DS8749 00

®
RT8749
Digital Single-Phase Full Wave BLDC Fan Controller
General Description
Features
The RT8749 is a highly integrated digital control IC for
regulating single-phase full wave brushless DC (BLDC)
fans at a programmed speed. The controller IC accepts a
Pulse-Width Modulated (PWM) signal provided by the
host, and decodes the duty-ratio of this PWM signal to
256 counts. The decoded duty-ratio will then be used for
mapping to the programmed speed which is stored at the
embedded flash memory. This speed profile can be
programmed by users for different fan models and
applications. By integrating a low RDS(ON) power MOSFET,

the RT8749 minimizes component count on the PCB, thus
reducing board size and cost of the motor/fan module.
A frequency generator output is included to provide
commutation signals to the host for the current rotating
speed. The control IC also provides several protection
features, including the peak-current limit, thermal shutdown
protection, under-voltage protection and motor lock
protection. An automatic restart circuit is designed to
rotate the motor after the lock condition is released.
Embedded 256 x 16 Bits Flash Memory
Built-in Low RDS(ON) Power MOSFET
 External PWM Speed Control
 Wide Range External PWM Input Frequency
(100Hz to 100kHz)
 Built-in Frequency Generator with Selectable FG
or FG/2 Output Signal
 Built-in Peak Current Limit
 Built-in Motor Lock Protection and Automatic
Restart Circuit
 Built-in Thermal Shutdown Protection
 Low Power Standby Mode (when PWM Input is
Low)
 RoHS Compliant and Halogen Free

Applications



PC Fan
Cooling Fan
Single-Phase BLDC Motor
Simplified Application Circuit
RT8749
RNF
OUT1
OUT2
BOOT1
VDD12 BOOT2
VDD
VDD12M
External Voltage Source (up
to 12V) or V5DDA (V5DDA
will disable at Standby Mode)
RRNF
V5DDD
V5DDA
V5DDA
ROSC
HN
ROSC
RFG
HP
FG
PWM
H
GND
VSS12
PWM Signal
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
DS8749-00 January 2015
is a registered trademark of Richtek Technology Corporation.
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1
RT8749
Ordering Information
Marking Information
RT8749
2U= : Product Code
Package Type
QW : WDFN-16L 4x4
YMDNN : Date Code
2U=YM
DNN
Lead Plating System
G : Green (Halogen Free and Pb Free)
Note :
Pin Configurations
Richtek products are :

(TOP VIEW)
RoHS compliant and compatible with the current requireOUT1
BOOT1
VDD12M
VDD12
VSS12
ROSC
FG
PWM
ments of IPC/JEDEC J-STD-020.

