Fine tuning the FETs

Have done some more modeling and think I am about at the end of incremental improvements using this tool.  I posted the .xls sheet with the additional drivers, FETs, and inductors I have been using in the reference tab above.

Below as the detailed results for three potential FETs.  All SMT, one the new PQFP package and two DPAK ones.  Costs are 1x qty from Mouser.com  Parameters use for each run was:

                Vpanel = 32.0v

                Vbat      = 13.8v

                22uF inductor

                100Khz PWM frequency

Early on I had to look to increase the operating frequency from 50Khz to 100Khz else the output capacity ESR losses became very large.  Unfortunately, increasing the frequency also increased switching losses in the FETs…  And at this point the switching losses for the high side FET are in the 350mW range.   Here are the detailed tables:

1)  IRFH7185 – PQFP - $3.92

IOUT (A)	HS Conduction Losses	LS Conduction Losses	HS Switching Losses	Diode Conduction Losses	Reverse Recovery Losses	MOSFET Output Capacitance Losses	High Side Gate Drive Losses	Low Side Gate Drive Losses	Inductor Winding Losses	Output Power (W)	Input Power (W)	Efficiency	HS Die Temperature (˚C)	LS Die Temperature (˚C)
.00	.0021	.0025	.0000	.0000	.3520	.1096	.0360	.0360	.0000	.00	.5382	0.00%	41.23	25.09
1.00	.0042	.0049	.0386	.0032	.3520	.1096	.0360	.0360	.0029	13.80	14.3873	95.92%	42.65	25.28
2.00	.0104	.0121	.0771	.0064	.3520	.1096	.0360	.0360	.0114	27.60	28.2511	97.70%	44.22	25.65
3.00	.0209	.0242	.1157	.0096	.3520	.1096	.0360	.0360	.0257	41.40	42.1297	98.27%	45.94	26.18
4.00	.0358	.0413	.1543	.0128	.3520	.1096	.0360	.0360	.0458	55.20	56.0235	98.53%	47.81	26.89
5.00	.0554	.0635	.1929	.0160	.3520	.1096	.0360	.0360	.0715	69.00	69.9328	98.67%	49.84	27.78
6.00	.0798	.0909	.2314	.0192	.3520	.1096	.0360	.0360	.1030	82.80	83.8579	98.74%	52.05	28.85
7.00	.1093	.1239	.2700	.0224	.3520	.1096	.0360	.0360	.1401	96.60	97.7993	98.77%	54.43	30.12
8.00	.1442	.1626	.3086	.0256	.3520	.1096	.0360	.0360	.1830	110.40	111.7576	98.79%	57.00	31.59
9.00	.1848	.2073	.3471	.0288	.3520	.1096	.0360	.0360	.2317	124.20	125.7333	98.78%	59.77	33.26
10.00	.2314	.2585	.3857	.0320	.3520	.1096	.0360	.0360	.2860	138.00	139.7272	98.76%	62.75	35.17
11.00	.2845	.3167	.4243	.0352	.3520	.1096	.0360	.0360	.3461	151.80	153.7403	98.74%	65.96	37.32
12.00	.3444	.3822	.4629	.0384	.3520	.1096	.0360	.0360	.4118	165.60	167.7733	98.70%	69.41	39.72
13.00	.4117	.4557	.5014	.0416	.3520	.1096	.0360	.0360	.4833	179.40	181.8273	98.67%	73.12	42.40

2)  IPD096N08N3 – DPAK - $1.78

IOUT (A)	HS Conduction Losses	LS Conduction Losses	HS Switching Losses	Diode Conduction Losses	Reverse Recovery Losses	MOSFET Output Capacitance Losses	High Side Gate Drive Losses	Low Side Gate Drive Losses	Inductor Winding Losses	Output Power (W)	Input Power (W)	Efficiency	HS Die Temperature (˚C)	LS Die Temperature (˚C)
.00	.0054	.0063	.0000	.0000	.2912	.0502	.0260	.0260	.0000	.00	.4051	0.00%	42.34	25.32
1.00	.0106	.0124	.0321	.0040	.2912	.0502	.0260	.0260	.0029	13.80	14.2553	96.81%	44.20	25.82
2.00	.0264	.0306	.0641	.0080	.2912	.0502	.0260	.0260	.0114	27.60	28.1339	98.10%	46.59	26.93
3.00	.0533	.0616	.0962	.0120	.2912	.0502	.0260	.0260	.0257	41.40	42.0423	98.47%	49.55	28.68
4.00	.0923	.1062	.1283	.0160	.2912	.0502	.0260	.0260	.0458	55.20	55.9820	98.60%	53.10	31.11
5.00	.1445	.1656	.1604	.0200	.2912	.0502	.0260	.0260	.0715	69.00	69.9553	98.63%	57.31	34.28
6.00	.2113	.2418	.1924	.0240	.2912	.0502	.0260	.0260	.1030	82.80	83.9658	98.61%	62.25	38.29
7.00	.2944	.3368	.2245	.0280	.2912	.0502	.0260	.0260	.1401	96.60	98.0173	98.55%	68.02	43.24
8.00	.3963	.4542	.2566	.0320	.2912	.0502	.0260	.0260	.1830	110.40	112.1155	98.47%	74.71	49.31
9.00	.5201	.5980	.2886	.0360	.2912	.0502	.0260	.0260	.2317	124.20	126.2678	98.36%	82.51	56.70
10.00	.6693	.7740	.3207	.0400	.2912	.0502	.0260	.0260	.2860	138.00	140.4834	98.23%	91.57	65.70
11.00	.8488	.9910	.3528	.0440	.2912	.0502	.0260	.0260	.3461	151.80	154.7760	98.08%	102.15	76.75
12.00	1.0658	1.2600	.3848	.0480	.2912	.0502	.0260	.0260	.4118	165.60	169.1639	97.89%	114.60	90.40
13.00	1.3280	1.5970	.4169	.0520	.2912	.0502	.0260	.0260	.4833	179.40	183.6706	97.67%	129.31	107.45

