RT8810B [RICHTEK]
暂无描述;
| 型号： | RT8810B |
| 厂家： | 
RICHTEK TECHNOLOGY CORPORATION |
| 描述： | 暂无描述 |
| 文件： | 总22页 (文件大小：424K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
RT8810
Dual-Phase Synchronous Buck PWM Controller
General Description
Features
z Single IC Supply Voltage : 4.5V to 13.2V
z Supports Manual / Auto Dynamic Phase Number
Control
The RT8810 is a dual phase synchronous buck controller
which can provide users with a compact, high efficient,
well protected and cost effective solution. The RT8810's
integrated high driving capability MOSFET drivers makes
it more attractive for high current application. The built-in
bootstrap diode simplifies the circuit design and reduces
external part count and PCB space. For output voltage
control, the RT8810 can precisely regulate feedback
voltage according to the internal reference voltage 0.6V or
external reference voltage from 0.4V to 2.5V.
z Integrated Bootstrap Diode
z Lossless RDS(ON) Current Sensing for Current Balance
z Adjustable Operation Frequency : 100kHz to 1MHz
z Adjustable Over Current Protection
z Capacitor Programmable Soft-Start
z Support 0% to 80% Duty Cycle
z Selectable Internal/External VREF
z Voltage Mode PWM Control with External
Feedback Loop Compensation
The MODE pin programs single phase or dual phase
operation, making the RT8810 suitable for dual power input
applications such as PCI-Express interface graphic cards.
To set RT8810 at automatic mode, the RT8810 operates
in single phase at light load condition and maintains high
efficiency over a wide range of output currents. In addition,
the RT8810 features adjustable gate driving voltage for
maximum efficiency and optimum performance.
z Phase Crosstalk Jitter Suspend (CJSTM
z Programmable Quick Response
z Driver Shoot Through Protection
z Supports Current Reporting
)
z 16-Lead WQFN and 24-Lead WQFN Packages
z RoHS Compliant and Halogen Free
The RT8810 adopts lossless RDS(ON) current sensing
technique for channel current balance and over current
protection. Other features include adjustable soft-start,
adjustable operation phase, and adjustable over current
threshold.
Applications
z GPU Core Power
z Desktop PC Memory, VTT Power
z Low Output Voltage, High Power Density DC/DC
Converters
z Voltage Regulator Modules
Ordering Information
RT8810
Package Type
QW : WQFN-16L 3x3 (W-Type)
QW : WQFN-24L 4x4 (W-Type)
Lead Plating System
G : Green (Halogen Free and Pb Free)
Z : ECO (Ecological Element with
Halogen Free and Pb free)
Product Classification
A : Only for WQFN-24L 4x4
B : Only for WQFN-16L 3x3
(With MODE Pin)
C : Only for WQFN-16L 3x3
(With REFIN Pin)
Note :
Richtek products are :
` 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.
D : Only for WQFN-24L 4x4
DS8810-01 June 2011
www.richtek.com
1
RT8810
Marking Information
RT8810BGQW
RT8810CGQW
RT8810DGQW
RT8810AGQW
EL=YM
DNN
JU=YM
DNN
JV=YM
DNN
02=YM
DNN
EL= : Product Code
YMDNN : Date Code
JU= : Product Code
YMDNN : Date Code
JV= : Product Code
YMDNN : Date Code
02= : Product Code
YMDNN : Date Code
RT8810BZQW
RT8810CZQW
RT8810DZQW
RT8810AZQW
EL YM
DNN
JU YM
DNN
JV YM
DNN
02 YM
DNN
EL : Product Code
YMDNN : Date Code
JU : Product Code
YMDNN : Date Code
JV : Product Code
YMDNN : Date Code
02 : Product Code
YMDNN : Date Code
Pin Configurations
(TOP VIEW)
24 23 22 21 20 19
16 15 14 13
1
2
3
18
NC
PGND
UGATE1
BOOT1
AGND
PHASE2
1
2
3
4
12
11
10
9
PHASE1
UGATE1
BOOT1
MODE
PHASE2
UGATE2
BOOT2
SS/EN
17
PGND
UGATE2
16
PGND
PGND
4
5
6
15
14
13
BOOT2
SS/EN
QR1
17
25
REFIN
5
6
7
8
7
8
9
10 11 12
WQFN-24L 4x4
RT8810A
WQFN-16L 3x3
RT8810B
24 23 22 21 20 19
16 15 14 13
1
2
3
18
NC
PGND
UGATE1
BOOT1
AGND
PHASE2
PGND
UGATE2
BOOT2
SS/EN
QR1
1
2
3
4
12
PHASE1
UGATE1
BOOT1
REFIN
PHASE2
UGATE2
BOOT2
SS/EN
17
16
11
10
9
PGND
PGND
4
5
6
15
14
13
17
25
REFIN
5
6
7
8
7
8
9 10 11 12
WQFN-16L 3x3
RT8810C
WQFN-24L 4x4
RT8810D
www.richtek.com
DS8810-01 June 2011
2
RT8810
Typical Application Circuit
V
IN
12V
C7
10µF x 5
RT8810
R1
10
BOOT1
VCC
R
0
C
BOOT1
C1
1µF
BOOT1
0.1µF
VOUT
1.1V
PVCC9
PVCC
UGATE1
Q1
C6
1µF
R
L1
1µH
UG1
0
R2
0
PHASE1
LGATE1
BOOT2
C2
1µF
C8
820µF x 2
/2.5V
C9
R11*
C17*
Q2
10µF x 4
/16V
V
REFIN
REFIN
R
0
BOOT2
C14
0.1µF
C
C10
10µF x 5
BOOT2
MODE
IMAX
