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BQ25504
SLUSAH0F – OCTOBER 2011 – REVISED NOVEMBER 2019
BQ25504 Ultra Low-Power Boost Converter With Battery Management For Energy
Harvester Applications
1 Features
3 Description
•
The BQ25504 device is the first of a new family of
intelligent integrated energy harvesting nano-power
management solutions that are well suited for
meeting the special needs of ultra low power
applications. The device is specifically designed to
efficiently acquire and manage the microwatts (µW)
to miliwatts (mW) of power generated from a variety
of DC sources like photovoltaic (solar) or thermal
electric generators. The BQ25504 is the first device
of its kind to implement a highly efficient boost
converter/charger targeted toward products and
systems, such as wireless sensor networks (WSNs)
which have stringent power and operational
demands. The design of the BQ25504 starts with a
DC-DC boost converter/charger that requires only
microwatts of power to begin operating.
1
•
•
•
•
Ultra low-power with high-efficiency DC-DC boost
converter/charger
– Continuous energy harvesting from low-input
sources: VIN ≥ 130 mV (Typical)
– Ultra-low quiescent current: IQ < 330 nA
(Typical)
– Cold-start voltage: VIN ≥ 600 mV (typical)
Programmable dynamic maximum power point
tracking (MPPT)
– Integrated dynamic maximum power point
tracking for optimal energy extraction from a
variety of energy generation sources
– Input voltage regulation prevents collapsing
input source
Energy storage
– Energy can be stored to rechargeable li-ion
batteries, thin-film batteries, super-capacitors,
or conventional capacitors
Battery charging and protection
– User Programmable undervoltage and
overvoltage levels
– On-chip temperature sensor with
programmable overtemperature shutoff
Battery status output
– Battery good output pin
– Programmable threshold and hysteresis
– Warn attached microcontrollers of pending loss
of power
– Can be used to enable or disable system loads
2 Applications
•
•
•
•
•
•
•
•
•
•
Energy harvesting
Solar chargers
Thermal electric generator (TEG) harvesting
Wireless sensor networks (WSNs)
Industrial monitoring
Environmental monitoring
Bridge and structural health monitoring (SHM)
Smart building controls
Portable and wearable health devices
Entertainment system remote controls
Once started, the boost converter/charger can
effectively extract power from low-voltage output
harvesters such as thermoelectric generators (TEGs)
or single- or dual-cell solar panels. The boost
converter can be started with VIN as low as 600 mV,
and once started, can continue to harvest energy
down to VIN = 130 mV.
Device Information(1)
PART NUMBER
BQ25504
PACKAGE
BODY SIZE (NOM)
VQFN (16)
3.00 mm x 3.00 mm
(1) For all available packages, see the orderable addendum at
the end of the datasheet.
Solar Application Circuit
LBST
CFLTR
CSTOR
Battery
CHVR
Solar
Cell
SYSTEM
LOAD
VSTOR
+
-
16
15
LBST
VSTOR
`
14
13
VBAT
VSS
1
VSS
2
VIN_DC
3
VOC_SAMP
OK_PROG
10
VREF_SAMP
OK_HYST
9
AVSS
12
VBAT_OK
11
bq25504
ROC 2
ROC 1
VBAT_OK
CREF
ROK1
ROK2
4
OT_PROG VBAT_OV VRDIV VBAT_UV
5
6
7
ROK3
8
ROV2
RUV 2
ROV1
RUV 1
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
BQ25504
SLUSAH0F – OCTOBER 2011 – REVISED NOVEMBER 2019
www.ti.com
Table of Contents
1
2
3
4
5
6
7
8
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Description (continued).........................................
Pin Configuration and Functions .........................
Specifications.........................................................
1
1
1
2
4
5
6
7.1
7.2
7.3
7.4
7.5
7.6
6
6
6
7
7
9
Absolute Maximum Ratings .....................................
ESD Ratings..............................................................
Recommended Operating Conditions.......................
Thermal Information ..................................................
Electrical Characteristics...........................................
Typical Characteristics ..............................................
Detailed Description ............................................ 11
8.1
8.2
8.3
8.4
Overview .................................................................
Functional Block Diagram .......................................
Feature Description.................................................
Device Functional Modes........................................
11
12
12
15
9
Application and Implementation ........................ 18
9.1 Application Information............................................ 18
9.2 Typical Applications ................................................ 20
10 Power Supply Recommendations ..................... 27
11 Layout................................................................... 27
11.1 Layout Guidelines ................................................. 27
11.2 Layout Example .................................................... 28
11.3 Thermal Considerations ........................................ 28
12 Device and Documentation Support ................. 29
12.1
12.2
12.3
12.4
12.5
12.6
12.7
Device Support......................................................
Documentation Support ........................................
Receiving Notification of Documentation Updates
Support Resources ...............................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
29
29
29
29
29
29
29
13 Mechanical, Packaging, and Orderable
Information ........................................................... 29
4 Revision History
Changes from Revision E (March 2019) to Revision F
•
Page
Deleted Not Recommended for New Designs ....................................................................................................................... 1
Changes from Revision D (December 2018) to Revision E
Page
•
Changed Feature From: VIN ≥ 80 mV (Typical) To: VIN ≥ 130 mV (Typical) .......................................................................... 1
•
Changed From: VIN as low as 330 mV To: VIN as low as 600 mV in the Description ............................................................ 1
•
Changed From: "harvest energy down to VIN = 80 mV." To: "harvest energy down to VIN = 130 mV." in the Description.... 1
•
Changed From: "330 mV typical,.." To: "600 mV typical,.." in the second paragraph of the Overview section ................... 11
•
Changed Figure 11 .............................................................................................................................................................. 14
•
Changed From: "VIN(CS) = 330 mV typical." To: "VIN(CS) = 600 mV typical." in the second paragraph of the ColdStart Operation section......................................................................................................................................................... 16
Changes from Revision C (June 2015) to Revision D
Page
•
Changed Feature From: Cold-Start Voltage: VIN ≥ 330 mV (Typical) To: Cold-Start Voltage: VIN ≥ 600 mV (Typical) ........ 1
•
Changed the RGT Package appearance .............................................................................................................................. 5
•
Moved Tstg to the Absolute Maximum Ratings table............................................................................................................... 6
•
Changed Handling Ratings To: ESD Ratings......................................................................................................................... 6
•
Increased VIN(CS) From: TYP = 330 mV and MAX = 450 mV To: TYP = 600 mV and MAX = 700 mV in Electrical
Characteristics table ............................................................................................................................................................... 7
Changes from Revision B (December 2014) to Revision C
Page
•
Changed the Test Condition for PIN(CS) in the Electrical Characteristics ............................................................................... 7
•
Changed the values for PIN(CS) in the Electrical Characteristics From: TYP = 10, MAX = 50 To: TYP = 15, MAX
deleted ................................................................................................................................................................................... 7
•
Changed CFLTR To: CBYP Figure 14 ..................................................................................................................................... 20
2
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•
Changed CBYP = 0.1 µF To: CBYP = 0.01 µF in Detailed Design Procedure .................................................................... 20
•
Changed CFLTR To: CBYP in Figure 21 .................................................................................................................................. 23
•
Changed CBYP = 0.1 µF To: CBYP = 0.01 µF in Detailed Design Procedure .................................................................... 23
•
Changed CFLTR To: CBYP in Figure 28 ................................................................................................................................. 25
•
Changed CBYP = 0.1 µF To: CBYP = 0.01 µF in Detailed Design Procedure .................................................................... 25
•
Changed Figure 34 .............................................................................................................................................................. 28
Changes from Revision A (September 2012) to Revision B
•
Page
Added Handling Rating table, Feature Description section, Device Functional Modes, Application and
Implementation section, Power Supply Recommendations section, Layout section, Device and Documentation
Support section, and Mechanical, Packaging, and Orderable Information section................................................................ 1
Changes from Original (October 2011) to Revision A
Page
•
Added the INTENDED OPERATION section ....................................................................................................................... 11
•
Changed the Cold -Start Operation section ......................................................................................................................... 15
•
Changed the Boost Converter, Charger Operation section.................................................................................................. 16
•
Changed the Storage Element section................................................................................................................................. 16
•
Changed the CAPACITOR SELECTION section ................................................................................................................. 19
•
Added CFLTR and Notes 1 and 2 to Figure 14 ..................................................................................................................... 20
•
Added CFLTR and Notes 1 and 2 to Figure 21 ..................................................................................................................... 23
•
Added CFLTR and Notes 1 and 2 to Figure 28 ..................................................................................................................... 25
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SLUSAH0F – OCTOBER 2011 – REVISED NOVEMBER 2019
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5 Description (continued)
The BQ25504 also implements a programmable maximum power point tracking sampling network to optimize the
transfer of power into the device. Sampling the VIN_DC open-circuit voltage is programmed using external
resistors, and held with an external capacitor (CREF).
