runpatrick/sa-sim-pcb

sim/pdn.results.txt

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Circuit: * sa-sim v1 — pdn impedance analysis

Doing analysis at TEMP = 27.000000 and TNOM = 27.000000

Warning: i_test: has no value, DC 0 assumed
Warning: can't parse 'vm': ignored

No. of Data Rows : 161

Error: measure  z_100meg  (AT) : out of interval
 .meas ac z_100meg find vm(modem_vbat) at=100meg failed!

z_dc                =  1.100000e-01
z_1k                =  1.086471e-01
z_100k              =  4.092310e-02
z_10meg             =  3.668897e-02
z_max               =  1.100000e-01 at=  1.000000e+00

                     * sa-sim v1 — pdn impedance analysis
                     AC Analysis  Thu Apr 30 22:36:48  2026
--------------------------------------------------------------------------------
Index   frequency       vm(modem_vbat)  
--------------------------------------------------------------------------------
0	1.000000e+00	1.100000e-01	
1	1.122018e+00	1.100000e-01	
2	1.258925e+00	1.100000e-01	
3	1.412538e+00	1.100000e-01	
4	1.584893e+00	1.100000e-01	
5	1.778279e+00	1.100000e-01	
6	1.995262e+00	1.100000e-01	
7	2.238721e+00	1.100000e-01	
8	2.511886e+00	1.100000e-01	
9	2.818383e+00	1.100000e-01	
10	3.162278e+00	1.100000e-01	
11	3.548134e+00	1.100000e-01	
12	3.981072e+00	1.100000e-01	
13	4.466836e+00	1.100000e-01	
14	5.011872e+00	1.100000e-01	
15	5.623413e+00	1.100000e-01	
16	6.309573e+00	1.099999e-01	
17	7.079458e+00	1.099999e-01	
18	7.943282e+00	1.099999e-01	
19	8.912509e+00	1.099999e-01	
20	1.000000e+01	1.099999e-01	
21	1.122018e+01	1.099998e-01	
22	1.258925e+01	1.099998e-01	
23	1.412538e+01	1.099997e-01	
24	1.584893e+01	1.099996e-01	
25	1.778279e+01	1.099996e-01	
26	1.995262e+01	1.099994e-01	
27	2.238721e+01	1.099993e-01	
28	2.511886e+01	1.099991e-01	
29	2.818383e+01	1.099989e-01	
30	3.162278e+01	1.099986e-01	
31	3.548134e+01	1.099982e-01	
32	3.981072e+01	1.099978e-01	
33	4.466836e+01	1.099972e-01	
34	5.011872e+01	1.099965e-01	
35	5.623413e+01	1.099956e-01	
36	6.309573e+01	1.099944e-01	
37	7.079458e+01	1.099930e-01	
38	7.943282e+01	1.099912e-01	
39	8.912509e+01	1.099889e-01	
40	1.000000e+02	1.099860e-01	
41	1.122018e+02	1.099824e-01	
42	1.258925e+02	1.099778e-01	
43	1.412538e+02	1.099721e-01	
44	1.584893e+02	1.099649e-01	
45	1.778279e+02	1.099558e-01	
46	1.995262e+02	1.099444e-01	
47	2.238721e+02	1.099300e-01	
48	2.511886e+02	1.099119e-01	
49	2.818383e+02	1.098891e-01	
50	3.162278e+02	1.098605e-01	
51	3.548134e+02	1.098246e-01	
52	3.981072e+02	1.097794e-01	
53	4.466836e+02	1.097227e-01	
54	5.011872e+02	1.096515e-01	