0.1µF
R
MODE
Q3
Q4
UGATE2
PHASE2
L2
33k
R
UG2
0
1µH
R
IMAX
100k
C11
820µF x 2
/2.5V
C13
NC
C12
10µF x 4
/16V
RT
R12*
LGATE2
PGND
FB
R7
1.5k
R
18k
RT
SS/EN
C18*
R9
NC
C
SS
0.1µF
24k
R10
COMP
AGND
R8
1.8k
QR2
QR1
C5
4.7nF
C4
33pF
C15
100pF
C16
NC
R6
20k
* : Option
Figure 1. RT8810A/D
DS8810-01 June 2011
www.richtek.com
3
RT8810
V
IN
12V
C7
10µF x 5
R1
10
RT8810
BOOT1
VCC
R
0
BOOT1
C1
1µF
C
BOOT1
0.1µF
PVCC9
PVCC
VOUT
1.1V
C6
UGATE1
Q1
L1
1µH
1µF
R
R2
0
UG1
0
PHASE1
LGATE1
BOOT2
C9
10µF x 4
/16V
C2
1µF
C8
820µF x 2
/2.5V
R11*
C17*
Q2
MODE
IMAX
R
BOOT2
0
R
MODE
33k
C
BOOT2
C10
10µF x 5
0.1µF
R
IMAX
100k
Q3
Q4
UGATE2
PHASE2
L2
1µH
R
UG2
0
RT
R
RT
18k
C12
C13
NC
C11
SS/EN
R12*
C18*
820µF x 2
10µF x 4
C
0.1µF
SS
LGATE2
PGND
FB
R7
1.5k
/2.5V
/16V
R9
NC
COMP
R8
1.8k
C5
4.7µF
AGND
C4
33pF
R6
20k
* : Option
Figure 2. RT8810B
www.richtek.com
4
DS8810-01 June 2011
RT8810
V
IN
12V
C7
10µF x 5
R1
10
RT8810
BOOT1
VCC
R
0
C
BOOT1
C1
1µF
BOOT1
0.1µF
PVCC9
PVCC
VOUT
1.1V
C6
UGATE1
Q1
L1
1µH
1µF
R
R2
0
UG1
0
PHASE1
LGATE1
BOOT2
C2
1µF
C9
10µF x 4
/16V
C8
R11*
C17*
Q2
820µF x 2
/2.5V
V
REFIN
IMAX
REFIN
R
0
C14
0.1µF
BOOT2
C10
C
BOOT2
10µF x 5
0.1µF
R
100k
IMAX
Q3
Q4
UGATE2
PHASE2
L2
R
RT
UG2
0
1µH
R
18k
RT
SS/EN
C13
NC
C12
10µF x 4
C11
820µF x 2
C
0.1µF
SS
R12*
C18*
LGATE2
PGND
FB
/16V
R7
/2.5V
R9
NC
1.5k
COMP
C5
R8
1.8k
4.7nF
AGND
C4
33pF
R6
20k
* : Option
Figure 3. RT8810C
DS8810-01 June 2011
www.richtek.com
5
RT8810
Functional Pin Description
Pin No.
Pin Name
Pin Function
WQFN-16L
3x3
WQFN-24L
4x4
--
1
NC
No Internal Connection.
Power Ground for the IC. These pins are ground returns for the
gate drivers. Tie these pins to the ground island/plane through the
lowest impedance connection available. The exposed pad must be
soldered to a large PCB and connected to PGND for maximum
power dissipation.
2, 17,
25
(Exposed Pad)
17
PGND
(Exposed Pad)
Upper Gate Driver Output for Channel 1. Connect this pin to the
gate of upper MOSFET. This pin is monitored by the adaptive shoot
through protection circuitry to determine when the upper MOSFET
has turned off.
2
3
4
UGATE1
BOOT1
Bootstrap Supply for the Floating Upper Gate Driver of Channel 1.
Connect the bootstrap capacitor C
1 between BOOT1 pin and
BOOT
3
the PHASE1 pin to form a bootstrap circuit. The bootstrap capacitor
provides the charge to turn on the upper MOSFET.
All voltages levels are measured with respect to this pin. Tie this pin
to the ground island/plane through the lowest impedance
connection available.
--
5
6
AGND
REFIN
External Reference Input. This is the input pin for the external
reference voltage. If external reference voltage is not available,
leave this pin open for default internal 0.6V reference.
4
(RT8810C)
Operation Phase Control Input. Connect a resistor R
from this
MODE
pin to GND to set the threshold current level for single and dual
phase operations. The RT8810 operates in dual phase if the output
current is higher than the threshold current level; in single phase if
the output current is lower than the threshold current level; see the
related sections for detail. Tie this pin to GND for continuous single
phase operation. Leave this pin open for continuous dual phase
operation. Both upper and lower switches of PHASE2 are turned off
when operating in single phase.
4
7
MODE
(RT8810B)
Output Current Indication. Connect this pin to ground with a resistor
to set the output over current protection level.
5
6
8
9
IMAX
RT
Operation Frequency Setting. Connect a resistor between this pin
and AGND to set the operation frequency.
Error Amplifier Output. This is the output of the Error Amplifier (EA)
and the non-inverting input of the PWM comparators. Use this pin in
combination with the FB pin to compensate the voltage-control
feedback loop of the converter
7
8
10
11
COMP
FB
Feedback Voltage. This pin is the inverting input to the error
amplifier. Aresistor divider from the output to GND is used to set the
regulation voltage.
--
--
12
13
QR2
QR1
Quick Response Setting Pin for Load Transition.
Quick Response Setting Pin for Load Transition.
Soft-Start Output. Connect a capacitor from this pin to GND to set
the soft-start interval. Pulling this pin low to 0.4V will shut down the
RT8810.
