SC802 SEMTECH [Semtech Corporation], SC802 Datasheet - Page 9

• Manufacturer Part Number: SC802
• Description: Fully Integrated Lithium-Ion Battery Charger System with Timer
• Manufacturer: SEMTECH [Semtech Corporation]

perature returns to the valid range the SC802 automati-
cally resumes the charge cycle. The charge timer will
time-out when the SC802 output on-time exceeds the
timer setting regardles of how long it has been disabled
due to temperature. 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 = 50
Tcold = 0
Find R3 and RT1
Step 1: Pick an RT1 value high enough to prevent self-
heating.
In general lower values of RT1 provide more noise 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 1
The DC value for this NTC is 3mW and the voltage across
the NTC is 2.5V for a 5V adapter. Therefore RT1 > 2k.
Step 2: Find R3 to set the correct Hot level trip point
The closest standard resistor value is 9.53k. RT(temp)/
RT(25
temp. For this NTC at 50
Step 3: Calculate the Tcold value.
The ratio for the Curve 2 NTC at 0
ence represents less than 1/2
-0.5
© 2005 Semtech Corp.
POWER MANAGEMENT
PRELIMINARY
Applications Information Cont.
o
C instead of 0
o
C) is often referred to as the ratio at the given
o
R3
C
o
C
=
⎛
⎜ ⎜
⎝
RT
2.33
RT
COLD
o
RT1
25
C.) For temperature trip values other
×
Set RT1 = 10k
⎛
⎜
⎜
⎝
⎞
⎟ ⎟
⎠
R
≥
=
T25
o
(
3
C the ratio is 0.4086.
V(RT1)
×
×
⎛
⎜
⎝
⎛
⎜
⎜
⎝
DC
o
10k
R
R
R3
C (ie actual trip would be
o
T50
T25
C self heating error.
o
⎞
⎟
⎠
)
is 2.816. The differ-
2
⎞
⎟
⎟
⎠
=
⎞
⎟
⎟
⎠
2.86
=
9.52k
9
than 0
can be used or an additional resistor can be added to
the Rntc divider to alter the temperture coefficient.
LED Flags
There are two LED drivers on the SC802: CHRGB (Charge)
and CPB (Charger Present). These outputs are open drain
NMOS drivers for controlling LEDs directly. The Table be-
low defines each LED output state.
The CPB output can be used for a VCC indicator. Re-
gardless of the state of EN, the CPB output reflects the
voltage of the VCC (adapter) input. When VCC is between
the UVLO and OVP thresholds the CPB output is low.
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 during the charge cycle when the output current
is less than Itermination. This latch is reset when the
battery enters a re-charge cycle, or if BIPB, EN, or VCC
are toggled. The CHRGB indicator operates the same
way in both charge and ldo mode.
There are five fault modes detected by the SC802; (In-
put under voltage, input over voltage, NTC temperature,
Max die temperature or OT and pre-charge timeout) The
LED states for these fault modes are shown below.
* Output remains on when timer is enabled and t < timeout
o
C
C and 50
F
H
C
L
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R
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