Reported by Nikolaus Schaller, Mar 23, 2014
Maybe this is a solution? http://www.linear.com/product/LTC3355
Comment 1 by Joerg Reisenweber, Mar 24, 2014
Nice chip. The supposed config would be: USB Vbus -> $<charger> (TWL4030/bq??? charger) out -> main battery -> LTC3355 V(in) LTC3355 V(out) -> TWL4030 (ex-Vbat) MAIN BAT V???.IN [[doc: SWCS032E; p.33 Figure 4.1]] The TPS65950/TWL4030 (if I understand correctly) is shutting down hard to "off" state at 2.7V(bat) the latest, and has the following quiescent current "Ground current I(q)" on V???.IN, in "Off at 30°C" [[doc: SWCS032E; p.35 Table 4-3 ff.]] 3 uA : Table 4-3. VDD1 dc-dc Regulator Characteristics 1 uA : Table 4-4. VDD2 dc-dc Regulator Characteristics 1 uA : Table 4-5. VIO dc-dc Regulator Characteristics 1 uA : Table 4-6. VDAC LDO Regulator Characteristics (("Off mode at 55°C")) 1 uA : Table 4-7. VPLL1 LDO Regulator Characteristics 1 uA : Table 4-8. VPLL2 LDO Regulator Characteristics 1 uA : Table 4-9. VMMC1 LDO Regulator Characteristics 1 uA : Table 4-10. VMMC2 LDO Regulator Characteristics 1 uA : Table 4-11. VSIM LDO Regulator Characteristics 1 uA : Table 4-12. VAUX1 LDO Regulator Characteristics 1 uA : Table 4-13. VAUX2 LDO Regulator Characteristics 1 uA : Table 4-14. VAUX3 LDO Regulator Characteristics 1 uA : Table 4-15. VAUX4 LDO Regulator Characteristics (1uA : Table 4-21. VRRTC LDO Regulator Characteristics; this will stay on anyway, to power RTC from main bat) 10uA : "Sleep mode, I(OUT) = 0"; 11uA for "I(OUT) = 1 mA" "Table 4-22. Power Consumption" states: Mode: "Wait-on" Description: "The phone is apparently off for the user, a main battery is present and well-charged. The RTC registers (registers in the backup domain) are maintained. Wake-up capabilities (like the PWRON button) are available." Typical Consumption: 64uA * 3.8V = 243.2 μW Yet unclear to me if all those quiescent currents would drop even further when main battery goes <2.7V. For sure the VRRTC power source gets switched from main bat to backup bat, thus reducing load to main bat and thus reducing the risk to quickly drain it to an irrecoverable state. Now for the LTC3355 we'd need to keep this chip active (when using above sketched config) to power the RTC and other stuff in backup- and wakeup-domain. The datasheet states [[doc: http://www.linear.com/docs/44566 p.3]] I(Q) V(IN) Quiescent Current CONDITIONS:" Charger Off, Not Switching, VOUT = 3.3V, No Load in Regulation, Supercapacitor Charged" min 60, nom 120, max 215 μA we need to consider carefully if those 0.22mA constant inevitable load are accepatble even for drained batteries that must not get drained further, from - say - 3.0V down to 2.5V which would destroy the cell. The remaining capacity in such LiIon cell at 3.0V for discharge down to 2.5 is only a few tens of mAh, making for a few 50s of hours a drained battery may sit in device. we may consider if we can find a solution that reliably stops further battery drain when battery reaches 3.0V. Pulling "PFI (Pin 1): Input to the Power-Fail Comparator" to GND may result in chip significantly reducing I(Q) Links: http://www.ti.com/product/tps65950 http://www.ti.com/general/docs/lit/getliterature.tsp?genericPartNumbe r=tps65950&fileType=pdf TPS65950 Integrated Power Management/Audio Codec Silicon Revision 1.2 Data Manual SWCS032E http://www.linear.com/docs/44566
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