9
14
SS/EN
To be continued
www.richtek.com
6
DS8810-01 June 2011
RT8810
Pin No.
Pin Name
Pin Function
WQFN-16L WQFN-24L
3x3
4x4
Bootstrap Supply for the Floating Upper Gate Driver of Channel 2.
Connect the bootstrap capacitor between BOOT2 pin and the PHASE2
pin to form a bootstrap circuit. The bootstrap capacitor provides the
charge to turn on the upper MOSFET.
10
15
BOOT2
Upper Gate Driver Output for Channel 2. Connect this pin to the gate of
upper MOSFET. This pin is monitored by the adaptive shoot through
protection circuitry to determine when the upper MOSFET has turned off.
11
12
16
18
UGATE2
Switch Node for Channel 2. Connect this pin to the source of the upper
MOSFET and the drain of the lower MOSFET. This pin is used as the sink
for the UGATE2 driver. This pin is also monitored by the adaptive shoot
through protection circuitry to determine when the upper MOSFET has
turned off.
PHASE2
Lower Gate Driver Output for Channel 2. Connect this pin to the gate of
lower MOSFET. This pin is monitored by the adaptive shoot through
protection circuitry to determine when the lower MOSFET has turn off.
13
14
19
20
LGATE2
VCC
Supply Voltage. This pin is the input pin of the internal 9V LDO, which
provides current for PVCC9 and PVCC pins. Place a minimum 1μF
ceramic capacitor physically near the pin to locally bypass the supply
voltage.
21
(RT8810A)
22
Supply Input. This pin receives a supply voltage from 4.5V to 13.2V and
provides bias current for the internal control circuit. Physically place a
minimum 1μF ceramic capacitor near it. This pin to bypass it.
--
PVCC
(RT8810D)
22
Supply Input. This pin is the output of the internal 9V LDO regulator. It
provides current for lower gate drivers and bootstrap current for upper
drivers.
(RT8810A)
21
(RT8810D)
15
16
PVCC9
Lower Gate Driver Output for Channel 1. Connect this pin to the gate of
lower MOSFET. This pin is monitored by the adaptive shoot through
protection circuitry to determine when the lower MOSFET has turn off.
23
24
LGATE1
Switch Node for Channel 1. Connect this pin to the source of the upper
MOSFET and the drain of the lower MOSFET. This pin is used as the sink
for the UGATE driver. This pin is also monitored by the adaptive shoot
through protection circuitry to determine when the upper MOSFET has
turned off.
1
PHASE1
DS8810-01 June 2011
www.richtek.com
7
RT8810
Function Block Diagram
SS/EN
PVCC
VCC
LV
Regulator
HV
Regulator
Bias
REF
SEL
Soft-Start
REFIN
+
-
POR
PVCC9
FB
COMP
SD
Fault
BOOT2
BOOT1
-
+
OC
UGATE2
Logic
UGATE1
Gate
Control
+
-
+
-
Gate
Control
PHASE2
LGATE2
PHASE1
LGATE1
+
-
+
-
Current
Balance
S/H
S/H
PGND
AGND
VB
VB
Phase
Control
Oscillator
+
Transient
Response
Enhancement
QR1
QR2
IMAX
MODE
RT
www.richtek.com
8
DS8810-01 June 2011
RT8810
Absolute Maximum Ratings (Note 1)
z VCC, PVCC, PVCC9 to AGND---------------------------------------------------------------- 15V
z BOOTx to PHASEx ------------------------------------------------------------------------------ 15V
z PHASEx to PGNDx
DC---------------------------------------------------------------------------------------------------- −0.5V to 15V
<20ns ----------------------------------------------------------------------------------------------- −5V to 25V
z UGATEx to PHASEx
DC---------------------------------------------------------------------------------------------------- −0.3V to (BOOTx − PHASEx+ 0.3V)
<20ns ----------------------------------------------------------------------------------------------- −5V to (BOOTx − PHASEx + 5V)
z LGATEx to PGNDx
DC---------------------------------------------------------------------------------------------------- −0.3V to (PVCC9 + 0.3V)
<20ns ----------------------------------------------------------------------------------------------- −5V to (PVCC9 + 5V)
z Input, Output or I/O Voltage -------------------------------------------------------------------- (AGND − 0.3V) to 6V
z Power Dissipation, PD @ TA = 25°C
WQFN-16L 3x3 ----------------------------------------------------------------------------------- 1.471W
WQFN-24L 4x4 ----------------------------------------------------------------------------------- 1.923W
z Package Thermal Resistance (Note 2)
WQFN-16L 3x3, θJA ------------------------------------------------------------------------------ 68°C/W
WQFN-16L 3x3, θJC ----------------------------------------------------------------------------- 7.5°C/W
WQFN-24L 4x4, θJA ------------------------------------------------------------------------------ 52°C/W
WQFN-24L 4x4, θJC ----------------------------------------------------------------------------- 7°C/W
z Junction Temperature ---------------------------------------------------------------------------- 150°C
z Lead Temperature (Soldering, 10 sec.)------------------------------------------------------ 260°C
