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參數資料
| 型號： | SC805 |
| 廠商： | Semtech Corporation |
| 英文描述： | Miniature Integrated High Current Lithium-Ion Battery Charger |
| 中文描述： | 微型集成高電流鋰離子電池充電器 |
| 文件頁數： | 14/15頁 |
| 文件大?。?/td> | 294K |
| 代理商： | SC805 |
8
2005 Semtech Corp.
www.semtech.com
SC805
POWER MANAGEMENT
Step 3: Calculate the Tcold value.
2.86
10K
R2
3
RT
25
COLD
=
=
The ratio for the curve 2 NTC at 0oC is 2.816. The differ-
ence represents less than 1/2oC (i.e., actual trip would
be -0.5oC instead of 0oC.) For temperature trip values
other than 0oC and 50oC alternate curve-type NTC ele-
ments can be used or an additional resistor can be added
to the Rntc divider to alter the temperture coefficient.
CHRGB LED Flag
The CHRGB LED driver on the SC805 can be used to
drive two external LEDs: CHRGB=Low (Charging) and
CHRGB=High (Charge Complete).
The CHRGB output
will be high impedance when the VCC is in a UV condi-
tion. The Table below defines the CHRGB LED output
states.
D
E
Lh
g
i
Hw
o
LZ
-
h
g
i
Hg
n
i
k
n
il
B
B
G
R
H
Cm
r
e
tI
<
t
u
o
Im
r
e
t
>
t
u
o
IV
U
<
C
V
e
g
r
a
h
C
e
r
P
C
T
N
r
o
V
O
tl
u
a
F
The CHRGB output can be used for a VCC indicator. When
the SC805 is enabled the CHRGB output is either high
or low providing the VCC input is above UVLO.
The CHRGB output signifies the charging status. When
the output current is > Itermination, CHRGB=low. CHRGB
is high when Iout is < Itermination. The CHRGB output is
latched high at the end of the charge cycle when the
output current is less than Itermination. The CHRGB
output will remain high until the timer expires and vbatt
enters a re-charge cycle, or if EN, or VCC are toggled.
Applications Information (Cont.)
The NTC external component configuration is shown in
the typical application schematic on page 1 of the
datasheet. When the NTC voltage from the divider is
above or below the cold and hot temperature threshold
values the SC805 will suspend the charge cycle by turn-
ing off the output, freezing the charge timer, and indicat-
ing a fault on the CHRGB LED. Hysteresis is included for
both hot and cold thresholds to avoid chatter at the NTC
trip points. When the temperature returns to the valid
range the SC805 will automatically resume the charge
cycle. The charge timer will time-out when the SC805
output on-time exceeds the timer setting regardless of
how long it has been disabled due to the NTC tempera-
ture. The internal NTC thresholds of 30% and 75% VCC
were designed to work with Curve-2 type thermistors
available from numerous vendors.
Design Example based on the typical application sche-
matic of page 1 using a Curve 2 Vishay-Dale NTC.
Thot = 50oC
Tcold = 0oC
Find R2 and RT1
Step 1: Pick an RT1 value high enough to prevent self-
heating.
()
DC
V(R T 1 )
RT 1
2
≥
In general lower values of RT1 provide more noise immu-
nity for the NTC voltage at the expense of bias current
from the input adapter. The dissipation constant DC is
the power rating of the NTC resulting in a 1oC self heat-
ing error.
The DC value for this NTC is 3mW and the voltage across
the NTC is 2.5V for a 5V adapter. Therefore RT1 > 2K,
Set RT1 = 10k
Step 2: Find R2 to set the correct Hot level trip point,
9.52k
R
*
R
2.33
R2
T25
T50
T25
=
=
The closest standard resistor value is 9.53k. RT(temp)/
RT(25oC) is often referred to as the ratio at the given
temp. For this NTC at 50oC the ratio is 0.4086.
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