RT8297A/B

®
RT8297A/B
1.5A, 17V, 340/800kHz Synchronous Step-Down Converter
General Description
Features
The RT8297A/B is a high efficiency, monolithic
synchronous step-down DC/DC converter that can operate
at 340kHz/800kHz, while delivering up to 1.5A output
current from a 4V to 17V input supply. The RT8297A/B's
current mode architecture allows the transient response
to be optimized. Cycle-by-cycle current limit provides
protection against shorted outputs and soft-start eliminates
input current surge during start-up. Fault conditions also
include output under voltage protection, output over voltage
protection, and thermal shutdown. The low current (<5μA)
shutdown mode provides output disconnect, enabling easy
power management in battery-powered systems. The
RT8297A/B is available in a WDFN-8L 2x2 package.
z
4V to 17V Input Voltage Range
z
1.5A Output Current
Internal N-MOSFETs
Current Mode Control
Fixed Frequency Operation : 340kHz/800kHz
Output Adjustable from 0.8V to 12V
Up to 95% Efficiency
Internal Compensation
Stable with Low ESR Ceramic Output Capacitors
Cycle-by-Cycle Over Current Protection
Input Under Voltage Lockout
Output Under Voltage Protection
Output Over Voltage Protection
Power Good Indicator
Thermal Shutdown Protection
RoHS Compliant and Halogen Free
z
z
z
z
z
z
z
z
z
z
z
z
Ordering Information
z
RT8297A/B
z
Lead Plating System
Z : ECO (Ecological Element with
Halogen Free and Pb free)
A : 340kHz
B : 800kHz
Note :
Richtek products are :
`
RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020.
`
Applications
z
z
z
z
z
Industrial and Commercial Low Power Systems
Computer Peripherals
LCD Monitors and TVs
Green Electronics/Appliances
Point of Load Regulation for High-Performance DSPs,
FPGAs, and ASICs
Pin Configurations
(TOP VIEW)
Suitable for use in SnPb or Pb-free soldering processes.
Marking Information
RT8297AZQW
00 : Product Code
00W
SW
VIN
BOOT
EN
1
2
3
4
GND
Package Type
QW : WDFN-8L 2x2 (W-Type)
9
8
7
6
5
GND
GND
PGOOD
FB
WDFN-8L 2x2
W : Date Code
RT8297BZQW
71 : Product Code
71W
W : Date Code
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8297A/B-06 June 2013
is a registered trademark of Richtek Technology Corporation.
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1
RT8297A/B
Typical Application Circuit
RT8297A
VIN
4V to 17V
2 VIN
BOOT 3
CIN
10µF
CBOOT
10nF
SW 1
6 PGOOD
PGOOD
Chip Enable
7, 8, 9 (Exposed Pad)
R1
110k
FB 5
4 EN
L
15µH
VOUT
3.3V
1.5A
COUT
22µF x 2
R2
36k
GND
RT8297B
VIN
4V to 17V
2 VIN
BOOT 3
CIN
10µF
CBOOT
10nF
SW 1
6 PGOOD
PGOOD
Chip Enable
7, 8, 9 (Exposed Pad)
R1
47k
FB 5
4 EN
L
6.8µH
VOUT
3.3V
1.5A
COUT
22µF x 2
R2
15k
GND
Table 1. Recommended Component Selection
RT8297A
VOUT (V)
L (μH)
R1 (kΩ)
R2 (kΩ)
COUT (μF)
1.2
4.7
110
220
22 x 2
2.5
10
110
51
22 x 2
3.3
15
110
36
22 x 2
5
22
120
22
22 x 2
VOUT (V)
L (μH)
R1 (kΩ)
R2 (kΩ)
COUT (μF)
1.2
3.6
47
91
22 x 2
2.5
4.7
47
22
22 x 2
3.3
6.8
47
15
22 x 2
5
10
62
12
22 x 2
RT8297B
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is a registered trademark of Richtek Technology Corporation.
DS8297A/B-06 June 2013
RT8297A/B
Functional Pin Description
Pin No.
Pin Name
1
SW
2
VIN
3
BOOT
4
EN
5
FB
6
PGOOD
7, 8, 9 (Exposed Pad)
Pin Function
Switch Node. Connect to external L-C filter.
Input Supply Voltage. Must bypass with a suitably large ceramic
capacitor.
Bootstrap for High Side Gate Driver. Connect 0.01μF or greater ceramic
capacitor from BOOT to SW pin.
Chip Enable. A logic-high enables the converter; a logic-low forces the
RT8297A/B into shutdown mode, reducing the supply current to less
than 5μA. Attach this pin to VIN with a 100kΩ pull up resistor for
automatic startup.
Feedback Input Pin. For an adjustable output, connect an external
resistive voltage divider to this pin.
Power Good Indicator. The output of this pin is low if the output voltage is
12.5% less than the nominal voltage. Otherwise, it is an open drain.
Ground. The exposed pad must be soldered to a large PCB and
connected to GND for maximum power dissipation.
GND
Function Block Diagram
VIN
Internal
Regulator
EN
Enable
Comparator
+
2.5V
5k
3V
1V
0.4V
OSC
340kHz/800kHz
VA VCC
Slope Comp
+
Current Sense
Amplifier
Foldback
Control
VA
+
BOOT
OV
OV Comparator
+
+
UV
-
-
UV Comparator
0.8V
FB
-
S
Q
R
Current
Comparator
Q
145m
SW
140m
+
Error Amp
PGOOD
Comparator
+
35pF 400k
-
1pF
GND
0.7V
FB
PGOOD
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
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3
RT8297A/B
Absolute Maximum Ratings
z
z
z
z
z
z
z
z
z
z
(Note 1)
Supply Voltage, VIN ----------------------------------------------------------------------------------------SW --------------------------------------------------------------------------------------------------------------BOOT to SW -------------------------------------------------------------------------------------------------All Other Pins ------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C
WDFN-8L 2x2 ------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2)
WDFN-8L 2x2, θJA -------------------------------------------------------------------------------------------WDFN-8L 2x2, θJC -------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) -----------------------------------------------------------------Junction Temperature ---------------------------------------------------------------------------------------Storage Temperature Range ------------------------------------------------------------------------------ESD Susceptibility (Note 3)
HBM (Human Body Model) --------------------------------------------------------------------------------MM (Machine Model) ----------------------------------------------------------------------------------------
Recommended Operating Conditions
z
z
z
−0.3V to 19V
−0.3V to (VIN + 0.3V)
−0.3V to 6V
−0.3V to 6V
0.833W
120°C/W
8.2°C/W
260°C
150°C
−65°C to 150°C
2kV
200V
(Note 4)
Supply Input Voltage, VIN ---------------------------------------------------------------------------------- 4V to 17V
Junction Temperature Range ------------------------------------------------------------------------------- −40°C to 125°C
Ambient Temperature Range ------------------------------------------------------------------------------- −40°C to 85°C
Electrical Characteristics
(VIN = 12V, TA = 25°C, unless otherwise specified)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
Shutdown Supply Current
ISHDN
VEN = 0V
--
1
5
μA
Supply Current
IOUT
VEN = 3V, VFB = 0.9V
--
0.6
1
mA
0.788
0.800
0.812
V
--
10
--
nA
RDS(ON)1
--
145
--
mΩ
RDS(ON)2
--
140
--
mΩ
2.45
3
4.65
A
--
1
--
A
For RT8297A
300
340
380
For RT8297B
700
800
900
VFB = 0V, For RT8297A
--
95
--
VFB = 0V, For RT8297B
--
170
--
VFB = 0.7V, For RT8297A
--
93
--
%
VFB = 0.7V, For RT8297B
--
84
--
%
Feedback Reference Voltage VREF
4V ≤ VIN ≤ 17V
Feedback Current
High Side Switch On
Resistance
Low Side Switch On
Resistance
VFB = 0.8V
IFB
Upper Switch Current Limit
Min. Duty Cycle, VBOOT − VSW = 4.8V
Maximum Loading = 1.5A
Lower Switch Current Limit
From Drain to Source
Oscillation Frequency
fOSC1
Short-Circuit Oscillation
Frequency
fOSC2
Maximum Duty Cycle
DMAX
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kHz
kHz
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DS8297A/B-06 June 2013
RT8297A/B
Parameter
Minimum On-Time
Input Under Voltage Lockout
Threshold
Input Under Voltage Lockout
Threshold Hysteresis
EN Threshold
Voltage
Symbol
Test Conditions
Min
Typ
Max
Unit
tON
--
100
125
ns
VUVLO
--
3.5
--
V
ΔVUVLO
--
200
--
mV
2.5
--
--
--
--
0.4
--
1
--
μA
Logic-High VIH
Logic-Low
VIL
EN Pull Low Current
VEN = 2V, VFB = 1V
V
Soft-Start Period
tSS
--
1
--
ms
Thermal Shutdown
TSD
--
150
--
°C
Thermal Shutdown
Hysteresis
Power Good Threshold
Rising
Power Good Threshold
Hysteresis
Power Good Pull Down
Resistance
Output OVP Trip Threshold
ΔTSD
--
15
--
°C
--
0.7
--
V
--
130
--
mV
--
12
--
Ω
--
125
--
%VREF
Output OVP Prop Delay
--
10
--
μs
Output UVP Trip Threshold
--
50
--
%VREF
Output UVP Prop Delay
--
2
--
μs
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 © 2013 Richtek Technology Corporation. All rights reserved.
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RT8297A/B
Typical Operating Characteristics
Efficiency vs. Output Current
Efficiency vs. Output Current
100
100
90
90
80
VOUT = 5V
VOUT = 3.3V
VOUT = 1.2V
70
60
Efficiency (%)
Efficiency (%)
80
50
40
30
20
70
VOUT = 5V
VOUT = 3.3V
VOUT = 1.2V
60
50
40
30
20
10
10
RT8297A, VIN = 12V
0
0.01
0.10
1.00
RT8297B, VIN = 12V
0
0.01
10.00
0.10
Output Current (A)
Output Voltage vs. Output Current
5.10
3.40
5.06
3.36
Output Voltage (V)
Output Voltage (V)
10.00
Output Current (A)
Output Voltage vs. Output Current
5.02
4.98
3.32
3.28
3.24
4.94
RT8297B, VIN = 12V, VOUT = 3.3V
RT8297A, VIN = 12V, VOUT = 5V
3.20
4.90
0.0
0.3
0.6
0.9
1.2
0.0
1.5
0.3
0.5
0.8
1.0
1.3
1.5
Output Current (A)
Output Current (A)
Reference Voltage vs. Temperature
Reference Voltage vs. Temperature
1.00
1.00
0.95
0.95
Reference Voltage (V)
Reference Voltage (V)
1.00
0.90
0.85
0.80
0.75
0.70
0.90
0.85
0.80
0.75
0.70
0.65
0.65
RT8297A, VIN = 12V, IOUT = 0A
RT8297B, VIN = 12V, IOUT = 0A
0.60
0.60
-50
-25
0
25
50
75
100
Temperature (°C)
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125
-50
-25
0
25
50
75
100
125
Temperature (°C)
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RT8297A/B
Frequency vs. Input Voltage
860
350
850
345
Frequency (kHz)1
Frequency (kHz)1
Frequency vs. Input Voltage
355
340
335
330
325
320
840
830
820
810
800
790
315
RT8297A, VOUT = 3.3V, IOUT = 0.3A
RT8297B, VOUT = 3.3V, IOUT = 0.3A
310
780
4
6
8
10
12
14
16
18
4
6
8
Frequency vs. Temperature
14
16
18
900
875
Frequency (kHz)1
375
Frequency (kHz)1
12
Frequency vs. Temperature
400
350
325
300
275
850
825
800
775
750
725
RT8297A, VOUT = 3.3V, IOUT = 0.3A
250
RT8297B, VOUT = 3.3V, IOUT = 0.3A
700
-50
-25
0
25
50
75
100
125
-50
-25
0
25
50
75
100
125
Temperature (°C)
Temperature (°C)
Quiescent Current vs. Input Voltage
Quiescent Current vs. Input Voltage
1000
900
950
850
Quiescent Current (μA)
Quiescent Current (μA)
10
Input Voltage (V)
Input Voltage (V)
800
750
700
650
900
850
800
750
700
650
RT8297B, VEN = 3.3V, VFB = 0.85V
RT8297A, VEN = 3.3V, VFB = 0.85V
600
600
4
6
8
10
12
14
16
Input Voltage (V)
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18
4
6
8
10
12
14
16
18
Input Voltage (V)
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RT8297A/B
Quiescent Current vs. Temperature
0.90
0.85
0.85
Quiescent Current (mA)
Quiescent Current (mA)
Quiescent Current vs. Temperature
0.90
0.80
0.75
0.70
0.65
0.80
0.75
0.70
0.65
RT8297A, VIN = 12V, VEN = 3.3V, VFB = 0.85V
RT8297B, VIN = 12V, VEN = 3.3V, VFB = 0.85V
0.60
0.60
-50
-25
0
25
50
75
100
-50
125
-25
0
Temperature (°C)
RT8297A
3.8
3.6
Current Limit (A)
Current Limit (A)
3.2
3.0
VOUT = 1.2V
2.6
RT8297B
125
VOUT = 3.3V
3.2
3.0
2.8
2.6
2.4
2.2
2.2
2.0
VOUT = 1.2V
3.4
2.4
2.0
4
6
8
10
12
14
16
18
4
6
8
Input Voltage (V)
10
12
14
16
18
Input Voltage (V)
Current Limit vs. Temperature
3.9
100
3.6