z Storage Temperature Range ------------------------------------------------------------------- −65°C to 150°C
z ESD Susceptibility (Note 3)
HBM (Human Body Mode) --------------------------------------------------------------------- 2kV
MM (Machine Mode) ----------------------------------------------------------------------------- 200V
Recommended Operating Conditions (Note 4)
z Supply Voltage, VCC ----------------------------------------------------------------------------- 4.5V to 13.2V
z Junction Temperature Range------------------------------------------------------------------- −40°C to 125°C
z Ambient Temperature Range------------------------------------------------------------------- −40°C to 85°C
DS8810-01 June 2011
www.richtek.com
9
RT8810
Electrical Characteristics
(VCC = 12V, VPVCC9 = 9V, TA = 25°C, unless otherwise specified)
Parameter
Supply Input
Symbol
Test Conditions
Min
Typ
Max
Unit
Bias Voltage
VPVCC
VPVCC9
ICC
4.5
8
--
9
13.2
10
--
V
V
Regulated Bias Voltage
Supply Current
UGATE, LGATE Open
UGATE, LGATE Open
--
6.5
4
mA
mA
Shutdown Current
Power-On Reset
VCC POR Threshold
Power On Reset Hysteresis
Oscillator
ISHDN
--
--
VPVCC9R_th VCC9 Rising
VPVCC9_hys
3.8
--
4.1
0.3
4.4
--
V
V
Frequency
fOSC
RRT = 30kΩ
175
100
--
200
--
225
1000
--
kHz
kHz
VP-P
%
Frequency Range
Ramp Amplitude
Minimum Duty Cycle
Minimum LGATE Pulse
Reference
ΔVOSC
2
0
--
--
--
300
--
ns
Nominal Feedback Voltage
Error Amplifier
VFB
0.59
0.6
0.61
V
Open Loop DC Gain
Gain Bandwidth
ADC
GBW
SR
Guaranteed by Design
--
--
--
--
70
10
6
--
--
--
--
dB
Guaranteed by Design
MHz
V/μs
mA/V
Slew Rate
Guaranteed by Design, CL = 10pF
Transconductance
gm
1.8
Maximum Current (Source &
Sink)
ICOMPsk
--
360
--
μA
Soft-Start
SS Source Current
ISS
VSS/EN = 0V
7
10
13
--
μA
Re-Soft-Start Threshold
Level
--
0.5
V
Current Sense
Current Sense Gain
Mode Pin Voltage
145
--
165
0.6
185
--
μA/V
VMODE
IMODE
V
Forced Single Phase
Operation
250
--
--
--
--
1
μA
μA
Forced Dual Phase
Operation
IMODE
To be continued
www.richtek.com
10
DS8810-01 June 2011
RT8810
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
PWM Controller Gate Driver
V
− V
= 12V, Max.
PHASEx
BOOTx
Upper Gate Sourcing Ability
I
--
1.5
--
A
UGATEsr
Source Current
− V = 0.1V
PHASEx
Upper Gate R
Sinking
R
V
--
--
--
2
1.5
2
--
--
--
Ω
A
DS(ON)
UGATEsk
UGATEx
Lower Gate Sourcing Ability
I
V
V
= 12V, Max. Source Current
= 0.1V
LGATEsr
CC
Lower Gate R
Deadtime
Sinking
R
Ω
DS(ON)
LGATEsk
LGATEx
V
V
− V
= 1.2V
= 1.2V to
PHASEx
UGATEx
LGATEx
--
30
--
ns
Protection
Over Current Threshold
SS Enable Threshold
V
V
2.75
0.3
3
3.25
0.5
V
V
IMAX
EN
0.4
Note 1. Stresses listed as the above "Absolute Maximum Ratings" may cause permanent damage to the device. These are for
stress ratings. 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 for extended
periods may remain possibility to affect device reliability.
Note 2. θJA is measured in natural convection at TA = 25°C on a high effective thermal conductivity four-layer test board of
JEDEC 51-7 thermal measurement standard. The measurement case position of θJC is on the exposed pad of the
packages.
Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
DS8810-01 June 2011
www.richtek.com
11
RT8810
Typical Operating Characteristics
VREF vs. Temperature
Efficiency vs. Load Current
100
0.610
0.608
0.606
0.604
0.602
0.600
0.598
0.596
0.594
0.592
0.590
Phase 2 Active
95
90
85
80
75
70
65
60
VIN = VCC = 12V, VOUT = 1.1V
30 40 50 60
VIN = VCC = 12V, No Load
50 75 100 125
55
0
10
20
-50
-25
0
25
Temperature (°C)
Load Current (A)
Frequency vs. Temperature
RRT vs. Frequency
315
310
305
300
295
290
285
650
600
550
500
450
400
350
300
250
200
150
VIN = VCC = 12V, No Load
VIN = VCC = 12V, No Load
50 75 100 125
-50
-25
0
25
5
10
15
20
25
30
35
40
Temperature (°C)
RRT (kΩ)
Power On from EN
Inductor Current vs. Output Current
32
30
28
26
24
22
20
18
16
14
12
10
8
SS/EN
(1V/Div)
Phase1
Phase2
VOUT
(1V/Div)
UGATE1
(20V/Div)
6
4
2
0
UGATE2
(20V/Div)
VIN = VCC = 12V
VIN = VCC = 12V, IOUT = 40A
5
10 15 20 25 30 35 40 45 50 55 60
Output Current (A)
Time (4ms/Div)
www.richtek.com
12
DS8810-01 June 2011
RT8810
Power Off from EN
Power On from VCC
VCC
SS/EN
(10V/Div)
(1V/Div)
VOUT
(1V/Div)
VOUT
(1V/Div)
UGATE1
(20V/Div)
UGATE1
(20V/Div)
UGATE2
(20V/Div)
UGATE2
(20V/Div)
VIN = VCC = 12V, IOUT = 40A
VIN = VCC = 12V, IOUT = 40A
Time (4ms/Div)
Time (200μs/Div)
Dynamic Output Voltage Control
Power Off from VCC
VREFIN
(1V/Div)
VCC
(10V/Div)
VOUT
(1V/Div)
UGATE1
(20V/Div)
VOUT
(1V/Div)
UGATE1
(20V/Div)
UGATE2
(20V/Div)
UGATE2
(20V/Div)
VIN = VCC = 12V, IOUT = 20A, VREFIN = 0V to 1.1V
VIN = VCC = 12V, IOUT = 40A
Time (20ms/Div)
Time (400μs/Div)
Dynamic Output Voltage Control
Load Transient Response
VIN = VCC = 12V, IOUT = 0A to 40A
UGATE1
(20V/Div)
VREFIN
(1V/Div)
UGATE2
(20V/Div)
VOUT
(1V/Div)
UGATE1
(20V/Div)
IOUT
(50A/Div)
UGATE2
(20V/Div)
VOUT
(50mV/Div)
