RT4722C
Triple DC-DC Boost Converter for AMOLED
General Description
Features
The RT4722C is a triple channels DC-DC converter
Boost Converter to Supply Positive AVDD
Voltage from 5.8V to 7.9V
which is designed to provide the power of AMOLED. It
integrates step up DC-DC and an inverting converter to
Boost Converter to Supply AMOLED Positive
Voltage 4.6V
provide the positive and negative output voltage
required by AMOLED.
Inverter Converter to Supply AMOLED Negative
Voltage from 1.4V to 5.4V
For the portable application, board space and
efficiency are always major concerns. The high
Maximum Output Current up to 300mA for
AMOLED Positive & Negative Power Supply
switching frequency of the RT4722C allows the use of
low inductance inductor to save the board space. For
Maximum Output Current up to 55mA for AVDD
Output Voltage
the negative and AVDD output voltage, both can be
programmed by external MCU through single wire
(SWIRE pin). The output voltage range of negative
output voltage is 1.4V to 5.4V and AVDD voltage is
5.8V to 7.9V. RT4722C has OTP, SCP, UVLO and
over-current protections. The RT4722C is available in a
WQFN-16L 3x3 package to achieve saving PCB space.
Typical Peak Efficiency : 90% (40mA to 150mA)
PWM Mode @ 1.5MHz Switching Frequency
High Output Voltage Accuracy
Excellent Line and Load Transient
Excellent Line and Load Regulation
Programmable Negative and AVDD Voltage by
SWIRE Pin
Applications
Fast Outputs Discharge Function
AMOLED Panel
Low Quiescent Current < 1A in Shutdown Mode
PDAs and Smart Phones
Internal Soft-Start to limit Inrush Current
Probable Instrument
Over-Temperature Protection (OTP)
Over-Current Protection (OCP)
Short Circuit Protection (SCP)
Simplified Application Circuit
VBAT
L1
L3
CIN
PVIN
LX1
VPOS
CVO1
VPOS_FB
AVDD Enable
VO1, VO2 Enable and Program VO2
VO1
FBS
LX3
CAV
RT4722C
ENO3
FD
SWIRE
L2
LX2
VO2
PGND1 PGND2 AGND
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AVDD
CVO3
VO3
AVIN
VNEG
CVO2
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RT4722C
Ordering Information
Pin Configuration
(TOP VIEW)
RT4722C
AVIN
LX3
PGND2
VO3
Package Type
QW : WQFN-16L 3x3 (W-Type)
Lead Plating System
G : Green (Halogen Free and Pb Free)
16 15 14 13
LX1
PGND1
VO1
FBS
Note :
Richtek products are :
12
2
11
RoHS compliant and compatible with the current
9
5
Suitable for use in SnPb or Pb-free soldering processes.
Marking Information
LK=YM
DNN
10
17
4
requirements of IPC/JEDEC J-STD-020.
AGND
3
6
7
PVIN
LX2
VO2
SWIRE
8
FD
NC
AGND
ENO3
1
WQFN-16L 3x3
LK= : Product Code
YMDNN : Date Code
Functional Pin Description
Pin No.
Pin Name
Pin Function
1
LX1
1st
2
PGND1
Power ground.
3
VO1
1st boost converter output.
4
FBS
1st boost converter output feedback sense. Connect to VO1 pin if un-used.
5
FD
Active discharge enable/disable during shutdown. Default floating.
6
NC
No connected.
7,
AGND
17 (Exposed Pad)
boost converter switching node.
Signal ground. The exposed pad must be soldered to a large PCB and
connected to AGND for maximum power dissipation.
8
ENO3
2nd boost enable/disable pin.
9
SWIRE
VPOS, VNEG control pin (enable/disable pin).
10
VO2
Buck/Boost converter output (negative voltage).
11
LX2
Buck/Boost converter switching node.
12
PVIN
Power input voltage.
13
VO3
2nd boost converter output.
14
PGND2
Power ground.
15
LX3
2nd boost converter switching node.
16
AVIN
Analog input voltage.
