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Printed-Circuit-Board Layout Guideline www.ti.com
5. Type in 2944 (mA) in the Charge Current DAC and click Write. This sets the battery charge current
regulation threshold to 2.944A.
Measure → Ibat = 3000 mA ± 300 mA
Measure → V(TP(IOUT)) = 340 mV ± 40 mV
6. Enable the output of the Load #1.
Measure → Isys = 3000 mA ± 300 mA, Ibat = 1600 mA ± 300 mA, Iin = 4100 mA ± 400 mA
Measure → V(TP(IOUT)) = 820 mV ± 100 mV
7. Turn off the Load #1.
Measure → Isys = 0 ± 100 mA, Ibat = 3000 mA ± 300 mA.
2.4.4 Boost Mode – bq24735EVM Only
1. Set ChargeOption() bit [3] to 1, and click Write; this enables turbo boost function.
2. Replace Load #2 with PS#3. Ensure that a voltage meter is connected across J2 (BAT, GND).
3. Enable the output of the PS #3. Ensure that the output voltage is 10 V ± 500 mV.
4. Set the Load#1 load current to 5 A ± 50 mA. Enter boost mode
Measure → I
SYS
= 5000 mA ± 500 mA, I
BAT
= -2000 mA ± 300 mA, I
IN
= 4100 mA ± 400 mA
5. Set the Load#1 load current to 3 A ± 50 mA. Exit boost mode.
Measure → I
SYS
= 3000 mA ± 500 mA, I
BAT
= 1600 mA ± 300 mA, I
IN
= 4100 mA ± 400 mA
2.4.5 Power Path Selection
1. Type in 7801 in the Charge Option, and click Write; this disable charging.
Measure → V(J2(SYS)) = 19.5 V ± 1 V (adapter connected to system)
2. Turn off PS#1. (PS#3 setting per Section 2.4.4, Step 2 and Step 3.
Measure → V(J2(SYS)) = 10 V ± 1 V (battery connected to system)
Measure → V(J2(BAT)) = 10 V ± 1 V (battery connected to system)
3 Printed-Circuit-Board Layout Guideline
The switching node rise and fall times must be minimized for minimum switching loss. Proper layout of the
components to minimize high-frequency, current-path loop is important to prevent electrical and magnetic
field radiation and high-frequency resonant problems. The following is a printed-circuit-board (PCB) layout
priority list for proper layout. Layout of the PCB according to this specific order is essential.
1. Place input capacitor as close as possible to switching MOSFET’s supply and ground connections, and
use the shortest copper trace connection. These parts must be placed on the same layer of the PCB
instead of on different layers and using vias to make this connection.
2. The integrated circuit (IC) must be placed close to the switching MOSFET’s gate terminals and the
gate drive signal traces kept short for a clean MOSFET drive. The IC can be placed on the other side
of the PCB of switching MOSFETs.
3. Place the inductor input terminal as close as possible to the switching MOSFET’s output terminal .
Minimize the copper area of this trace in order to lower electrical and magnetic field radiation, but make
the trace wide enough to carry the charging current. Do not use multiple layers in parallel for this
connection. Minimize parasitic capacitance from this area to any other trace or plane.
4. The charging current-sensing resistor must be placed right next to the inductor output. Route the sense
leads connected across the sensing resistor back to the IC in the same layer, close to each other
(minimize loop area), and do not route the sense leads through a high-current path. Place decoupling
capacitor on these traces next to the IC.
5. Place output capacitor next to the sensing resistor output and ground.
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bq24735/725A Battery Charger Evaluation Module SLUU507A–June 2011–Revised September 2011
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