Time (400μs/Div)
Time (10μs/Div)
DS8810-01 June 2011
www.richtek.com
13
RT8810
Mode Transition
Load Transient Response
VIN = VCC = 12V, IOUT = 40A to 0A
UGATE1
(20V/Div)
UGATE1
(20V/Div)
UGATE2
(20V/Div)
UGATE2
(20V/Div)
IOUT
(50A/Div)
VOUT
VOUT
(20mV/Div)
(50mV/Div)
VIN = VCC = 12V, single to dual phase
Time (10μs/Div)
Time (10μs/Div)
Mode Transition
Over Current Protection
UGATE1
(20V/Div)
VOUT
(500mV/Div)
UGATE2
(20V/Div)
IL1
(10A/Div)
VOUT
(20mV/Div)
IL2
(10A/Div)
VIN = VCC = 12V, dual to single phase
VIN = VCC = 12V
Time (10ms/Div)
Time (10μs/Div)
www.richtek.com
14
DS8810-01 June 2011
RT8810
Application Information
Frequency vs. RRT
Dual Supply Voltage (VCC, PVCC) with Internal
Regulator
700
600
500
400
300
200
100
The RT8810 requires an external bias supply for PVCC
and VCC. PVCC receives a supply voltage from 4.5V to
13.2V and provides bias current for internal control circuit.
VCC is the input pin of the internal 9V LDO which provides
current for the PVCC9 pin. PVCC9 is the output pin of the
internal 9V LDO regulator. It provides current for lower
gate drivers and bootstrap current for upper drivers.
Physically place a minimum 1μF ceramic capacitor near
PVCC and VCC to locally bypass the supply voltage.
The Power-On-Reset (POR) circuit monitors the supply
voltage at the PVCC pin. If PVCC exceeds the POR rising
threshold voltage, the controller is reset and prepares the
PWM for operation. If PVCC falls below the POR falling
threshold during normal operation, all MOSFETs stop
switching. The POR rising and falling threshold has a
hysteresis to prevent noise caused reset.
5
10
15
20
25
30
35
RRT (kΩ)
Figure 4. RRT vs. Switching Frequency
A resistor of 8.6kΩ to 18kΩ corresponds to a switching
frequency of 500kHz to 300kHz, respectively.
External Reference Input
The RT8810 supports external reference input to provide
more flexible applications. The REFINpin is implemented
to be the external reference input. The mode selection is
determined and latched after POR. If REFINpin is floating,
a 10μA current source will pull high the REFIN pin and if
the pin voltage exceeds 2.8V, the FB pin will follow the
internal reference voltage 0.6V. On the other hand, if an
external voltage is applied to the REFIN pin, the RT8810
enters tracking mode and regulates FB to be close to this
voltage. The applied voltage must be within the tracking
range (typically between 0.4V to 2.5V).
Soft-Start
The RT8810 provides external soft-start function to prevent
large inrush current and output voltage overshoot when
the converter starts up. The soft-start begins when OCP
programming is complete.
During soft-start, an internal current source (10μA) is used
to charge the external soft-start capacitor at the SS/EN
pin. VSS/EN rises up, and the PWM logic and gate drives
become enabled. When the feedback voltage crosses
0.6V, the internal 0.6V reference takes over the behavior
of the error operational transconductance amplifier and soft-
start is complete. The RT8810 turns off the internal 10μA
current source when soft-start is complete.
If the applied voltage is less than 0.3V, the controller will
be shut down.
Current Sensing and Reporting
Switching Frequency
The RT8810 monitors per phase current for current balance
and over current protection. Per phase current is sensed
by the on-resistance of low side MOSFET when turned
on. The GM amplifier senses the voltage drop across the
lower switch and converts it into a current signal each
time it turns on. The sensed current is expressed as :
High frequency operation optimizes the application by
allowing smaller component size, but trades off efficiency
due to higher switching losses. Low frequency operation
offers the best overall efficiency, but at the expense of
component size and board space.
Connect a resistor (RRT) between RT and ground to set
the switching frequency (fSW) per phase. Users can refer
to Figure 4 for switching frequency setting.
ICS = 3.3 x IL x RDS(ON) x 10−4 + 5.5μA
DS8810-01 June 2011
www.richtek.com
15
RT8810
where IL is the per phase current inAmpere, RDS(ON) is the
on-resistance of low side MOSFET in mΩ, and 5.5μAis a
constant to compensate the offset of the current sensing
circuit. Note that the valley inductor current is sampled
and held. The sampled and hold current is the averaged
inductor current minus half of inductor ripple current :
MOSFETs but continues to charge CSS with a constant
current of 10μA until soft-start ends. The shutdown status
can only be reset by the POR function.
Current Balance
The RT8810 senses each phase current from low side
MOSFET RDS(ON), and fine tunes the duty cycle of each
phase for current balance as shown in Figure 5. If the
current of PHASE1 is smaller than the current of PHASE2,
the RT8810 increases the duty cycle of the corresponding
phase to increase its phase current accordingly.