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RT4722C
Functional Block Diagram
AVIN
LX3
PVIN
PVIN
UVLO
Switching
Well
VO3
SCP3
ZCD3
ENO3
VO3
P3
RP6
FB3
Pulse
Diming
PWM
Logic
RP5
N3
OCP3
Soft-start
VRX3
GM
LX1
FB3
1.5MHz
OSC
VR1
PVIN1 Switching
Well
VO1
VO1
FBS
R1A
GM
P1
VRX’
RP2
R1B
FB1
PWM
Logic
OCP1
VRX
N1
SCP1
RP1
Soft-start
GM
Swire
FB1
PVIN
Pulse Dimming
VRX’
NN1
RDIMP
OCP2
RDIMN
LX2
PWM
Logic
FB2
GM
SCP2
Softstart
NN2
VO2
VO2
VO1
Fast Discharge
VO2
OTP
VO3
FD
AGND
PGND1
PGND2
Operation
The RT4722C is a triple channels DC-DC converter
process. The VO2 negative output voltage is produced
which is designed to provide the power of AMOLED
from the DC-DC Buck-Boost converter and the
that can support the input voltage range from 2.9V to
negative output voltage range is 1.4V to 5.4V. It can
4.5V. The VO1 & VO2 output current can be up to
be programmed by external MCU through single wire
300mA, and the VO3 output current can be up to 55mA.
(SWIRE pin). The VO3 positive output voltage is
The RT4722C uses current mode architecture for the
produced from the DC-DC Boost converter and is set
purpose of high efficiency and high transient response.
from 5.8V to 7.9V by SWIRE pin. When SWIRE goes
The VO1 positive output voltage is produced from the
DC-DC Boost converter and is set at a typical value of
4.6V. When the SWIRE goes high, the positive output
high and VO1 soft-start had finished already, negative
output voltage VO2 will be enabled with an internal
soft-start process.
voltage will be enabled with an internal soft-start
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RT4722C
Table 1. SWIRE Command LUT for VO2
Bit (Pulse)
VNEG (V)
Bit (Pulse)
VNEG (V)
Bit (Pulse)
AVDD (V)
0
4 (Default)
21
3.4
0
6.1 (Default)
1
5.4
22
3.3
42
7.9
2
5.3
23
3.2
43
7.6
3
5.2
24
3.1
44
7.3
4
5.1
25
3
45
7
5
5
26
2.9
46
6.7
6
4.9
27
2.8
47
6.4
7
4.8
28
2.7
48
6.1
8
4.7
29
2.6
49
5.8
9
4.6
30
2.5
10
4.5
31
2.4
11
4.4
32
2.3
12
4.3
33
2.2
13
4.2
34
2.1
14
4.1
35
2
15
4
36
1.9
16
3.9
37
1.8
17
3.8
38
1.7
18
3.7
39
1.6
19
3.6
40
1.5
20
3.5
41
1.4
Table 2. SWIRE Pin Characteristics
Rating
Symbol
Min
Typ
Max
Unit
Initial Waiting Time
twait_int
--
50
--
s
Signal Stop Indicate Time
tstop
100
--
--
s
Turn-off Detection Time
toff_dly
30
--
80
s
SWIRE Rising Time
tr
--
--
200
ns
SWIRE Falling Time
tf
--
--
200
ns
Clock SWIRE High
tsH
2
10
20
s
Clock SWIRE Low
tsL
2
10
20
s
Input SWIRE Frequency
fswire
25
--
250
kHz
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RT4722C
Table 3. Fast Discharge Selection
SWIRE (Pulse)
0
50
51
FD Pin
Discharge
High
ON
Low
OFF
High
ON
Low
ON
High
OFF
Low
OFF
Note
FD Control
SWIRE Control
SWIRE Control
Table 4. Control of Transient Time
CTRL (Pulse)
Step Voltage per 100mV (mV)
Note
0
0
No Division Change
52
50
2 Division Change
53
25
4 Division Change
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RT4722C
Timing Diagram
SWIRE Command Timing Diagram
twait_int > 50µs (typ.)
