RT8048

RT8048
3MHz 1A Step-Down Converter
General Description
Features
The RT8048 is a high-efficiency Pulse-Width-Modulated
(PWM) step-down DC/DC converter. Capable of delivering
1A output current over a wide input voltage range from
2.5V to 5.5V, the RT8048 is ideally suited for portable
electronic devices that are powered from 1-cell Li-ion
battery or from other power sources such as cellular
phones, PDAs and hand-held devices. Two operating
modes are available including : PWM/Low Dropout auto
switch and shut-down mode. The internal synchronous
rectifier with low RDS(ON) dramatically reduces conduction
loss at PWM mode. No external Schottky diode is
required in practical application. The RT8048 enters LowDropout mode when normal PWM cannot provide regulated
output voltage by continuously turning on the upper
P-MOSFET. The RT8048 enters shut-down mode and
consumes less than 0.1μA when EN pin is pulled low. The
switching ripple is easily smoothed-out by small package
filtering elements due to a fixed operating frequency of
3MHz.
z
2.5V to 5.5V Input Range
z
3MHz Fix-Frequency PWM Operation
1A Output Current
90% Efficiency
No Schottky Diode Required
0.6V Reference Allows Low Output Voltage
Low Dropout Operation : 100% Duty Cycle
RoHS Compliant and Halogen Free
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z
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Applications
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Portable Instruments
Microprocessors and DSP Core supplies
Cellular Phones
Wireless and DSL Modems
PC Cards
Pin Configurations
Ordering Information
RT8048(-
)
Package Type
QW : WDFN-6L 2x2 (W-Type)
Lead Plating System
Z : ECO (Ecological Element with
Halogen Free and Pb free)
Output Voltage
Default : Adjustable
10 : 1.0V
12 : 1.2V
15 : 1.5V
18 : 1.8V
25 : 2.5V
33 : 3.3V
NC
1
EN
VIN
2
GND
(TOP VIEW)
3
7
6
FB/VOUT
5
GND
LX
4
WDFN-6L 2x2
Marking Information
HB : Product Code
HBW
W : Date Code
Note :
Richtek products are :
`
RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020.
`
Suitable for use in SnPb or Pb-free soldering processes.
DS8048-01 June 2011
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1
RT8048
Typical Application Circuit
RT8048
3
VIN
CIN
LX
VIN
L
4
VOUT
2 EN
5, 7(Exposed Pad)
C1
FB
R1
COUT
6
GND
R2
Figure 1. Adjustable Voltage Regulator
RT8048
3
VIN
CIN
VIN
LX
4
L
VOUT
COUT
2 EN
5, 7(Exposed Pad)
VOUT
6
GND
Figure 2. Fixed Voltage Regulator
Table 1. Recommended Component Selection
VOUT (V)
L (μH)
R1 (kΩ)
R2 (kΩ)
COUT (μF)
1.2
0.47
82
82
4.7
1.8
0.47
100
49.9
4.7
2.5
1
91
28.7
4.7
3.3
1
82
18
10
Function Pin Description
Pin No.
Pin Name
Pin Function
Adjustable
Output Voltage
Fixed Output
Voltage
1
1
NC
No Internal Connection.
2
2
EN
Chip Enable (Active High).
3
3
VIN
Power Input.
4
4
LX
Switch Node.
5,
5,
GND
7 (Exposed Pad) 7 (Exposed Pad)
Ground. The exposed pad must be soldered to a large PCB and
connected to GND for maximum power dissipation.
6
--
FB
Feedback.
--
6
VOUT
Output Voltage.