1
⎝ 2
⎛
⎞
⎟
⎠
IL_SH = IL_AVG
−
x ΔIL
⎜
where ΔIL is the inductor ripple current
One half of the summation of the sampled and hold current
signal (ICS1 + ICS2) / 2 is injected to the IMAX pin, that
results in a voltage VIMAX across the resistor RIMAX
connecting IMAX and AGND for over current protection.
And VIMAX is equal to
PWM1
V
+
+
-
COMP
Ramp1
+
+
+
I
I
CS1
-
-
PWM2
+
-
CS2
ICS1 + ICS2
+
V
IMAX
=
x RIMAX
Ramp2
2
+
3.3 x I
+ IL2_SH xRDS(ON)x10−4 + 11μA
⎡
⎢
⎤
⎥
(
)
L1_SH
=
2
⎢
⎥
Figure 5. Current Balance Control Circuit
⎣
⎦
Therefore, IMAX pin could be used for current reporting.
Dynamic Phase Number Control
The RT8810 adaptively controls the operation phase
number according to the load current. Figure 6 shows the
dynamic phase number control circuit. The phase adding
Over Current Protection
The RT8810 features over current protection. The voltage
at the IMAX pin (VIMAX) is compared with a 3.0V reference
voltage. If VIMAX is higher than 3.0V, OCP is triggered.
The over current setting resistor (RIMAX) value for dual phase
threshold can be calculated according to
and dropping threshold can be set by a resistor, RMODE
,
which is connected from the MODE pin to AGND. A
current, IMODE, flows through the resistor, RMODE, as
0.6
I
=
RIMAX
=
MODE
R
MODE
3V
1.65 x IO_MAX − ΔIL x RDS(ON) x 10−4 + 5.5μA
Once IIMAX is higher than 3 / 5 of IMODE, the controller will
transit to 2-phase operation. When IIMAX is lower than 2 / 5
of IMODE, the active phase number will return to one phase.
(
)
And the RIMAX value for single phase threshold will be
R
For example, if RMODE = 30kΩ, RDS(ON) = 3mΩ,ΔIL = 5A.
The load current threshold for adding phase can be
calculated as
IMAX
3V
=
−4
⎡
⎤
⎦
1.5 x 1.65x I
− ΔI x R
x10 + 2.75μA
(
)
O_MAX
L
DS(ON)
⎣
3 x IMODE
The RT8810 features hiccup and shutdown mode OCP. If
OCP is triggered after soft-start ends, the RT8810 turns
off both upper and lower MOSFETs and discharges CSS
with a constant current of 10μA. When VSS exceeds 0.5V,
the RT8810 initiates another soft-start cycle. The RT8810
shuts down after 3 hiccups. If the OCP is triggered during
soft-start cycle, the RT8810 turns off both upper and lower
5
−4
⎡
⎢
⎤
⎥
3.3 x10 x I
− 2.5 A x 3mΩ + 5.5μA
(
)
OUT_2P
=
2
⎢
⎥
⎣
⎦
IOUT_2P = 21.2A
And the load current threshold for dropping phase can be
calculated as
www.richtek.com
16
DS8810-01 June 2011
RT8810
2 x IMODE
V
QR2
RT8810
5
EAP
3.3 x 10−4x I
−5 A x 3mΩ + 11μA
⎡
⎤
⎥
V
FB
(
)
OUT_2P
1µA
⎢
=
2
⎢
⎥
QR comp.
-
⎣
⎦
QR2
Min. on
IOUT_2P = 10A
+
R
QR2
EAP
FB
2/5 x I
3/5 x I
MODE
V
FB
-
+
2/5
3/5
QR
C
QR1
Drop Phase
Add Phase
QR1
T
QR
MODE
+
-
Figure 7. Quick Response Active
Feedback and Compensation
0.6V
+
-
I
I
IMAX
CS1
CS2
I
MODE
The RT8810 allows the output voltage of the DC/DC
converter to be adjusted from 0.6V to 85% of VIN supply
via an external resistor divider. It will try to maintain the
feedback pin at internal reference voltage (0.6V).
I
R
MODE
Figure 6. Dynamic PhaseNumber Control Circuit
V
OUT
Manual Phase Number Control
R1
R2
FB
The RT8810 supports manual selecting of single phase or
dual phase operation. If IMODE is higher than 150μA, the
RT8810 operates in forced single phase mode. If IMODE is
smaller than 4μA, the RT8810 operates in forced dual
phase mode.
According to the resistor divider network above, the output
voltage is set as :
⎛
⎜
⎝
⎞
⎟
V
REF
Note that, the MODE pin is not available for the RT8810C.
It supports only two phase operation.
R = R x
2
1
V
− V
OUT
REF ⎠
The RT8810 is a voltage mode controller and requires
external compensation to have an accurate output voltage
regulation with fast transient response.
Load Transient Quick Response
The RT8810 utilizes a new quick response feature to supply
heavy load current demand during instantaneous load
application transient. The RT8810 detects load transient
and reacts via VOUT pin. When VOUT drops during load
application transient, the quick response comparator will
send asserted signals to turn on high side MOSFETs and
turn off low side MOSFETs. The QR signal will turn on all
phase' high side MOSFETs while turning off low side
MOSFETs. Therefore, the influence of total quick response
function of the RT8810 is adjustable. The quick response
The RT8810 uses a high gain Operational
Transconductance Amplifier (OTA) as the error amplifier.
