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RT8030
1A, 2.2MHz, Synchronous Step-Down Regulator
General Description
Features
The RT8030 is a high efficiency synchronous, step-down
DC/DC converter. Its input voltage range is from 2.6V to
5.5V and provides an adjustable regulated output voltage
from 0.8V to 5V while delivering output current up to 1A.
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The internal synchronous low on-resistance power
switches increase efficiency and eliminate the need for
an external Schottky diode. Switching frequency is set
by an external resistor or can be synchronized to an
external clock. 100% duty cycle provides low dropout
operation extending battery life in portable systems.
Current mode operation with external compensation
allows the transient response to be optimized over a wide
range of loads and output capacitors.
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High Efficiency : Up to 95%
Low RDS(ON) Internal Switches : 160mΩ
Ω
Programmable Frequency : 300kHz to 2.5MHz
No Schottky Diode Required
0.8V Reference Allows Low Output Voltage
Forced Continuous Mode Operation
Low Dropout Operation : 100% Duty Cycle
RoHS Compliant and Halogen Free
Applications
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RT8030 operation in forced continuous PWM Mode which
minimizes ripple voltage and reduces the noise and RF
interference. 100% duty cycle in Low Dropout Operation
further maximize battery life.
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Portable Instruments
Battery-Powered Equipment
Notebook Computers
Distributed Power Systems
IP Phones
Digital Cameras
Ordering Information
RT8030
Pin Configurations
Package Type
S : SOP-8
(TOP VIEW)
SHDN/RT
Lead Plating System
G : Green (Halogen Free and Pb Free)
8
COMP
GND
2
7
FB
Note :
LX
3
6
VDD
Richtek products are :
PGND
4
5
PVDD
`
RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020.
SOP-8
`
Suitable for use in SnPb or Pb-free soldering processes.
Typical Application Circuit
RT8030
VIN
2.6V to 5.5V
CIN
10µF x 2
5 PVDD
LX
6 VDD
FB 7
4
ROSC
137k
3
PGND
1 SHDN/RT
COMP 8
GND
2
L1
2.2µH
VOUT
1.5V/1A
R1
210k
COUT
10µF x 2
RCOMP 13k
CCOMP
1nF
R2
240k
Note : Using all Ceramic Capacitors
DS8030-02 March 2011
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RT8030
Functional Pin Description
Pin No.
Pin Name
Pin Function
1
SHDN/RT
2
GND
3
LX
Internal Power MOSFET Switches Output. Connect this pin to the inductor.
4
PGND
Power Ground. Connect this pin close to the (−) terminal of C IN and COUT .
5
PVDD
Power Input Supply. Decouple this pin to PGND with a capacitor.
6
VDD
7
FB
Oscillator Resistor Input. Connecting a resistor to ground from this pin sets the switching
frequency. Forcing this pin to V DD causes the device to be shut down.
Signal Ground. All small-signal components and compensation components should
connect to this ground, which in turn connects to PGND at one point.
Signal Input Supply. Decouple this pin to GND with a capacitor. Normally VDD is equal to
PVDD.
Feedback Pin. Receives the feedback voltage from a resistive divider connected across
the output.
Error Amplifier Compensation Point. The current comparator threshold increases with
8
COMP
this control voltage. Connect external compensation elements to this pin to stabilize the
control loop.
Function Block Diagram
SHDN/RT
PVDD
ISEN
SD
OSC
Slope
Com
COMP
0.8V
EA
FB
OC
Limit
Output
Clamp
Driver
Int-SS
LX
0.9V
Control
Logic
0.7V
NISEN
VDD
POR
0.4V
VREF
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2
PGND
NMOS I Limit
OTP
GND
DS8030-02 March 2011
RT8030
Operation
Main Control Loop
Slope Compensation and Inductor Peak Current
The RT8030 is a monolithic, constant-frequency, current
mode step-down DC/DC converter. During normal
operation, the internal top power switch (P-MOSFET) is
turned on at the beginning of each clock cycle. Current in
the inductor increases until the peak inductor current reach
the value defined by the voltage on the COMP pin. The
error amplifier adjusts the voltage on the COMP pin by
comparing the feedback signal from a resistor divider on
the FB pin with an internal 0.8V reference. When the load
current increases, it causes a reduction in the feedback
voltage relative to the reference. The error amplifier raises
the COMP voltage until the average inductor current
matches the new load current. When the top power
MOSFET shuts off, the synchronous power switch
(N-MOSFET) turns on until either the bottom current limit
is reached or the beginning of the next clock cycle.