Index   frequency       vm(modem_vbat)  
--------------------------------------------------------------------------------
55	5.623413e+02	1.095622e-01	
56	6.309573e+02	1.094504e-01	
57	7.079458e+02	1.093105e-01	
58	7.943282e+02	1.091358e-01	
59	8.912509e+02	1.089180e-01	
60	1.000000e+03	1.086471e-01	
61	1.122018e+03	1.083114e-01	
62	1.258925e+03	1.078968e-01	
63	1.412538e+03	1.073872e-01	
64	1.584893e+03	1.067645e-01	
65	1.778279e+03	1.060088e-01	
66	1.995262e+03	1.050995e-01	
67	2.238721e+03	1.040163e-01	
68	2.511886e+03	1.027414e-01	
69	2.818383e+03	1.012617e-01	
70	3.162278e+03	9.957188e-02	
71	3.548134e+03	9.767678e-02	
72	3.981072e+03	9.559405e-02	
73	4.466836e+03	9.335477e-02	
74	5.011872e+03	9.100249e-02	
75	5.623413e+03	8.859014e-02	
76	6.309573e+03	8.617512e-02	
77	7.079458e+03	8.381350e-02	
78	7.943282e+03	8.155434e-02	
79	8.912509e+03	7.943528e-02	
80	1.000000e+04	7.747994e-02	
81	1.122018e+04	7.569740e-02	
82	1.258925e+04	7.408324e-02	
83	1.412538e+04	7.262166e-02	
84	1.584893e+04	7.128801e-02	
85	1.778279e+04	7.005125e-02	
86	1.995262e+04	6.887602e-02	
87	2.238721e+04	6.772429e-02	
88	2.511886e+04	6.655658e-02	
89	2.818383e+04	6.533300e-02	
90	3.162278e+04	6.401433e-02	
91	3.548134e+04	6.256332e-02	
92	3.981072e+04	6.094637e-02	
93	4.466836e+04	5.913571e-02	
94	5.011872e+04	5.711191e-02	
95	5.623413e+04	5.486636e-02	
96	6.309573e+04	5.240331e-02	
97	7.079458e+04	4.974087e-02	
98	7.943282e+04	4.691046e-02	
99	8.912509e+04	4.395456e-02	
100	1.000000e+05	4.092310e-02	
101	1.122018e+05	3.786894e-02	
102	1.258925e+05	3.484342e-02	
103	1.412538e+05	3.189258e-02	
104	1.584893e+05	2.905461e-02	
105	1.778279e+05	2.635861e-02	
106	1.995262e+05	2.382451e-02	
107	2.238721e+05	2.146388e-02	
108	2.511886e+05	1.928117e-02	
109	2.818383e+05	1.727520e-02	
110	3.162278e+05	1.544062e-02	
111	3.548134e+05	1.376922e-02	
112	3.981072e+05	1.225102e-02	

Index   frequency       vm(modem_vbat)  
--------------------------------------------------------------------------------
113	4.466836e+05	1.087520e-02	
114	5.011872e+05	9.630800e-03	
115	5.623413e+05	8.507334e-03	
116	6.309573e+05	7.495363e-03	
117	7.079458e+05	6.587054e-03	
118	7.943282e+05	5.776880e-03	
119	8.912509e+05	5.062542e-03	
120	1.000000e+06	4.446196e-03	
121	1.122018e+06	3.935882e-03	
122	1.258925e+06	3.546430e-03	
123	1.412538e+06	3.298039e-03	
124	1.584893e+06	3.210202e-03	
125	1.778279e+06	3.292224e-03	
126	1.995262e+06	3.538065e-03	
127	2.238721e+06	3.931352e-03	
128	2.511886e+06	4.455433e-03	
129	2.818383e+06	5.100514e-03	
130	3.162278e+06	5.866297e-03	
131	3.548134e+06	6.762566e-03	
132	3.981072e+06	7.809987e-03	
133	4.466836e+06	9.042537e-03	
134	5.011872e+06	1.051288e-02	
135	5.623413e+06	1.230303e-02	
136	6.309573e+06	1.454528e-02	
137	7.079458e+06	1.746493e-02	
138	7.943282e+06	2.147229e-02	
139	8.912509e+06	2.736623e-02	
140	1.000000e+07	3.668897e-02	
141	1.122018e+07	5.052668e-02	
142	1.258925e+07	5.424626e-02	
143	1.412538e+07	3.590088e-02	
144	1.584893e+07	2.106935e-02	
145	1.778279e+07	1.236786e-02	
146	1.995262e+07	7.180536e-03	
147	2.238721e+07	4.908092e-03	
148	2.511886e+07	5.735152e-03	
149	2.818383e+07	8.052557e-03	
150	3.162278e+07	1.076598e-02	
151	3.548134e+07	1.364334e-02	
152	3.981072e+07	1.667226e-02	
153	4.466836e+07	1.988898e-02	
154	5.011872e+07	2.334191e-02	
155	5.623413e+07	2.708355e-02	
156	6.309573e+07	3.116916e-02	
157	7.079458e+07	3.565732e-02	
158	7.943282e+07	4.061079e-02	
159	8.912509e+07	4.609767e-02	
160	1.000000e+08	5.219253e-02	


Total analysis time (seconds) = 0.001

Total elapsed time (seconds) = 0.005 

Total DRAM available = 64253.918 MB.
DRAM currently available = 14199.102 MB.
Maximum ngspice program size =   20.012 MB.
Current ngspice program size =   12.312 MB.

Shared ngspice pages =   10.395 MB.
Text (code) pages =    5.316 MB.
Stack = 0 bytes.
Library pages =    2.066 MB.


