NICK BRYLSKI

DESIGN CONSIDERATIONS FOR BATTERY

CHARGERS TO ACHIEVE THE BEST USER
EXPERIENCE
Agenda
• Charger basics.
• Stand-alone vs. host-controlled chargers.
• Power-path management.
• Charging accuracy.
• Power consumption.
• Protections.
• Input detection (D+/D–).
• On-the-go (OTG) mode.
• Additional resources to help complete your design.

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Charger basics

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Charging thresholds
Charging fundamentals Typical charging profile

• Battery-charger IC regulates battery voltage

and current.
• Chemistry and capacity determine safe
charging voltages and current.
• Li-ion has distinct pre-charge, fast charge and
taper regions charge.
• Follows a constant-current, constant-voltage
(CC-CV) charging curve.

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Charger topologies
Linear chargers Switch-mode chargers

• Low charge current: <1.5 A. • Higher charge current: >1.0 A.

• Thermal performance depends on VOUT/VIN. • Good thermal performance.

• No EMI concerns. • Switching noise dependent on layout.

• Lower efficiency. • Higher efficiency.

• Typically lower cost. • Typically higher cost.

V
+ VIN Q2
System
IN Battery Q3

Battery
Linear charger Switching charger 5
Stand-alone vs. host-controlled chargers

6
Stand-alone vs. 2
IC (host controlled)
Stand-alone vs. I2C comparison External components

• Stand-alone – configured by passive resistor values:

– For straightforward applications, use our RC-
settable devices.
– Faster development time with no firmware needed.
– Typically less options to configure; limited
diagnostics.
• Host controlled (I2C):
– Wider range of system functionality.
– Configurable charging thresholds, TS ranges.
– Rich status and fault reporting; interrupts.
– ADC-enabled chargers enable continuous current,
voltage, temperature monitoring.
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Power path and VINDPM

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 Power-path management
What is a power path? Power-path charger
• Adapter supplies power through Q1; Q2 controls
charge current.
• Separates charge current path from system current path,
with priority given to system current.
• Suitable topology when powering a system and charging
a battery simultaneously is a requirement.
• System input enables instant system turnon when plugged Non-power-path charger
in, even with a totally discharged battery, enables accurate
termination as charging and system paths are different.
• Non-power-path, system and battery connected in
parallel.
Featured products
BQ25180 | 1-A power-path 1S linear charger BQ25723 | 16-A power-path 1S to 4S buck-boost charger
BQ25170 | 800-mA non-power-path 1S linear charger BQ25303J | 3-A non-power-path 1S buck charger
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Dynamic power-path management (DPPM)
What is DPPM? DPPM functional block diagram

• DPPM monitors the input current, input voltage and

SYS
output currents of a power-path device and
automatically gives priority to the system when the
adapter cannot support system and charging loads.
• The figure shows a DPPM circuit in a linear charger.
The same principle applies for switching chargers.
• DPPM tries to keep SYS above a desired minimum
voltage threshold to keep the system running.
• Allows for system power when the battery has been
▀
deeply discharged (Q3 off).
• Terminates current with higher accuracy than a non-
power-path device where current into the battery is
shared with load.
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Input voltage dynamic power management (VINDPM)
What is VINDPM? How does VINDPM work?

• A VINDPM control loop prevents the adapter voltage

from dropping below the set VINDPM threshold.
• For most adapter types, the adapter output voltage
(VIN to the charger IC) will start to droop as it is
overloaded.
• When the input voltage drops, the device will limit
the input current, while charging can still occur.
• Without VINDPM, the device can enter a “hiccup
mode” if the input source is overloaded (VIN falls to
undervoltage lockout [ULVO] trip level).
• In hiccup mode, user sees charging start and stop
and a reduced charging rate.
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Does VINDPM = DPPM?
• No!
– VINDPM prevents the adapter from hitting a brownout condition through the current-regulating loop.
– A charger can have VINDPM and not have power path (DPPM).
– Charge current and system current are combined, and the charger does not know how much current is
being delivered only to the battery.

• DPPM enables the charger to know exactly how much current is going to the battery.
– With this information, the charger can reduce the charge current and extend the charging safety timer
in the event that the system demands higher currents.

• Which one does your design require?

– For devices that stay plugged into adapter for long periods, power path. Power path ensures that the
adapter exclusively powers the system, reducing battery cycle counts.
– Non-power-path is suitable for low-cost or very-high-current applications.
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 Supplement mode – use case
Using supplement mode Supplement-mode scope capture
• Smartphone plugged in, user
starts playing a game.
• Load step on the SYS rail draws
more current than the adapter
can support.
• VINDPM reduces input current to
prevent VIN from collapsing.
• Supplement mode turns on
wherein the system load is
supplemented by the battery
while still drawing current from
the adapter.