Suitable for use in SnPb or Pb-free soldering processes.
1
2
3
4
5
6
7
8
GND
17
16
15
14
13
12
11
10
9
RNF
OUT2
BOOT2
V5DDD
GND
V5DDA
HN
HP
WDFN-16L 4x4
Functional Pin Description
Pin No.
Pin Name
Pin Function
1
OUT1
Driver Output to Motor Terminal 1.
2
BOOT1
Bootstrap Supply for Motor Terminal 1. Connect a capacitor between this pin
and OUT1.
3
VDD12M
Input Power Source for H-Bridge Power MOSFET and Driver.
4
VDD12
Input Power Source for Internal Circuits.
5
VSS12
Ground of Internal Circuits.
6
ROSC
Internal Oscillator Frequency Setting. Connect a resistor with low temperature
coefficient between this pin and grand.
7
FG
Frequency Output Signal with Open-Drain Logic.
8
PWM
External PWM Input. With an internal pull-high resistor (200k).
9
HP
Positive Input Signal of Hall Sensor.
10
HN
Negative Input Signal of Hall Sensor.
11
V5DDA
Regulated 5V Power Source for Hall Sensor.
12, 17 (Exposed Pad) GND
Ground. The exposed pad must be soldered to a large PCB and connected to
GND for maximum power dissipation.
13
V5DDD
Regulated 5V Power Source for Digital Circuit.
14
BOOT2
Bootstrap Supply for Motor Terminal 2. Connect a capacitor between this pin
and OUT2.
15
OUT2
Driver Output to Motor Terminal 2.
16
RNF
Output Current Detection. Connect to a resistor for H-Bridge over-current
protection.
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DS8749-00 January 2015
RT8749
VDD12M
V5DDA
VSS12
VDD12
V5DDD
HN
HP
Function Block Diagram
V5DDD
Prog
Hall Intf
Regulator
BOOT1
Prog Intf
Confi.
Regs
Digital
Controller
RNF
Driver
VDD12M
V5DDD
Duty-to-RPM
PWM
ROSC
Flash Memory
OUT1
BOOT2
OUT2
OSC
Prog
GND
TSD
OCP
RNF
FG
Operation
The highly integrated digital controlled fan controller
RT8749 integrates several functions as follows :
OTP
The over-temperature protection block is activated when
the junction temperature exceeds 150°C. It will be released
when the temperature cools below 120°C. The hysteresis
is 30°C.
OCP
The RT8749 features over-current protection function to
protect the power MOSFET. Users need to add a resistor
RRNF between the low-side N-MOSFET and GND. If over
current protection is activated, the RT8749 will be
shutdown.
Hall Interface
The Hall Interface receives hall element signal and then
helps the RT8749 to recognize the fan position. The
controller will control the current direction by recognized
fan position.
Oscillator
The Oscillator generates the high accuracy 1MHz clock
signal for PWM output frequency. The PWM output
frequency is 31.25kHz typically.
Digital Controller
This block generates control signal to the driver for motor
operation control. It controls the motor speed depending
on duty to RPM converter, reference speed table and
control parameters which are stored in the flash memory.
Regulator
The inherent voltage regulator generates regulated 5V
output for V5DDD & V5DDA respectively.
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DS8749-00 January 2015
Program Interface
The Program Interface is used for programming flash
memory purpose.
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RT8749
Absolute Maximum Ratings














(Note 1)
Supply Voltage, VDD12M, VDD12 ------------------------------------------------------------------------------------Output Current, IOUT -----------------------------------------------------------------------------------------------------Input Voltage, PWM -----------------------------------------------------------------------------------------------------Output Voltage, OUT1, OUT2, FG ------------------------------------------------------------------------------------BOOT1 to OUT1 ----------------------------------------------------------------------------------------------------------BOOT2 to OUT2 ----------------------------------------------------------------------------------------------------------FG Output Current --------------------------------------------------------------------------------------------------------Other Pins ------------------------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C
WDFN-16L 4x4 ------------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2)
WDFN-16L 4x4, θJA ------------------------------------------------------------------------------------------------------WDFN-16L 4x4, θJC ------------------------------------------------------------------------------------------------------Junction Temperature Range -------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------Storage Temperature Range -------------------------------------------------------------------------------------------ESD Susceptibility (Note 3)
HBM (Human Body Model) ----------------------------------------------------------------------------------------------
Recommended Operating Conditions



−0.3V to 20V
0.95A
−0.3V to 20V
−0.3V to 20V
−0.3V to 6V
−0.3V to 6V
15mA
−0.3V to 6V
3.38W
29.5°C/W
7.5°C/W
150°C
260°C
−65°C to 150°C
4kV
(Note 4)
Supply Input Voltage, VDD12 ------------------------------------------------------------------------------------------- 5.8V to 14V
Junction Temperature Range -------------------------------------------------------------------------------------------- −40°C to 125°C
Ambient Temperature Range -------------------------------------------------------------------------------------------- −40°C to 85°C
Electrical Characteristics
(VDD12 = 12V, TA = 25°C, unless otherwise specified)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
Power Dissipation
Power Supply Current 1
IDD1
VPWM = 5V Without Loading
--
--
10
mA
Power Supply Current 2
IDD2
VPWM = 0V
--
--
300
A
UGATE On-Resistance
(N-MOSFET)
RDS(ON)_UGATE
IOUT = 0.8A
--
0.4
0.8