================================================================================
SA-SIM v1 — PDN Impedance Analysis Summary
Generated: 2026-04-30  ngspice-36  Batch Mode
================================================================================

NETLIST:  sim/pdn.spice
ANALYSIS: AC decade sweep, 1Hz to 100MHz, 20 pts/decade (161 points)
STIMULUS: 1A AC current source at modem_vbat node
METRIC:   V(modem_vbat) = Z(f)  [Ohms, since I=1A]
TARGET:   Z < 50mΩ at all PDN-critical frequencies

--- Physical Model (series path: battery → JST → FET → PCB trace → BG95 pin) ---
  R_batt_int  : 50mΩ  (Li-ion internal resistance)
  R_jst       : 30mΩ  (JST connector + wire)
  L_wire      :  5nH  (battery wire)
  R_fet       : 25mΩ  (reverse-polarity FET Rds_on)
  C_fet_par   :  5pF  (FET drain-source parasitic)
  R_trace     :  5mΩ  (PCB trace BAT_P, 5mm × 0.5mm)
  L_trace     :  2nH  (PCB trace inductance)
  Series R total = 110mΩ  (sets low-frequency impedance floor)

--- Decoupling Network at modem_vbat ---
  3× 10µF X5R 0603   (C_BG95_BAT1/2/3)  ESR=10mΩ  ESL=1nH
  4× 100nF 0402 MLCC (C_d1–C_d4)        ESR=20mΩ  ESL=0.5nH
  1× 100µF tantalum  (C_bulk, FAB risk#6 fix)  ESR=200mΩ  ESL=2nH

--- Measured Impedance at Key Frequencies ---
  Frequency   |  Z (mΩ)  |  Status
  ------------|----------|-----------------------------
  1Hz  (DC)   |  110.0   |  CONCERN — series R floor
  1kHz        |  108.6   |  CONCERN — series R floor
  100kHz      |   40.9   |  PASS
  10MHz       |   36.7   |  PASS
  ~12.6MHz    |   54.2   |  CONCERN — anti-resonance peak
  100MHz      |   52.2   |  CONCERN — rising inductance

--- ngspice .meas Results ---
  z_dc     = 110.0 mΩ  (at 1Hz)
  z_1k     = 108.6 mΩ  (at 1kHz)
  z_100k   =  40.9 mΩ  (at 100kHz)
  z_10meg  =  36.7 mΩ  (at 10MHz)
  z_100meg =  N/A  (out of sweep interval — see row 160: 52.2mΩ at 1e8Hz)
  z_max    = 110.0 mΩ  (at 1Hz, dominated by series R)

--- Analysis ---

LOW-FREQUENCY CONCERN (DC–1kHz, Z≈110mΩ):
  The 110mΩ floor is the physically correct sum of all series resistances in
  the current path from battery to BG95 VBAT pin. This is not a simulation
  error. The BG95 draws burst current (up to ~2A peak during LTE-M TX) through
  this path. At 110mΩ, a 2A burst causes ΔV = 220mV sag on VBAT.
  The BG95 VBAT min is 3.3V; at 3.7V nominal, 220mV sag leaves 3.48V — safe.
  However, reducing JST wire length and using a lower Rds_on FET (e.g., 10mΩ)
  would improve margin.
  RECOMMENDATION: Select FET with Rds_on < 10mΩ (e.g., AO3401A, Rds_on=45mΩ
  max but typically ~20mΩ; or DMG3415U). Shorten battery wire to ≤30mm.

ANTI-RESONANCE PEAK (~12.6MHz, Z=54.2mΩ):
  Caused by parallel resonance between the 100µF tantalum (going inductive at
  ~11MHz due to ESL=2nH) and the 100nF ceramics (still capacitive at that freq).
  This peak at 54.2mΩ just exceeds the 50mΩ target.
  RECOMMENDATION: Add a 1µF X5R 0402 MLCC (ESR<5mΩ, ESL<0.3nH) on modem_vbat.
  This fills the impedance "valley" between tantalum and 100nF, smoothing the
  anti-resonance. A 4.7µF 0402 (LCSC C19666) would also work and is already
  in the BOM for VBAT rails.

HIGH-FREQUENCY (100MHz, Z=52.2mΩ):
  The 100nF ceramics go inductive above ~50MHz (ESL=0.5nH → X_L=314mΩ at
  100MHz but parallel combination with many caps reduces effective ESL).
  Adding 10nF or 1nF 0201 caps (lower ESL ~0.2nH) adjacent to BG95 VBAT pins
  would extend the flat impedance region to 100MHz.

--- Pass/Fail Summary ---
  100kHz, 10MHz:  PASS (well below 50mΩ target)
  DC, 1kHz:       CONCERN (110mΩ — physical series R; voltage sag ~220mV @ 2A, within BG95 spec)
  ~12.6MHz:       CONCERN (54.2mΩ anti-resonance peak — add 1µF MLCC to fix)
  100MHz:         CONCERN (52.2mΩ rising — add 10nF 0201 caps to fix)

--- Recommended BOM Additions for Full Compliance ---
  1. Replace reverse-polarity FET with Rds_on ≤ 10mΩ device
  2. Add 1× 4.7µF X5R 0402 MLCC on modem_vbat (LCSC C19666, already in BOM)
  3. Add 2× 10nF 0402 MLCC (ESL~0.2nH) at BG95 VBAT pins for 100MHz coverage
  4. Use shortest possible JST wire (target ≤ 30mm)

ngspice exit code: 0 (success)
================================================================================