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BLF driver GT-buck [rev 04][tried and tested]

author: DEL
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2 layer board of 1.82 x 1.82 inches (46.2 x 46.2 mm)
Uploaded: September 26, 2017
Shared: December 08, 2017
Total Price: $16.50

This is the driver used in the production version of the BLF GT light.

[Bunny logo is the property of Lumintop, manufacturer of the GT]

Features

  • 2.5 A buck regulator with constant current output
  • Attiny85 MCU, supported by NarsilM 1.2 and up firmware
  • Most BLF ‘1-channel’ and ‘2-channel’ firmware can be made to work with a few simple changes
  • 0.4 V dropout voltage, <150 μA parasitic drain
  • Support for button indicator light

Revision changes

  • 00 - driver prototype
  • 01 - cosmetic changes
  • 02 - adapted to the prototype 1 hosts and cell cradles (dedicated ground ring)
  • 03 - copper added back to retaining ring area
  • 04 - adapted to the production version hosts and cell cradles (retaining ring for ground)

Suggested parts list

Part no. Value Type Package
C1 1u X7R, 25 V C0603
C2 3.3u - 10u X5R, 16 V C0805
C4 1u X7R, 25 V C0603
C11 4u7 X7R, 50 V C1206
C12 4u7 X7R, 50 V C1206
C13 4u7 X7R, 50 V C1206
C14 4u7 X7R, 50 V C1206
C15 470p C0G, 50 V C0603
C16 1u X7R, 25 V C0603
C17 4u7 X7R, 50 V C1206
D1 SS34 Schottky, 40 V, 3 A SMC/DO-214AB
L1 10u Bourns SRR1208-100ML 12x12x8 mm
Q1 AOD417 P-chan <50 mohm <20 nC TO252 / DPAK
R1 1M 1% R0603
R2 47k 1% R0603
R3 10R 1% R0603
R4 10k 1% R0603
R5 3k3 1% R0603
R6 n/p
R7 1k 1% R0603
R8 33k 1% R0603
R11 0R091 1%, <300 ppm/C, 1-3 W R2512
R12 47k 1% R0603
R13 n/p
R14 4k7 1% R0603
U1 ATTINY85-20SU SOIC-8
U2 MIC5235-5 5 V LDO regulator SOT23-5
U3 LM3409 Buck controller HVSSOP-10

Output current range is determined by the R4/R5 ratio and the sense resistor (R11) value. R4/R5 could be used to lower the current, but to increase the current R11 should be adjusted:

  • Iout = 0.248 / R11 - 0.15
  • or R11 = 0.248 / (Iout + 0.15)

(the 0.15 offset is determined by the inductor ripple current and will change if the inductor value or switching frequency is modified)

alt text

This is the driver used in the production version of the BLF GT light.

[Bunny logo is the property of Lumintop, manufacturer of the GT]

Features

  • 2.5 A buck regulator with constant current output
  • Attiny85 MCU, supported by NarsilM 1.2 and up firmware
  • Most BLF ‘1-channel’ and ‘2-channel’ firmware can be made to work with a few simple changes
  • 0.4 V dropout voltage, <150 μA parasitic drain
  • Support for button indicator light

Revision changes

  • 00 - driver prototype
  • 01 - cosmetic changes
  • 02 - adapted to the prototype 1 hosts and cell cradles (dedicated ground ring)
  • 03 - copper added back to retaining ring area
  • 04 - adapted to the production version hosts and cell cradles (retaining ring for ground)

Suggested parts list

Part no. Value Type Package
C1 1u X7R, 25 V C0603
C2 3.3u - 10u X5R, 16 V C0805
C4 1u X7R, 25 V C0603
C11 4u7 X7R, 50 V C1206
C12 4u7 X7R, 50 V C1206
C13 4u7 X7R, 50 V C1206
C14 4u7 X7R, 50 V C1206
C15 470p C0G, 50 V C0603
C16 1u X7R, 25 V C0603
C17 4u7 X7R, 50 V C1206
D1 SS34 Schottky, 40 V, 3 A SMC/DO-214AB
L1 10u Bourns SRR1208-100ML 12x12x8 mm
Q1 AOD417 P-chan <50 mohm <20 nC TO252 / DPAK
R1 1M 1% R0603
R2 47k 1% R0603
R3 10R 1% R0603
R4 10k 1% R0603
R5 3k3 1% R0603
R6 n/p
R7 1k 1% R0603
R8 33k 1% R0603
R11 0R091 1%, <300 ppm/C, 1-3 W R2512
R12 47k 1% R0603
R13 n/p
R14 4k7 1% R0603
U1 ATTINY85-20SU SOIC-8
U2 MIC5235-5 5 V LDO regulator SOT23-5
U3 LM3409 Buck controller HVSSOP-10

Output current range is determined by the R4/R5 ratio and the sense resistor (R11) value. R4/R5 could be used to lower the current, but to increase the current R11 should be adjusted:

  • Iout = 0.248 / R11 - 0.15
  • or R11 = 0.248 / (Iout + 0.15)

(the 0.15 offset is determined by the inductor ripple current and will change if the inductor value or switching frequency is modified)

alt text

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