LGATE On-Resistance
(N-MOSFET)
RDS(ON)_LGATE
IOUT = 0.8A
--
0.4
0.8

V5DDA Output Voltage
VDDA5
Load Current = 15mA
4.65
5
5.35
V
V5DDD Output Voltage
VDDD5
Load Current = 15mA
4.65
5
5.35
V
--
0.2
0.3
V
0.2
1.3
3
V
Output Driver
V5DDA & V5DDD Output
FG Output
FG Output Low Level Voltage VFG
IFG = 5mA
HP, HN Inputs
Input Voltage Level
VHP, VHN
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RT8749
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
PWM Input
PWM Input
Voltage
Level-High
VPWMH
2.2
--
VDD12
Level-Low
VPWML
0
--
0.7
--
--
50
A
0.1
--
100
kHz
VPW M = 0V
V
PWM Internal Pull-up Current
IPWMIN
PWM Input Frequency
fPWMIN
ROSC Frequency
fROSC
ROSC = 150k
--
1
--
MHz
Current Limit
ILIM
RRNF = 0.25
--
1
--
A
Threshold Voltage
VRNF
0.2
0.25
0.3
V
--
150
--
°C
Current Limitation
Thermal Protection
Thermal Shutdown Temperature
T SD
Note 1. Stresses beyond those listed “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 in
the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions may
affect device reliability.
Note 2. θJA is measured at TA = 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. θJC is
measured at the exposed pad of the package.
Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
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is a registered trademark of Richtek Technology Corporation.
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RT8749
Typical Application Circuit
RT8749
16
RNF
OUT1
15
OUT2
2
BOOT1
4
VDD12 BOOT2 14
V5DDD 13
3
VDD12M
11
V5DDA
1
1µF
VDD
10µF
External Voltage Source (up
to 12V) or V5DDA (V5DDA
will disable at Standby Mode)
6
RRNF
0.25
4.7µF
V5DDA
4.7µF
ROSC
ROSC
150k
RFG
10k
1µF
HN
7
FG
8
PWM
10
H
HP 9
12, 17 (Exposed Pad)
GND
5
VSS12
PWM Signal
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RT8749
Applications Information
Speed Control
The motor speed can be controlled by the external signal
on the PWM pin or controlled by the input voltage on the
VDD12 pin. (Switching input voltage is not allowed). When
the RT8749 operates in input voltage control mode, the
input voltage on VDD12 must be higher than 6V. When
the PWM input is fixed at a high level voltage or floating,
the motor will rotate with memory table's highest bit speed.
When the PWM input is fixed at a low level voltage, the
motor will decelerate to stop if the standby mode is
enabled. Otherwise, the motor will rotate with memory
table's lowest bit speed. When a switching signal is sent
as the PWM input, the duty ratio of the input signal will
be sampled and converted to a 8-bit code. This code is
correspondent to an rotation speed which is stored in the
embedded flash memory. The controller will regulate the
fan motor's speed to this target speed by adjusting the
switching duty ratio of the output drivers. It should be
noted that the input PWM frequency is independent of
the switching frequency of the output drivers. Hence, the
input PWM frequency can be chosen within a wide range,
from 100Hz to 100kHz, while keeping the output switching
frequency at 31.25kHz.
Peak Current Limitation
The DC-link current of the inverter is limited to protect the
power transistors and the motor. When the measured
0.25V
current exceeds the current limit (
), gate signals
RRNF
to the output drivers will be all turned off until the next
switching cycle.
Limit Current
0.25V
RRNF
DC-Link
Current
OCEN
Output
Gate Signal
Desired ONTime
Desired ONTime
Figure 1
Motor Lock Protection and Automatic Restart
Function
When the motor is locked, a lock detection circuit will
detect this situation within a time duration (TLOCK) ,and
will disable the output drivers regardless of the duty ratio
of the PWM to prevent the motor coil from burnout. After
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
DS8749-00 January 2015
the time duration (TREL), the IC will automatically try to
restart the motor. If the motor is still locked, then the
iteration of the lock detection and restart will be repeated
until the lock condition is released or the external PWM
input is pulled low.
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RT8749
PWM
Motor
Speed
FG
TLOCK
Lock
Indicator
TREL
Figure 2. Sequence of Lock and Restart
Low Power Standby Mode
If the PWM input maintains a low level voltage for 20ms
when the standby mode is enabled, the IC will enter the
