Design Notes	
Lower Half Elex Board, Coastal Profiling Float

2018-05-01	ECM	create
2018-08-15	ECM	change LT4314 I2C mux to distributed analog switches
2019-01-08	ECM	change 4060 timer to 14536; I2C port to 6408

Requirements
(from GM email 2018-01-30)
1. Manage 6 Inspired Energy 8S1P sticks, selectable 2 thru 6.  Voltage 20 – 33.6V.  
	Charge sequentially, discharge in parallel
	I2C SmartBattery communication

2. Battery stick ratings are 1.5A charge, 4A discharge.  Application max discharge 8A total.
	Provide input and output overcurrent protection as appropriate.

3. Charge source is Inspired Energy ‘smart charger’ model PH4000A, 36V max at 1.5A max.  
	a) Sequence 1 charger through all 6 sticks at rates between 1 min and 10 min per step.
	b) deadface charge input connector when not connected

4. Allow motherboard/controller I2C bus access to all 6 packs for charge and discharge monitoring.  Mobo 5V supply available for I2C interface.

5. Battery on/off control via reed switches on endcap (set/reset momentary).

6. Battery on/off sleep timer under Mobo control if possible, override via reed switches

7. Pump motor drive (Elmo) power control: on/off, soft start, overcurrent, energy monitor
	8 A max expected operating current at 20V low batt
	NO regen control other than stoutest available TVS diode(s)

8. Package in prescribed C-shaped PWB, keep top surface free of live traces if possible

9.  Board has power inputs from three sources: 
	Charger 	regulated charge voltage/current, plus 36V pilot signal
	Batteries	battery discharge voltage
	Mobo		5V logic supply for I2C interface

Operational modes need max reliability and min power draw:
Deployed – run:		Battery power, Mobo power
Deployed – sleep	Battery power
Charge – run:		Charger power, Battery power, Mobo power
Charge – sleep:		Charger power, Battery power, Mobo sleeping
Test modes need to not damage any parts of the system: 
Charge only		Charger power only (batteries and Mobo disconnected)
Mobo only		Mobo power only (batteries and charger disconnected)
Battery only		Battery power only (charger and Mobo disconnected)

10. Optional, future, or be-nice-if:
	Position sensor ADC
	Motorized valve controller
	Elmo Twitter connectorization
	“Jostle” wakeup input to sleep timer

Description

Design Notes

Oscillator/Sequencer

Use MC14536 with RC osc to generate 1/min to 1/10 min clock (600 sec period), use clock to advance HC161 sync counter, use HC138 to decode counter, use 138 outputs to select batt sticks for charging (N_ChgSel).  Feed back one N_ChgSel via Stick Count Select jumpers, use it to synchronously Load (Preset) the HC161 to a count of 1.  HC161 counts 1-6, depending on stick count, before re-loading.    

MC14536 Configuration: Keep RC osc above 400 Hz based on note in old Motorola HC4060 spec sheet.  Dynamic Icc per specs is 1.5uA/kHz @ 5V.  Slowest scan 10 min or 600 sec period. 
600 / 2^18 = 2.29 msec  437 Hz.  Spec sheet Fig.12 says Fosc = 1 / 2.3*R*C, 10k and 0.1uF give 435 Hz with a 5% tol X7R capacitor available (NP0 caps are all 1206 or 1210 size, with boardflex concerns).  Icc in this config would be 1.5uA * 0.435 = 0.65uA.  Icc would rise to 6.5 uA at 4.37 Khz, but sequencer only runs when charger is connected so power not a concern.  Decode Stage inputs (A,B,C,D) for 2^18 are 1001 and must be tied high or low; set this up as hardwired default but run through SolderBlob pads to allow blue-wire changes if necessary. 

Power-On Reset (N_POR):  Good to hold osc and counters in reset when charger (Chg5V) not present, to save power during deployment  Also good to start count from a known initialized condition.  Seek supervisor circuit with Sense input independent of Vcc pin; totem-pole output to save power (versus open-drain) since N_POR will be active during deployment; internal V divider convenient and probably higher impedance, but not mandatory since divider only powered when Chg5V is present.  Considered MIC803, TPS3808, and LTC2934; choose LTC2934-2 for sub-uA Icc and totem-pole output.  Choose 200msec delay since there are no specific requirements and we’re not in any big hurry.

I2C Mux

Two approaches considered
1) LTC4314 4-channel I2C Mux/Buffer (2 ea).  

Diode/Load Switches

Charge bus requires load switch per battery stick, to enable/disable charge current in sequence.  The charge bus needs diode functionality at least at the charger input, to prevent reverse current flow out the charge port or in to the charger.  It seems safer to have diode functionality on each load switch to each stick, to prevent sticks reverse-driving the charge bus (although there’s normally nowhere for that current to go except through an enabled switch into another stick).  

Discharge bus requires diode functionality to prevent battery sticks from back-driving each other in event of charge imbalance, or more importantly in event of shorted cell.  Discharge bus also can use load switch functionality to enable power control of the whole platform.

Simplest solution would adopt a common ideal-diode/load-switch circuit for each stick charge input and discharge output.  An alternate (not pursued) would be an ideal diode at charger input, charge bus load switches at each stick, discharge bus ideal diodes at each stick, and a load switch at the platform power output.

Ideal diodes considered:
  LTC4412HV – a little slow with large FETs, but lowest standby power, ~15uA typ
  LTC4414 – better with large FETs but ~30uA standby
  Various N-ch ideal diode drivers w/ charge pumps – due to topology can’t function as load switches

Pump ECB/Inrush/Load Switch

Power feed to VB pump motor drive needs Load Switch function, Inrush control, and ECB function.  LTC4380 provides all three.  Could provide OV protection too but would require back-to-back FETs

Load Switch:  

Standby Current Budget

Inspired Energy PH2059HD34 sticks are 3230 mAh each or 19,380 mAh for full set of 6.
Goal: allow 5% for P2 board or 969 mAh or 111 uA standby for 1 year

Disch28V

Batt5V (adds to Disch28V)
TPS7A16 LDO				10	uA

Mobo5V
LTC2934 divider + chip			 7	uA

Joint4V7 (adds to Mobo5V and Chg28V)
TCA6408 ports, 2 ea			14	uA  (max, 3 uA typ) 

Chg28V

Chg5V (adds to Chg28V)
MC14536 dynamic			 6	uA
TPS7A16 LDO				10	uA
LTC2934 divider + chip			 7	uA

Questions for Review:

1. What supplies should I2C busses be pulled up to
2. Blinkylights (LEDs) to show channel scan active?
3. OK to take Sleep Timer power from just 1 stick?
4. 5% tolerance on Scan and Sleep time OK?  Trimpot?
5. Location of Mobo-side I2C pullups.  Pull to what voltage.