®
RT9451
Switch-Mode Single Cell Li-ion Battery Charger with USB OTG
General Description
The RT9451 integrates a high efficiency USB friendly switch
mode charger with On-The-Go (OTG) support for single
cell Li-ion and Li-polymer batteries, D+D− detection, and
a 50mA LDO regulator into a single chip.
The charger features a synchronous 375kHz PWM
controller with integrated power MOSFETs, input current
sensing and regulation, Minimum Input Voltage Regulation
(MIVR), high accuracy charge current and voltage
regulation, and charge termination. It charges the battery
in three phases : low current pre-charge, constant current
fast charge, and constant voltage trickle charge. The input
current is automatically limited to the value set by the
host. The charger can be configured to terminate charge
based on user-selectable minimum current level and
automatically restart the charge cycle if the battery voltage
falls below the recharge threshold. A safety timer with
reset control provides a safety backup for I
2
C interface.
The charger automatically enters sleep mode or high
impedance mode when the input supply is removed. The
charge status is reported to the host using the I
2
C interface
and the STAT pin. The D+D− detection circuit allows
automatic detection of a USB wall charger. If a wall charger
is detected, the input current limit will automatically
increase from 500mA to 975mA.
In OTG mode, the PWM controller boosts the battery
voltage to 5V and provides up to 1.6A of current to the
USB output. At very light load, the Boost operates in burst
mode to optimize efficiency. OTG mode can be enabled
either through I
2
C interface or GPIO control.
Applications
Mobile Phones and Smart Phones
MP3 Players
Handheld Devices
Ordering Information
RT9451
Package Type
QW : WQFN-32L 4x4 (W-Type)
Lead Plating System
G : Green (Halogen Free and Pb Free)
Note :
Richtek products are :
½
RoHS compliant and compatible with the current require-
ments of IPC/JEDEC J-STD-020.
Suitable for use in SnPb or Pb-free soldering processes.
½
Simplified Application Circuit
RT9451
V
IN
C
IN
SCL
SDA
VIO
USB Charger
Detection
DP
DM
GND
BATS
LX
C
SYSS
+
Battery
VIN
MID
C
MID
L
Control
Inputs
Copyright
©
2017 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS9451-01 March 2017
www.richtek.com
1
RT9451
Features
Marking Information
0Q= : Product Code
Integrated Switching Charger and 50mA LDO in a
Single Package
Charges Faster Than Linear Chargers
High Accuracy Voltage and Current Regulation
½
Charge Voltage Regulation Accuracy :
±
1%
½
Charge Current Regulation Accuracy :
±
5%
Minimum Input Voltage Regulation : 4.2V to 4.76V
with Step of 80mV
Bad Adaptor Detection and Rejection
Safety Limit Register for Maximum Charge Voltage
and Current Limiting
High Efficiency Mini-USB/AC Battery Charger for
Single Cell Li-Ion and Li-Polymer Battery Packs
28V Absolute Maximum Input Voltage Rating
12V Maximum Operating Input Voltage
Built-In Input Current Sensing and Limiting
Integrated Power FETs for Up to 4A Charge Rate
Programmable Charge Parameters through I
2
C
Interface (up to 400 Kbps) :
½
Input Current
½
Fast Charge/Termination Current
½
Charge Voltage (3.5V to 4.44V)
½
Safety Timer
½
Termination Enable
Synchronous Fixed Frequency PWM Controller
Operating at 375kHz With 0% to 99% Duty Cycle
Automatic High Impedance Mode for Low Power
Consumption
Safety Timer with Reset Control
Thermal Regulation and Protection
Input/Output Over-Voltage Protections
Status Output for Charging and Faults
USB Friendly Boot-Up Sequence
Automatic Charging
Boost Mode Operation for USB OTG
½
Input Voltage Range (BATS) : 2.5V to 4.5V
½
Output Voltage for VIN : 4.425V to 5.506V
RoHS Compliant and Halogen Free
0Q=YM
DNN
YMDNN : Date Code
Pin Configuration
(TOP VIEW)
MID
MID
LX
LX
LX
LX
LX
PGND
32 31 30 29 28 27 26 25
VIN
VIN
VIN
VIN
INT
VIO
DP
DM
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16
24
23
22
21
20
33
19
18
17
GND
PGND
PGND
PGND
PGND
GND
VDDP
BOOT
MID_LDO
Copyright
©
2017 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
2
SCL
SDA
STAT
OTG
BATS
ISENL
ISENR
LDO
WQFN-32L 4x4
DS9451-01 March 2017
RT9451
Functional Pin Description
Pin No.
1 to 4
5
6
7
8
9
10
11
Pin Name
VIN
INT
VIO
DP
DM
SCL
SDA
STAT
Pin Function
Power input. Bypass to PGND with a 10F ceramic capacitor. It also provides
power to the load in boost mode.
Interrupt pin (open-drain). This pin is pulled low when a fault occurs.
I/O reference voltage. A VIO level above 0.6V disables automatic D+/D
detection.
USB port D+ input connection.
USB port D input connection.
I
2
C interface clock input. Open-drain output, connect a 10k pull-up resistor.
I
2
C interface data input. Open-drain output, connect a 10k pull-up resistor.
Charge status indicator. Pull low when charge is in progress. Open-drain for
other conditions. This pin can also be controlled through I
2
C register. The STAT
can be used to drive a LED or communicate with a host processor.
Boost mode enable control. Boost mode is turned on whenever this pin is active.
Polarity is user defined through I
2
C register. The pin is disabled by default and
can be enabled through I
2
C register bit.
Auxiliary power supply. Connect to the battery pack to provide power in high
impedance mode. Bypass to GND with a 1F ceramic capacitor.
