WikiSysop at 22:17, 7 August 2015

2015-08-07T22:17:14Z

← Older revision		Revision as of 22:17, 7 August 2015
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	[[File:Boost_Chrg_Brd.png\|thumb\|right\|Figure 2: PCB Layout for the Boost Converter/LiPo Charger Test Board.]]		[[File:Boost_Chrg_Brd.png\|thumb\|right\|Figure 2: PCB Layout for the Boost Converter/LiPo Charger Test Board.]]

	The TPS61085, made by TI, is a 650kHz/1.2MHz boost converter capable of boosting an input voltage of 2.3-6V up to an output of 18.5V, with a 2A switch current. <ref>Texas Instruments Inc., "TPS61085 650 kHz/1.2 MHz, 18.5 V Step-Up DC-DC Converter," June 2008. [Online]. Available: http://www.ti.com/lit/ds/symlink/tps61085.pdf. [Accessed 5 February 2012].</ref> This device will be used to produce the 9V required by the lithium polymer (LiPo) charging IC from the 5V provided by a standard USB port or 5V regulated wall adapter. The ~~MC73844~~ is a dual-cell LiPo charge management controller, providing an adjustable charge current via an external sense resistor and P-Channel MOSFET. The IC can precondition cells that have dropped below 2.85V per cell, after which a constant current/constant voltage charge cycle begins.<ref>Microchip Technology Inc., "MCP73841/2/3/4 Advanced Single or Dual Cell Lithium-Ion/Lithium-Polymer Charge Management Controllers," 2004. [Online]. Available: http://ww1.microchip.com/downloads/en/DeviceDoc/21823c.pdf. [Accessed 5 February 2012].</ref> The test board provides all the necessary support components for the TPS61085 and MCP73844, including the datasheet suggested components for a 5V to 9V step up, and an external MOSFET and sense resistor, specifying a charge current of 220mA, selected for the maximum charge current given the boost converter’s efficiency and maximum USB port supply current of 500mA. <ref name="usb">R. Kollman, "Power electronics from the USB port," 2002. [Online]. Available: http://www.ti.com/lit/an/slyt118/slyt118.pdf. [Accessed 5 February 2012].</ref> The charge current was selected using the following formulas:		The TPS61085, made by TI, is a 650kHz/1.2MHz boost converter capable of boosting an input voltage of 2.3-6V up to an output of 18.5V, with a 2A switch current. <ref>Texas Instruments Inc., "TPS61085 650 kHz/1.2 MHz, 18.5 V Step-Up DC-DC Converter," June 2008. [Online]. Available: http://www.ti.com/lit/ds/symlink/tps61085.pdf. [Accessed 5 February 2012].</ref> This device will be used to produce the 9V required by the lithium polymer (LiPo) charging IC from the 5V provided by a standard USB port or 5V regulated wall adapter. The MCP73844 is a dual-cell LiPo charge management controller, providing an adjustable charge current via an external sense resistor and P-Channel MOSFET. The IC can precondition cells that have dropped below 2.85V per cell, after which a constant current/constant voltage charge cycle begins.<ref>Microchip Technology Inc., "MCP73841/2/3/4 Advanced Single or Dual Cell Lithium-Ion/Lithium-Polymer Charge Management Controllers," 2004. [Online]. Available: http://ww1.microchip.com/downloads/en/DeviceDoc/21823c.pdf. [Accessed 5 February 2012].</ref> The test board provides all the necessary support components for the TPS61085 and MCP73844, including the datasheet suggested components for a 5V to 9V step up, and an external MOSFET and sense resistor, specifying a charge current of 220mA, selected for the maximum charge current given the boost converter’s efficiency and maximum USB port supply current of 500mA. <ref name="usb">R. Kollman, "Power electronics from the USB port," 2002. [Online]. Available: http://www.ti.com/lit/an/slyt118/slyt118.pdf. [Accessed 5 February 2012].</ref> The charge current was selected using the following formulas:

	<math>\large P_{in}\cdot \eta = P_{out}</math>		<math>\large P_{in}\cdot \eta = P_{out}</math>

WikiSysop: Created page with "==Summary== Figure 1: Schematic for the Boost Converter/LiPo Charger Test Board. File:Boost_Chrg_Brd.png|thumb|right|Figure 2: PCB La..."