As Figure 8 shows, the OTA works as the voltage
controlled current source. The characteristic of OTAis as
below :
ΔIOUT
gm =
,
ΔVM
where ΔV = V
− V
(
IN−
and ΔVCOMP = ΔIOUT x ZOUT
(
)
)
M
IN+
threshold can be set by RQR2. QR is triggered if VEAP
>
I
OUT
V
IN+
+
-
1μA x RQR2 + VFB. The QR width can be set according
to :
GM
V
COMP
V
IN-
Z
OUT
C
QR1
x 0.8V
T
QR
=
300μA
Figure 8. Operational TransconductanceAmplifier, OTA
DS8810-01 June 2011
www.richtek.com
17
RT8810
Figure 9 shows a typical buck control loop using Type II
compensator. The control loop consists of the power stage,
PWM comparator and a compensator. The PWM
comparator compares VCOMP with oscillator (OSC)
sawtooth wave to provide a Pulse-Width Modulated (PWM)
with an amplitude of VIN at the PHASE node. The PWM
wave is smoothen by the output filter LOUT and COUT. The
output voltage (VOUT) is sensed and fed to the inverting
input of the error amplifier.
The DC gain of the modulator is the input voltage (VIN)
divided by the peak-to-peak oscillator voltage VOSC
.
V
IN
Gain
=
modulator
ΔV
OSC
The output LC filter introduces a double pole, 40dB/decade
gain slope above its corner resonant frequency, and a total
phase lag of 180 degrees. The resonant frequency of the
LC filter is expressed as :
V
IN
fLC
=
V
IN
2π LOUT x COUT
The ESR zero is contributed by the ESR associated with
the output capacitance. Note that this requires the output
capacitor to have enough ESR to satisfy stability
requirements. The ESR zero of the output capacitor is
expressed as follows :
UGATE
PHASE
PWM
L
OUT
Comparator
V
OUT
+
-
Driver
Logic
C
OUT
LGATE
V
OSC
V
+
REF
R
FB1
GM
FB
-
1
R
f
=
FB2
ESR
2π x C
x ESR
OUT
The goal of the compensation network is to provide
adequate phase margin (usually greater than 45 degrees)
and the highest bandwidth (0dB crossing frequency). It is
also recommended to manipulate loop frequency response
so that its gain crosses over 0dB at a slope of −20dB/
dec. According to Figure 8, the compensation network
frequency is as below :
COMP
V
COMP
C
R
C
C
P
C
Figure 9. Typical Voltage Mode Buck Converter Control
Loop
The modulator transfer function is the small signal transfer
function of VOUT / VCOMP (output voltage over the error
amplifier output). This transfer function is dominated by a
DC gain, a double pole, and an ESR zero as shown in
Figure 10.
F
P1 = 0
1
F
P2
=
=
⎛
⎞
⎟
CC x CP
2π x RC x
⎜
⎝
CC + CP ⎠
1
FZ1
2π x RC x CC
Determining the 0dB crossing frequency (FC, control loop
bandwidth) is the first step of compensator design. Usually,
FC is set to 0.1 to 0.3 times the switching frequency. The
second step is to calculate the open loop modulator gain
and find out the gain loss at FC. The third step is to design
a compensator gain that can compensate the modulator
gain loss at FC. The final step is to design FZ1 and FZ2 to
allow the loop sufficient phase margin.
FZ1 is designed to cancel one of the double poles of
modulator. Usually, FZ1 is placed before fLC. FP2 is usually
placed below the switching frequency (typically, 0.5 to
1.0 times switching frequency) to eliminate high frequency
noise.
Figure 10. Typical Bode plot of a Voltage Mode Buck
Converter
www.richtek.com
18
DS8810-01 June 2011
RT8810
Inductor Selection
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 :
The inductor plays an important role in the buck converter
because energy from the input power rail is stored in it
and then released to the load. From the viewpoint of
efficiency, the inductor'sDC Resistance (DCR) should be
as small as possible since the inductor constantly carries
current. In addition, the inductor takes up most of the
board space, so its size is also important. Low profile
inductors can save board space, especially when there is
a height limitation.
PD(MAX) = (TJ(MAX) − TA) / θJA
where TJ(MAX) is the maximum junction temperature, TAis
the ambient temperature, and θJA is the junction to ambient
thermal resistance.
For recommended operating condition specifications of
the RT8810, the maximum junction temperature is 125°C
and TA is the ambient temperature. The junction to ambient
thermal resistance, θJA, is layout dependent. For WQFN-
16L 3x3 packages, the thermal resistance, θJA, is 68°C/
Won a standard JEDEC 51-7 four-layer thermal test board.
For WQFN-24L 4x4 packages, the thermal resistance,
θJA, is 52°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 :
Additionally, larger inductance results in lower ripple
current, and therefore lower power loss. However, the
inductor current rising time increases with inductance value.
This means the inductor will have a longer charging time
before its current reaches the required output current.
Since the response time is increased, the transient
response performance will be decreased. Therefore, the
inductor design is a trade-off between performance, size
and cost.
PD(MAX) = (125°C − 25°C) / (68°C/W) = 1.471W for
WQFN-16L 3x3 package
In general, inductance is designed such that the ripple
current ranges between 20% to 30% of full load current.
The inductance can be calculated using the following
equation.
PD(MAX) = (125°C − 25°C) / (52°C/W) = 1.923W for
WQFN-24L 4x4 package
V
IN − VOUT
VOUT
The maximum power dissipation depends on the operating
ambient temperature for fixed TJ(MAX) and thermal
resistance, θJA. For the RT8810 package, the derating
curves in Figure 11 allow the designer to see the effect of
rising ambient temperature on the maximum power
dissipation.
L(MIN)
=
x
fSW x k x IOUT(MAX)
V
IN
where k is 0.2 to 0.3.
Output Capacitor Selection
Output capacitors are used to maintain high performance
for the output beyond the bandwidth of the converter itself.