tstop > 100µs
30µs < toff_dly < 80µs
2µs < tsH < 20µs
SWIRE
0
4.6V
VO1
0
0
0
0
VO2
4V
ten_dly < 13ms
4.2V
2µs < tsL < 20µs
Power Sequence
tSS1 < 2ms
30µs < toff_dly < 80µs
tSSD = 8ms
tSS2 < 2ms
SWIRE
0
4.6V
VO1
0
0
0
0
VO2
4V
toff_dly > 300µs
tSSet < 4ms
ENO3
0
6.1V
VO3
0
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RT4722C
Absolute Maximum Ratings
(Note 1)
PVIN, AVIN, VO1, LX1, FBS, FD, ENO3, SWIRE------------------------------------------------------------ 0.3V to 6V
VO3, LX3 --------------------------------------------------------------------------------------------------------------- 0.3V to 12V
VO2 ---------------------------------------------------------------------------------------------------------------------- 6V to 0.3V
LX2----------------------------------------------------------------------------------------------------------------------- 6V to 6V
Power Dissipation, PD @ TA = 25C
WQFN-16L 3x3 ------------------------------------------------------------------------------------------------------- 3.33W
Package Thermal Resistance
(Note 2)
WQFN-16L 3x3, JA ------------------------------------------------------------------------------------------------- 30C/W
WQFN-16L 3x3, JC ------------------------------------------------------------------------------------------------- 7.5C/W
Lead Temperature (Soldering, 10sec.) -------------------------------------------------------------------------- 260C
Junction Temperature ----------------------------------------------------------------------------------------------- 150C
Storage Temperature Range -------------------------------------------------------------------------------------- 65C to 150C
ESD Susceptibility
(Note 3)
HBM (Human Body Model) ---------------------------------------------------------------------------------------- 2kV
Recommended Operating Conditions
(Note 4)
Supply Input Voltage ----------------------------------------------------------------------------------------------- 2.9V to 4.5V
Ambient Temperature Range ------------------------------------------------------------------------------------ 40C to 85C
Junction Temperature Range ------------------------------------------------------------------------------------ 40C to 125C
Electrical Characteristics
(VIN = 3.7V, VO1 = 4.6V, VO2 = 4V, VO3 = 6.1V, TA = 25C, unless otherwise specified)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
2.9
3.7
4.5
V
2.3
2.4
2.5
V
Power Supply
Input Voltage Range
VIN
Under Voltage Lockout High
UVLO_H
Under Voltage Lockout Hys
UVLO_Hys VIN hysteresis
--
0.2
--
V
VIN Shutdown Current
ISHDN
ENO3 = GND, SWIRE = GND
--
--
1
A
ENO3, SWIRE, FD Input High
Threshold
VIH
VIN = 2.9V to 4.5V
1.2
--
--
V
ENO3, SWIRE, FD Input Low
Threshold
VIL
VIN = 2.9V to 4.5V
--
--
0.4
V
ENO3 Pull Down Current
IENO3
--
--
10
A
SWIRE Pull-down Resistor
RSWIRE
--
150
--
k
1.35
1.5
1.65
MHz
VIN rising
Operation Section
Switching Frequency
fSW
PWM mode
VO1 Maximum Duty
DMAX_N1
No load
--
87
--
%
VO2 Maximum Duty
DMAX_NN1
No load
--
87
--
%
VO3 Maximum Duty
DMAX_N3
No load
--
87
--
%
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RT4722C
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
Over-Temperature Protection
OTP
--
140
--
℃
Over-Temperature Protection
Hysteresis
OTPHYST
