Recalculate values for LP8867 and modify schematic and layout accordingly.

pcb/WhiteLEDs.sch

@@ -132,29 +132,29 @@ Wire Wire Line
 Wire Wire Line
 	2900 3500 1850 3500
 Wire Wire Line
-	1850 3500 1850 3700
+	1850 3500 1850 4500
 $Comp
 L Device:R R12
 U 1 1 6060F6AC
-P 1850 3850
+P 1850 4650
-F 0 "R12" H 1920 3896 50  0000 L CNN
+F 0 "R12" H 1920 4696 50  0000 L CNN
-F 1 "33k" H 1920 3805 50  0000 L CNN
+F 1 "39k" H 1920 4605 50  0000 L CNN
-F 2 "Resistor_SMD:R_0603_1608Metric" V 1780 3850 50  0001 C CNN
+F 2 "Resistor_SMD:R_0603_1608Metric" V 1780 4650 50  0001 C CNN
-F 3 "~" H 1850 3850 50  0001 C CNN
+F 3 "~" H 1850 4650 50  0001 C CNN
-	1    1850 3850
+	1    1850 4650
 	1    0    0    -1  
 $EndComp
 Wire Wire Line
-	1850 4000 1850 4150
+	1850 4800 1850 4950
 $Comp
 L power:GND #PWR0143
 U 1 1 60610BC6
-P 1850 4150
+P 1850 4950
-F 0 "#PWR0143" H 1850 3900 50  0001 C CNN
+F 0 "#PWR0143" H 1850 4700 50  0001 C CNN
-F 1 "GND" H 1855 3977 50  0000 C CNN
+F 1 "GND" H 1855 4777 50  0000 C CNN
-F 2 "" H 1850 4150 50  0001 C CNN
+F 2 "" H 1850 4950 50  0001 C CNN
-F 3 "" H 1850 4150 50  0001 C CNN
+F 3 "" H 1850 4950 50  0001 C CNN
-	1    1850 4150
+	1    1850 4950
 	1    0    0    -1  
 $EndComp
 Wire Wire Line
@@ -194,7 +194,7 @@ L Device:R R11
 U 1 1 6061C45B
 P 1500 3850
 F 0 "R11" H 1430 3804 50  0000 R CNN
-F 1 "147k" H 1430 3895 50  0000 R CNN
+F 1 "56k" H 1430 3895 50  0000 R CNN
 F 2 "Resistor_SMD:R_0603_1608Metric" V 1430 3850 50  0001 C CNN
 F 3 "~" H 1500 3850 50  0001 C CNN
 	1    1500 3850
@@ -223,8 +223,8 @@ L Device:L_Core_Ferrite L2
 U 1 1 60625C92
 P 3350 2400
 F 0 "L2" V 3575 2400 50  0000 C CNN
-F 1 "DE1205-33" V 3484 2400 50  0000 C CNN
+F 1 "DE0704-22" V 3484 2400 50  0000 C CNN
-F 2 "shimatta_inductor:FerroCore_DE1205" H 3350 2400 50  0001 C CNN
+F 2 "shimatta_inductor:FerroCore_DE0704" H 3350 2400 50  0001 C CNN
 F 3 "https://www.tme.eu/Document/d1f8b47d020ebf11f3b92c6891638dfa/de.pdf" H 3350 2400 50  0001 C CNN
 	1    3350 2400
 	0    -1   -1   0   
@@ -345,7 +345,7 @@ L Device:R R10
 U 1 1 6064ADF7
 P 5800 3000
 F 0 "R10" V 5593 3000 50  0000 C CNN
-F 1 "130k" V 5684 3000 50  0000 C CNN
+F 1 "100k" V 5684 3000 50  0000 C CNN
 F 2 "Resistor_SMD:R_0603_1608Metric" V 5730 3000 50  0001 C CNN
 F 3 "~" H 5800 3000 50  0001 C CNN
 	1    5800 3000
@@ -356,7 +356,7 @@ L Device:R R9
 U 1 1 6064B526
 P 5800 2600
 F 0 "R9" V 5593 2600 50  0000 C CNN
-F 1 "680k" V 5684 2600 50  0000 C CNN
+F 1 "560k" V 5684 2600 50  0000 C CNN
 F 2 "Resistor_SMD:R_0603_1608Metric" V 5730 2600 50  0001 C CNN
 F 3 "~" H 5800 2600 50  0001 C CNN
 	1    5800 2600
@@ -389,7 +389,7 @@ L Device:C C57
 U 1 1 60654433
 P 6000 2600
 F 0 "C57" H 6115 2646 50  0000 L CNN
-F 1 "10p" H 6115 2555 50  0000 L CNN
+F 1 "14p" H 6115 2555 50  0000 L CNN
 F 2 "Capacitor_SMD:C_0603_1608Metric" H 6038 2450 50  0001 C CNN
 F 3 "~" H 6000 2600 50  0001 C CNN
 	1    6000 2600
@@ -875,7 +875,7 @@ Wire Wire Line
 Wire Wire Line
 	4300 5650 7350 5650
 Text Notes 7700 2650 0    50   ~ 0
-LEDs: L128-4095HA3500001\nVf: 3V\nIf: ~~70 mA
+LEDs: L128-4095HA3500001\nVf: 3V\nIf: ~~60 mA
 Text Notes 5550 2250 0    50   ~ 0
 V  = ~~ 24V
 Text Notes 5550 2350 0    50   ~ 0
@@ -926,4 +926,12 @@ F 3 "~" H 6650 2000 50  0001 C CNN
 $EndComp
 Wire Wire Line
 	6450 2000 6450 2400
+Text Notes 3250 2100 0    50   ~ 0
+22 uH
+Text Notes 2150 4650 0    50   ~ 0
+Max Current = 60 mA
+Text Notes 850  3900 0    50   ~ 0
+f = 1.08 MHz
+Text Notes 1650 1850 0    50   ~ 0
+For the calculation of the component values see 'lp8867-calc.py'
 $EndSCHEMATC

