®
RT8580
36V DC-DC Boost Converter
General Description
Features
The RT8580 is a high performance, low noise, DC-DC Boost
Input Operating Range : 3V to 5.5V
Converter with an integrated 0.5A, 1 internal switch. The
RT8580's input voltage ranges from 3V to 5.5V, and it can
Wide Output Range : VCC to 40V
Internal Power N-MOSFET Switch
500kHz Fixed Switching Frequency
support the output voltage up to 40V. When used in optical
(Avalanche Photo Diode), the output voltage of the RT8580
Minimize the External Component Counts
Internal Soft-Start
can be doubled up by a typical voltage doubler circuit.
The RT8580 adapts fixed frequency, current mode PWM
Internal Compensation
Under-Voltage Lockout Protection
control loop to regulate the output voltage with fast transient
Over-Temperature Protection
response and cycle-by-cycle current limit protection. The
RoHS Compliant and Halogen Free
receiver applications requiring 80V to drive the APD
protection features of the RT8580 include : 1) input undervoltage lockout, 2) output over-voltage protection, and 3)
Applications
over-temperature protection. The soft-start function and
Cellular Phones
PWM loop compensation is built-in internally to save
external soft-start capacitor and PWM loop compensation
Digital Cameras
Portable Instruments
components. By operating at 500kHz switching frequency,
the RT8580 system board can be made compact to achieve
low system BOM cost. The RT8580 is available in the
Avalanche Photodiode Biasing
tiny package type SOT-23-6.
Ordering Information
RT8580
Package Type
E : SOT-23-6
Marking Information
Lead Plating System
G : Green (Halogen Free and Pb Free)
0E= : Product Code
0E=DNN
DNN : 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.
Simplified Application Circuit
D1
L1
VIN
VOUT
C1
RT8580
R1
VCC
LX
SHDN
FB
GND
C2
R2
PGND
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1
RT8580
Pin Configuration
(TOP VIEW)
LX VCC SHDN
6
5
4
2
3
PGND GND FB
SOT-23-6
Functional Pin Description
Pin No.
Pin Name
Pin Function
1
PGND
Power ground.
2
GND
Ground.
3
FB
Feedback voltage input. Connect a resistor to GND to setting the current.
4
SHDN
Shutdown control input. Apply a logic-low voltage to SHDN to shut down the
device. Connect SHDN to VIN for normal operation. Ensure that SHDN is not
greater than the input voltage, VCC.
5
VCC
Supply voltage input.
6
LX
Switch node.
Functional Block Diagram
VCC
LX
GND
UVLO
OCP
Internal
Compensation
OTP
PWM
Internal
Soft-Start
Logic Control,
Minimum On
Time
+
EA
GM
Driver
PGND
Slope
Compensation
LPF
Enable
Logic
Shutdown
20ms
1µA
Bias
Current
SHDN
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PWM
Oscillator
Reference
Voltage
VREF
FB
CurrentSense
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DS8580-01 January 2017
RT8580
Operation
The RT8580 is a constant frequency, current mode Boost
regulator. In normal operation, the N-MOSFET is turned
When the RT8580 is enabled by SHDN pin, the internal
on when the PWM control circuit is set by the oscillator.
period. There is also a built-in soft-start function. Both
As the N-MOSFET is on, the inductor current ramps up.
ensure that the output voltage rises slowly to reduce the
input inrush current.
The N-MOSFET will be turned off when the inductor current
hits the level set by the PWM control loop. After the
N-MOSFET is turned off, the inductor current will ramp
down through the external catch diode until the OSC sets
high for the next switching cycle and the next cycle
repeats.
The operation of the RT8580 can be better understood by
referring to the block diagram. The voltage at the output of
VREF ramps up to the target voltage in a specific time
The protection features of the RT8580 include : 1) input
under-voltage lockout, 2) output over-voltage protection,
and 3) over-temperature protection. When the input voltage
is lower than the UVLO threshold, the RT8580 will be
turned off. There is a 100mV hysteresis for the UVLO
control. When the junction temperature exceeds 150C,
the over-temperature protection function will shut down
the error amplifier is an amplified version of the difference
between the 1.25V reference voltage and the output
the switching operation. Once the junction temperature
feedback voltage. If the feedback voltage drops below
automatically resume switching.
cools down by approximately 25C, the converter will
(above) 1.25V, the output of the error amplifier increases
(decreases). This results in higher (lower) PWM turn on
duty and thus higher (lower) inductor peak current flowing
through the power FET. By this control loop operation,
the increased (decreased) power will be delivered to the
output to bring up (down) the output feedback voltage back
to 1.25V.