--
15
--
℃
VO3 AVDD Output
AVDD Output Voltage Range
VO3
42 to 49 pulses by SWIRE pin
5.8
6.1
7.9
V
AVDD Output Voltage Total
Variation
VO3_ACY
No load
2
--
2
%
Maximum Output Current
IO3MAX
VIN = 2.9V to 4.5V
--
--
55
mA
VIN = 3.7V, ILX-N3 = 20mA
--
0.4
--
VIN = 3.7V, ILX-P3 = 20mA
--
1
--
0.28
0.35
0.42
A
--
0.01
--
%/V
--
0.4
--
%/A
--
4.6
--
V
0.5
--
0.5
%
VIN = 2.9V to 4.5V
--
--
300
mA
VIN = 3.7V, ILX-N1 = 100mA
--
0.2
--
VIN = 3.7V, ILX-P1 = 100mA
--
0.2
--
0.8
1
1.2
A
N3 N-MOSFET On-Resistance
P3 P-MOSFET On-Resistance
RDSON3
Current Limit
IOCP3
Line Regulation
VO3Line_R
Load Regulation
VO3Load_R
IO3 = 15mA
VO1 Positive Output
Positive Output Range
Positive Output Voltage
Variation
VO1
Maximum Output Current
IO1MAX
N1 N-MOSFET On-Resistance
P1 P-MOSFET On-Resistance
RDS(ON)1
Current Limit
IOCP1
Line Regulation
VO1Line_R
IO1 = 100mA
--
0.02
--
%/V
Load Regulation
VO1Load_R
IO1 = 5mA to 300mA
--
0.4
--
%/A
Adjustable Negative Output
Voltage Range
VO2
41 different values set by SWIRE pin
5.4
4
1.4
V
Negative Output Voltage
Variation
VO2_ACY
VO2 = 2.4V, No Load
50
--
50
mV
Maximum Output Current
IO2MAX
VIN = 2.9V to 4.5V
--
--
300
mA
VIN = 3.7V, ILX-NN1 = 100mA
--
0.2
--
VIN = 3.7V, ILX-NN2 = 100mA
--
0.2
--
1.6
1.9
2.2
A
--
0.02
--
%/V
VO2 Negative Output
NN1 N-MOSFET
On-Resistance
NN2 N-MOSFET
On-Resistance
RDS(ON)2
Current Limit
IOCP2
Line Regulation
VO2Line_R
Load Regulation
VO2Load_R
--
0.4
--
%/A
VO1 Discharge Resistor Value
RDIS1
--
40
--
VO2 Discharge Resistor Value
RDIS2
--
40
--
VO3 Discharge Resistor Value
RDIS3
--
30
--
IO2 = 100mA
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RT4722C
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. JA is measured under natural convection (still air) at TA = 25°C with the component mounted on a high
effective-thermal-conductivity four-layer test board on a JEDEC 51-7 thermal measurement standard. JC is measured
at the exposed pad of the package.
Note 3. Devices are ESD sensitive. Handling precaution recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
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RT4722C
Typical Application Circuit
VBAT
(2.9V to 4.5V)
L1 4.7µH
L3 10µH
CIN
10µFx3
PVIN
LX1
VPOS
(Fixed 4.6V)
CVO1
22µF
LX3
VO1
AVIN
VPOS_FB
FBS
AVDD
(5.8V to 7.9V)
CVO3
22µF
VO3
RT4722C
CAV
1µF
L2 4.7µH
LX2
AVDD Enable
VO1, VO2 Enable and Program VO2
ENO3
FD
SWIRE
PGND1
VO2
PGND2
AGND
CVO2
22µF
VNEG
(-1.4V to -5.4V)
Table 5. Typical BOM List
Reference
Qty
Part Number
Description
Package
Supplier
CIN
3
GRM188R61C106KAAL
10F/16V/X5R
0603
Murata
CVO1, CVO2, CVO3
1
GRM219R61C226ME15
22F/16V/X5R
0805
Murata
CAV
1
GRM185R61C105KE44
1F/16V/X5R
0603
Murata
L1, L2
1
1239AS-H-4R7M = P2
4.7H
2.5 x 2.0 x 1.2mm
Toko
L3
1
1239AS-H-100M = P2
10H
2.5 x 2.0 x 1.2mm
Toko
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RT4722C
Typical Operating Characteristics
VO3 Efficiency vs. Load Current
100
95
95
Efficiency (%)
Efficiency (%)
VO1 & VO2 Efficiency vs. Load Current
100
90
VIN = 4.5V
85
VIN = 3.7V
VIN = 2.9V
80
90
VIN = 4.5V
VIN = 3.7V
85
VIN = 2.9V
80
75
75
VO1 = 4.6V, VO2 = 4V
VO3 = 6.1V
70
70
0
50
100
150
200
250
0
300
10
Load Current (mA)
30
40
50
60
Load Current (mA)
VO1 Voltage vs. Load Current
VO2 Voltage vs. Load Current
4.64
-3.96
4.63
-3.97
4.62
-3.98
