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SC802AIMLTRT Datasheet(PDF) 9 Page - Semtech Corporation |
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SC802AIMLTRT Datasheet(HTML) 9 Page - Semtech Corporation |
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9 / 16 page  9 © 2005 Semtech Corp. www.semtech.com SC802/SC802A POWER MANAGEMENT PRELIMINARY Applications Information Cont. 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 = 50oC Tcold = 0oC Find R3 and RT1 Step 1: Pick an RT1 value high enough to prevent self- heating. () DC V(RT1) RT1 2 ≥ 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 1oC self heating 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 R3 to set the correct Hot level trip point 9.52k R R R 2.33 R3 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. Step 3: Calculate the Tcold value. 2.86 10k R3 3 RT RT 25 COLD = ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ × = ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ The ratio for the Curve 2 NTC at 0o is 2.816. The differ- ence represents less than 1/2oC (ie actual trip would be -0.5oC instead of 0oC.) For temperature trip values other than 0oC and 50oC alternate curve-type NTC elements 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. D E L G A L F N OF F Og n i k n i l B B P C O L V U < C C V < P V O r e w o P d o o G t o N X B G R H C > t u o I m r e t I < t u o I * m r e t I e g r a h C e r P C T N r o t l u a F * Output remains on when timer is enabled and t < timeout 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. t l u a FB P CB G R H C O L V U C C V r o P V O C C V f f of f o t l u a F C T N n og n i k n il B e g r a h C - e r P t u o - e m i T n og n i k n il B C 0 5 1 > j T f f of f o |
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