2015-08-07T00:43:58Z

New page

==Summary==
[[File:Boost_Chrg_Sch.png|thumb|right|Figure 1: Schematic for the Boost Converter/LiPo Charger Test Board.]]
[[File:Boost_Chrg_Brd.png|thumb|right|Figure 2: PCB Layout for the Boost Converter/LiPo Charger Test Board.]]

The TPS61085, made by TI, is a 650kHz/1.2MHz boost converter capable of boosting an input voltage of 2.3-6V up to an output of 18.5V, with a 2A switch current. <ref>Texas Instruments Inc., "TPS61085 650 kHz/1.2 MHz, 18.5 V Step-Up DC-DC Converter," June 2008. [Online]. Available: http://www.ti.com/lit/ds/symlink/tps61085.pdf. [Accessed 5 February 2012].</ref> This device will be used to produce the 9V required by the lithium polymer (LiPo) charging IC from the 5V provided by a standard USB port or 5V regulated wall adapter. The MC73844 is a dual-cell LiPo charge management controller, providing an adjustable charge current via an external sense resistor and P-Channel MOSFET. The IC can precondition cells that have dropped below 2.85V per cell, after which a constant current/constant voltage charge cycle begins.<ref>Microchip Technology Inc., "MCP73841/2/3/4 Advanced Single or Dual Cell Lithium-Ion/Lithium-Polymer Charge Management Controllers," 2004. [Online]. Available: http://ww1.microchip.com/downloads/en/DeviceDoc/21823c.pdf. [Accessed 5 February 2012].</ref> The test board provides all the necessary support components for the TPS61085 and MCP73844, including the datasheet suggested components for a 5V to 9V step up, and an external MOSFET and sense resistor, specifying a charge current of 220mA, selected for the maximum charge current given the boost converter’s efficiency and maximum USB port supply current of 500mA. <ref name="usb">R. Kollman, "Power electronics from the USB port," 2002. [Online]. Available: http://www.ti.com/lit/an/slyt118/slyt118.pdf. [Accessed 5 February 2012].</ref> The charge current was selected using the following formulas:

<math>\large P_{in}\cdot \eta = P_{out}</math>

Where <math>\eta</math> is the switching regulator efficiency, approximately 85% at 220mA load.

<math>\large P_{in} = I_{in}\cdot V_{in}</math>

<math>\large P_{out} = I_{out}\cdot V_{out}</math>

<math>\large I_{out}=\frac{I_{in}\cdot V_{in}\cdot \eta}{V_{out}}</math>

Thus, given a 500mA 5V supply, the maximum output current at 9V is approximately 240mA.

The schematic for this test board is shown in Figure 1, and the board is shown in Figure 2.

The schematic, layout and Gerber files can be downloaded here: http://www.rev0proto.com/files/BoostConv_2SCharger.zip

==Testing==
* '''Output Voltage''' = 9.009V
* '''Charge Current''' = 212.3mA
* '''Charge Termination Voltage''' = 8.382V
* '''Output Power''' = 1.913W
* '''Input Voltage''' = 4.974V
* '''Input Current''' = 437.5mA
* '''Input Power''' = 2.176W
* '''Efficiency''' = 87.9%
* '''Heat Power''' = 263mW
* '''Reverse Leakage Current (Charger disabled)''' = 0.2uA
* '''Reverse Leakage Current (Charger unpowered)''' = 895uA

The results show that the charger and boost converter produce the necessary voltages to function (within 0.2%), and maintain a current draw of less than 500mA at the full charge current, as required by USB.<ref name="usb">R. Kollman, "Power electronics from the USB port," 2002. [Online]. Available: http://www.ti.com/lit/an/slyt118/slyt118.pdf. [Accessed 5 February 2012].</ref> Additionally, the reverse leakage current is negligible; a concern for battery drain when in use and when the device is off. The device has a very high efficiency of 87.9%, so little power is wasted as heat.

