 10.2. For a 300V output, choose
N equal to 302/31.5 or 9.6. The next parameter that needs
to be set is the primary inductance, LPRI. Choose LPRI
according to the following formula:
L
V
NI
PRI
OUT
PK
200 10
9
where VOUT is the desired output voltage. N is the trans-
former turns ratio. IPK is 1.4 (LT3585-0), 0.7 (LT3585-1),
1 (LT3585-2) and 2 (LT3585-3). LPRI needs to be equal
or larger than this value to ensure that the LT3585 series
has adequate time to respond to the yback waveform.
All other parameters need to meet or exceed the recom-
mended limits as shown in Table 1. A particularly important
parameter is the leakage inductance, LLEAK. When the
power switch of the LT3585 series turns off, the leakage
inductance on the primary of the transformer causes a
voltage spike to occur on the SW pin. The height of this
spike must not exceed 50V, even though the absolute
maximum rating of the SW pin is 60V. The 60V absolute
maximum rating is a DC blocking voltage specication,
which assumes that the current in the power NPN is zero.
Figure 4 shows the SW voltage waveform for the circuit
of Figure 8 (LT3585-0). Note that the absolute maximum
rating of the SW pin is not exceeded. Make sure to check
the SW voltage waveform with VOUT near the target output
voltage, as this is the worst-case condition for SW volt-
age. Figure 5 shows the various limits on the SW voltage
during switch turn off.
Table 1. Recommended Transformer Parameters
PARAMETER
NAME
TYPICAL RANGE
LT3585-0
TYPICAL RANGE
LT3585-1
TYPICAL RANGE
LT3585-2
TYPICAL RANGE
LT3585-3
UNITS
LPRI
Primary Inductance
>5
>10
>7
>3.5
H
LLEAK
Primary Leakage Inductance
100 to 300
200 to 500
100 to 300
nH
N
Secondary/Primary Turns Ratio
8 to 12
VISO
Secondary to Primary Isolation
Voltage
>500
V
ISAT
Primary Saturation Current
>1.6
>0.8
>1.0
>2
A
RPRI
Primary Winding Resistance
<300
<500
<400
<200
m
Ω
RSEC
Secondary Winding Resistance
<40
<80
<60
<30
Ω
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