Slope compensation provides stability in constant
frequency architectures by preventing sub-harmonic
oscillations at duty cycles greater than 50%. It is
accomplished internally by adding a compensating ramp
to the inductor current signal. Normally, the maximum
inductor peak current is reduced when slope compensation
is added. In the RT8030, however, separated inductor
current signals are used to monitor over current condition.
This keeps the maximum output current relatively constant
regardless of duty cycle.
The operating frequency is set by an external resistor
connected between the RT pin and ground. The practical
switching frequency can range from 300kHz to 2.5MHz.
Short Circuit Protection
When the output is shorted to ground, the inductor current
decays very slowly during a single switching cycle. A
current runaway detector is used to monitor inductor
current. As current increasing beyond the control of current
loop, switching cycles will be skipped to prevent current
runaway from occurring.
Dropout Operation
When the input supply voltage decreases toward the output
voltage, the duty cycle increases toward the maximum
on-time. Further reduction of the supply voltage forces
the main switch to remain on for more than one cycle
eventually reaching 100% duty cycle.
The output voltage will then be determined by the input
voltage minus the voltage drop across the internal
P-MOSFET and the inductor.
Low Supply Operation
The RT8030 is designed to operate down to an input supply
voltage of 2.6V. One important consideration at low input
supply voltages is that the RDS(ON) of the P-Channel and
N-Channel power switches increases. The user should
calculate the power dissipation when the RT8030 is used
at 100% duty cycle with low input voltages to ensure that
thermal limits are not exceeded.
DS8030-02 March 2011
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RT8030
Absolute Maximum Ratings
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(Note 1)
Supply Input Voltage, VDD, PVDD ------------------------------------------------------------------------------- −0.3V to 6V
LX Pin Switch Voltage -------------------------------------------------------------------------------------------- −0.3V to (PVDD + 0.3V)
Other I/O Pin Voltages ------------------------------------------------------------------------------------------- −0.3V to (VDD + 0.3V)
LX Pin Switch Current -------------------------------------------------------------------------------------------- 4A
Power Dissipation, PD @ TA = 25°C
SOP-8 --------------------------------------------------------------------------------------------------------------- 0.909W
Package Thermal Resistance (Note 2)
SOP-8, θJA ---------------------------------------------------------------------------------------------------------- 110°C/W
Junction Temperature --------------------------------------------------------------------------------------------- 150°C
Lead Temperature (Soldering, 10 sec.) ----------------------------------------------------------------------- 260°C
Storage Temperature Range ------------------------------------------------------------------------------------ −65°C to 150°C
ESD Susceptibility (Note 3)
HBM (Human Body Mode) -------------------------------------------------------------------------------------- 2kV
MM (Machine Mode) ---------------------------------------------------------------------------------------------- 200V
Recommended Operating Conditions
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(Note 4)
Input Voltage Range, VDD ------------------------------------------------------------------------------------------------------------------------------ 2.6V to 5.5V
Junction Temperature Range ------------------------------------------------------------------------------------ −40°C to 125°C
Ambient Temperature Range ------------------------------------------------------------------------------------ −40°C to 85°C
Electrical Characteristics
(VDD = 3.3V, TA = 25°C, unless otherwise specified)
Parameter
Min
Typ
Max
Unit
0.784
0.8
0.816
V
Active, VFB = 0.78V, Not Switching
--
460
--
μA
Shutdown
--
--
1
μA
VIN = 2.7V to 5.5V
--
0.04
--
%/V
0A < ILOAD < 1A
--
0.25
--
%
gm
--
800
--
μS
Current Sense Transresistance RT
--
0.4
--
Ω
ROSC = 332k
0.8
1
1.2
MHz
Switching Frequency
0.3
--
2.5
MHz
Feedback Reference Voltage
Symbol
VREF
DC Bias Current
Output Voltage Line Regulation
Output Voltage Load
Regulation
Error Amplifier
Transconductance
Test Conditions
Switching Frequency
Switch On Resistance, High
RPMOS
I SW = 0.5A
--
150
--
mΩ
Switch On Resistance, Low
RNMOS
I SW = 0.5A
--
160
--
mΩ
Peak Current Limit
ILIM
2.2
3.2
--
A
VDD Rising
--
2.4
--
V
VDD Falling
--
2.3
--
V
Under Voltage Lockout
Threshold
Shutdown Threshold
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VSHDN/RT
--
VIN – 0.7 VIN – 0.4
V
DS8030-02 March 2011
RT8030
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 the natural convection at TA = 25°C on 4-layers high effective thermal conductivity 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.