For example solar cells that operate at maximum power point (MPP) of 80% of their open-circuit voltage, the
resistor divider can be set to 80% of the VIN_DC voltage and the network will control the VIN_DC to operate
near that sampled reference voltage. Alternatively, an external reference voltage can be provide by a MCU to
produce a more complex MPPT algorithm.
The BQ25504 was designed with the flexibility to support a variety of energy storage elements. The availability of
the sources from which harvesters extract their energy can often be sporadic or time-varying. Systems will
typically need some type of energy storage element, such as a rechargeable battery, super capacitor, or
conventional capacitor. The storage element ensures that constant power is available when needed for the
systems. The storage element also allows the system to handle any peak currents that cannot directly come from
the input source.
To prevent damage to a customer’s storage element, both maximum and minimum voltages are monitored
against the user programmed undervoltage (UV) and overvoltage (OV) levels.
To further assist users in the strict management of their energy budgets, the BQ25504 toggles the battery good
flag to signal an attached microprocessor when the voltage on an energy storage battery or capacitor has
dropped below a preset critical level. This warning should trigger the shedding of load currents to prevent the
system from entering an undervoltage condition. The OV, UV, and battery good thresholds are programmed
independently.
All the capabilities of BQ25504 are packed into a small-footprint, 16-lead, 3-mm x 3-mm VQFN package.
4
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6 Pin Configuration and Functions
VSS
1
VIN_DC
2
LBST
VSTOR
VBAT
VSS
16
15
14
13
RGT Package
16 Pins
Top View
12
AVSS
11
VBAT_OK
10
OK_PROG
9
OK_HYST
Thermal
6
7
8
VRDIV
VBAT_UV
4
VBAT_OV
VREF_SAMP
Pad
5
3
OT_PROG
VOC_SAMP
Not to scale
Pin Functions
PIN
I/O
DESCRIPTION
NAME
NO.
AVSS
12
Supply
LBST
16
Input
Inductor connection for the boost charger switching node. Connect a 22 µH inductor between this pin and pin 2
(VIN_DC).
OK_HYST
9
Input
Connect to the mid-point of external resistor divider between VRDIV and GND for setting the VBAT_OK hysteresis
threshold. If not used, connect this pin to GND.
OK_PROG
10
Input
Connect to the mid-point of external resistor divider between VRDIV and GND for setting the VBAT_OK threshold.
If not used, connect this pin to GND.
OT_PROG
5
Input
Digital Programming input for IC overtemperature threshold. Connect to GND for 60 C threshold or VSTOR for
120 C threshold.
VBAT
14
I/O
VBAT_OK
11
Output
Digital output for battery good indicator. Internally referenced to the VSTOR voltage. Leave floating if not used.
VBAT_OV
6
Input
Connect to the mid-point of external resistor divider between VRDIV and GND for setting the VSTOR = VBAT
overvoltage threshold.
VBAT_UV
8
Input
Connect to the mid-point of external resistor divider between VRDIV and GND for setting the VBAT undervoltage
threshold. The PFET between VBAT and VSTOR opens if the voltage on VSTOR is below this threshold.
VIN_DC
2
Input
DC voltage input from energy harvesters. Connect at least a 4.7 µF capacitor as close as possible between this
pin and pin 1.
VOC_SAMP
3
Input
Sampling pin for MPPT network. Connect to the mid-point of external resistor divider between VIN_DC and GND
for setting the MPP threshold voltage which will be stored on the VREF_SAMP pin. To disable the MPPT sampling
circuit, connect to VSTOR.
VRDIV
7
Output
VREF_SAMP
4
Input
Connect a 0.01 µF low leakage capacitor from this pin to GND to store the voltage to which VIN_DC will be
regulated. This voltage is provided by the MPPT sample circuit. When MPPT is disabled, either use an external
voltage source to provide this voltage or tie this pin to GND to disable input voltage regulation (i.e. operate from a
low impedance power supply).
Signal ground connection for the device
Connect a rechargeable storage element with at least 100 uF of equivalent capacitance to this pin.
Resistor divider biasing voltage.
VSS
1
Input
General ground connection for the device
VSS
13
Supply
General ground connection for the device
VSTOR
15
Output
Connection for the output of the boost charger, which is typically connected to the system load. Connect at least a
4.7 µF capacitor in parallel with a 0.1 µF capacitor as close as possible to between this pin and pin 1 (VSS).
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SLUSAH0F – OCTOBER 2011 – REVISED NOVEMBER 2019
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7 Specifications
7.1 Absolute Maximum Ratings (1)
over operating free-air temperature range (unless otherwise noted)
Input voltage
Peak Input Power, PIN_PK
VIN_DC, VOC_SAMP, VREF_SAMP, VBAT_OV, VBAT_UV, VRDIV,
OK_HYST, OK_PROG, VBAT_OK, VBAT, VSTOR, LBST (2)
MIN
MAX
UNIT
–0.3
5.5
V
400
mW
Operating junction temperature range, TJ
–40
125
°C
Storage temperature range, Tstg
–65
150
°C
(1)
(2)
Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only and functional operation of the device at these or any other conditions beyond those indicated under Recommended Operating
Conditions is not implied. Exposure to absolute–maximum–rated conditions for extended periods may affect device reliability.
All voltage values are with respect to VSS/ground terminal.
7.2 ESD Ratings
MIN
V(ESD)
(1)
(2)
Electrostatic discharge
MAX
Human body model (HBM), per ANSI/ESDA/JEDEC JS-001, all
pins (1)
UNIT
2
Charged device model (CDM), per JEDEC specification
JESD22-C101, all pins (2)
kV
500
V
JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.
7.3 Recommended Operating Conditions
MIN
VIN (DC)
DC input voltage into VIN_DC (1)
VBAT
Battery voltage range (2)
CHVR
Input capacitance
4.23
CSTOR
Storage capacitance
4.23
CBAT
Battery pin capacitance or equivalent battery capacity
100
CREF
Sampled reference storage capacitance
ROC1 + ROC2
Total resistance for setting for MPPT reference.
ROK1 + ROK2 + ROK3
NOM
MAX
UNIT
0.13
3
V
2.5
5.25
V
4.7
5.17
µF
4.7
5.17
µF
µF
9
10
11
nF
18
20
22
MΩ
Total resistance for setting reference voltage.
9
10
11
MΩ
RUV1 + RUV2
Total resistance for setting reference voltage.
9
10
11
MΩ
ROV1 + ROV2
Total resistance for setting reference voltage.
9
10
11
MΩ
LBST
Input inductance
19.8
22
24.2
µH
TA
Operating free air ambient temperature
–40
85
°C
TJ
Operating junction temperature
–40
105
°C
(1)
(2)
6
Maximum input power ≤ 300 mW. Cold start has been completed
VBAT_OV setting must be higher than VIN_DC
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7.4 Thermal Information
BQ25504
THERMAL METRIC (1)
QFN
UNIT
16 PINS
RθJA
Junction-to-ambient thermal resistance
48.5
RθJC(top)
Junction-to-case (top) thermal resistance
63.9
RθJB
Junction-to-board thermal resistance
22
ψJT
Junction-to-top characterization parameter
1.8
ψJB
Junction-to-board characterization parameter
22
RθJC(bot)
Junction-to-case (bottom) thermal resistance
6.5
(1)
°C/W
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report, .
7.5 Electrical Characteristics
Over recommended temperature range, typical values are at TA = 25°C. Unless otherwise noted, specifications apply for
conditions of VIN_DC = 1.2V, VBAT = VSTOR = 3V. External components LBST = 22 µH, CHVR = 4.7 µF CSTOR= 4.7 µF.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
3000
mV
BOOST CONVERTER \ CHARGER STAGE
VIN(DC)
DC input voltage into VIN_DC
Cold-start completed
IIN(DC)
Peak Current flowing from VIN into VIN_DC input
0.5V < VIN < 3 V; VSTOR = 4.2 V
PIN
Input power range for normal charging
VBAT > VIN_DC; VIN_DC = 0.5 V
VIN(CS)
Cold-start Voltage. Input voltage that will start charging of
VSTOR
VBAT < VBAT_UV; VSTOR = 0 V;
0°C < TA < 85°C
PIN(CS)
Minimum cold-start input power to start normal charging
VBAT < VSTOR(CHGEN)
VIN_DC clamped to VIN_CS by cold start circuit
VBAT = 100 µF ceramic
VSTOR_CHGEN
Voltage on VSTOR when cold start operation ends and
normal charger operation begins
RBAT(on)
Resistance of switch between VBAT and VSTOR when
turned on.
130
200
0.01
600
300
mA
300
mW
700
mV
15
1.6
1.77
µW
1.95
V
VBAT = 4.2 V; VSTOR load = 50 mA
2
Ω
VBAT = 2.1 V
2
VBAT = 4.2 V
2
VBAT = 2.1 V
5
VBAT = 4.2 V
5
Charger Low Side switch ON resistance
Ω
RDS(on)
Charger rectifier High Side switch ON resistance
fSW_BST
Ω
Boost converter mode switching frequency
1
MHz
5
nA
80
nA
BATTERY MANAGEMENT
VBAT = 2.1 V; VBAT_UV = 2.3 V, TJ = 25°C
VSTOR = 0 V
IVBAT
Leakage on VBAT pin
1
VBAT = 2.1 V; VBAT_UV = 2.3 V,
–40°C < TJ < 65°C, VSTOR = 0 V
VSTOR Quiescent current Charger Shutdown in UV
Condition
VIN_DC = 0V;
VBAT < VBAT_UV = 2.4V;
VSTOR = 2.2V, No load on VBAT
330
750
nA
VSTOR Quiescent current Charger Shutdown in OV
Condition
VIN_DC = 0V,
VBAT > VBAT_OV, VSTOR = 4.25,
No load on VBAT
570
1400
nA
VBAT_OV
Programmable voltage range for overvoltage threshold
(Battery voltage is rising)
VSTOR increasing
2.5
5.25
V
VBAT_OV_HYST
Battery voltage overvoltage hysteresis threshold (Battery
voltage is falling), internal threshold
VSTOR decreasing
18
VBAT_UV
Programmable voltage range for under voltage threshold
(Battery voltage is falling)
VSTOR decreasing; VBAT_UV > VBias
2.2
VBAT_UV_HYST
Battery under voltage threshold hysteresis, internal
thershold
VSTOR increasing
40
VBAT_OK
Programmable voltage range for threshold voltage for
high to low transition of digital signal indicating battery is
OK,
VSTOR decreasing
VBAT_OK_HYST
Programmable voltage range for threshold voltage for low
to high transition of digital signal indicating battery is OK,
VSTOR increasing
VBAT_ACCURACY
Overall Accuracy for threshold values, UV, OV, VBAT_OK
Selected resistors are 0.1% tolerance
VBAT_OKH
VBAT OK (High) threshold voltage
Load = 10 µA
IVSTOR
35
89
VBAT_OV
80
125
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V
mV
VBAT_UV
VBAT_OV
V
50
VBAT_OVVBAT_UV
mV
–5%
5%
VSTOR200mV
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V
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Electrical Characteristics (continued)
Over recommended temperature range, typical values are at TA = 25°C. Unless otherwise noted, specifications apply for
conditions of VIN_DC = 1.2V, VBAT = VSTOR = 3V. External components LBST = 22 µH, CHVR = 4.7 µF CSTOR= 4.7 µF.
PARAMETER
TEST CONDITIONS
MIN
TYP
VBAT_OKL
VBAT OK (Low) threshold voltage
Load = 10 µA
TSD_PROTL
The temperature at which the boost converter is disabled
and the switch between VBAT and VSTOR is
disconnected to protect the battery
OT_Prog = LO
65
OT_Prog = HI
120
TSD_PROTH
MAX
UNIT
100
mV
°C
Voltage for OT_PROG High setting
2
V
OT_Prog
Voltage for OT_PROG Low setting
0.3
V
BIAS and MPPT CONTROL STAGE
VOC_sample
Sampling period of VIN_DC open circuit voltage
16
s
VOC_Settling
Sampling period of VIN_DC open circuit voltage
256
ms
VIN_Reg
Regulation of VIN_DC during charging
VIN_shutoff
DC input voltage into VIN_DC when charger is turned off
40
MPPT_Disable
Threshold on VOC_SAMP to disable MPPT functionality
VSTOR-15
mV
VBIAS
Voltage node which is used as reference for the
programmable voltage thresholds
8
0.5 V 130 mV)
Charger resumes
charging
VSTOR_CHGEN = 1.8 V typical
GND
Signal to turn off
system load on
VSTOR
VBAT disconnected
from VSTOR to
prevent overdischarge
Cold Start Circuit on
(if VIN_DC > 600 mV)
P(harvester) x Kbq255xx < P(load)
P(harvester) x Kbq255xx > P(load)
Increasing
VSTOR voltage
Decreasing
VSTOR voltage
Figure 11. Summary of VSTOR Threshold Voltages
8.3.5 Nano-Power Management and Efficiency
The high efficiency of the BQ25504 charger is achieved via the proprietary Nano-Power management circuitry
and algorithm. This feature essentially samples and holds the VSTOR voltage in order to reduce the average
quiescent current. That is, the internal circuitry is only active for a short period of time and then off for the
remaining period of time at the lowest feasible duty cycle. A portion of this feature can be observed in Figure 19
where the VRDIV node is monitored. Here the VRDIV node provides a connection to the VSTOR voltage (first
pulse) and then generates the reference levels for the VBAT_OV and VBAT_OK resistor dividers for a short
period of time. The divided down values at each pin arecompared against VBIAS as part of the hysteretic control.
Since this biases a resistor string, the current through these resistors is only active when the Nano-Power
management circuitry makes the connection—hence reducing the overall quiescent current due to the resistors.
This process repeats every 64 ms.
The BQ25504 boost charger efficiency is shown for various input power levels in Figure 1 through Figure 7. All
data points were captured by averaging the overall input current. This must be done due to the periodic biasing
scheme implemented via the Nano-Power management circuitry. In order to properly measure the resulting input
current when calculating the output to input efficiency, the input current efficiency data was gathered using a
source meter set to average over at least 50 samples. Quiescent current curves into VSTOR over temperature
and voltage is shown at Figure 8.
14
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8.4 Device Functional Modes
The BQ25504 has three functional modes: cold-start operation, main boost charger enabled and thermal
shutdown. The cold start circuitry is powered from VIN_DC. The main boost charger circuitry is powered from
VSTOR while the boost power stage is powered from VIN_DC. Details of entering and exiting each mode are
explained below.
8.4.1 Cold-Start Operation (VSTOR < VSTOR_CHGEN, VIN_DC > VIN(CS) and PIN > PIN(CS))
Whenever VSTOR < VSTOR_CHGEN, VIN_DC ≥ VIN(CS) and PIN > PIN(CS), the cold-start circuit is on. This
could happen when there is not input power at VIN_DC to prevent the load from discharging the battery or during
a large load transient on VSTOR. During cold start, the voltage at VIN_DC is clamped to VIN(CS) so the energy
harvester's output current is critical to providing sufficient cold start input power, PIN(CS) = VIN(CS) X IIN(CS).
The cold-start circuit is essentially an unregulated, hysteretic boost converter with lower efficiency compared to
the main boost charger. None of the other features function during cold start operation. The cold start circuit's
goal is to charge VSTOR higher than VSTOR_CHGEN so that the main boost charger can operate. When a
depleted storage element is initially attached to VBAT, as shown in Figure 12 and the harvester can provide a
voltage > VIN(CS) and total power at least > PIN(CS), assuming minimal system load or leakage at VSTOR and
VBAT, the cold start circuit can charge VSTOR above VSTOR_CHGEN. Once the VSTOR voltage reaches the
VSTOR_CHGEN threshold, the IC
1. first performs an initialization pulse on VRDIV to reset the feedback voltages,
2. then disables the charger for 32 ms (typical) to allow the VIN_DC voltage to rise to the harvester's opencircuit voltage which will be used as the input voltage regulation reference voltage until the next MPPT
sampling cycle and
3. lastly performs its first feedback sampling using VRDIV, approximately 64 ms after the initialization pulse.
Figure 12. Charger Operation After a Depleted Storage Element is Attached and Harvester is Available
The energy harvester must supply sufficient power for the IC to exit cold start. Due to the body diode of the
PFET connecting VSTOR and VBAT, the cold start circuit must charge both the capacitor on CSTOR up to the
VSTOR_CHGEN and the storage element connected to VBAT up to VSTOR_CHGEN less a diode drop. When a
rechargeable battery with an open protector is attached, the intial charge time is typically short due to the
minimum charge needed to close the battery's protector FETs. When large, discharged super capacitors with
high DC leakage currents are attached, the intial charge time can be signficant.
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Device Functional Modes (continued)
When the VSTOR voltage reaches VSTOR_CHGEN, the main boost charger starts up. When the VSTOR
voltage rises to the VBAT_UV threshold, the PMOS switch between VSTOR and VBAT turns on, which provides
additional loading on VSTOR and could result in the VSTOR voltage dropping below both the VBAT_UV
threshold and the VSTOR_CHGEN voltage, especially if system loads on VSTOR or VBAT are active during this
time. Therefore, it is not uncommon for the VSTOR voltage waveform to have incremental pulses (i.e. stair steps)
as the IC cycles between cold-start and main boost charger operation before eventually maintaing VSTOR above
VSTOR_CHGEN.
The cold start circuit initially clamps VIN_DC to VIN(CS) = 600 mV typical. If sufficient input power (i.e.,output
current from the harvester clamped to VIN(CS)) is not available, it is possible that the cold start circuit cannot
raise the VSTOR voltage above VSTOR_CHGEN in order for the main boost conveter to start up. It is highly
recommended to add an external PFET between the system load and VSTOR. An inverted VBAT_OK signal can
be used to drive the gate of this system-isolating, external PFET. See the Power Supply Recommendations
section for guidance on minimum input power requirements.
8.4.2 Main Boost Charger Enabled (VSTOR > VSTOR_CHGEN, VIN_DC > VIN(DC) and EN = LOW )
One way to avoid cold start is to attach a partially charged storage element as shown in Figure 13.
Figure 13. Charger Operation after a Partially Charged Storage Element
is Attached and Harvester Power is Available
When no input source is attached, the VSTOR node should be discharged to ground before attaching a storage
element. Hot-plugging a storage element that is charged (e.g., the battery protector PFET is closed) and with the
VSTOR node more than 100 mV above ground results in the PFET between VSTOR and VBAT remaining off
until an input source is attached.
Assuming the voltages on VSTOR and VBAT are both below 100mV, when a charged storage element is
attached (i.e. hot-plugged) to VBAT, the IC.
1. first turns on the internal PFET between the VSTOR and VBAT pins for tBAT_HOT_PLUG (45ms) in order to
charge VSTOR to VSTOR_CHGEN then turns off the PFET to prevent the battery from overdischarge,
2. then performs an initialization pulse on VRDIV to reset the feedback voltages,
3. then disables the charger for 32 ms (typical) to allow the VIN_DC voltage to rise to the harvester's opencircuit voltage which will be used as the input voltage regulation reference voltage until the next MPPT
sampling cycle and
4. lastly performs its first feedback sampling using VRDIV, approximately 64 ms after the initialization pulse.
16
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Device Functional Modes (continued)
If the VSTOR pin voltage remains above the internal under voltage threshold (VBAT_UV) for the additional 64 ms
after the VRDIV initialization pulse (following the 45-ms PFET on time), the internal PFET turns back on and the
main boost charger begins to charge the storage element assuming there is sufficient power available from the
harvester at the VIN_DC pin. If VSTOR does not reach the VBAT_UV threshold, then the PFET remains off until
the main boost charger can raise the VSTOR voltage to VBAT_UV. If a system load tied to VSTOR discharges
VSTOR below VSTOR_GEN or below VBAT_UV during the 32 ms initial MPPT reference voltage measurement
or within 110 ms after hot plug, it is recommended to add an external PFET between the system load and
VSTOR. An inverted VBAT_OK signal can be used to drive the gate of this system-isolating, external PFET.
Otherwise, the VSTOR voltage waveform will have incremental pulses as the IC turns on and off the internal
PFET controlled by VBAT_UV or cycles between cold-start and main boost charger operation.