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Charging accuracy

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 Charge voltage accuracy
Impact of charge accuracy Charge accuracy vs. capacity difference
• The higher the charge voltage, the
higher the initial capacity.
• Overcharging can shorten battery
cycle life and at extreme scenarios
can cause thermal runaway. 1% accuracy saves >10% on
• Undercharging results in an battery capacity vs. 2%
underutilization of the battery’s
maximum capacity.
• ±1% charge accuracy helps better
utilize battery capacity while
maintaining lifetime.

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 Charge and termination current accuracy
Impact of charge accuracy Benefits of accurate termination
• High charging accuracy enables a more
consistent user experience across many
devices.
• Lower termination current will charge the
battery closer to full capacity. However, setting
it too low can impact charging duration.
• Good termination accuracy necessary to get
the most out of your battery and deliver a
consistent full capacity being restored.

Featured products • Charged 41-mAh battery at 40-mA fast charge current (1C).
BQ25100 | 250-mA 1-mA termination 1S linear charger
• Termination at 4 mA (10%) or 1 mA.
BQ25618 | 1.5-A 20-mA termination 1S buck charger • Shaded area represents additional 5% capacity restored on each
charge.
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Power consumption

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Low battery leakage
Impact of leakage/IQ

• Low battery quiescent current (IQ) is critical for extending the shelf life of small batteries.

• For further extend the battery shelf life, look for products that support “ship mode” or “shutdown
mode,” where the IQ can be as low as 2 nA.

For a device that uses a 50-mAh battery and must sit in storage, how much capacity is lost?

BAT leakage current 250nA 1 µA 5 µA 10 µA 20 µA 50 µA

Lost battery capacity (mAh )
0.5% 2.2% 10.9% 21.8% 43.7% 100.0%
3-month shelf time
Lost battery capacity (mAh )
1.1% 4.4% 21.8% 43.7% 87.4% 100.0%
Featured products 6-month shelf time
Lost battery capacity (mAh )
2.2% 8.8% 43.8% 87.6% 100.0% 100.0%
BQ25175 | 800-mA 350-nA IQ 1S linear charger 12-month shelf time
BQ25302 | 2-A 200-nA IQ 1S buck charger Table 1: Battery capacity percentage lost for a 50-mA battery for different shelf-life durations
BQ25155 | 500-mA 450-nA IQ 1S linear charger

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 Leakage/IQ – functional modes
IQ modes BQ25155 example
• Many chargers offer multiple power modes
to allow a high level of system
customization: Battery-only mode IQ (typ)
• Ship mode. Minimal circuitry is
powered inside the charger looking for Ship mode 10 nA
a user input. System is off. Best for
devices sitting in storage before Low-power mode 460 nA
reaching the user.
• Low-power mode. Default mode of the
Active battery mode 18 µA
device when the battery is connected.
Limited feature set (no I 2C or ADC).
• Active battery mode. I2C is enabled
for communication with host. ADC
channels enabled.
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Protections

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Safe charging – system protections
Various types of integrated protection features
VBUS VSYS
OVP, ILIM, OCP System AP
Adapter power
thermal regulation, OVP
VINDPM, D+/D– detect, thermal shutdown,
IINDPM, ABS MAX
Charge protection:
poor adapter detection
• Battery short.
BQ battery BAT BAT • Pre-charge.
OTG
• Battery OVP.
(where
chargers • Safety timer.
Portable applicable) • Battery temperature monitoring.
device • Battery undervoltage.
OVP, OCP
Discharge protection:
• Overcurrent.
• Short circuit.

*Note: Pack-side protection is integrated into the battery pack.

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 Protection against voltage transients
Safe charging overview VBUS OVP response – scope capture
• Chargers often directly interface to the adapter cable
and require protection against transient voltage spikes.
• Integrated OVP enables the charger to protect the
system from any spikes at the input without
System
damaging the charger or downstream devices shuts
off
when using low-cost adapters or converters with
poor regulation. Response
• OVP is not the absolute maximum rating; time to turn off
OVP=6.4V
electrical overstress can occur when voltage or
current exceeds absolute maximum ratings.
• Chargers with integrated OVP save board area and
cost.

Featured products
BQ25171-Q1 | 800-mA 40-V absolute maximum 1S linear charger
BQ25798 | 5-A 30-V absolute maximum 1S to 4S buck-boost charger 22
 Battery undervoltage lockout (BUVLO)
What is BUVLO? BUVLO control loop

• In BUVLO, BATFET is off; isolate the SYS from SYS

the battery.
• Turning off BATFET (Q4) when below the Q1 Q2
UVLO threshold prevents deep battery
discharge.
• BUVLO voltage threshold is configurable for Q3
variable applications, typically around 2.2 V to
3.0 V.
• Preventing over discharge increases the
lifespan of the battery. BAT
• Less need for an additional battery-protector Q4
IC.

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 Safety timers
Safety timer modes of operation Safety timer – flow chart

• 10-hour safety timer limits the time during

which the device can be in fast charge mode.
• 30-minute safety timer for pre-charge.
• Prevents continuous charging of a damaged
battery or defective board.
• Safety timer duration doubles during faults that
reduce charging current (VINDPM, TS).
• Configurable by the host on I2C chargers or
through the TMR pin on stand-alone offerings.