Two different settings of output capacitors can be found,
bulk capacitors closely located to the inductors and
ceramic output capacitors in close proximity to the load.
Latter ones are for mid frequency decoupling with
especially small ESR and ESL values, while the bulk
capacitors have to provide enough stored energy to
overcome the low frequency bandwidth gap between the
regulator and theGPU.
2.0
Four-Layer PCB
1.9
1.8
1.7
1.6
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
WQFN-24L 4x4
WQFN-16L 3x3
Thermal Considerations
0
25
50
75
100
125
For continuous operation, do not exceed absolute
maximum junction temperature. The maximum power
dissipation depends on the thermal resistance of the IC
Ambient Temperature (°C)
Figure 11.Derating Curves for the RT8810 Packages
DS8810-01 June 2011
www.richtek.com
19
RT8810
Layout Considerations
` Place all of the high frequency decoupling ceramic
capacitors close to their decoupling targets.
Careful PC board layout is critical to achieve low switching
losses and clean, stable operation. The switching power
stage requires particular attention. If possible, mount all
of the power components on the top side of the board
with their ground terminals flush against one another.
Follow these guidelines for optimum PC board layout :
` Small signal components should be located as close to
the IC as possible. The small signal components include
the feedback components, current sensing components,
the compensation components, function setting
components and any bypass capacitors. These
components belong to the high impedance circuit loop
and are inherently sensitive to noise pick-up. Therefore,
they must be located close to their respective controller
pins and away from the noisy switching nodes.
` Power components should be placed first. Place the
input capacitors close to the power MOSFETs, then
locate the filter inductors and output capacitors between
the power MOSFETs and the load.
` A multi layer PCB design is recommended. Make use
of one single layer as the power ground and have a
separate control signal ground as the reference of all
signals.
` Place both the ceramic and bulk input capacitor close to
the drain pin of the high side MOSFET. This can reduce
the impedance presented by the input bulk capacitance
at high switching frequency. If there is more than one
high side MOSFET in parallel, each should have its own
individual ceramic capacitor.
` Keep the power loops as short as possible. For low
voltage high current applications, power components
are the most critical part in the layout because they
switch a large amount of current. The current transition
from one device to another at high speed causes voltage
spikes due to the parasitic components on the circuit
board. Therefore, all of the high current switching loops
should be kept as short as possible with large and thick
copper traces to minimize the radiation of
electromagnetic interference.
` Minimize the trace length between the power MOSFETs
and its drivers. Since the drivers use short, high current
pulses to drive the power MOSFETs, the driving traces
should be sized as short and wide as possible to reduce
the trace inductance. This is especially true for the low
side MOSFET, since this can reduce the possibility of
shoot through.
` Provide enough copper area around the power MOSFETs
and the inductors to aid in heat sinking. Use thick
copper PCB to reduce the resistance and inductance
for improved efficiency.
` The bank of output capacitor should be placed physically
close to the load. This can minimize the impedance
seen by the load, and then improve the transient
response.
www.richtek.com
20
DS8810-01 June 2011
RT8810
Outline Dimension
SEE DETAIL A
D
D2
L
1
E
E2
1
2
1
2
e
b
DETAILA
A
A3
Pin #1 ID and Tie Bar Mark Options
A1
Note : The configuration of the Pin #1 identifier is optional,
but must be located within the zone indicated.
Dimensions In Millimeters
Dimensions In Inches
Symbol
Min
Max
Min
Max
A
A1
A3
b
0.700
0.000
0.175
0.180
2.950
1.300
2.950
1.300
0.800
0.050
0.250
0.300
3.050
1.750
3.050
1.750
0.028
0.000
0.007
0.007
0.116
0.051
0.116
0.051
0.031
0.002
0.010
0.012
0.120
0.069
0.120
0.069
D
D2
E
E2
e
0.500
0.020
L
0.350
0.450
0.014
0.018
W-Type 16L QFN 3x3 Package
DS8810-01 June 2011
www.richtek.com
21
RT8810
D2
SEE DETAIL A
L
D
1
E
E2
1
2
1
2
e
b
DETAILA
A
Pin #1 ID and Tie Bar Mark Options
A3
A1
Note : The configuration of the Pin #1 identifier is optional,
but must be located within the zone indicated.
Dimensions In Millimeters
Dimensions In Inches
Symbol
Min
Max
Min
Max
A
A1
A3
b
0.700
0.000
0.175
0.180
3.950
2.300
3.950
2.300
0.800
0.050
0.250
0.300
4.050
2.750
4.050
2.750
0.028
0.000
0.007
0.007
0.156
0.091
0.156
0.091
0.031
0.002
0.010
0.012
0.159
0.108
0.159
0.108
D
D2
E
E2
e
0.500
0.020
L
0.350
0.450
0.014
0.018
W-Type 24L QFN 4x4 Package
Richtek Technology Corporation
Headquarter
Richtek Technology Corporation
Taipei Office (Marketing)
5F, No. 20, Taiyuen Street, Chupei City
Hsinchu, Taiwan, R.O.C.
5F, No. 95, Minchiuan Road, Hsintien City
Taipei County, Taiwan, R.O.C.
Tel: (8863)5526789 Fax: (8863)5526611
Tel: (8862)86672399 Fax: (8862)86672377
Email: marketing@richtek.com
Information that is provided by Richtek Technology Corporation is believed to be accurate and reliable. Richtek reserves the right to make any change in circuit design,
specification or other related things if necessary without notice at any time. No third party intellectual property infringement of the applications should be guaranteed
by users when integrating Richtek products into any application. No legal responsibility for any said applications is assumed by Richtek.
www.richtek.com
22
DS8810-01 June 2011
相关型号：
©2020 ICPDF网 联系我们和版权申明