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DS8048-01 June 2011
RT8048
Function Block Diagram
EN
OSC &
Shutdown
Control
Slope
Compensation
VIN
RS1
Current
Limit
Detector
Current
Sense
FB/VOUT
Error
Amplifier
RC
Control
Logic
Driver
LX
PWM
Comparator
RS2
COMP
DS8048-01 June 2011
UVLO &
Power Good
Detector
GND
VREF
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3
RT8048
Absolute Maximum Ratings
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z
z
z
z
(Note 1)
Supply Input Voltage, VIN ---------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C
WDFN-6L 2x2 ------------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2)
WDFN-6L 2x2, θJA ------------------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) ----------------------------------------------------------------------------Junction Temperature --------------------------------------------------------------------------------------------------Storage Temperature Range ------------------------------------------------------------------------------------------ESD Susceptibility (Note 3)
HBM -----------------------------------------------------------------------------------------------------------------------MM --------------------------------------------------------------------------------------------------------------------------
Recommended Operating Conditions
6.5V
0.833W
120°C/W
260°C
150°C
−65°C to 150°C
2kV
200V
(Note 4)
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Supply Input Voltage, VIN ---------------------------------------------------------------------------------------------- 2.5V to 5.5V
Junction Temperature Range ------------------------------------------------------------------------------------------ −40°C to 125°C
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Ambient Temperature Range ------------------------------------------------------------------------------------------ −40°C to 85°C
z
Electrical Characteristics
(VIN = 3.6V, TA = 25°C unless otherwise specified)
Parameter
Symbol
Reference Voltage
IQ
VREF
Under Voltage Lockout Threshold
VUVLO
Quiescent Current
Test Conditions
Min
Typ
Max
Unit
--
81
--
μA
0.588
0.6
0.612
V
VIN Rising
--
2.3
--
VIN Falling
--
2.1
--
V
Shutdown Current
ISHDN
--
0.1
1
μA
Switching Frequency
fOSC
--
3
--
MHz
1.5
--
VIN
VIL
--
--
0.4
Thermal Shutdown Temperature
TSD
--
140
--
°C
Switch On Resistance, High
RPFET
ILX = 0.2A
--
250
--
mΩ
Switch On Resistance, Low
RNFET
ILX = 0.2A
--
260
--
mΩ
Peak Current Limit
ILIM
--
1.5
--
A
EN Input Threshold
Voltage
Logic-High VIH
Logic-Low
V
Output Voltage Line Regulation
VIN = 2.5V to 5.5V
--
--
1
%/V
Output Voltage Load Regulation
0mA < ILOAD < 0.6A
--
--
1
%
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DS8048-01 June 2011
RT8048
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.
Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
DS8048-01 June 2011
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RT8048
Typical Operating Characteristics
Efficiency vs. Output Current
Efficiency vs. Output Current
100
100
90
90
80
VIN = 3.3V
VIN = 5V
70
Efficiency (%)
Efficiency (%)
80
60
50
40
30
70
60
50
40
30
20
20
10
10
VOUT = 1.2V, L = 1μH
VIN = 5V, VOUT = 3.3V, L = 1μH
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0.1
1.0
0.2
0.3
0.4
Reference Voltage vs. Temperature
0.6
0.7
0.8
0.9
1.0
Frequency vs. Temperature
3.5
0.620
3.4
Frequency (MHz)1
0.615
Reference Voltage (V)
0.5
Output Current (A)
Output Current (A)
0.610
0.605
0.600
0.595
3.3
3.2
3.1
3.0
2.9
2.8
0.590
2.7
0.585
2.6
0.580
2.5
-50
-25
0
25
50
75
100
VIN = 5V, VOUT = 3.3V, IOUT = 0.3A
-50
125
-25
0
25
50
75
100
125
Temperature (°C)
Temperature (°C)
Current Limit vs. Temperature
Current Limit vs. Input Voltage
2.6
2.1
2.3
Current Limit (A)
Current Limit (A)
1.9
2.0
1.7
1.4
1.1
VOUT = 1.2
1.7
VOUT = 3.3
1.5
1.3
0.8
VOUT = 1.2V
VIN = 5V
1.1
0.5
2.5
3.0
3.5
4.0
4.5
Input Voltage (V)