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Thermal regulation and protection loops
Thermal management functions Power dissipation
• TREG – regulates the IC junction temperature by
reducing charge current above 125°C.
• TSHUT – turns off the charger when the IC
junction temperature is excessive, >150°C.
• Slow down the safety timers when the charge
current is reduced by the thermal loop, avoiding a
false safety timer fault.

Calculating thermal budget

• Maximum power dissipated in the IC occurs at the

minimum fast charge voltage (usually 2.5 V to 3 V). PLOSS = (VIN – VBAT) × ICHG
• RθJA represents the junction-to-ambient
thermal resistance, available in data sheets
or EVM user’s guides.
TJ = TAMB + RθJA × PLOSS 25
 NTC monitoring
Types of NTC monitoring
• Charging the battery at safe temperatures is very important to improve battery life.
• Charging is allowed at safe temperatures, typically 0 – 60C
• TI chargers have two types of NTC monitoring: current and voltage based

Current-based monitoring Voltage-based monitoring

Internal current source

Bias derived from adapter

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 Battery temperature monitoring – beyond JEITA
Using the charger’s temperature-monitoring capability
• Various applications these days demand operation over wide thermal regions.
• Making BOM changes or adding Rs/Rp to adjust for JEITA is often not possible.
• Using a charger that can support software configurability of cutoffs and actions provides design and
BOM flexibility.

Most chargers: TI chargers with configurable JEITA:

Fixed thresholds Variable thresholds on software
VCOLD
<10°C
VCOLD VCOLD
0-10°C VCOOL VCOOL VCOOL
Full
10-45°C NORMAL NORMAL control
NORMAL
45-60°C VWARM VWARM
>60°C VHOT VHOT VHOT 27
Input detection (D+/D–)

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 What is USB D+/D– detection?
D+/D– detection overview

• Industry standard:
– Used to identify current and communications capability of adapters.
– USB Battery Charging Specification Rev 1.2 (BC1.2) compatibility.
• Why USB D+/D– detection?
– Maximize current potential of adapter.
– More efficient power management.
– Universal charging for convenience.
– Less e-waste.

Featured products
BQ25611D | 3-A 1S buck charger with USB detection
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OTG mode

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OTG boost
OTG overview OTG control loops

• OTG boost saves a switching

converter for power-bank-type
applications.
• Provides an adjustable boost
output voltage.
• Battery temperature monitoring for
safe discharging.
Featured products
BQ25619 | 1.5-A buck charger
BQ25611D | 3-A 1S buck charger

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Chargers – application diagrams

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BQ25171-Q1: Application diagram for lithium-based batteries
Automatic charge cycle control of pre-
Wide input voltage range supports charge, fast-charge and CV modes
1S or 2S charging with 18-V OVP with IPRECHG and ITERM
Abs Max: 40 V 3.0-mm-by-3.0-mm2 QFN 10-pin package Battery OVP and OCP

1s-2s Li-Ion, LiFePO4

VIN: 3.0V – 18V IN OUT
1s-6s NiMH
CHM_TMR programs chemistry and
charge timer: VREF Four-state battery charger
Safety timer disable 1µF 1µF status indicator
56 - 100kΩ 10k
10 hours CHM_TMR STAT1
5 hours

3.3 - 100 kΩ 10k

VSET programmable levels: STAT2
VSET
1S: 2S:
3.5 V 7.0 V 0.375 -
3.6 V 7.2 V 30k 10k NTC
3.7 V 7.4 V ISET TS Battery temperature sensing for
3.8 V safe battery charging with
3.9 V hot/cold profile
4.05 V GND /CE HOST
4.1 V 8.2 V BQ25171-Q1
4.2 V 8.4 V
4.35 V /CE pin for immediate host
Pin-short and pin-open protection control of charger function
Continuously programmable charge-
current pin from 10 mA to 800 mA
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BQ25898 application diagram
100-mA to 3.25-A IINDPM with 50 mA/step

3.9-V to 4-V VINDPM with 100 mV/step

VBUS SYS: 3.5V-4.5V
Input 3.9V-14V SW
Q1
Q2 BTST
USB host or PMID
adapter selection
REGN
PSEL Q3 PGND Integration of power
PHY
path and switching
VOK MOSFETs
SYS
ILIM Q4
BAT Up to 4-A charge current
Input current +
setting /PG BATSEN

STAT /QON Battery

remote
Host SDA sensing
SCL REGN Q4 control (exit
INT ship mode) (full
OTG TS system reset)
/CE

I2C Thermal
interface OTG and PAD Thermistor monitoring
default USB
current 34
Additional resources to help complete
your design

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TI.com charger selection
• TI.com/chargers is a great tool to select the
right charger for your system.
• You can select multiple parameters like
battery chemistry, control topology and
features to meet system requirements.

36
 How to leverage TI to expedite your design process
• TI E2E™ design forums.
• Application-specific system
design pages.
• Reference designs.
• Training videos.
• All accessible from our home
page.

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SLYP818

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