Charge current sense input. Battery current is sensed via the voltage drop
across an external sense resistor. A 0.1F ceramic capacitor to PGND is
required.
Battery voltage and current sense input. Bypass to PGND with a ceramic
capacitor (minimum 0.1F) if there are long inductive leads to battery.
LDO output. LDO is regulated to 4.9V and drives 60mA of current. Bypass LDO
to GND with a minimum 1F ceramic capacitor. LDO is enabled when VIN is
above the VIN UVLO threshold.
LDO input voltage. Please connect to MID.
Bootstrap supply for high-side gate driver. Connect a 100nF ceramic capacitor
(voltage rating above 10V) from BOOT pin to LX pin.
Internal bias regulator voltage for driver. Connect a 1F ceramic capacitor from
this output to PGND. External loads on VDDP is not allowed.
Pure ground. The exposed pad must be soldered to a large PCB and connected
to GND for maximum thermal dissipation.
Power ground.
Switch node.
Connection point between reverse blocking MOSFET and high-side MOSFET.
Bypass to PGND with a minimum of 10F capacitor. No other circuits are
recommended to connect at MID pin.
12
OTG
13
14
15
16
17
18
19
20, 33
(Exposed Pad)
21 to 25
26 to 30
31, 32
BATS
ISENL
ISENR
LDO
MID_LDO
BOOT
VDDP
GND
PGND
LX
MID
Copyright
©
2017 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS9451-01 March 2017
www.richtek.com
3
RT9451
Functional Block Diagram
VIN
MID_LDO
LDO
VDDP
LDO
V
REF
I
BIAS
LX
Switching
Charger
MID
BASE
VIO
DP
DM
Protection
D+/D-
Detection
STAT
PGND
BOOT
ISENL
ISENR
BATS
INT
Logic
I C
Interface
2
SCL
SDA
GND
OTG
OSC
Operation
The RT9451 is designed for single cell Li-Ion battery charger
in portable applications.
Base Circuits
Base circuits provide the internal power, VDD and reference
voltage and bias current.
Protection Circuits
The protection circuits include the OVP, UVLO and OTP
circuits. The protection circuits turn off the charging when
the input power or die temperature is in abnormal level.
Switching Charger
The switching charger controls the operation during the
charging process. The controller will make sure the battery
is well charged in a suitable current, voltage, and die
temperature.
Logic Circuits
The STAT and INT indicate the charger and interrupt
condition. During the charging process, the STAT pin is
Copyright
©
2017 Richtek Technology Corporation. All rights reserved.
pulled low and pulled high when the charger is under
abnormal condition or charge done. The INT pin indicates
the fault condition. When any fault occurs, the INT is pulled
low.
LDO
The RT9451 provides a 50mA LDO to support the peripheral
circuits. The output voltage is regulated to 4.9V and the
maximum output current is 120mA.
OSC
The oscillator runs at fixed 375kHz frequency for the PWM
control of switching charger.
I
2
C Interface
The I
2
C interface is used to program battery voltage, charge
current, termination current, MIVR level, and OTG voltage.
D+/D− Detection
−
The D+/D− detection can detect the devices which are
inserted to the USB connector.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
4
DS9451-01 March 2017
RT9451
Absolute Maximum Ratings
(Note 1)
−0.3V
to 28V
−0.3V
to 28V
−0.3V
to 6V
±6V
4A
100mA
Supply Voltage VIN -------------------------------------------------------------------------------------------------------
MID, BOOT to PGND ----------------------------------------------------------------------------------------------------
Other Pins ------------------------------------------------------------------------------------------------------------------
V
ISENL
to V
ISENR
-----------------------------------------------------------------------------------------------------------
Output Current (average) LX --------------------------------------------------------------------------------------------
Output Current (continuous) LDO -------------------------------------------------------------------------------------
Power Dissipation, P
D
@ T
A
= 25°C
WQFN-32L 4x4 ------------------------------------------------------------------------------------------------------------ 3.59W
Package Thermal Resistance (Note 2)
WQFN-32L 4x4,
θ
JA
------------------------------------------------------------------------------------------------------ 27.8°C/W
WQFN-32L 4x4,
θ
JC
------------------------------------------------------------------------------------------------------
Junction Temperature ----------------------------------------------------------------------------------------------------
Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------
Storage Temperature Range --------------------------------------------------------------------------------------------
7°C/W
150°C
260°C
−65°C
to 150°C
ESD Susceptibility (Note 3)
HBM (Human Body Model) --------------------------------------------------------------------------------------------- 2kV
MM (Machine Model) ----------------------------------------------------------------------------------------------------- 200V
(Note 4)
Recommended Operating Conditions
Supply Input Voltage Range, VIN -------------------------------------------------------------------------------------- 4.3V to 12V
Junction Temperature Range -------------------------------------------------------------------------------------------
−40°C
to 125°C
Ambient Temperature Range -------------------------------------------------------------------------------------------
−40°C
to 85°C
Electrical Characteristics
(V
BATS
= 3.6V
±
5%, T
A
= 25°C, unless otherwise specified)
Parameter
Input Currents
Symbol
Test Conditions
Min
Typ
Max
Unit
Battery Discharge Current in
High impedance mode,
High Impedance Mode
I
DISCHARGE
V
BATS
= 4.2 V
SDA = SCL = 0
(ISENL, ISENR, LX, BATS
Pins)
VIN Supply Current
Voltage Regulation
Output Charge Voltage
Voltage Regulation
Accuracy
V
OREG
Operating in voltage regulation,
programmable
0 to 85°C
I
Q
V
IN
> V
IN(MIN)
Charger PWM ON
Charger PWM OFF
--
2
30
A
--
--
10000
--
--
5000
A
3.5
1
--
--
4.44
1
V
%
Copyright
©
2017 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS9451-01 March 2017
www.richtek.com
5
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