DS8030-02 March 2011
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RT8030
Typical Operating Characteristics
Efficiency vs. Output Current
100
Output Voltage vs. Output Current
1.515
VIN = 3.3V
90
1.510
VIN = 5V
Output Voltage (V)
Efficiency (%)
80
70
60
50
40
30
20
1.505
1.500
1.495
1.490
10
VOUT = 1.5V, L = 2.2uH
VIN = 5V, VOUT = 1.5V
1.485
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0
1
0.1
0.2
0.3
Output Voltage vs. Input Voltage
0.6
0.7
0.8
0.9
1
Output Voltage vs. Temperature
1.515
1.510
1.510
Output Voltage (V)
1.515
1.505
1.500
1.495
1.490
1.505
1.500
1.495
1.490
VIN = 5V, VOUT = 1.5V
VOUT = 1.5V
1.485
1.485
2.5
3
3.5
4
4.5
5
5.5
-50
-25
0
Input Voltage (V)
25
50
75
100
125
Temperature (°C)
Switching Frequency vs. Input Voltage
Switching Frequency vs. Temperature
2.40
2.40
2.35
2.35
Switching Frequency (MHz)
Switching Frequency (MHz)
0.5
Output Current (A)
Output Current (A)
Output Voltage (V)
0.4
2.30
2.25
2.20
2.15
2.10
2.05
2.30
2.25
2.20
2.15
2.10
2.05
VIN = 5V, VOUT = 1.5V, IOUT = 300mA, ROSC = 137kΩ
VOUT = 1.5V, IOUT = 300mA, ROSC = 137kΩ
2.00
2.00
2.5
3
3.5
4
4.5
Input Voltage (V)
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5
5.5
-50
-25
0
25
50
75
100
125
Temperature (°C)
DS8030-02 March 2011
RT8030
Load Transient Response
Quiescent Current vs. Input Voltage
550
Quiescent Current (uA)
VOUT
(50mV/Div)
IOUT
(1A/Div)
530
510
490
470
VIN = 5V, VOUT = 1.5V, IOUT = 0A to 1A
450
Time (50us/Div)
3
3.25 3.5 3.75
4
4.25 4.5 4.75
5
5.25 5.5
Input Voltage (V)
Quiescent Current vs. Temperature
Output Current Limit vs. Input Voltage
500
4.0
Output Current Limit (A)
Quiescent Current (uA)
3.8
480
460
440
420
3.5
3.3
3.0
2.8
2.5
2.3
VIN = 3.3V
400
-50
-25
0
25
50
75
100
VOUT = 1.5V
2.0
2.5
125
Temperature (°C)
3
3.5
4
4.5
5
5.5
Input Voltage (V)
Output Current Limit vs. Temperature
Output Ripple
4.0
Output Current Limit (A)
3.8
VOUT
(5mV/Div)
3.5
3.3
3.0
2.8
VLX
(5V/Div)
2.5
2.3
VIN = 5V, VOUT = 1.5V
VIN = 5V, VOUT = 1.5V, IOUT = 0A
2.0
-50
-25
0
25
50
75
100
125
Time (250ns/Div)
Temperature (°C)
DS8030-02 March 2011
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RT8030
Power On
Power Off
VIN = 5V, VOUT = 1.5V, IOUT = 1A
VIN
(5V/Div)
VIN
(2V/Div)
VOUT
(1V/Div)
VOUT
(1V/Div)
IOUT
(0.5A/Div)
IOUT
(0.5A/Div)
VIN = 5V, VOUT = 1.5V, IOUT = 1A
Time (1ms/Div)
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Time (5ms/Div)
DS8030-02 March 2011
RT8030
Application Information
Operating Frequency
Selection of the operating frequency is a tradeoff between
efficiency and component size. High frequency operation
allows the use of smaller inductor and capacitor values.