Once VSTOR is above VSTOR_CHGEN, the main boost charger employs pulse frequency modulation (PFM)
mode of control to regulate the voltage at VIN_DC close to the desired reference voltage. The reference voltage
is set by the MPPT control scheme as described in the features section. Input voltage regulation is obtained by
transferring charge from the input to VSTOR only when the input voltage is higher than the voltage on pin
VREF_SAMP. The current through the inductor is controlled through internal current sense circuitry. The peak
current in the inductor is dithered internally to up to three pre-determined levels in order to maintain high
efficiency of the charger across a wide input current range. The charger transfers up to a maximum of 100 mA
average input current (230mA typical peak inductor current). The boost charger is disabled when the voltage on
VSTOR reaches the user set VBAT_OV threshold to protect the battery connected at VBAT from overcharging.
In order for the battery to charge to VBAT_OV, the input power must exceed the power needed for the load on
VSTOR. See the Power Supply Recommendations section for guidance on minimum input power requirements.
Steady state operation for the boost charger is shown in Figure 16. These plots highlight the inductor current, the
VSTOR voltage ripple, input voltage regulation and the LBOOST switching node. The cycle-by-cycle minor
switching frequency is a function of the boost converter's inductor value, peak current limit and voltage levels on
each side of each inductor. Once the VSTOR capacitor, CSTOR, droops below a minimum value, the hysteretic
switching repeats.
CAUTION
If VIN_DC is higher than VSTOR and VSTOR is higher than VBAT_OV, the input
VIN_DC is pulled to ground through a small resistance to stop further charging of the
attached battery or capacitor. It is critical that if this case is expected, the impedance of
the source attached to VIN_DC be higher than 20 Ω and not a low impedance source.
8.4.3 Thermal Shutdown
Rechargeable Li-ion batteries need protection from damage due to operation at elevated temperatures. The
application should provide this battery protection and ensure that the ambient temperature is never elevated
greater than the expected operational range of 85°C.
The BQ25504 uses an integrated temperature sensor to monitor the junction temperature of the device. If the
OT_PROG pin is tied low, then the temperature threshold for thermal protection is set to TSD_ProtL which is
65°C typically. If the OT_PROG is tied high, then the temperature is set to TSD_ProtH which is 120°C typically.
Once the temperature threshold is exceeded, the boost converter/charger is disabled and charging ceases. Once
the temperature of the device drops below this threshold, the boost converter and or charger can resume
operation. To avoid unstable operation near the overtemp threshold, a built-in hysteresis of approximately 5°C
has been implemented. Care should be taken to not over discharge the battery in this condition since the boost
converter/charger is disabled. However, if the supply voltage drops to the VBAT_UV setting, then the switch
between VBAT and VSTOR will open and protect the battery even if the device is in thermal shutdown.
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9 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
9.1 Application Information
9.1.1 Storage Element Selection
In order for the charge management circuitry to protect the storage element from over-charging or discharging,
the storage element must be connected to VBAT pin and the system load tied to the VSTOR pin. Many types of
elements can be used, such as capacitors, super capacitors or various battery chemistries. A storage element
with 100 uF equivalent capacitance is required to filter the pulse currents of the PFM switching charger. The
equivalent capacitance of a battery can be computed as computed as:
CEQ = 2 x mAHrBAT(CHRGD) x 3600 s/Hr / VBAT(CHRGD)
(6)
In order for the storage element to be able to charge VSTOR capacitor (CSTOR) within the tVB_HOT_PLUG (50 ms
typical) window at hot-plug; therefore preventing the IC from entering cold start, the time constant created by the
storage element's series resistance (plus the resistance of the internal PFET switch) and equivalent capacitance
must be less than tVB_HOT_PLUG . For example, a battery's resistance can be computed as:
RBAT = VBAT / IBAT(CONTINUOUS) from the battery specifications.
(7)
The storage element must be sized large enough to provide all of the system load during periods when the
harvester is no longer providing power. The harvester is expected to provide at least enough power to fully
charge the storage element while the system is in low power or sleep mode. Assuming no load on VSTOR (i.e.,
the system is in low power or sleep mode), the following equation estimates charge time from voltage VBAT1 to
VBAT2 for given input power is:
Refer to SLUC462 for a design example that sizes the storage element.
PIN × ηEST × tCHRG = 1/2 × CEQ X (VBAT22 - VBAT12)
(8)
Note that if there are large load transients or the storage element has significant impedance then it may be
necessary to increase the CSTOR capacitor from the 4.7uF minimum or add additional capacitance to VBAT in
order to prevent a droop in the VSTOR voltage. See below for guidance on sizing capacitors.
9.1.2 Inductor Selection
The boost charger needs an appropriately sized inductor for proper operation. The inductor's saturation current
should be at least 25% higher than the expected peak inductor currents recommended below if system load
transients on VSTOR are expected. Since this device uses hysteretic control, the boost charger is considered
naturally stable systems (single order transfer function).
For the boost charger to operate properly, an inductor of appropriate value must be connected between
LBOOST, pin 20, and VIN_DC, pin 2. The boost charger internal control circuitry is designed to control the
switching behavior with a nominal inductance of 22 µH ± 20%. The inductor must have a peak current capability
of > 300 mA with a low series resistance (DCR) to maintain high efficiency.
A list of inductors recommended for this device is shown in Table 1.
Table 1. Recommended Inductors
(1)
18
Inductance (µH)
Dimensions (mm)
Part Number
Manufacturer (1)
22
4.0x4.0x1.7
LPS4018-223M
Coilcraft
22
3.8x3.8x1.65
744031220
Wurth
22
2.8x2.8x2.8
744025220
Wurth
See WHAT? concerning recommended third-party products.
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9.1.3 Capacitor Selection
In general, all the capacitors need to be low leakage. Any leakage the capacitors have will reduce efficiency,
increase the quiescent current and diminish the effectiveness of the IC for energy harvesting.
9.1.3.1 VREF_SAMP Capacitance
The MPPT operation depends on the sampled value of the open circuit voltage and the input regulation follows
the voltage stored on the CREF capacitor. This capacitor is sensitive to leakage since the holding period is
around 16 seconds. As the capacitor voltage drops due to any leakage, the input regulation voltage also drops
preventing proper operation from extraction the maximum power from the input source. Therefore, it is
recommended that the capacitor be an X7R or COG low leakage capacitor.
9.1.3.2 VIN_DC Capacitance
Energy from the energy harvester input source is initially stored on a capacitor, CIN, connected to VIN_DC, pin
2, and VSS, pin 1. For energy harvesters which have a source impedance which is dominated by a capacitive
behavior, the value of the harvester capacitor should scaled according to the value of the output capacitance of
the energy source, but a minimum value of 4.7 µF is recommended.
9.1.3.3 VSTOR Capacitance
Operation of the BQ25504 requires two capacitors to be connected between VSTOR, pin 15, and VSS, pin 1. A
high frequency bypass capacitor of at 0.1 µF should be placed as close as possible between VSTOR and VSS.
In addition, a low ESR capacitor of at least 4.7 µF should be connected in parallel.
9.1.3.4 Additional Capacitance on VSTOR or VBAT
If there are large, fast system load transients and/or the storage element has high resistance, then the CSTOR
capacitors may momentarily discharge below the VBAT_UV threshold in response to the transient. This causes
the BQ25504 to turn off the PFET switch between VSTOR and VBAT and turn on the boost charger. The
CSTOR capacitors may further discharge below the VSTOR_CHGEN threshold and cause the BQ25504 to enter
Cold Start. For instance, some Li-ion batteries or thin-film batteries may not have the current capacity to meet the
surge current requirements of an attached low power radio. To prevent VSTOR from drooping, either increasing
the CSTOR capacitance or adding additional capacitance in parallel with the storage element is recommended.