VO2 Voltage (V)
VO1 Voltage (V)
20
4.61
4.60
4.59
4.58
-3.99
-4.00
-4.01
-4.02
-4.03
4.57
VIN = 3.7V, IO2 = 5 to 300mA
VIN = 3.7V, IO1 = 5 to 300mA
-4.04
4.56
0
50
100
150
200
250
300
0
50
100
150
200
250
300
Load Current (mA)
Load Current (mA)
VO3 Voltage vs. Load Current
VO1 & VO2 Power On
6.120
CTRL
(5V/Div)
6.115
VO3 Voltage (V)
6.110
6.105
VO1
(2V/Div)
6.100
6.095
VO2
(2V/Div)
6.090
6.085
VIN = 3.7V, IO3 = 1 to 55mA
IIN
(500mA/Div)
VIN = 3.7V
6.080
0
10
20
30
40
50
Load Current (mA)
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Time (2ms/Div)
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RT4722C
VO1 & VO2 Power Off
VO1 & VO2 Power Off
CTRL
(5V/Div)
CTRL
(5V/Div)
VO1
(2V/Div)
VO1
(2V/Div)
VO2
(2V/Div)
VO2
(2V/Div)
IIN
(500mA/Div)
VIN = 3.7V, FD = H
IIN
(500mA/Div)
VIN = 3.7V, FD = L
Time (2ms/Div)
Time (2ms/Div)
VO3 Power On
VO3 Power Off
EN_VO3
(5V/Div)
EN_VO3
(5V/Div)
VO3
(2V/Div)
VO3
(2V/Div)
IIN
(500mA/Div)
IIN
(500mA/Div)
VIN = 3.7V
Time (2ms/Div)
VIN = 3.7V, FD = H
Time (2ms/Div)
VO3 Power Off
EN_VO3
(5V/Div)
VO3
(2V/Div)
IIN
(500mA/Div)
VIN = 3.7V, FD = L
Time (2ms/Div)
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RT4722C
Application Information
The RT4722C is a triple channels DC-DC converter,
If OCP occurs keep more than 1ms IC will shut down
which integrates dual step up converter and an
and need reset enable signal to recovery.
inverting converter to provide the positive and negative
Short Circuit Protection (SCP)
output voltage required by AMOLED. Both positive
The RT4722C has an advanced short circuit protection
(VO1) and negative (VO2) voltage can be programmed
mechanism which prevents damage to the device from
by external MCU through single wire (SWIRE pin) and
unexpected applications. When the output becomes
another step up converter is from 5.8V to 7.9V output
lower than about 90% shorted to ground, over 1ms the
voltage by SWIRE pin. The RT4722C protection
device enters shutdown mode.
function includes Over-Temperature Protection (OTP),
Over-Current Protection (OCP) and Short Circuit
Under-Voltage Lockout (UVLO)
Protection (SCP), VO2 and VO3 have Pulse Skipping
To prevent abnormal operation of the IC in low voltage
Mode (PSM) to provide high efficiency during light load.
condition, an under voltage lockout is included, which
shuts down the device at voltages lower than 2.2V. All
Soft-Start
functions will be turned off in this state.
The RT4722C use an internal soft-start feature to avoid
high inrush currents during step-up.
It is suggested that system need start loading after soft
start finished and output voltage was ready.
Input Capacitor Selection
Each channel input ceramic capacitors with 10F
capacitance
are
suggested
for
the
RT4722C
applications. However, to achieve best performance
Fast Discharge Function
with the RT4722C, larger capacitance can be used. For
All outputs voltage use an embedded discharge
better voltage filtering, select ceramic capacitors with
function to discharge the remaining output to 0V rapidly,
low ESR, X5R and X7R types which are suitable
preventing phenomena such as residual image on the
because of their wider voltage and temperature ranges.
display during shutdown.
Boost Inductor Selection
The inductance depends on the maximum input current.