Operation at lower frequency improves efficiency by
reducing internal gate charge and switching losses but
requires larger inductance and/or capacitance to maintain
low output ripple voltage.
The operating frequency of the RT8030 is determined by
an external resistor that is connected between the RT pin
and ground. The value of the resistor sets the ramp current
that is used to charge and discharge an internal timing
capacitor within the oscillator. The ROSC resistor value can
be determined by examining the frequency vs. ROSC curve.
Although frequencies as high as 2.5MHz are possible,
the minimum on-time of the RT8030 imposes a minimum
limit on the operating duty cycle. The minimum on-time
is typically 110ns. Therefore, the minimum duty cycle is
equal to 100 x 110ns x f(Hz).
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 ⎦
⎣ f × 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 ΔI = 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 :
DS8030-02 March 2011
⎡ VOUT ⎤ ⎡
VOUT ⎤
L=⎢
⎥
⎥ ⎢1 − V
f
I
×
Δ
L(MAX)
IN(MAX)
⎦
⎦⎣
⎣
The transition from low current operation begins when the
peak inductor current falls below the minimum peak
current. Lower inductor values result in higher ripple current
which causes this to occur at lower load currents. This
causes a dip in efficiency in the upper range of low current
operation.
2.5
ROSC = 154k for 2MHz
2.0
Frequency (MHz)
The basic RT8030 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.
1.5
ROSC = 332k for 1MHz
1.0
0.5
0.0
0
100 200 300 400 500 600 700 800 900 1000
100
0
ROSC Resistance
RRT (k⎝ ) (kΩ)
Figure 1. Switching Frequency vs. ROSC Resistance
Inductor Core Selection
Once the value for L is known, the type of inductor must
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 mollypermalloy
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 copper losses
will increase.
Ferrite designs have very low core losses and are preferred
at high switching frequencies, so design goals can
concentrate on copper loss and preventing saturation.
Ferrite core material saturates “hard”, which means that
inductance collapses abruptly when the peak design
current is exceeded.
This result in an abrupt increase in inductor ripple current
and consequent output voltage ripple.
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RT8030
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 which style inductor 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
I RMS = I OUT/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 further
derate the capacitor, or 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.
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 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 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
polymer, aluminum electrolytic and ceramic capacitors are
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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.
Output Voltage Programming
The output voltage is set by an external resistive divider
according to the following equation :
VOUT = VREF × ⎛⎜1 + R1 ⎞⎟
⎝ R2 ⎠
where VREF equals to 0.8V typical.
The resistive divider allows the FB pin to sense a fraction
of the output voltage as shown in Figure 2.
V OUT
R1
FB
RT8030
R2
GND
Figure 2. Setting the Output Voltage
DS8030-02 March 2011
RT8030
Outline Dimension
H
A
M
J
B
F
C
I
D
Dimensions In Millimeters
Dimensions In Inches
Symbol
Min
Max
Min
Max
A
4.801
5.004
0.189
0.197
B
3.810
3.988
0.150
0.157
C
1.346
1.753
0.053
0.069
D
0.330
0.508
0.013
0.020
F
1.194
1.346
0.047
0.053
H
0.170
0.254
0.007
0.010
I
0.050
0.254
0.002
0.010
J
5.791
6.200
0.228
0.244
M
0.400
1.270
0.016
0.050
8-Lead SOP Plastic 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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