VOUT = 3.3V
2.8
75
Current Limit vs. Input Voltage
4.0
3.4
50
Temperature (°C)
Current Limit vs. Input Voltage
3.8
25
Current Limit vs. Temperature
4.0
RT8297A
RT8297B
3.7
3.3
Current Limit (A)
Current Limit (A) 1
3.6
3.0
2.7
2.4
2.1
3.4
3.1
2.8
1.8
VIN = 12V, VOUT = 1.2V
1.5
-50
-25
0
25
50
75
100
Temperature (°C)
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125
VIN = 12V, VOUT = 1.2V
2.5
-50
-25
0
25
50
75
100
125
Temperature (°C)
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DS8297A/B-06 June 2013
RT8297A/B
Load Transient Response
Load Transient Response
RT8297A
RT8297B
VOUT
(100mV/Div)
VOUT
(50mV/Div)
IOUT
(1A/Div)
IOUT
(1A/Div)
VIN = 12V, VOUT = 3.3V, IOUT = 0.1A to 1.5A
VIN = 12V, VOUT = 3.3V, IOUT = 0.1A to 1.5A
Time (1ms/Div)
Time (1ms/Div)
Switching
Switching
RT8297A
RT8297B
VSW
(10V/Div)
VSW
(10V/Div)
VOUT
(5mV/Div)
VOUT
(5mV/Div)
IL
(1A/Div)
IL
(1A/Div)
VIN = 12V, VOUT = 3.3V, IOUT = 1.5A
VIN = 12V, VOUT = 3.3V, IOUT = 1.5A
Time (5μs/Div)
Time (500ns/Div)
Power On from EN
Power On from EN
RT8297A
RT8297B, VIN = 12V, VOUT = 3.3V, IOUT = 1.5A
VEN
(5V/Div)
VEN
(5V/Div)
PGOOD
(5V/Div)
PGOOD
(5V/Div)
VOUT
(2V/Div)
VOUT
(2V/Div)
IOUT
(2A/Div)
IOUT
(2A/Div)
VIN = 12V, VOUT = 3.3V, IOUT = 1.5A
Time (500μs/Div)
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Time (500μs/Div)
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RT8297A/B
Power Off from EN
Power Off from EN
RT8297A
RT8297B, VIN = 12V, VOUT = 3.3V, IOUT = 1.5A
VEN
(5V/Div)
VEN
(5V/Div)
PGOOD
(5V/Div)
PGOOD
(5V/Div)
VOUT
(2V/Div)
VOUT
(2V/Div)
IOUT
(2A/Div)
VIN = 12V, VOUT = 3.3V, IOUT = 1.5A
Time (100μs/Div)
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IOUT
(2A/Div)
Time (100μs/Div)
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RT8297A/B
Application Information
The RT8297A/B is a synchronous high voltage buck
converter that can support the input voltage range from
4V to 17V and the output current can be up to 1.5A.
Output Voltage Setting
The resistive divider allows the FB pin to sense the output
voltage as shown in Figure 1.
Thermal Shutdown
Thermal shutdown is implemented to prevent the chip from
operating at excessively high temperatures. When the
junction temperature is higher than 150°C, the whole chip
is shutdown. The chip is automatically re-enable when
the junction temperature cools down by approximately
15 degrees.
VOUT
R1
FB
RT8297A/B
R2
GND
Over Voltage Protection (OVP)
The RT8297A/B provides Over Voltage Protection function
when output voltage over 125%. The internal MOS will be
turned off. The control will return to normal operation if
over voltage condition is removed.
Figure 1. Output Voltage Setting
Under Voltage Protection (UVP)
The output voltage is set by an external resistive divider
according to the following equation :
R1 ⎞
⎛
VOUT = VREF ⎜ 1 +
⎟
⎝ R2 ⎠
Where VREF is the feedback reference voltage (0.8V typ.).
External Bootstrap Diode
Connect a 10nF low ESR ceramic capacitor between the
BOOT pin and SW pin. This capacitor provides the gate
driver voltage for the high side MOSFET. It is recommended
to add an external bootstrap diode between an external
5V and the BOOT pin for efficiency improvement when
input voltage is lower than 5.5V or duty ratio is higher
than 65%. The bootstrap diode can be a low cost one
such as 1N4148 or BAT54. The external 5V can be a 5V
fixed input from system or a 5V output of the RT8297A/B.
Note that the external boot voltage must be lower than
5.5V
5V
BOOT
RT8297A/B
10nF
SW
Figure 2. External Bootstrap Diode
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DS8297A/B-06 June 2013
For the RT8297A/B, it provides Hiccup Mode Under
Voltage Protection (UVP). When the FB voltage drops
below 50% of the feedback reference voltage, the UVP
function will be triggered and the RT8297A/B will shut down
for a period of time and then recover automatically. The
Hiccup Mode UVP can reduce input current in short-circuit
conditions.
Inductor Selection
The inductor value and operating frequency determine the
ripple current according to a specific input and output
voltage. The ripple current ΔIL increases with higher VIN
and decreases with higher inductance.
⎤
⎡V
⎤⎡ V
ΔIL = ⎢ OUT ⎥ ⎢1− OUT ⎥
VIN ⎦
⎣ f ×L ⎦ ⎣
Having a lower ripple current reduces not only the ESR
losses in the output capacitors but also the output voltage
ripple. High frequency with small ripple current can achieve
highest efficiency operation. However, it requires a large
inductor to achieve this goal. For the ripple current
selection, the value of ΔIL = 0.2(IMAX) will be a reasonable
starting point. The largest ripple current occurs at the
highest VIN. To guarantee that the ripple current stays
below the specified maximum, the inductor value should
be chosen according to the following equation :
⎡ VOUT ⎤ ⎡
VOUT ⎤
L= ⎢
⎥ ⎢1 −
⎥
⎢⎣ f × ΔIL(MAX) ⎥⎦ ⎢⎣ VIN(MAX) ⎥⎦
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RT8297A/B
Table 2. Suggested Inductors for Typical
Application Circuit
Component
Supplier
TDK
TDK
TAIYO
YUDEN
Series
Dimensions
(mm)
VLF10045
SLF12565
10 x 9.7 x 4.5
12.5 x 12.5 x 6.5
NR8040
8x8x4
CIN and COUT Selection
The input capacitance, C IN, is needed to filter the
trapezoidal current at the source of the high side MOSFET.
To prevent large ripple current, a low ESR input capacitor
sized for the maximum RMS current should be used. The
RMS current is given by :
V
IRMS = IOUT(MAX) OUT
VIN
VIN
−1
VOUT
This formula has a maximum at VIN = 2VOUT, where IRMS =
IOUT/2. This simple worst-case condition is commonly used
for design because even significant deviations do not offer
much relief. Choose a capacitor rated at a higher
temperature than required. Several capacitors may also
be paralleled to meet size or height requirements in the
design. For the input capacitor, a 10μF low ESR ceramic
capacitor is recommended. For the recommended
capacitor, please refer to table 3 for more detail. The
selection of COUT is determined by the required ESR to
minimize voltage ripple. Moreover, the amount of bulk
capacitance is also a key for COUT selection to ensure
that the control loop is stable. Loop stability can be
checked by viewing the load transient response as
described in a later section. The output ripple, ΔVOUT , is
determined by :
1
⎤
ΔVOUT ≤ ΔIL ⎡⎢ESR +
8fCOUT ⎥⎦
⎣
The output ripple will be highest at the maximum input
voltage since ΔIL increases with input voltage. Multiple
capacitors placed in parallel may be needed to meet the
ESR and RMS current handling requirement. Dry tantalum,
special polymer, aluminum electrolytic and ceramic
capacitors are all available in surface mount packages.
Special polymer capacitors offer very low ESR value.
However, it provides lower capacitance density than other
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12
types. Although Tantalum capacitors have the highest
capacitance density, it is important to only use types that
pass the surge test for use in switching power supplies.
Aluminum electrolytic capacitors have significantly higher
ESR. However, it can be used in cost-sensitive applications
for ripple current rating and long term reliability
considerations. Ceramic capacitors have excellent low
ESR characteristics but can have a high voltage coefficient
and audible piezoelectric effects. The high Q of ceramic
capacitors with trace inductance can also lead to significant
ringing.