Over-Temperature Protection (OTP)
The
RT4722C
includes
an
Over-Temperature
Protection (OTP) feature to prevent excessive power
dissipation from overheating the device. The OTP will
shut
down
switching
temperature exceeds
operation
when
junction
140C. Once the junction
temperature cools down by approximately 15C, the
As a general rule, the inductor ripple current range is
20% to 40% of the maximum input current. If 40% is
selected as an example, the inductor ripple current can
be calculated according to the following equations :
IIN(MAX) =
VOUT IOUT(MAX)
η VIN
IL = 0.4 IIN(MAX)
converter resumes operation.
the
where η is the efficiency of the converter, IIN(MAX) is the
maximum junction temperature from rising above
maximum input current, and IL is the inductor ripple
125C.
current. The input peak current can then be obtained
To
maintain
continuous
operation,
prevent
Over-Current Protection (OCP)
by adding the maximum input current with half of the
inductor ripple current as shown in the following
The RT4722C includes a current sensing circuitry
equation :
which monitors the inductor current during each ON
IPEAK = 1.2×IIN(MAX)
period after soft start finished. If the current value
Note that the saturated current of the inductor must be
becomes greater than the current limit, the switch that
greater than IPEAK.
pertains to inductor charging will turn off, forcing the
inductor to leave charging stage and enter discharge
stage.
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RT4722C
The
inductance
can
eventually
be
determined
according to the following equation :
η VIN VOUT -VIN
2
L=
0.4 VOUT IOUT(MAX) fOSC
2
where fOSC is the switching frequency. For better
system performance, a shielded inductor is preferred to
avoid EMI problems.
Boost Output Capacitor Selection
The output ripple voltage is an important index for
estimating chip performance. This portion consists of
Figure 1. The Output Ripple Voltage without the
two parts. One is the product of the inductor peak
Contribution of ESR
current with the ESR of the output capacitor, while the
other part is formed by the charging and discharging
Buck-boost Converter Inductor Selection
process of the output capacitor. As shown in Figure 1,
The first step in the design procedure is to verify
ΔVOUT1 can be evaluated based on the ideal energy
whether the maximum possible output current of the
equalization. According to the definition of Q, the Q
buck-boost converter supports the specific application
value can be calculated as the following equation :
requirements. To simply the calculation, the fastest
1
1
1
IIN + IL -IOUT + IIN - IL -IOUT
2
2
2
approach is to estimate converter efficiency by taking
Q=
VIN
1
= COUT VOUT1
VOUT fOSC
the efficiency numbers from provided efficiency curves
or to use a worst case assumption for the expected
efficiency, e.g., 80%.
The calculation
must be
performed for the minimum assumed input voltage
where fOSC is the switching frequency and ΔIL is the
where the peak switch current is the highest. The
inductor ripple current. Bring COUT to the left side to
inductor has an internal switch to be able to handle this
estimate the value of VOUT1 according to the following
current.
equation :
VOUT1 = VESR +
D IOUT
η COUT fOSC
where VESR = IC x RC_ESR = IPEAK x RC_ESR
D=
accordingly. It is suggested that use better DC bias
Two ceramic 10F capacitor is enough generally.
-VOUT
VIN η-VOUT
Maximum output current :
VIN D
IOUT = IPEAK 1-D
2 fOSC L
The output capacitor, COUT, should be selected
performance capacitor for stability and output ripple.
Converter Duty Cycle :
Inductor peak current :
IPEAK =
IOUT
VIN D
+
1-D 2 fOSC L
As for inductance, we are going to derive the transition
point, where the converter toggles from CCM to DCM.
We need to define the point at which the inductor
current ripple touches zero, and as the power switch
SW is immediately reactivated, the current ramps up
again. Figure 2 portrays the input current activity of the
buck-boost converter.
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is a registered trademark of Richtek Technology Corporation.
DS4722C-00
September 2017
RT4722C
For continuous operation, the maximum operating
junction temperature indicated under Recommended
Operating
Conditions
is
125°C.
The
junction-to-ambient thermal resistance, JA, is highly
package dependent. For a WQFN-16L 3x3 package,
the thermal resistance, JA, is 30°C/W on a standard
JEDEC 51-7 high effective-thermal-conductivity
four-layer test board. The maximum power dissipation
Figure 2. The Buck-Boost Input Signature in BCM
The
inductance
can
eventually
be
determined
PD(MAX) = (125°C - 25°C) / (30°C/W) = 3.33W for a
WQFN-16L 3x3 package.
according to the following equation :
VOUT η
VIN
Lcritical =
2 fOSC IOUT VIN + VOUT
at TA = 25°C can be calculated as below :
The maximum power dissipation depends on the
2
operating ambient temperature for the fixed T J(MAX) and
the thermal resistance, JA. The derating curves in
Figure 3 allows the designer to see the effect of rising
Buck-Boost Converter Output Capacitor Selection
ambient
For the best output voltage filtering, low ESR ceramic
dissipation.
capacitors are recommended. One 22F output
Maximum Power Dissipation (W)1
adequate for most applications. Additional capacitors
can be added to improve load transient response.