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RT8580
Absolute Maximum Ratings
(Note 1)
VCC, SHDN, FB to GND -------------------------------------------------------------------------------------------------- n0.3V to 6V
LX to GND -------------------------------------------------------------------------------------------------------------------- n0.3V to 50V
Power Dissipation, PD @ TA = 25C
SOT-23-6 --------------------------------------------------------------------------------------------------------------------- 0.48W
Package Thermal Resistance (Note 2)
SOT-23-6,
JA ---------------------------------------------------------------------------------------------------------------- 208.2C/W
Junction Temperature ------------------------------------------------------------------------------------------------------ 150C
Lead Temperature (Soldering, 10 sec.) -------------------------------------------------------------------------------- 260C
Storage Temperature Range --------------------------------------------------------------------------------------------- n65C to 150C
ESD Susceptibility (Note 3)
HBM (Human Body Model) ----------------------------------------------------------------------------------------------- 2kV
MM (Machine Model) ------------------------------------------------------------------------------------------------------ 200V
Recommended Operating Conditions
(Note 4)
Input Voltage, VCC --------------------------------------------------------------------------------------------------------- 3V to 5.5V
Junction Temperature Range --------------------------------------------------------------------------------------------- n40C to 125C
Ambient Temperature Range --------------------------------------------------------------------------------------------- n40C to 85C
Electrical Characteristics
(VCC = 3.3V, TA = 25C, unless otherwise specified)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
--
2
2.4
V
0.6
0.8
1.2
mA
--
2
5
A
--
--
2
A
Overall
Under-Voltage Lockout Threshold
VUVLO
VCC Quiescent Current
IQ
VCC Shutdown Current
Shutdown Input Current
SHDN = 0V
ISHDN
Logic-High
VIH
1.4
--
--
Logic-Low
VIL
--
--
0.5
Switching Frequency
f SW
450
500
550
kHz
Maximum Duty in Steady State
Operation
DMAX
91
93
97
%
1.5
--
1.5
%
1.22
1.25
1.28
V
--
100
500
nA
--
0.7
1
--
--
4
A
--
330
--
mA
SHDN Threshold
Voltage
V
Oscillator
Line Regulation
VCC = 3.3V to 4.3V
Feedback Reference Voltage
Feedback Input Current
IFB
LX On-Resistance
RDS(ON)
LX Leakage Current
Switch Current Limit
VFB = VFB_SET
VLX = 40V
ILIM
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DS8580-01 January 2017
RT8580
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
--
150
--
C
--
25
--
C
Thermal Protection
Thermal Shutdown Temperature
Thermal Shutdown Hysteresis
TSD
TSD
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 = 25C with the component mounted on a high effective-
thermal-conductivity four-layer test board on a 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.
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5
RT8580
Typical Application Circuit
VIN
3V to 5.5V
C1
2.2µF
5
RT8580
VCC
4 SHDN
2
GND
1
PGND
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6
D1
L1
LX
FB
6
VOUT
30V
R1
150k
C2
4.7µF
3
R2
6.2k
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RT8580
Typical Operating Characteristics
Quiescent Current vs. Input Voltage
Efficiency vs. Load Current
100
1000
90
950
80
900
70
850
60
VIN = 5.5V
VIN = 4.8V
VIN = 3.3V
50
40
800
750
30
700
20
650
10
Device Not Switching
VOUT = 30V
600
0
0
0.5
1
1.5
2
2.5
3
3.5
2
4
2.5
3
3.5
4
4.5
5
5.5
6
Input Voltage (V)
Load Current (mA)
No Load Quiescent Current vs. Input Voltage
Quiescent Current vs. Temperature
900
16
14
VIN = 5V
850
12
800
10
8
750
6
VIN = 3V
700
4
650
2
VOUT = 30V
0
Device Not Switching
600
2.5
3
3.5
4
4.5
5
-50
5.5
-25
0
25
50
75
100
125
Temperature (°C)
Input Voltage (V)
Switching Frequency vs. Temperature
Feedback Voltage vs. Temperature
1.30
520
515
1.28
510
505
1.26
500
495
VIN = 5V
VIN = 3V
1.24
490
485
480
1.22
475
VIN = 5V, VOUT = 30V
470
1.20
-50
-25
0
25
50
75
100
Temperature (°C)
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DS8580-01 January 2017
125
-50
-25
0
25
50
75
100
125
Temperature (°C)
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RT8580
Light Load Switching
Heavy Load Switching
VOUT_ac
(2mV/Div)
VOUT_ac
(2mV/Div)
LX
(20V/Div)
LX
(20V/Div)
IL
(100mA/Div)
IL
(100mA/Div)
VIN = 5V, VOUT = 30V, IOUT = 4mA
VIN = 5V, VOUT = 30V, IOUT = 0.1mA
Time (1s/Div)
Time (1s/Div)
Power On from SHDN
Power Off from SHDN
VOUT
(20V/Div)
VOUT
(20V/Div)
SHDN
(5V/Div)
SHDN
(5V/Div)
IL
(100mA/Div)
IL
(100mA/Div)
VIN = 5V, VOUT = 30V, IOUT = 2mA
Time (10ms/Div)
VIN = 5V, VOUT = 30V, IOUT = 2mA
Time (50ms/Div)
Load Transient Response
VOUT_ac
(100mV/Div)
IOUT
(2mA/Div)
VIN = 5V, VOUT = 30V, IOUT = 0 to 4mA
Time (1ms/Div)
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RT8580
Application Information
The RT8580 current-mode PWM controllers operate in
should have a current rating greater than the current-limit
wide range of DC-DC conversion applications for boost.