For example, if boost charger is configured to charge the storage element to 4.2 V and a 500 mA load transient
of 50 µs duration infrequently occurs, then, solving I = C x dv/dt for CSTOR gives:
CSTOR ³
500 mA ´ 50 ms
= 10.5 mF
(4.2 V - 1.8 V)
(9)
Note that increasing CSTOR is the recommended solution but will cause the boost charger to operate in the less
efficient cold start mode for a longer period at startup compared to using CSTOR = 4.7 µF. If longer cold start run
times are not acceptable, then place the additional capacitance in parallel with the storage element.
For a recommended list of standard components, see the EVM User’s Guide (SLUUAA8).
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9.2 Typical Applications
9.2.1 Solar Application Circuit
LBST
CBYP
(1)
(2)
CSTOR
4.7 µF
(min)
22µH
Solar
Cell
+
Battery(>100µF)
VSTOR
CHVR
4.7µF
1
-
16
15
LBST
VSTOR
`
14
13
VBAT
VSS
VSS
AVSS
12
VBAT_OK
2
ROC2
VIN_DC
11
ROK1
bq25504
4.42 MΩ
ROC 1
15.62MΩ
VBAT_OK
3
VOC_SAMP
4
VREF_SAMP
OK_PROG
CREF
0.01µF
OK_HYST
10
9
OT_PROG VBAT_OV VRDIV VBAT _UV
5
6
7
ROV2
4.02MΩ
ROV1
5.90MΩ
(1)
Place close as possible to IC pin 15 (VSTOR) and pin 13 (VSS)
(2)
See the Capacitor Selection section for guidance on sizing CSTOR
8
4.42 MΩ
ROK2
4.22 MΩ
ROK3
1.43MΩ
RUV2
4.42 MΩ
RUV 1
5.60 MΩ
Figure 14. Typical Solar Application Circuit
9.2.1.1 Design Requirements
The desired voltage levels are VBAT_OV = 3.15 V, VBAT_UV = 2.20 V, VBAT_OK = 2.44 V, VBAT_OK_HYST =
2.80 V and MPP (VOC) = 78% which is typical for solar panels. There are no large load transients expected. The
IC must stop charging if its junction temperature is above 65°C. The simulated solar panel open circuit voltage is
1.0 V.
9.2.1.2 Detailed Design Procedure
The recommended L1 = 22 µH, CBYP = 0.01 µF and low leakage CREF = 10 nF are selected. In order to ensure
the fastest recovery of the harvester output voltage to the MPPT level following power extraction, the minimum
recommended CIN = 4.7 µF is selected. Because no large system load transients are expected and to ensure
fast charge time during cold start, the minimum recommended CSTOR = 4.7 µF. To stop charging when the IC
junction temperature is above 65°C, the OT_PROG pin is tied to ground.
• With VBAT_UV < VBAT_OV ≤ 5.5 V, to size the VBAT_OV resistors, first choose RSUMOV = ROV1 + ROV2 =
10 MΩ then solve Equation 3 for
3 RSUMOV ´ VBIAS 3 10 MW ´ 1.25 V
ROV1 = ´
´
= 5.95 MW ® 5.90 MW closest 1% value then
2
VBAT _ OV
2
3.15 V
(10)
•
20
ROV2 = RSUMOV - ROV1 = 10 MΩ - 5.95 MΩ = 4.05 MΩ → 4.02 MΩ resulting in VBAT_OV = 3.15 V
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Typical Applications (continued)
•
To size the VBAT_UV resistors, first choose RSUMUV = RUV1 + RUV2 = 10 MΩ then solve Equation 2 for
RSUMUV ´ VBIAS 10 MW ´ 1.25 V
RUV1 =
=
= 5.68 MW ® 5.60 MW closest 1% value then
VBATUV
2.2 V
•
RUV2 = RSUMUV - RUV1 = 10 MΩ - 5.60 MΩ = 4.4 MΩ → 4.42 MΩ closest 1% resistor resulting in
VBAT_UV = 2.2 V.
With VBAT_OV ≥ VBAT_OK_HYST > VBAT_OK ≥ VBAT_UV, to size the VBAT_OK and VBAT_OK_HYST
resistors,
first choose RSUMOK = ROK1 + ROK2 + ROK3 = 10 MΩ then solve Equation 4 and Equation 5 for
VBIAS ´ RSUMOK
æ 1.25 V ö
ROK1 =
=ç
´ 10 MW = 4.46 MW ® 4.42 MW closest 1% resistor then
VBAT _ OK _ HYST è 2.8 V ø÷
(12)
•
•
•
æ VBAT _ OK _ PROG ö
æ 2.45 V
ö
- 1÷ ´ ROK1 = ç
- 1÷ ´ 4.24 MW = 4.07 MW, then
ROK2 = ç
VBIAS
1.2
5
V
è
ø
è
ø
(13)
ROK3 = RSUMOK - ROK1 - ROK2 = 10 MΩ - 4.42 MΩ - 4.22 MΩ = 1.36 MΩ → 1.43 MΩ to give
VBAT_OK = 2.44 V and VBAT_OK_HYST = 2.85 V.
Keeping in mind that VREF_SAMP stores the MPP voltage for the harvester, first choose RSUMOC = ROC1 +
ROC2 = 20 MΩ then solve Equation 1 for
æ VREF _ SAMP ö
ROC1 = ç
÷ ´ RSUMOC = 0.78 ´ 20 MW = 15.6 MW, then
è VIN _ DC(OC) ø
•
(11)
(14)
æ
VREF _ SAMP ö
ROC2 = RSUMOC ´ ç 1 ÷ = 20 MW (1 - 0.78 ) = 4.4 MW closest 1% resistors
VIN _ DC(OC) ø
è
SLURAQ1 provides help on sizing and selecting the resistors.
(15)
9.2.1.3 Application Curves
VINDC = sourcemeter with VSOURCE = 1.0 V and compliance of
2.75 mA
VBAT connected to 0.1 F depleted supercap
No resistance load on VSTOR
Figure 15. Startup into Depleted Storage Element
VIN_DC = sourcemeter with VSOURCE = 1 V and compliance of
10.5 mA
VBAT = 0.1 F supercap
VSTOR = 2 kΩ resistive load
Figure 16. Boost Charger Operational Waveforms
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Typical Applications (continued)
VIN_DC = sourcemeter with VSOURCE = 1 V and compliance of
10.5 mA
VBAT = 0.1 F supercap
VSTOR = open to 500 Ω to open resistive load (IL = load current
on VSTOR)
VIN_DC = sourcemeter with VSOURCE = 1 V and compliance of
10.5 mA
VBAT = sourcemeter with VSOURCE = 2.8V and compliance
of 1A
IL = inductor current
Figure 17. 5 mA Load Transient on VSTOR
VIN_DC = sourcemeter with VSOURCE = 1 V and compliance of
10.5 mA
VBAT = sourcemeter with VSOURCE = 2.8 V and compliance
of 1A
Figure 18. MPPT Operation
VIN_DC = sourcemeter with VSOURCE = 1 V and compliance of
2.75 mA
No storage element on VBAT
VSTOR artificially ramped from 0V to 3.15 V to 0 V using a
power amp driven by a function generator
Figure 20. VBAT_OK Operation
Figure 19. VRDIV Operation
22
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Typical Applications (continued)
9.2.2 TEG Application Circuit
L BST
CBYP
(1)
(2)
CSTOR
4.7 µF
(min)
22µH
Battery(>100µF)
VSTOR
CHVR
4.7µF
16
15
LBST
VSTOR
`
14
13
VBAT
VSS
1
VSS
2
VIN_DC
3
VOC_SAMP
OK_PROG
VREF _SAMP
OK_HYST
AVSS
12
VBAT_OK
Thermo electric
generator
ROC2
10 MΩ
11
ROK1
bq25504
10 MΩ
ROC1
VBAT_OK
CREF
4
0.01µF
10
9
6
7
ROK2
6.12 MΩ
ROK3
OT_PROG VBAT_OV VRDIV VBAT_UV
5
3.32 MΩ
8
542kΩ
VSTOR
ROV2
5.62MΩ
ROV1
4.42MΩ
(1)
Place close as possible to IC pin 15 (VSTOR) and pin 13 (VSS)
(2)
See the Capacitor Selection section for guidance on sizing CSTOR
RUV 2
6.12MΩ
RUV 1
3.83MΩ
Figure 21. Typical TEG Application Circuit
9.2.2.1 Design Requirements
The desired voltage levels are VBAT_OV = 4.25 V, VBAT_UV = 3.20 V, VBAT_OK = 3.55 V, VBAT_OK_HYST =
3.76 V and MPP (VOC) = 50% which is typical for TEG harvesters. The IC must stop charging if its junction
temperature is above 120°C. The simulated TEG open circuit voltage is 1.0 V.
