Lithium Ion Battery Charging ICs

Up:	AvionicsPowerSystemLv2
Xref:	BatteryPackLv2, Lv2PowerUsage, BatteryPack

Requirements:

Recharges a 4 cell Li Ion pack (14.4V nominal, 16.8V max)
Minimal parts count - and especially no weird resistor needed
Minimum design time on circuit - i.e., clear application notes
Vaguely modern - no "crufty" chips
Small footprint

So far:

Linear Technology LTC4006: http://www.linear.com/prod/datasheet.html?datasheet=1001

High Conversion Efficiency: Up to 96%
Output Currents Exceeding 4A
±0.8% Accurate Preset Voltages: 8.4V, 12.6V, 16.8V
Built-In Charge Termination with Automatic Restart
AC Adapter Current Limiting Maximizes Charge Rate*
Automatic Conditioning of Deeply Discharged Batteries
Thermistor Input for Temperature Qualified Charging
Wide Input Voltage Range: 6V to 28V
0.5V Dropout Voltage; Maximum Duty Cycle: 98%
Programmable Charge Current: ±5% Accuracy
Indicator Outputs for Charging, C/10 Current Detection and AC Adapter Present
Charging Current Monitor Output
16-Pin Narrow SSOP Package

This looks pretty good. We can also combine it with the LTC4412 "ideal diode" - it replaces a BASD (big ass schottkey diode) with a SOT23-6 IC (using only 11uA) and a MOSFET... which with a 0.01 ohm MOSFET saves us 0.3V drop * 4A - 4A^2 * 0.01 ohm = 1.0 watts!!!

Maxim equivalent: the MAX745 - http://pdfserv.maxim-ic.com/en/ds/MAX745.pdf

Battery fuel gage: http://www.maxim-ic.com/quick_view2.cfm?qv_pk=1793&ln=

Linear Technology LT1513: http://www.linear.com/prod/datasheet.html?datasheet=346

Continuous charge current of 2A for 4.1V cells
Peak output current of 3A
Fixed or programmable charge current
±1% accuracy in fixed voltage mode
Charges any number of cells up to 20V
Accomodates topologies that charge batteries with voltages above supply voltage
500 KHz switching frequency allows for use of small, less expensive inductors

One of the pros of this part is its ability to boost its input voltage to provide a higher charging voltage. However, the data sheet indicates that at higher voltages the charging current of the LT1513 drops. Charging a cell at 16 volts, for example, the LT1513 can only provide 1 amp. In our situation this means it would take about five hours to charge the currently planned battery pack for the LV2 rocket payload. A closer to ideal charging chip would provide boost capability from, say, 18 VDC out given 12 VDC supply at 4A. We'll look a little longer, but probably won't find a chip that meets these specifications.

Other chips:

MAX1737: http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2217
Maxim IC parametric search: http://para.maxim-ic.com/ss.asp?Fam=Batt_Chrg
MAX1909: nice chip, switched diodes, lots of nice options, hot swap pack, BUT: requires host.

Parts:

Interesting but possibly not applicable:

http://www.linear.com/prod/datasheet.html?datasheet=1048: a smart battery charger that DOESN'T NEED a host to operate! That's very, very interesting... we could use a smart battery with very little impact on ourselves - let the battery charge itself and then add charging software later. For example, a Dell 7000/7500 uses a 14.8 V 5.1 Ah smart battery... we could plug that into this smart charger and everthing might just "work".... uh huh, sure.