Wearable Electronics
Figure 2. Autonomous headroom tracking for a typical lithium-ion battery charge cycle. Continues from page 44
applications also stand to benefit from a technology called autonomous headroom tracking, which minimises the voltage dropped over the battery charging circuitry while providing optimal headroom to regulate the charge current. This reduces power loss and heat dissipation in the charging circuit without requiring additional components, which results in a wearable device that stays cool while charging and can even be allowed to charge faster. The MAX77659 is a SIMO PMIC designed to improve efficiency and reduce the system board space and BOM size in wearable consumer and medical devices. This PMIC has three buck-boost outputs with efficiency
up to 90 per cent all utilising the same inductor. It also includes an additional low dropout (LDO) regulator for sensitive applications requiring high power supply rejection ratio (PSRR), such as VSM. Furthermore, the SIMO architecture has intrinsic benefits in terms of efficiency, and it can provide ultralow quiescent current at minimal solution size.
The MAX77659’s autonomous headroom tracking uses one of the SIMO outputs to minimise the voltage drop over the battery charging transistor while providing optimal headroom to regulate the charge current. The result is reduced power loss across the transistor and reduced heat dissipation, all without requiring additional components.
Figure 4. The MAXREFDES1323 reference design board.
A visualisation of autonomous headroom tracking throughout the fast-charging process is provided in Figure 2.
MAX77659 reference design The reference design shown in Figure 3 compares the MAX77659 SIMO PMIC solution against a typical linear charging solution. Since the MAX77659 SIMO PMIC includes autonomous headroom tracking,
the buck-boost regulator used in traditional solutions (Figure 3, Cradle B) can be omitted (Figure 3, Cradle A). This improves the overall system battery life by increasing charging efficiency while reducing solution size and BOM cost.
Figure 4 shows the full PCB for the MAX77659 reference design. The design includes two pairs of cradle/earbud solutions - one utilises the MAX77659 SIMO PMIC design (Cradle/Earbud A), while the other follows the typical linear charger design (Cradle/Earbud B), using a MAX77734 linear charger. Push-buttons on the base board toggle charging for both the A and B branches, and an OLED display shows the charge current and temperature measured from the earbud’s MAX17260 fuel gauges. The screen also displays the charger status, which shows when the charger must reduce charge current because of overheating.
Battery management system charging standards
Figure 3. A block diagram for a reference design comparing the proposed solution and a traditional solution for TWS earbuds. 46 July/August 2024 Components in Electronics
The Japan Electronics and Information Technology Industries Association (JEITA) publish standards related to battery management systems that provide rigorous and robust methods to promote system safety and reliability for the end user by reducing system and battery wear. It is common for end applications to utilise integrated JEITA protection features that reduce charge current and voltage levels during the constant current (CC) and constant voltage (CV) phases of battery
www.cieonline.co.uk
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64
