Electronic Components Datasheet Search |
|
LT1621CGN Datasheet(PDF) 8 Page - Linear Technology |
|
LT1621CGN Datasheet(HTML) 8 Page - Linear Technology |
8 / 12 page 8 LT1620/LT1621 APPLICATIONS INFORMATION reduces battery charging current until the external load subsides. In Figure 4 the LT1620 is coupled with an LT1513 SEPIC battery charger IC to create an input overcurrent protected charger circuit. The programming voltage (VCC – VPROG) is set to 1.0V through a resistor divider (RP1 and RP2) from the 5V input supply to ground. In this configuration, if the input current drawn by the battery charger combined with the system load requirements exceeds a current limit threshold of 3A, the battery charger current will be reduced by the LT1620 such that the total input supply current is limited to 3A. Refer to the LT1513 data sheet for additional information. PROGRAMMING ACCURACY CONSIDERATIONS PWM Controller Error Amp Maximum Source Current In a typical battery charger application, the LT1620 con- trols charge current by servoing the error amplifier output pin of the associated PWM controller IC. Current mode control is achieved when the LT1620 sinks all of the current available from the error amplifier. Since the LT1620 has finite transconductance, the voltage required to gen- erate its necessary output current translates to input offset error. The LT1620 is designed for a typical IOUT sink current of 130 µA to help reduce this term. Knowing the current source capability of the associated PWM control- ler in a given application will enable adjustment of the required programming voltage to accommodate the de- sired charge current. A plot of typical VPROG voltage offset vs PWM source capability is shown in Figure 5a. For example, the LTC1435 has a current source capability of about 75 µA. This translates to about –15mV of induced programming offset at VPROG (the absolute voltage at the PROG pin must be 15mV lower). VCC – VPROG Programmed Voltage ≠ 0.8V The LT1620 sense amplifier circuit has an inherent input referred 3mV offset when IN+ – IN– = 0V to insure closed- loop operation during light load conditions. This offset vs input voltage has a linear characteristic, crossing 0V as IN+ – IN– = 80mV. The offset is translated to the AVG output (times a factor of 10), and thus to the programming voltage VPROG. A plot of typical VPROG offset voltage vs IN+ – IN– is pictured in Figure 5b. For example, if the desired load current corresponds to 100mV across the sense resistor, the typical offset, at VPROG is 7.5mV (the absolute voltage at the PROG pin must be 7.5mV higher). This error term should be taken into consideration when using VID values significantly away from 80mV. VCC – VPROG2 Programmed Voltage ≠ 1.6V (LT1620GN Only) The offset term described above for VPROG also affects the VPROG2 programming voltage proportionally (times an addi- tional factor of 2). However, VPROG2 voltage is typically set well below the zero offset point of 1.6V, so adjustment for this term is usually required. A plot of typical VPROG2 offset voltage vs IN+ – IN– is pictured in Figure 5c. For example, setting the VPROG2 voltage to correspond to IN+ – IN–= 15mV typically requires an additional –50mV offset (the absolute voltage at the PROG2 pin must be 50mV lower). Sense Amplifier Input Common Mode < (VCC – 0.5V) The LT1620 sense amplifier has additional input offset tolerance when the inputs are pulled significantly below the VCC supply. The amplifier can induce additional input referred offset of up to 11mV when the inputs are at 0V common-mode. This additional offset term reduces roughly linearly to zero when VCM is about VCC – 0.5V. In typical applications, this offset increases the charge current tol- erance for “cold start” conditions until VBAT moves away from ground. The resulting output current shift is generally negative; however, this offset is not precisely controlled. Precision operation should not be attempted with sense amplifier common mode inputs below VCC – 0.5V. Input referred offset tolerance vs VCM is shown in Figure 5d. VCC ≠ 5V The LT1620 sense amplifier induces a small additional offset when VCC moves away from 5V. This offset follows a linear characteristic and amounts to about ±0.33mV (input-referred) over the recommended operating range of VCC, centered at 5V. This offset is translated to the AVG and AVG2 outputs (times factors of 10 and 20), and thus to the programming voltages. A plot of programming offsets vs VCC is shown in Figure 5e. |
Similar Part No. - LT1621CGN |
|
Similar Description - LT1621CGN |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.NET |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | 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 |