3) IPB090N06N3 – DPAK - $1.73,  60V max part

IOUT (A)	HS Conduction Losses	LS Conduction Losses	HS Switching Losses	Diode Conduction Losses	Reverse Recovery Losses	MOSFET Output Capacitance Losses	High Side Gate Drive Losses	Low Side Gate Drive Losses	Inductor Winding Losses	Output Power (W)	Input Power (W)	Efficiency	HS Die Temperature (˚C)	LS Die Temperature (˚C)
.00	.0037	.0046	.0000	.0000	.1280	.0655	.0360	.0360	.0000	.00	.2739	0.00%	32.89	25.19
1.00	.0072	.0091	.0302	.0040	.1280	.0655	.0360	.0360	.0029	13.80	14.1188	97.74%	34.24	25.52
2.00	.0178	.0223	.0603	.0080	.1280	.0655	.0360	.0360	.0114	27.60	27.9855	98.62%	35.87	26.21
3.00	.0358	.0446	.0905	.0120	.1280	.0655	.0360	.0360	.0257	41.40	41.8742	98.87%	37.79	27.26
4.00	.0614	.0763	.1207	.0160	.1280	.0655	.0360	.0360	.0458	55.20	55.7856	98.95%	40.03	28.69
5.00	.0950	.1176	.1509	.0200	.1280	.0655	.0360	.0360	.0715	69.00	69.7206	98.97%	42.58	30.51
6.00	.1371	.1693	.1810	.0240	.1280	.0655	.0360	.0360	.1030	82.80	83.6799	98.95%	45.47	32.73
7.00	.1882	.2319	.2112	.0280	.1280	.0655	.0360	.0360	.1401	96.60	97.6650	98.91%	48.72	35.40
8.00	.2490	.3065	.2414	.0320	.1280	.0655	.0360	.0360	.1830	110.40	111.6775	98.86%	52.36	38.54
9.00	.3203	.3939	.2715	.0360	.1280	.0655	.0360	.0360	.2317	124.20	125.7189	98.79%	56.41	42.19
10.00	.4029	.4955	.3017	.0400	.1280	.0655	.0360	.0360	.2860	138.00	139.7916	98.72%	60.93	46.42
11.00	.4979	.6129	.3319	.0440	.1280	.0655	.0360	.0360	.3461	151.80	153.8983	98.64%	65.93	51.27
12.00	.6066	.7482	.3621	.0480	.1280	.0655	.0360	.0360	.4118	165.60	168.0423	98.55%	71.49	56.85
13.00	.7307	.9036	.3922	.0520	.1280	.0655	.0360	.0360	.4833	179.40	182.2275	98.45%	77.66	63.23

System overhead:

         o    Output capacitor losses – est:   26mW (using 3.57A inductor ripple current)
         o    Input capacitor losses    - est:  162mW using 9A load.

·                O       +5v rail:  25mA -->   125mW

o   uC consumption:       14mA @5v (per datasheet typical)

o   OpAmps:                     100uA @ 5v (per datasheet typical)

o   CAN consumption:     6mA @ 5v (assuming a 1% dominate/recessive ratio)

o   Various pull-ups:         5mA @ 5v (WAG)

·    ·           O       uC power supply loss:  134mW

o   Switcher loss:                    9mW (Per datasheet, 25mA load, 36v Vin)

o   Linear Loss:                   125mW  (10v à 5v = 5v drop at 25mA)  -- Clearly need to look at this closer…

·    ·           O       Vbat & Vpan resistor network:  1.2mW

o   Vbat:                     190uW

o   Vpanel:                1mW

Total estimated overhead:  26mW + 162 + 125mW + 134mW + 1.2mW =   449mW  --> 450mW

Based on 250w input this would be a 0.18% reduction in the above efficiency numbers.  So, the IRFH7185 selection, instead of being 98.78% efficiency would come in at 98.60% overall.

If one did a depopulated (one bank only) configuration, and eliminated the CAN subsystem – that would save 60mW in losses between the CAN transceiver and uC power supplies.

The straw-man has a liner LDO regulator taking the 10v from the LTC3639 SPW down to 5v.  I had selected this as a cost trade-off in support of very low +5 current consumption if the uC is placed into sleep.  Most low cost small switching power supplies need a min of 5-10mA to remain stable, and in sleep the uC will be in the low uA range.  Perhaps need to consider another switching power supply, but a more costly one as the 125mW loss associated with the LDO is very significant.

How does this look, does it seem like I have missed something?

-al-