Higher values, lower cost ceramic capacitors are now
becoming available in smaller case sizes. Their high ripple
current, high voltage rating and low ESR make them ideal
for switching regulator applications. However, care must
be taken when these capacitors are used at input and
output. When a ceramic capacitor is used at the input
and the power is supplied by a wall adapter through long
wires, a load step at the output can induce ringing at the
input, VIN. At best, this ringing can couple to the output
and be mistaken as loop instability. At worst, a sudden
inrush of current through the long wires can potentially
cause a voltage spike at VIN large enough to damage the
part.
Checking Transient Response
The regulator loop response can be checked by looking
at the load transient response. Switching regulators take
several cycles to respond to a step in load current. When
a load step occurs, VOUT immediately shifts by an amount
equal to ΔILOAD (ESR) also begins to charge or discharge
COUT generating a feedback error signal for the regulator
to return VOUT to its steady-state value. During this
recovery time, VOUT can be monitored for overshoot or
ringing that would indicate a stability problem.
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 :
is a registered trademark of Richtek Technology Corporation.
DS8297A/B-06 June 2013
RT8297A/B
PD(MAX) = (TJ(MAX) − TA ) / θJA
Layout Consideration
where TJ(MAX) is the maximum junction temperature, TA is
the ambient temperature, and θJA is the junction to ambient
thermal resistance.
Follow the PCB layout guidelines for optimal performance
of the RT8297A/B
PD(MAX) = (125°C − 25°C) / (120°C/W) = 0.833W for
WDFN-8L 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 3 allows the
designer to see the effect of rising ambient temperature
on the maximum power dissipation.
Keep the traces of the main current paths as short and
wide as possible.
`
Put the input capacitor as close as possible to the device
pins (VIN and GND).
`
SW node is with high frequency voltage swing and
should be kept at small area. Keep sensitive
components away from the SW node to prevent stray
capacitive noise pickup.
`
Place the feedback components to the FB pin as close
as possible.
`
The GND and Exposed Pad should be connected to a
strong ground plane for heat sinking and noise protection.
SW should be connected to
inductor by wide and short trace.
VOUT
Keep sensitive components
away from this trace.
L
COUT
Maximum Power Dissipation (W)
0.9
Four-Layer PCB
0.8
0.7
0.6
CIN
Input capacitor must
be placed as close
to the IC as possible.
CBOOT
SW
VIN
BOOT
EN
1
2
3
4
GND
For recommended operating condition specifications, the
maximum junction temperature is 125°C. The junction to
ambient thermal resistance, θJA, is layout dependent. For
WDFN-8L 2x2 package, the thermal resistance, θJA, is
120°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 :
`
9
8
7
6
5
GND
GND
PGOOD
FB
R1
R2
VOUT
SW
0.5
GND
The resistor divider must be
connected as close to the
device as possible.
0.4
0.3
Figure 4. PCB Layout Guide
0.2
0.1
0.0
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 3. Derating Curve of Maximum Power Dissipation
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8297A/B-06 June 2013
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
13
RT8297A/B
Table 3. Suggested Capacitors for CIN and COUT
Location
Component Supplier
Part No.
Capacitance (μF)
Case Size
CIN
MURATA
GRM31CR61E106K
10
1206
CIN
TDK
C3225X5R1E106K
10
1206
CIN
TAIYO YUDEN
TMK316BJ106ML
10
1206
COUT
MURATA
GRM32ER61E226M
22
1210
COUT
MURATA
GRM21BR60J226M
22
0805
COUT
TDK
C3225X5R0J226M
22
1210
COUT
TAIYO YUDEN
EMK325BJ226MM
22
1210
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
www.richtek.com
14
is a registered trademark of Richtek Technology Corporation.
DS8297A/B-06 June 2013
RT8297A/B
Outline Dimension
D2
D
L
E
E2
1
e
SEE DETAIL A
b
2
1
2
1
A
A1
A3
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.
Dimensions In Millimeters
Dimensions In Inches
Symbol
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
0.200
0.300
0.008
0.012
D
1.950
2.050
0.077
0.081
D2
1.000
1.250
0.039
0.049
E
1.950
2.050
0.077
0.081
E2
0.400
0.650
0.016
0.026
e
L
0.500
0.300
0.020
0.400
0.012
0.016
W-Type 8L DFN 2x2 Package
Richtek Technology Corporation
5F, No. 20, Taiyuen 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.
DS8297A/B-06 June 2013
www.richtek.com
15