==Bill of Materials==

{| border="1"
|style="text-align:center;" |'''Part'''
|style="text-align:center;" |'''Quantity'''
|style="text-align:center;" |'''Unit Cost'''
|style="text-align:center;" |'''Total Cost'''
|style="text-align:center;" |'''Source'''
|-

|TPS61085DGKT
|1
|style="text-align:right;" |$3.30
|style="text-align:right;" |$3.30
|[http://search.digikey.com/us/en/products/TPS61085DGKT/296-23550-1-ND/1880953 Digi-Key]
|-

|MCP73844-840I/MS
|1
|style="text-align:right;" |$1.56
|style="text-align:right;" |$1.56
|[http://search.digikey.com/us/en/products/MCP73844-840I%2FMS/MCP73844-840I%2FMS-ND/593751 Digi-Key]
|-

|0603 Capacitor
|3
|style="text-align:right;" |$0.0096
|style="text-align:right;" |$0.03
|[http://myworld.ebay.com/mib_instruments eBay - mib_instruments]
|-

|0603 Resistor
|5
|style="text-align:right;" |$0.00294
|style="text-align:right;" |$0.02
|[http://myworld.ebay.com/mib_instruments eBay - mib_instruments]
|-

|1206 10uF Capacitor
|4
|style="text-align:right;" |$0.297
|style="text-align:right;" |$1.19
|[http://search.digikey.com/us/en/products/C2012X5R1C106K%2F0.85/445-7644-1-ND/2733716 Digi-Key]
|-

|PMEG3020ER
|1
|style="text-align:right;" |$0.48
|style="text-align:right;" |$0.48
|[http://search.digikey.com/us/en/products/PMEG3020ER,115/568-6518-1-ND/2531805 Digi-Key]
|-

|STS5PF20V
|1
|style="text-align:right;" |$0.24
|style="text-align:right;" |$0.24
|[http://search.digikey.com/us/en/products/STS5PF20V/497-3230-1-ND/654591 Digi-Key]
|-

|0603 Green LED
|1
|style="text-align:right;" |$0.11
|style="text-align:right;" |$0.11
|[http://search.digikey.com/us/en/products/LG%20Q971-KN-1/475-1409-1-ND/1802597 Digi-Key]
|-

|SDR0302-3R3ML
|1
|style="text-align:right;" |$0.42
|style="text-align:right;" |$0.42
|[http://search.digikey.com/us/en/products/SDR0302-3R3ML/SDR0302-3R3MLCT-ND/2127069 Digi-Key]
|-

|Male Header
|3
|style="text-align:right;" |$0.01
|style="text-align:right;" |$0.03
|[http://www.ebay.com/ eBay]
|-

|PCB
|1.225"x0.5125"/3
|style="text-align:right;" |$5.00
|style="text-align:right;" |$1.05
|[http://dorkbotpdx.org/wiki/pcb_order Laen's PCB]
|-

|'''Total Unit Cost'''
|
|
|style="text-align:right;" |'''$8.43'''
|
|-
|}

==PCB/Construction Photos==
<gallery perrow=3 widths=240px heights=120px>
File:Boost_Chrg_PCB_Bottom.jpg|Bottom of unpopulated PCB
File:Boost_Chrg_PCB_Top.jpg|Top of unpopulated PCB
File:Boost_Chrg_Top.jpg|Populated PCB
</gallery>

==References==
<references/>

Boost Converter LiPo Charger - Revision history

WikiSysop at 22:17, 7 August 2015

WikiSysop: Created page with "==Summary== Figure 1: Schematic for the Boost Converter/LiPo Charger Test Board. File:Boost_Chrg_Brd.png|thumb|right|Figure 2: PCB La..."