pcb/lp8867-calc.py

@@ -0,0 +1,98 @@
+#!/bin/python
+
+import numpy as np
+import eseries as es
+
+def calc_fsw_from_r_fset(r_fset):
+    fsw = 67600 / (r_fset / 1e3 + 6.4)
+    fsw = fsw * 1e3
+    return fsw
+
+def calc_r_fset_from_fsw(fsw):
+    fsw = fsw / 1e3
+    r = 67600 / (fsw) - 6.4
+    r = r * 1e3
+    return r
+
+def calc_r_iset_from_i(i):
+    i = i * 1e3
+    r = 2000 * 1.2 / i
+    r = r * 1e3
+    return r
+def calc_i_from_r_iset(r):
+    r = r * 1e-3
+    i = 2000 * 1.2 / r
+    i = i * 1e-3
+    return i
+
+def calc_vout(r1, r2, k):
+    r1 = r1 / 1000
+    r2 = r2 / 1000
+    v = (1.2 / r2 + k * 0.0387) * r1 + 1.2
+    return v
+
+switching_freq = 1.1e6
+output_voltage_nom = 24 + 0.9
+inductor_value = 22e-6
+input_voltage = 12
+output_current_per_lane = 60e-3
+desired_e_series = es.E12
+r1 = 560e3
+r2 = 100e3
+
+# Calculate the parameters
+print('Calculating for the given parameters:')
+print(f'{switching_freq = }')
+print(f'{output_voltage_nom = } and {input_voltage = }')
+print(f'{inductor_value =}')
+print(f'{desired_e_series = }')
+print('')
+
+rfset = calc_r_fset_from_fsw(switching_freq)
+print(f'{rfset = }')
+
+# Find the nearest value in the e series
+rfset = es.find_nearest(desired_e_series, rfset)
+f_sw = calc_fsw_from_r_fset(rfset)
+
+print(f'The nearest value from the E series is: {rfset = }')
+freq_error = (f_sw - switching_freq) / switching_freq * 100
+print(f'Resulting switching frequency is {f_sw} (Error: {freq_error:.1f} %)')
+
+print(f"Desired output current per lane is {output_current_per_lane} A")
+r_iset = calc_r_iset_from_i(output_current_per_lane)
+print(f'Resulting in {r_iset = }')
+r_iset = es.find_nearest(desired_e_series, r_iset)
+output_current_per_lane = calc_i_from_r_iset(r_iset)
+print(f'Nearest e series value {r_iset = } resulting in an LED current of {output_current_per_lane} A')
+
+d = (output_voltage_nom - input_voltage) / output_voltage_nom
+d_inv = 1-d
+print(f"Expected duty cycle: {d}")
+i_ripple = (output_voltage_nom- input_voltage) / (2 * inductor_value * f_sw) * (input_voltage / output_voltage_nom)
+print(f'Ripple current: {i_ripple} A')
+i_sat_min = output_current_per_lane * 4 / d_inv + i_ripple
+print(f'Minimum saturation current of inductor: {i_sat_min:.3f} A')
+
+print(f'Voltage divider {r1 = } | {r2 = }')
+print(f'Output voltage initial: {calc_vout(r1, r2, 0.88)} V')
+print(f'Output voltage maximum: {calc_vout(r1, r2, 1)} V')
+print(f'Output voltage minimum: {calc_vout(r1, r2, 0)} V')
+
+ovp = output_voltage_nom + (r1/r2 + 1)*(2.3 - 1.2)
+
+print(f'Over voltage protection: {ovp} V')
+
+ratio = r1/r2
+print(f'Resistance ratio is {ratio}')
+if f_sw <= 1150e3:
+    ratio_range = (5, 10)
+else:
+    ratio_range = (10, 20)
+
+if ratio < ratio_range[0] or ratio > ratio_range[1]:
+    print('Ratio is outside recommended limits!')
+
+# Loop stability
+cfb = 1 / (2 * np.pi * 20e3 * r1 )
+print(f'Loop stability capacitor value: {cfb} F')