BQ25700A Datasheet, PDF (68/82 Pages) Texas Instruments – SMBus Multi-Chemistry Battery Buck-Boost Charge Controller With System Power Monitor and Processor Hot Monitor

bq25700A
SLUSCQ8 – MAY 2017
www.ti.com
I_on
=
V_REGN - V_{plt ,}
R_on
I_off
=
V_plt
R_off
(10)
The conduction loss of the bottom-side MOSFET is calculated with the following equation when it operates in
synchronous continuous conduction mode:
P_bottom = (1 - D) x I_CHG ² x R_DS(on)
(11)
When charger operates in non-synchronous mode, the bottom-side MOSFET is off. As a result all the
freewheeling current goes through the body-diode of the bottom-side MOSFET. The body diode power loss
depends on its forward voltage drop (V_F), non-synchronous mode charging current (I_NONSYNC), and duty cycle (D).
P_D = V_F x I_NONSYNC x (1 - D)
(12)
The maximum charging current in non-synchronous mode can be up to 0.25 A for a 10-mΩ charging current
sensing resistor or 0.5 A if battery voltage is below 2.5 V. The minimum duty cycle happens at lowest battery
voltage. Choose the bottom-side MOSFET with either an internal Schottky or body diode capable of carrying the
maximum non-synchronous mode charging current.
9.2.3 Application Curves
CH1: VBUS
CH2: VDDA
CH3: CHRG_OK
CH4: VSYS
2-cell without battery
Figure 43. Power Up from 20 V
CH1: VBUS
CH2: SW1
CH3: SW2
CH4: IL
3-cell VBAT = 10 V
Figure 45. Power Off from 12 V
CH1: VBUS
CH2: VDDA
CH3: CHRG_OK
CH4: VSYS
2-cell without battery
Figure 44. Power Up from 5 V
CH1: VBUS
CH2: SW1
CH3: SW2
CH4: VSYS with 9Vos
VBUS 5 V to 20 V
Figure 46. System Regulation
68
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