Electronic Components Datasheet Search |
|
LTC4068X-4.2 Datasheet(PDF) 9 Page - Linear Technology |
|
LTC4068X-4.2 Datasheet(HTML) 9 Page - Linear Technology |
9 / 12 page 9 LTC4068-4.2/LTC4068X-4.2 406842fa APPLICATIO S I FOR ATIO Stability Considerations The constant-voltage mode feedback loop is stable with- out an output capacitor, provided a battery is connected to the charger output. With no battery present, an output capacitor on the BAT pin is recommended to reduce ripple voltage. When using high value, low ESR ceramic capaci- tors, it is recommended to add a 1Ω resistor in series with the capacitor. No series resistor is needed if tantalum capacitors are used. In constant-current mode, the PROG pin is in the feedback loop, not the battery. The constant-current mode stability is affected by the impedance at the PROG pin. With no additional capacitance on the PROG pin, the charger is stable with program resistor values as high as 20k; how- ever, additional capacitance on this node reduces the maximum allowed program resistor. The pole frequency at the PROG pin should be kept above 100kHz. Therefore, if the PROG pin is loaded with a capacitance, CPROG, the following equation can be used to calculate the maximum resistance value for RPROG: R C PROG PROG ≤ π 1 2105 •• Average, rather than instantaneous charge current may be of interest to the user. For example, if a switching power supply operating in low current mode is connected in parallel with the battery, the average current being pulled out of the BAT pin is typically of more interest than the instantaneous current pulses. In such a case, a simple RC LTC4068-4.2 GND PROG RPROG 10k CFILTER 406842 F02 CHARGE CURRENT MONITOR CIRCUITRY Figure 2. Isolating Capacitive Load on PROG Pin and Filtering Power Dissipation It is not necessary to design for worst-case power dissi- pation scenarios because the LTC4068 automatically reduces the charge current during high power conditions. The conditions that cause the LTC4068 to reduce charge current through thermal feedback can be approximated by considering the power dissipated in the IC. Nearly all of this power dissipation is generated by the internal MOSFET—this is calculated to be approximately: PD = (VCC – VBAT) • IBAT where PD is the power dissipated, VCC is the input supply voltage, VBAT is the battery voltage and IBAT is the charge current. The approximate ambient temperature at which the thermal feedback begins to protect the IC is: TA = 120°C – PDθJA TA = 120°C – (VCC – VBAT) • IBAT • θJA Example: An LTC4068 operating from a 5V supply is programmed to supply 800mA full-scale current to a discharged Li-Ion battery with a voltage of 3.3V. Assuming θJA is 50°C/W (see Thermal Considerations), the ambient temperature at which the LTC4068 will begin to reduce the charge current is approximately: TA = 120°C – (5V – 3.3V) • (800mA) • 50°C/W TA = 120°C – 1.36W • 50°C/W = 120°C – 68°C TA = 52°C charged condition and eliminates the need for periodic charge cycle initiations. The CHRG output enters a pull- down state during recharge cycles. If the battery is removed from the charger, a sawtooth waveform of approximately 100mV appears at the charger output. This is caused by the repeated cycling between termination and recharge events. This cycling results in pulsing at the CHRG output; an LED connected to this pin will exhibit a blinking pattern, indicating to the user that a battery is not present. The frequency of the sawtooth is dependent on the amount of output capacitance. filter can be used on the PROG pin to measure the average battery current, as shown in Figure 2. A 10k resistor has been added between the PROG pin and the filter capacitor to ensure stability. |
Similar Part No. - LTC4068X-4.2 |
|
Similar Description - LTC4068X-4.2 |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.COM |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |