RT8720A

®
RT8720A
Single-Phase Full-Wave Fan Motor Driver
General Description
Features
The RT8720A is a single-phase driver IC for fan motors.
Rotation speed is controlled by supply voltage modulation
and PWM input signal. The RT8720A provides several
protection features including lock protection, thermal
shutdown, over-current protection and under-voltage
protection. In thermal shutdown mode, the supply current
is less than 100μA. The rotation frequency is generated
by FG output.

Low Supply Current

PWM Supply Voltage Control Fan Speed
Supply Voltage Speed Control
Smart Force Start-up Function
Built-in Lock Protection
Built-in Thermal Shutdown
Built-in Over-Current Protection
Built-in Frequency Generator with FG Output Signal
Include Hall Bias Circuit
RoHS Compliant and Halogen Free







Ordering Information

RT8720A
Applications
Package Type
QU : UDFN-8SL 2x2 (U-Type)

Lead Plating System
G : Green (Halogen Free and Pb Free)
Single-Phase Fan Motor for Notebook or PC
Pin Configurations
Note :
Richtek products are :
(TOP VIEW)
RoHS compliant and compatible with the current requireOUT2
H+
HB
H-
ments of IPC/JEDEC J-STD-020.

Suitable for use in SnPb or Pb-free soldering processes.
1
2
3
4
8
GND

9
7
6
5
OUT1
VCC
PWM
FG
UDFN-8SL 2x2
Marking Information
1U : Product Code
1UW
W : Date Code
Simplified Application Circuit
Optional
Supply
Voltage
RT8720A
OUT2
D1
VCC
D2
Pull-High Voltage
C1
RFG
Single-Phase
Brushless
DC Motor
OUT1
H+
FG
HB
PWM Control Signal
DS8720A-01 February 2014
Hall
PWM
GND
Copyright © 2014 Richtek Technology Corporation. All rights reserved.
M
H-
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1
RT8720A
Function Pin Description
Pin No.
Pin Name
Pin Function
1
OUT2
Output of H-Bridge for DC Motor.
2
H+
Positive Hall Input.
3
HB
Hall Bias Voltage Output.
4
H
Negative Hall Input.
5
FG
Output for Rotation Speed. This is an open drain output.
6
PWM
PWM Signal Input.
7
VCC
Power Supply Input.
8
OUT1
Output of H-Bridge for DC Motor.
9 (Exposed Pad)
GND
Power Ground. The Exposed Pad should be soldered to a large PCB and
connected to GND for maximum thermal dissipation.
Function Block Diagram
OUT2
VCC
H+
OUT1
+
VCC
-
-
+
Control
H-
PWM
+
+
-
-
OSC
Lock
Protection
GND
TSD
OCP
FG
+
-
Copyright © 2014 Richtek Technology Corporation. All rights reserved.
www.richtek.com
2
Hall
Bias
HB
is a registered trademark of Richtek Technology Corporation.
DS8720A-01 February 2014
RT8720A
Operation
Operation Mode
Motor Lock Protection and Automatic Restart
The operation mode of the RT8720A is determined by the
external PWM input. During power up, if the PWM input
stays at a low-level voltage, the IC will enter low-power
standby mode. If the PWM input is kept at a high-level
voltage or with a periodic pulse signal, the IC will operate
in normal mode. On the other hand, during normal mode
operation, when the PWM input is set to a low-level voltage
for more than 1ms (typ.), the IC will enter low-power standby
mode. In the standby mode, the supply current can be
reduced to 100μA. Once the PWM input is pulled high
again, the IC will be activated immediately for normal
operation.
When the motor is locked, the RT8720A will try to restart the motor within 0.5 seconds typically (tON). If the
H+
H-
tSD = 1ms
PWM
Mode
motor fails to re-start, the driver will disable the output
regardless of the PWM duty ratio to prevent the motor
coil from burnout. After the lock off-time of 5 seconds in
typical (tOFF), the driver will try to restart the motor again.
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 PWM input is pulled low.
OUT1
Normal Mode
Standby Mode
Normal Mode
OUT2
FG
ICC
tON
Copyright © 2014 Richtek Technology Corporation. All rights reserved.
DS8720A-01 February 2014
tOFF
tON
tOFF
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
3
RT8720A
Absolute Maximum Ratings











(Note 1)
Supply Input Voltage, VCC (<300ns) ----------------------------------------------------------------------------- −0.3V to 10V
Hall Input Voltage Range, H+, H− --------------------------------------------------------------------------------- −0.3V to 6V
PWM Input Voltage, PWM ------------------------------------------------------------------------------------------ −0.3V to 6V
Output Voltage, OUT1, OUT2, FG --------------------------------------------------------------------------------- −0.3V to 7V
Maximum Output Current, OUT1, OUT2 ------------------------------------------------------------------------- 1A
Power Dissipation, PD @ TA = 25°C
UDFN-8SL 2x2 --------------------------------------------------------------------------------------------------------- 2.78W
Package Thermal Resistance (Note 2)
UDFN-8SL 2x2, θJA --------------------------------------------------------------------------------------------------- 35.9°C/W
Junction Temperature ------------------------------------------------------------------------------------------------- 150°C
Lead Temperature (Soldering, 10 sec.) --------------------------------------------------------------------------- 260°C
Storage Temperature Range ---------------------------------------------------------------------------------------- −65°C to 150°C
ESD Susceptibility (Note 3)
HBM (Human Body Model) ------------------------------------------------------------------------------------------ 4kV
Recommended Operating Conditions





(Note 4)
Supply Input Voltage, VCC ------------------------------------------------------------------------------------------ 1.8V to 5.5V
Hall Input Voltage, H+, H− ------------------------------------------------------------------------------------------- 0.4V to (VCC − 1.1V)
PWM Input Voltage, PWM ------------------------------------------------------------------------------------------ 0V to VCC
Junction Temperature Range ---------------------------------------------------------------------------------------- −40°C to 125°C
Ambient Temperature Range ---------------------------------------------------------------------------------------- −40°C to 85°C
Electrical Characteristics
(VCC = 5V, TA = 25°C, Unless Otherwise specification)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
Operating Current
I CC1
Rotation Mode and Lock Protection
Mode
--
3.5
5
mA
Standby Current
I CC2
Standby Mode (PWM = 0)
--
100
A
kHz
PWM Input
Voltage
High-Level
V PWM_H
1.8
--
Low-Lev el
V PWM_L
0
--
200
V CC
+ 0.5
0.7
F PW M
2
--
50
High-Level
IPWM_H
--
0
5
Low-Lev el
IPWM_L
30
10
--
PWM Input Frequency
PWM Input
Leakage
V
V
A
Input-Output Gain
GIO
VOUT / H+  H- (Ratio)
42
44.6
47
dB
Output Voltage
VO
IO = 250mA, Upper and Lower total
--
0.2
0.4
V
FG Pin Low Voltage
V FG
IFG = 5mA
--
0.1
0.2
V
FG Pin Leak Current
I FG
VFG = 5V
--
--
1
A
Input Offset Voltage
V HOFS
--
--
6
mV
Input Hysteresis Voltage
V Hys
 5
10
15
mV
Copyright © 2014 Richtek Technology Corporation. All rights reserved.
www.richtek.com
4
is a registered trademark of Richtek Technology Corporation.
DS8720A-01 February 2014
RT8720A
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
Lock Detection On-Time
t ON
0.35
0.5
0.65
s
Lock Detection Off-Time
t OFF
3.5
5
6.5
s
Thermal Shutdown Threshold
--
160
--
C
Thermal Shutdown Hysteresis
--
30
--
C
Standby Detection Time
tSD
0.7
1
1.3
ms
Quick Start Enable Time
tQS
--
30
--
s
Hall Bias Voltage
VHB
1.26
1.3
1.34
V
Supply Voltage Threshold
VCC_TH
3
3.5
4
V
IHB = 5mA
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.
Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
Copyright © 2014 Richtek Technology Corporation. All rights reserved.
DS8720A-01 February 2014
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
5
RT8720A
Typical Application Circuit
Optional
Supply
Voltage
RT8720A
7 VCC
OUT2 1
D1
D2
C1
Single-Phase
Brushless
DC Motor
6 PWM
PWM Control Signal
RFG
Pull-High Voltage
M
OUT1 8
HB 3
5 FG
9 (Exposed Pad)
GND
H+ 2
4
H-
Hall
Figure 1. Fan Speed Controlled by Direct PWM Input, it's known as “PWM Mode”.
Optional
Supply
Voltage
RT8720A
7 VCC
OUT2 1
D1
D2
C1
6 PWM
Floating
Pull-High Voltage
Single-Phase
Brushless
DC Motor
RFG
5 FG
9 (Exposed Pad)
GND
M
OUT1 8
HB 3
H+ 2
4
H-
Hall
Figure 2. Fan Speed Controlled by Supply Voltage, it's known as “VCC Mode”.
Copyright © 2014 Richtek Technology Corporation. All rights reserved.
www.richtek.com
6
is a registered trademark of Richtek Technology Corporation.
DS8720A-01 February 2014
RT8720A
Application Information
PWM Speed Control
Quick Start Function
The motor speed can be controlled by the external signal
at PWM pin and the supply input voltage. When a PWM
signal is provided to the PWM pin, the driver output will
follow the duty ratio of the PWM input signal. The switching
frequency of the driver is dependent on the PWM input
frequency. Therefore, the motor speed is controlled by
the PWM signal. The available PWM input frequency range
is from 2kHz to 50kHz. When the PWM input is fixed at a
high-level voltage (>1.8V) or floating, the motor will rotate
with full speed. When the PWM input is fixed at a lowlevel voltage (<0.7V), the motor will decelerate to stop. In
standby mode, the supply current can be reduced to
100μA only.
If the PWM is pulled low for a delay time, tSD, the RT8720A
Frequency Generator (FG)
The FG pin is an open drain output. A pull-up resistor (1kΩ
to 10kΩ) is recommended to be connected from this pin
to a high level voltage (<5.5V) for frequency generator
function.
Thermal Shutdown
The RT8720A provides a thermal shutdown function to
prevent overheating due to excessive power dissipation.
The function shuts down the switching operation when
the junction temperature exceeds 160°C. Once the
junction temperature cools down by around 30°C, the main
converter will automatically resume switching. To maintain
continuous operation, the junction temperature should be
kept below 130°C.
Copyright © 2014 Richtek Technology Corporation. All rights reserved.
DS8720A-01 February 2014
will enter standby mode. Once a PWM signal is detected,
the RT8720A will provide outputs after a delay time, tQS.
Standby
PWM
FG
OUT
tSD
Figure 3
PWM
Standby
FG
OUT
tQS
Figure 4
Over-Current Protection
The RT8720A includes an Over-Current Protection (OCP)
feature to prevent the large supply current form supply
voltage to output. When the over-current occurs, the circuit
will disable the output and the motor rotor will stop. After
a time duration (tOFF, typical 5s), the IC will automatically
try to restart the motor. If the supply current is still larger,
the output will be shut down immediately.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
7
RT8720A
the motor to rotate because of its low duty, an internal
PWM signal with higher duty will be adopted to drive the
motor. The internal PWM duty varies according to input
voltage VCC (VCC ≥ 3.5V, duty = 50%; VCC < 3.5V, duty
Force Start-Up Control
The motor speed is controlled by the external PMW signal.
In order to successfully start the motor with lower PWM
duty, a start-up mechanism is applied to check if output
duty from the external PWM signal can drive the motor to
rotate in a period (0.4 x tON, typ. 0.2s). If it cannot drive
= 100%).
VCC_TH = 3.5V
VCC
FG
OUT
External PWM (Lower Duty)
50% Duty
External PWM (Lower Duty)
0.4 x tON (typ. 0.2s)
Max. ~0.6 x tON (typ. 0.3s)
Figure 5. Forced Start-Up when VCC > VCC_TH
VCC_TH = 3.5V
VCC
FG
OUT
External PWM (Lower Duty)
Output = VCC
0.4 x tON (typ. 0.2s)
Max. ~0.6 x tON (typ. 0.3s)
External PWM (Lower Duty)
Figure 6. Forced Start-Up-1 when VCC ≤ VCC_TH
FG Output when Motor is in the Lock State
VCC
Hall_Comp
FG
Lock Detection
On-Time
0.5s
Lock Detection Off-Time
5s
Figure 7. FG Output when Motor is in the Lock State
VCC
Hall_Comp
FG
Lock Detection
On-Time
0.5s
Lock Detection Off-Time
5s
Figure 8. FG Output when Motor is in the Lock State-1
Copyright © 2014 Richtek Technology Corporation. All rights reserved.
www.richtek.com
8
is a registered trademark of Richtek Technology Corporation.
DS8720A-01 February 2014
RT8720A
Truth Table
H-
H
L
L
H
H
L
L
H
H
L
L
H
--
--
PWM
H
L
-L
OUT1
OUT2
FG
H
L
L (Output : ON)
L
H
Z (Output : OFF)
L
L
L (Output : ON)
L
L
Z (Output : OFF)
L
L
Z (Output : OFF)
L
L
Z (Output : OFF)
L
L
Z (Output : OFF)
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 :
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.
For recommended operating condition specifications, the
maximum junction temperature is 125°C. The junction to
ambient thermal resistance, θJA, is layout dependent. For
UDFN-8SL 2x2 package, the thermal resistance, θJA, is
35.9°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 :
Maximum Power Dissipation (W)1
H+
Mode
Operation Mode
Lock Mode
Standby Mode
3.0
Four-Layer PCB
2.5
2.0
1.5
1.0
0.5
0.0
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 9. Derating Curve of Maximum Power Dissipation
PD(MAX) = (125°C − 25°C) / (35.9°C/W) = 2.78W for
UDFN-8SL 2x2 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 9 allows the
designer to see the effect of rising ambient temperature
on the maximum power dissipation.
Copyright © 2014 Richtek Technology Corporation. All rights reserved.
DS8720A-01 February 2014
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
9
RT8720A
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
0.500
0.600
0.020
0.024
A1
0.000
0.050
0.000
0.002
A3
0.100
0.175
0.004
0.007
b
0.200
0.300
0.008
0.012
D
1.900
2.100
0.075
0.083
D2
1.650
1.750
0.065
0.069
E
1.900
2.100
0.075
0.083
E2
0.850
0.950
0.033
0.037
e
L
0.500
0.250
0.020
0.350
0.010
0.014
U-Type 8SL DFN 2x2 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.
www.richtek.com
10
DS8720A-01 February 2014