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SC803IMLTR Datasheet(PDF) 7 Page - Semtech Corporation |
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SC803IMLTR Datasheet(HTML) 7 Page - Semtech Corporation |
7 / 17 page 7 2004 Semtech Corp. www.semtech.com SC803 POWER MANAGEMENT Applications Information (Cont.) The CP output can be used for a UVLO indicator. Regard- less of the state of EN, the CP output reflects the volt- age of the VCC (adapter) input. When VCC is above UVLO, CP is high, 2.8V. When VCC is below UVLO, CP is low, 0V. The CP pin can also put the device into the charge mode whenever the adaptor has power, by connecting it to the BIP pin. The OVP LED will light whenever the SC803 is enabled and there is an overvoltage on the VCC pins. When this occurs the SC803 will turn off and stay off as long as the overvoltage condition remains. As soon as the overvolt- age is removed the SC803 will resume operation. The OVP LED will not light if the part is disabled, even though an overvoltage is present on the VCC pins. Configuring the Output Voltage to the Battery The battery voltage is set by the VPRGM pin. If this pin is logic high the output voltage is set to 4.2V. If this pin is logic low the output voltage will be set to 4.1V. The VPRGM pin can be tied to the CP pin for 4.2V operation and ground for 4.1V operation. For a value other than 4.1V or 4.2V a resistor divider is required. This divider is set between the VOUT pin and the VPRGM pin with the divider tap connected to the BSEN pin. The schematic for such a connection and the equation to set the output voltage is given in Figure 1. The output voltage for Figure 1 will be set to 4.77V with the resistors shown. The capacitor C1 may be needed for stability and or reduced ripple volt- age. It is advisable to leave room on the PCB for adding this capacitor, since it can be left out if it is not needed. The evaluation board does have a place for the resistor divider and capacitor to allow an adjustable voltage to be set on this board via R1, R2 and C2 (see schematic on page 10). With JP7 removed, jumper JP2 should be added to complete the changes required for adjustable mode operation on the evaluation board. For further evaluation board information, see the section tilted Evalu- ation Board. R2 CHARGER BATTERY +5V PRESENT R4 59K C1 330pF STATUS SC803 14 1 3 7 4 15 9 10 2 11 5 8 13 6 16 12 VCC BSEN IPRGM EN ITERM VOUT OVP STAT VPRGM CP NC BIP VCC GND VOUT NC C2 1uF FAULT C3 2.2uF R1 R3 100K 3.0 R3 R4 1 VOUT • + = FIGURE 1 Remote Kelvin Sensing at the Battery Another nice feature of the SC803 is its ability to sense the battery voltage directly at the battery with its Kelvin BSEN pin. This allows the designer great flexibility in PCB layout and achieves a much greater accuracy in sensing the battery voltage where it counts, at the battery termi- nals! Therefore, when laying out the PCB the designer should route the BSEN pin directly to the terminal at which the battery gets connected. In addition, in the LDO mode, the BSEN pin will still need to sense the output voltage. In LDO mode, the BSEN pin becomes the regulation feed- back for the control-loop. In this case it is sensing the output voltage of itself, since the battery is not in place. Therefore BSEN should never be left floating..... Capacitor Selection Input and output capacitors can be low cost ceramic type. The output capacitance range is 1uF to 4.7uF. The input capacitor should be between 0.1uF to 1uF. Overcurrent and Temperature Protection Overcurrent protection is inherent to the SC803. The SC803 operates as a current source and the output cur- rent is limited by the mode it is in at the time. If in the fast-charge mode the current is limited by the IPRGM resistor, the fast-charge current. When the output volt- age is less than 2.8V, the current is limited by the ITERM resistor, the pre-charge current. Both of these functions protect the device in an event of a short circuit condition on the output. In the LDO mode the current is limited to the fast-charge current, provided there is voltage on the output. Under a short circuit condition in the LDO mode the current will enter a “hiccup” mode. The temperature shutdown can protect the device in conditions of excess current as well, by shutting down the device when its die temperature exceeds 165oC. G A L F D E LN OF F O H G I H E C N A D E P M I P C C C V O T R E W O P S N I P O T R E W O P O N S N I P C C V X P V O - R E V O C C V E G A T L O V E G A T L O V C C V L A M R O N X T A T S Y R E T T A B G N I G R A H C Y L L U F Y R E T T A B D E G R A H C E D O M O D L |
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