9.2.2.2 Detailed Design Procedure
The recommended L1 = 22 µH, CBYP = 0.01 µF and low leakage CREF = 10 nF are selected. In order to ensure
the fastest recovery of the harvester output voltage to the MPPT level following power extraction, the minimum
recommended CIN = 4.7 µF is selected. Because no large system load transients are expected and to ensure
fast charge time during cold start, the minimum recommended CSTOR = 4.7 µF. To stop charging when the IC
junction temperature is above 120°C, the OT_PROG pin is tied to VSTOR.
Referring back to the procedure in Detailed Design Procedure or using the spreadsheet calculator at SLURAQ1
gives the following values:
• ROV1 = 4.42 MΩ, ROV2 = 5.49 MΩ resulting in VBAT_OV = 4.26 V due to rounding to the nearest 1% resistor.
• RUV1 = 3.83 MΩ, RUV2 = 6.04 MΩ resulting in VBAT_UV = 3.22 V due to rounding to the nearest 1% resistor
• ROK1 = 3.32 MΩ, ROK2 = 6.04 MΩ, ROK3 = 0.536 MΩ resulting in VBAT_OK = 3.52 V and
VBAT_OK_HYST = 3.73 V after rounding.
• ROC1 = 10 MΩ and ROC2 = 10 MΩ gives 50% MPP voltage.
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Typical Applications (continued)
9.2.2.3 Application Curves
VINDC = sourcemeter with VSOURCE = 2.0 V and compliance
of 1 mA
VBAT connected to LiIon battery
VSTOR = 50 kΩ resistor
Figure 22. Startup by Attaching Charged Storage Element
VIN_DC = sourcemeter with VSOURCE = 2.0 V and compliance of
1 mA
VBAT connected to LiIon battery
VSTOR = open to 50Ω to open resistive load (IL = load current
on VSTOR)
VIN_DC = sourcemeter with VSOURCE = 2.0 V and compliance of
100 mA
VBAT connected to LiIon battery
VSTOR = 100 kΩ resistive load (IL = inductor current)
Figure 23. Boost Charger Operational Waveforms
VIN_DC = sourcemeter with VSOURCE = 2.0 V and compliance of
1 mA
VBAT connected to LiIon battery
IL = inductor current
Figure 24. 50 mA Load Transient on VSTOR
VIN_DC = sourcemeter with VSOURCE = 2.0 V and compliance of
1 mA
VBAT connected to LiIon battery
Figure 25. MPPT Operation
VIN_DC = sourcemeter with VSOURCE = 2.0 V and compliance of
1 mA
No storage element on VBAT
VSTOR artificially ramped from 0V to 4.25V to 0V using a power
amp driven by a function generator
Figure 27. VBAT_OK Operation
Figure 26. VRDIV Operation
24
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Typical Applications (continued)
9.2.3 MPPT Disabled, Low Impedance Source Application Circuit
L BST
Primary Battery or
other Low Z source
CBYP
(2)
(1)
CSTOR
22µH
VSTOR
CHVR
4.7µF
16
15
LBST
VSTOR
`
14
13
VBAT
VSS
1
VSS
2
VIN_DC
3
VOC_SAMP
OK_PROG
10
4
VREF _SAMP
OK_HYST
9
AVSS
12
VBAT_OK
VBAT_OK
11
ROK1
bq25504
VSTOR
OT_PROG VBAT_OV VRDIV VBAT_UV
5
6
7
8
ROK2
ROK3
VSTOR
ROV2
ROV1
(1)
Place close as possible to IC pin 15 (VSTOR) and pin 13 (VSS)
(2)
See the Capacitor Selection section for guidance on sizing CSTOR
Figure 28. Typical MPPT Disabled Application Circuit
(Low Iq Boost Converter from Low Impedance Source)
9.2.3.1 Design Requirements
The input source is a low impedance 1.2 V battery therefore MPPT is not needed. The output will be a low ESR
capacitor therefore VSTOR can be tied to VBAT and VBAT_UV is not needed. The desired voltage levels are
VBAT_OV = 3.30 V, VBAT_OK = 2.80 V, VBAT_OK_HYST = 3.10 V, and MPPT disabled. The IC must stop
charging if its junction temperature is above 65°C. Load transients are expected.
9.2.3.2 Detailed Design Procedure
The recommended L1 = 22 µH, CBYP = 0.01 µF and low leakage CREF = 10 nF are selected. The minimum
recommended CIN = 4.7 µF is selected. To prevent VSTOR from drooping during system load transients,
CSTOR is set to 100 µF. To disable the sampling for MPPT, the VOC_SAMP pin is tied to VSTOR. To disable
the input voltage regulation circuit, the VREF_SAMP pin is tied to GND. Since the VBAT_UV function is not
needed, the VBAT_UV can be tied to VSTOR. To stop charging when the IC junction temperature is above 65°C,
the OT_PROG pin is tied to GND.
Referring back to the procedure in Detailed Design Procedure or using the spreadsheet calculator at SLURAQ1
gives the following values:
• ROV1 = 5.62 MΩ, ROV2 = 4.22 MΩ resulting in VBAT_OV = 3.28 V due to rounding to the nearest 1% resistor.