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5.0
5.5
-50
-25
0
25
50
75
100
125
Temperature (°C)
DS8048-01 June 2011
RT8048
UVLO vs. Temperature
EN Threshold Voltage vs. Temperature
1.6
3.0
EN Threshold Voltage (V)
1.5
UVLO (V)
2.7
Rising
2.4
2.1
Falling
1.8
1.4
1.3
Rising
1.2
1.1
1.0
Falling
0.9
0.8
0.7
0.6
1.5
-50
-25
0
25
50
75
100
-50
125
-25
0
25
50
75
100
125
Temperature (°C)
Temperature (°C)
Output Voltage vs. Output Current
Output Voltage vs. Output Current
1.24
3.42
3.41
3.40
Output Voltage (V)
Output Voltage (V)
1.23
1.22
VIN = 5V
1.21
VIN = 3.3V
1.20
3.39
3.38
3.37
3.36
3.35
3.34
1.19
VOUT = 1.2V
1.18
3.33
VIN = 5V, VOUT = 3.3V
3.32
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0
0.2
0.3
0.4
0.5
0.6
0.7
Output Current (A)
Switching
Switching
VOUT
(10mV/Div)
VOUT
(10mV/Div)
VLX
(5V/Div)
VLX
(5V/Div)
IL
(2A/Div)
IL
(2A/Div)
VIN = 5V, VOUT = 1.2V, IOUT = 1A
Time (250ns/Div)
DS8048-01 June 2011
0.1
Output Current (A)
0.8
0.9
1
VIN = 5V, VOUT = 3.3V, IOUT = 1A
Time (250ns/Div)
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RT8048
Load Transient Response
Load Transient Response
VOUT
(50mV/Div)
VOUT
(50mV/Div)
IOUT
(0.5A/Div)
IOUT
(0.5A/Div)
VIN = 5V, VOUT = 3.3V, IOUT = 50mA to 1A
VIN = 3.3V, VOUT = 1.2V, IOUT = 50mA to 1A
Time (250μs/Div)
Time (250μs/Div)
Power On from EN
Power Off from EN
VEN
(10V/Div)
VEN
(10V/Div)
VOUT
(5V/Div)
VOUT
(5V/Div)
IOUT
(2A/Div)
IOUT
(2A/Div)
VIN = 5V, VOUT = 3.3V, IOUT = 1A
Time (100μs/Div)
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VIN = 5V, VOUT = 3.3V, IOUT = 1A
Time (10μs/Div)
DS8048-01 June 2011
RT8048
Application Information
The basic RT8048 application circuit is shown in Typical
Application Circuit. External component selection is
determined by the maximum load current and begins with
the selection of the inductor value and operating frequency
followed by CIN and COUT. Although frequency as high as
3MHz are possible, the minimum on-time of the RT8048
imposes a minimum limit on the operating duty cycle.
The minimum duty is equal to 70ns’ fOSC(Hz)’ 100%.
Inductor Selection
For a given input and output voltage, the inductor value
and operating frequency determine the ripple current. The
ripple current ΔIL increases with higher VIN and decreases
with higher inductance :
⎡ V
⎤⎡ V
⎤
ΔIL = ⎢ OUT ⎥ ⎢1− OUT ⎥
VIN ⎦
⎣ fOSC × L ⎦ ⎣
Having a lower ripple current reduces the ESR losses in
the output capacitors and the output voltage ripple. Highest
efficiency operation is achieved at low frequency with small
ripple current. This, however, requires a large inductor. A
reasonable starting point for selecting the ripple current
is ΔIL = 0.4 (IMAX). The largest ripple current occurs at the
highest VIN. To guarantee that the ripple current stays
below a specified maximum, the inductor value should be
chosen according to the following equation :
⎡
⎤⎡
⎤
VOUT
V
L= ⎢
⎥ ⎢1− OUT ⎥
⎣⎢ fOSC × ΔIL(MAX) ⎦⎥ ⎣⎢ VIN(MAX) ⎦⎥
Inductor Core Selection
Once the value for L is known, the type of inductor can be
selected. High efficiency converters generally cannot afford
the core loss found in low cost powdered iron cores, forcing
the use of more expensive ferrite or molypermalloy cores.
Actual core loss is independent of core size for a fixed
inductor value, but it is very dependent on the inductance
selected. As the inductance increases, core losses
decrease. Unfortunately, increased inductance requires
more turns of wire and, therefore, more copper losses.
Ferrite designs have very low core losses and are preferred
at high switching frequencies. Hence, design goals should
concentrate on copper loss and saturation prevention.
Ferrite core material saturates “ hard” , which means that
the inductance collapses abruptly when the peak design
DS8048-01 June 2011
current is exceeded. This result in an abrupt increase in
inductor ripple current and consequent output voltage ripple.