“low-power standby mode” until the PWM input is pulled
up to a high level voltage. When RT8749 is at standby
mode, V5DDA, OUT1 and OUT2 will be disabled.
PWM
20ms
Normal Mode
Standby Mode
Normal Mode
Figure 3. Sequence of Low Power Standby Mode
Over Temperature Protection
The RT8749 includes an Over Temperature Protection
(OTP) feature to prevent overheating due to excessive
power dissipation. The OTP function shuts down the
switching operation when the junction temperature
exceeds 150°C. Once the junction temperature cools
down by around 25°C, the main converter will
automatically resume switching. To maintain continuous
operation, the junction temperature should be kept below
125°C.
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RT8749
For recommended operating condition specifications, the
maximum junction temperature is 125°C. The junction to
ambient thermal resistance, θJA, is layout dependent. For
RT8749
RFG
VFG
60k
Max.
On : 60
VZ
6V
Figure 4
FG Pull-up Resistance Design
The RT8749's pull-up resistance will influence the FG pin's
high and low voltage. The function block diagram in Figure
4 shows the FG pin's internal circuits. Note that 60kΩ
have ±10% variation and 60Ω is the maximum
on-resistance.
The typical high and low level voltage of the FG pin can be
calculated by the following formula :
VFGHigh = VIN x (60k ±10%) / (RFG + 60k ±10%) + VZ x
RFG / (RFG + 60k ±10%)
VFGLow = VIN x 60 / (RFG +60)
For VIN > 6V, VZ = 6V
For VIN ≤ 6V, VZ = VIN
WDFN-16L 4x4 package, the thermal resistance, θJA, is
29.5°C/W on a standard JEDEC 51-7 four-layer thermal
test board. The maximum power dissipation at TA = 25°C
can be calculated by the following formula :
PD(MAX) = (125°C − 25°C) / (29.5°C/W) = 3.38W for
WDFN-16L 4x4 package
The maximum power dissipation depends on the operating
ambient temperature for fixed T J(MAX) and thermal
resistance, θJA. The derating curve in Figure 5 allows the
designer to see the effect of rising ambient temperature
on the maximum power dissipation.
Maximum Power Dissipation (W)1
VIN
4.00
Four-Layer PCB
3.50
3.00
2.50
2.00
1.50
1.00
0.50
0.00
Thermal Considerations
For continuous operation, do not exceed absolute
maximum junction temperature. The maximum power
dissipation depends on the thermal resistance of the IC
package, PCB layout, rate of surrounding airflow, and
difference between junction and ambient temperature. The
maximum power dissipation can be calculated by the
following formula :
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 5. Derating Curve of Maximum Power Dissipation
PD(MAX) = (TJ(MAX) − TA) / θJA
where TJ(MAX) is the maximum junction temperature, TA is
the ambient temperature, and θJA is the junction to ambient
thermal resistance.
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
DS8749-00 January 2015
is a registered trademark of Richtek Technology Corporation.
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RT8749
Outline Dimension
2
1
2
1
DETAIL A
Pin #1 ID and Tie Bar Mark Options
Note : The configuration of the Pin #1 identifier is optional,
but must be located within the zone indicated.
Symbol
Dimensions In Millimeters
Dimensions In Inches
Min.
Max.
Min.
Max.
A
0.700
0.800
0.028
0.031
A1
0.000
0.050
0.000
0.002
A3
0.175
0.250
0.007
0.010
b
0.150
0.250
0.006
0.010
D
3.900
4.100
0.154
0.161
D2
3.350
3.450
0.132
0.136
E
3.900
4.100
0.154
0.161
E2
2.650
2.750
0.104
0.108
0.450
e
L
0.350
0.018
0.450
0.014
0.018
W-Type 16L DFN 4x4 Package
Richtek Technology Corporation
14F, No. 8, Tai Yuen 1st Street, Chupei City
Hsinchu, Taiwan, R.O.C.
Tel: (8863)5526789
Richtek products are sold by description only. Richtek reserves the right to change the circuitry and/or specifications without notice at any time. Customers should
obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. Richtek cannot
assume responsibility for use of any circuitry other than circuitry entirely embodied in a Richtek product. Information furnished by Richtek is believed to be
accurate and reliable. However, no responsibility is assumed by Richtek or its subsidiaries for its use; nor for any infringements of patents or other rights of third
parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Richtek or its subsidiaries.
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