• ROK1 = 4.12 MΩ, ROK2 = 5.11 MΩ, ROK3 = 0.976 MΩ resulting in VBAT_OK = 2.80 V and VBAT_OK_HYST =
3.10 V after rounding.
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Typical Applications (continued)
9.2.3.3 Application Curves
VIN_DC = low impedance voltage source = 1.5 V
VBAT = VSTOR = 100 µF
VSTOR = 500 Ω resistor
VIN_DC = low impedance voltage source = 1.5 V
VBAT = VSTOR = 100 µF
VSTOR = 330 Ω resistive load (IL = inductor current)
Figure 29. Startup
Figure 30. Boost Charger Operational Waveforms
VIN_DC = low impedance voltage source = 1.5 V )
VBAT = VSTOR = 100 µF
VSTOR = open to 75 Ω to open resistive load (IL = load current
on VSTOR
VIN_DC = low impedance voltage source = 1.5 V
VBAT = VSTOR = 100 µF
Figure 31. 40 mA Load Transient on VSTOR
Figure 32. VRDIV Operation
VIN_DC = low impedance voltage source = 1.5 V
VBAT = VSTOR = 100 µF
VSTOR artificially ramped from 0 V to 3.3 V to 0 V using a power amp driven by a function generator
Figure 33. VBAT_OK Operation
26
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10 Power Supply Recommendations
The energy harvesting source (e.g., solar panel, TEG, vibration element) must provide a minimum level of power
for the IC to operate as designed. The IC's minimum input power required to exit cold start can be estimated as:
(1.8V )2
PIN > PIN(CS) = VIN(CS) ´ IIN(CS) >
(I - STR _ ELM _ LEAK@1.8V ´ 1.8V )+ RSTOR(CS)
0.05
(16)
where I-STR_ELM_LEAK@1.8V is the storage element leakage current at 1.8V and
RSTOR(CS) is the equivalent resistive load on VSTOR during cold start and 0.05 is an estimate of the worst
case efficiency of the cold start circuit.
Once the IC is out of cold start and the system load has been activated (e.g., using the VBAT_OK signal), the
energy harvesting element must provide the main boost charger with at least enough power to meet the average
system load. Assuming RSTOR(AVG) represents the average resistive load on VSTOR, the simplified equation
below gives an estimate of the IC's minimum input power needed during system operation:
PIN ´ hEST > PLOAD =
(VBAT _ OV )2
RSTOR(AVG)
+ VBAT _ OV ´ I - STR _ ELM _ LEAK @ VBAT _ OV
(17)
where ηEST can be derived from the datasheet efficiency curves for the given input voltage and current and
VBAT_OV. The simplified equation above assumes that, while the harvester is still providing power, the system
goes into low power or sleep mode long enough to charge the storage element so that it can power the system
when the harvester eventually is down. Refer to spreadsheet SLUC462 for a design example that sizes the
energy harvester.
11 Layout
11.1 Layout Guidelines
As for all switching power supplies, the PCB layout is an important step in the design, especially at high peak
currents and high switching frequencies. If the layout is not carefully done, the boost charger could show stability
problems as well as EMI problems. Therefore, use wide and short traces for the main current path and for the
power ground paths. The input and output capacitors as well as the inductors should be placed as close as
possible to the IC. For the boost charger, first priority are the output capacitors, including the 0.1 uF bypass
capacitor (CBYP), followed by CSTOR, which should be placed as close as possible between VSTOR, pin 15,
and VSS, pin 1 or 13. Next, the input capacitor, CIN, should be placed as close as possible between VIN_DC,
pin 2, and VSS, pin 1. Last in priority is the boost charger inductor, L1, which should be placed close to
LBOOST, pin 16, and VIN_DC, pin 2 if possible. It is best to use vias and bottom traces for connecting the
inductor to its respective pins instead of the capacitors.
To minimize noise pickup by the high impedance voltage setting nodes (VBAT_OV, VBAT_UV, OK_PROG,
OK_HYST), the external resistors should be placed so that the traces connecting the midpoints of each divider to
their respective pins are as short as possible. When laying out the non-power ground return paths (e.g. from
resistors and CREF), it is recommended to use short traces as well, separated from the power ground traces and
connected to AVSS pin 12. This avoids ground shift problems, which can occur due to superimposition of power
ground current and control ground current. The PowerPad should not be used as a power ground return path.
The remaining pins are digital signals with minimal layout restrictions. See Figure 34 for an example layout.
In order to maximize efficiency at light load, the use of voltage level setting resistors > 1 MΩ is recommended. In
addition, the sample and hold circuit output capacitor on VREF_SAMP must hold the voltage for 16 s. During
board assembly, contaminants such as solder flux and even some board cleaning agents can leave residue that
may form parasitic resistors across the physical resistors/capacitors and/or from one end of a resistor/capacitor
to ground, especially in humid, fast airflow environments. This can result in the voltage regulation and threshold
levels changing significantly from those expected per the installed components. Therefore, it is highly
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Layout Guidelines (continued)
recommended that no ground planes be poured near the voltage setting resistors or the sample and hold
capacitor. In addition, the boards must be carefully cleaned, possibly rotated at least once during cleaning, and
then rinsed with de-ionized water until the ionic contamination of that water is well above 50 Mohm. If this is not
feasible, then it is recommended that the sum of the voltage setting resistors be reduced to at least 5X below the
measured ionic contamination.
V
sy S T O
st R
em to
lo
ad
11.2 Layout Example
TOP
GND
TOP
VIN
ge
ra
to sto
VBAT t
en
elem
VBAT_OK signal
BOT
GND
BOT
GND
Figure 34. Recommended Layout
11.3 Thermal Considerations
Implementation of integrated circuits in low-profile and fine-pitch surface-mount packages typically requires
special attention to power dissipation. Many system-dependent issues such as thermal coupling, airflow, added
heat sinks and convection surfaces, and the presence of other heat-generating components affect the powerdissipation limits of a given component.
Three basic approaches for enhancing thermal performance are listed below.
• Improving the power-dissipation capability of the PCB design
• Improving the thermal coupling of the component to the PCB
• Introducing airflow in the system
For more details on how to use the thermal parameters in the Thermal Table, check the Thermal Characteristics
Application Note (SZZA017) and the IC Package Thermal Metrics Application Note (SPRA953).
28
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12 Device and Documentation Support
12.1 Device Support
12.1.1 Third-Party Products Disclaimer
TI'S PUBLICATION OF INFORMATION REGARDING THIRD-PARTY PRODUCTS OR SERVICES DOES NOT
CONSTITUTE AN ENDORSEMENT REGARDING THE SUITABILITY OF SUCH PRODUCTS OR SERVICES
OR A WARRANTY, REPRESENTATION OR ENDORSEMENT OF SUCH PRODUCTS OR SERVICES, EITHER
ALONE OR IN COMBINATION WITH ANY TI PRODUCT OR SERVICE.
12.1.2 Zip Files
•
•
•
http://www.ti.com/lit/zip/SLUC484
http://www.ti.com/lit/zip/SLURAQ1
http://www.ti.com/lit/zip/SLUC462
12.2 Documentation Support
12.2.1 Related Documentation
For related documentation see the following:
• EVM User’s Guide, SLUUAA8
• Thermal Characteristics Application Note, SZZA017
• IC Package Thermal Metrics Application Note, SPRA953
12.3 Receiving Notification of Documentation Updates
To receive notification of documentation updates, navigate to the device product folder on ti.com. In the upper
right corner, click on Alert me to register and receive a weekly digest of any product information that has
changed. For change details, review the revision history included in any revised document.
12.4 Support Resources
TI E2E™ support forums are an engineer's go-to source for fast, verified answers and design help — straight
from the experts. Search existing answers or ask your own question to get the quick design help you need.
Linked content is provided "AS IS" by the respective contributors. They do not constitute TI specifications and do
not necessarily reflect TI's views; see TI's Terms of Use.
12.5 Trademarks
E2E is a trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
12.6 Electrostatic Discharge Caution
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
12.7 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
13 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
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PACKAGE OPTION ADDENDUM
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10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
BQ25504RGTR
ACTIVE
VQFN
RGT
16
3000
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-40 to 85
B5504
BQ25504RGTT
ACTIVE
VQFN
RGT
16
250
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-40 to 85
B5504
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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