SLUSEK7 September 2024 BQ25773
PRODUCTION DATA
Refer to the PDF data sheet for device specific package drawings
The BQ25773 has two selectable fixed switching frequency 600 kHz/800 kHz. Higher switching frequency allows the use of smaller inductance. Inductor saturation current should be higher than the charging current (ICHG) plus half the ripple current (IRIPPLE):
The inductor ripple current in buck operation depends on input voltage (VIN), duty cycle (DBUCK = VOUT/VIN), switching frequency (fS) and inductance (L):
During boost operation, the duty cycle is:
DBOOST = 1 – (VIN/VBAT)
and the ripple current is:
IRIPPLE_BOOST = (VIN × DBOOST) / (fS × L)
The maximum inductor ripple current happens with D = 0.5 or close to 0.5. For example, the battery charging voltage range is from 12 V to 16.8 V for 4-cell battery pack. For 28-V adapter voltage, 14-V battery voltage gives the maximum inductor ripple current.
The recommended inductor DCR range is 5 mΩ ~ 25 mΩ for each phase. Inductor DCR beyond this range may hold system stability risk which is not recommended. Upon different switching frequency and VBUS input voltage recommended inductance are summarized in Table 8-6. Inductance lower than the recommendation could result in large inductor ripple and high inductor core loss which is not preferred.
VBUS = 20 V | VBUS = 28 V | VBUS = 36 V | |
---|---|---|---|
Fsw=600 kHz | 2.2 μH | 2.2 μH | 3.3 μH |
Fsw=800 kHz | 1.5 μH | 1.5 μH | 2.2 μH |