To calculate the output voltage ripple, the following
equations can be used :
D VOUT
fOSC RLOAD COUT
on
the
maximum
power
3.5
capacitors with sufficient voltage ratings in parallel are
ΔV =
temperature
+ΔVESR
where VESR = IC x RC_ESR = IPEAK x RC_ESR
Four-Layer PCB
3.0
2.5
2.0
1.5
1.0
0.5
0.0
ΔVESR can be neglected in many cases since ceramic
0
capacitors provides very low ESR.
25
50
75
100
125
Ambient Temperature (°C)
Thermal Considerations
Figure 3. Derating Curve of Maximum Power
The junction temperature should never exceed the
Dissipation
absolute maximum junction temperature T J(MAX), listed
under Absolute Maximum Ratings, to avoid permanent
Layout Considerations
damage to the device. The maximum allowable power
For the best performance of the RT4722C, the
dissipation depends on the thermal resistance of the IC
following PCB layout guidelines should be strictly
package, the PCB layout, the rate of surrounding
followed.
airflow, and the difference between the junction and
ambient
temperatures.
The
maximum
For good regulation, place the power components as
power
close to the IC as possible. The traces should be
dissipation can be calculated using the following
wide and short, especially for the high current output
formula :
loop.
PD(MAX) = (TJ(MAX) - TA) / JA
The input and output bypass capacitor should be
where TJ(MAX) is the maximum junction temperature,
placed as close to the IC as possible and connected
TA is the ambient temperature, and JA is the
to the ground plane of the PCB.
junction-to-ambient thermal resistance.
Copyright © 2017 Richtek Technology Corporation. All rights reserved.
DS4722C-00
September 2017
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
15
RT4722C
Minimize the size of the LX1, LX2, LX3 nodes and
Separate power ground (PGND) and analog ground
keep the traces wide and short. Care should be
(AGND). Connect the AGND and the PGND islands
taken to avoid running traces that carry any
at a single end. Make sure that there are no other
noise-sensitive signals near LX or high-current
connections between these separate ground planes.
traces.
Connect the exposed pad to a strong ground plane
for maximum thermal dissipation.
CIN2
AVDD
L3
VBAT
GND
CVO3
CIN1
CIN3
L1
AVIN
LX3
PGND2
VO3
14
13
1
12
PVIN
PGND1
2
11
LX2
VO1
3
10
VO2
FBS
4
9
SWIRE
6
7
8
NC
AGND
ENO3
AGND
5
R
VPOS
LX1
FD
CVO1
15
GND
1
6
CAV
VBAT
L2
CVO2
VNEG
GND
GND
Figure 4. PCB Layout Guide
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is a registered trademark of Richtek Technology Corporation.
DS4722C-00
September 2017
RT4722C
Outline Dimension
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
0.180
0.300
0.007
0.012
D
2.950
3.050
0.116
0.120
D2
1.300
1.750
0.051
0.069
E
2.950
3.050
0.116
0.120
E2
1.300
1.750
0.051
0.069
e
L
0.500
0.350
0.020
0.450
0.014
0.018
W-Type 16L QFN 3x3 Package
Copyright © 2017 Richtek Technology Corporation. All rights reserved.
DS4722C-00
September 2017
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
17
RT4722C
Footprint Information
Footprint Dimension (mm)
Package
Number
of Pin
P
Ax
Ay
Bx
By
C
D
Sx
Sy
V/W/U/XQFN3*3-16
16
0.50
3.80
3.80
2.10
2.10
0.85
0.30
1.50
1.50
Tolerance
±0.05
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.
Copyright © 2017 Richtek Technology Corporation. All rights reserved.
www.richtek.com
18
is a registered trademark of Richtek Technology Corporation.
DS4722C-00
September 2017
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