Do not allow the core to saturate! Different core materials
and shapes will change the size, current and price/current
relationship of an inductor. Toroid or shielded pot cores in
ferrite or permalloy materials are small and don’t radiate
energy, but generally cost more than powdered iron core
inductors with similar characteristics. The choice of
inductor type to use mainly depends on the price vs. size
requirements and any radiated field/EMI requirements.
CIN and COUT Selection
The input capacitance, C IN, is needed to filter the
trapezoidal current at the source of the top MOSFET. To
prevent large ripple voltage, a low ESR input capacitor
sized for the maximum RMS current should be used. RMS
current is given by :
IRMS = IOUT(MAX)
VOUT
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. Note that ripple current ratings from capacitor
manufacturers are often based on only 2000 hours of life,
which makes it advisable to either further derate the
capacitor or choose a capacitor rated at a higher
temperature than required. Several capacitors may also
be placed in parallel to meet size or height requirements
in the design. The selection of COUT is determined by the
effective series resistance (ESR) that is required to
minimize voltage ripple and load step transients, as well
as the amount of bulk capacitance that is necessary to
ensure that the control loop is stable. Loop stability can
be examined by viewing the load transient response as
described in a later section. The output ripple, ΔVOUT, is
determined by :
⎡
⎤
1
ΔVOUT ≤ ΔIL ⎢ESR +
⎥
8fOSC COUT ⎦
⎣
The output ripple is highest at 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 requirements. Dry tantalum, special
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RT8048
polymer, aluminum electrolytic and ceramic capacitors are
all available in surface mount packages. Special polymer
capacitors offer very low ESR, but have lower capacitance
density than other types. Tantalum capacitors have the
highest capacitance density, but it is important to only
use types that have been surge tested for use in switching
power supplies. Aluminum electrolytic capacitors have
significantly higher ESR but can be used in cost sensitive
applications provided that consideration is given to ripple
current ratings and long term reliability. 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.
Using Ceramic Input and Output Capacitors
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 the 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.
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 of
the RT8048, the maximum junction temperature is 125°C
and TA is the ambient temperature. The junction to ambient
thermal resistance, θJA, is layout dependent. For WDFN6L 2x2 packages, 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 :
PD(MAX) = (125°C − 25°C) / (120°C/W) = 0.833W for
WDFN-6L 2x2 package
The maximum power dissipation depends on the operating
ambient temperature for fixed T J(MAX) and thermal
resistance, θJA. For the RT8048 packages, the derating
curve in Figure 3 allows the designer to see the effect of
rising ambient temperature on the maximum power
dissipation.
Checking Transient Response
Maximum Power Dissipation (W)
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), where ESR is the effective series
resistance of COUT. ΔILOAD also begins to charge or
discharge COUT, generating a feedback error signal used
by the regulator to return VOUT to its steady-state value.
During this recovery time, VOUT can be monitored for
overshoot or ringing, which would indicate a stability
problem.
0.90
Four-Layer PCB
0.80
0.70
0.60
0.50
0.40
0.30
0.20
0.10
0.00
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 3. Derating Curve for the RT8048 Packages
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DS8048-01 June 2011
RT8048
Outline Dimension
D2
D
L
E
E2
1
2
e
1
2
1
b
A
A1
SEE DETAIL A
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.
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
0.200
0.350
0.008
0.014
D
1.950
2.050
0.077
0.081
D2
1.000
1.450
0.039
0.057
E
1.950
2.050
0.077
0.081
E2
0.500
0.850
0.020
0.033
e
L
0.650
0.300
0.026
0.400
0.012
0.016
W-Type 6L DFN 2x2 Package
Richtek Technology Corporation
Richtek Technology Corporation
Headquarter
Taipei Office (Marketing)
5F, No. 20, Taiyuen Street, Chupei City
5F, No. 95, Minchiuan Road, Hsintien City
Hsinchu, Taiwan, R.O.C.
Taipei County, Taiwan, R.O.C.
Tel: (8863)5526789 Fax: (8863)5526611
Tel: (8862)86672399 Fax: (8862)86672377
Email: [email protected]
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.
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