This converter provides low noise, high output voltages.
value. The inductor saturation current rating should be
considered to cover the inductor peak current.
Other features include shutdown, fixed 500kHz PWM
oscillator, and a input range : 3V to 5.5V for the RT8580.
The RT8580 operates in discontinuous mode in order to
reduce the switching noise at the output. Other continuous
mode Boost converters generate a large voltage spike at
the output when the LX switch turns on because there is
a conduction path between the output, diode, and switch
to ground during the time needed for the diode to turn off.
The SHDN pin provides shutdown control. Connect SHDN
to VCC for normal operation. To disable the device, connect
SHDN to GND.
Constant Output Voltage Control
The output voltage of the RT8580 is fixed at 30V. The
output voltage is set by two external resistors (R1 and
R2). First select the value of R2 in the 5k to 50k range.
R1 is then given by :
VOUT
VREF
current to an acceptable value at the beginning of power
on. The RT8580 provides a built-in soft-start function by
clamping the output voltage of error amplifier so that the
duty cycle of the PWM will be increased gradually in the
soft-start period.
The current flow through inductor as charging period is
detected by a current sensing circuit. As the value comes
across the current limiting threshold, the N-MOSFET will
be turned off so that the inductor will be forced to leave
charging stage and enter discharging stage. Therefore,
the inductor current will not increase over the current
limiting threshold.
Diode Selection
The RT8580's high switching frequency demands a highspeed rectifier. Schottky diodes are recommended for
1
most applications because of their fast recovery time and
where VREF is 1.25V
Determining Peak Inductor Current
If the Boost converter remains in the discontinuous mode
of operation, then the approximate peak inductor current,
ILPEAK, is represented by the formula below :
ILPEAK
The function of soft-start is made for suppressing the inrush
Current Limiting
SHDN Input
R1 R2
Soft-Start
2TS (VOUT
VIN )IOUT
L
where TS is the period, VOUT is the output voltage, VIN is
the input voltage, IOUT is the output current, and is the
efficiency of the boost converter.
Inductor Selection
The recommended value of inductor for 30V, 22H is the
low forward-voltage drop. Ensure that the diode's peak
current rating is greater than or equal to the peak inductor
current. Also, the diode reverse breakdown voltage must
be greater than VOUT.
Input Capacitor Selection
Low ESR ceramic capacitors are recommended for input
capacitor applications. Low ESR will effectively reduce
the input voltage ripple caused by switching operation. A
4.7F capacitor is sufficient for most applications.
Nevertheless, this value can be decreased for lower output
current requirement. Another consideration is the voltage
rating of the input capacitor which must be greater than
the maximum input voltage.
recommended inductor value when the output voltage is
30V and the input voltage is 5V. In general, the inductor
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RT8580
Over-Temperature Protection
The RT8580 has Over-Temperature Protection (OTP)
function to prevent the excessive power dissipation from
overheating. The OTP function will shut down switching
0.6
Four-Layer PCB
0.5
0.4
operation when the die junction temperature exceeds
150C. The chip will automatically start to switch again
when the die junction temperature cools off.
Thermal Considerations
The junction temperature should never exceed the
absolute maximum junction temperature TJ(MAX), listed
under Absolute Maximum Ratings, to avoid permanent
damage to the device. The maximum allowable power
dissipation depends on the thermal resistance of the IC
0.3
0.2
0.1
0.0
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 1. Derating Curve of Maximum Power Dissipation
package, the PCB layout, the rate of surrounding airflow,
and the difference between the junction and ambient
Layout Considerations
temperatures. The maximum power dissipation can be
calculated using the following formula :
PCB layout is very important when designing power
switching converter circuits. Some recommended layout
PD(MAX) = (TJ(MAX) n TA) /
guide lines are as follows :
JA
where TJ(MAX) is the maximum junction temperature, T A is
the ambient temperature, and JA is the junction-to-ambient
thermal resistance.
For continuous operation, the maximum operating junction
temperature indicated under Recommended Operating
The power components L1, D1 and C2 must be placed as
close to each other as possible to reduce the ac current
loop area. The PCB trace between power components
must be as short and wide as possible due to large current
flow through these traces during operation.
Conditions is 125C. The junction-to-ambient thermal
Place L1 and D1 as close to the LX Pin as possible. The
resistance, JA, is highly package dependent. For a SOT23-6, the thermal resistance, JA, is 208.2C/W on a
trace should be as short and wide as possible.
The input capacitor C1 must be placed as close to the
standard JEDEC 51-7 high effective-thermal-conductivity
four-layer test board. The maximum power dissipation at
VCC pin as possible.
TA = 25C can be calculated as below :
Locate input capacitor as
close to VCC as possible.
Place these components as
close as possible to the LX Pin.
C1
PD(MAX) = (125C n 25C) / (208.2C/W) = 0.48W for a
SOT-23-6 package.
The maximum power dissipation depends on the operating
ambient temperature for the fixed TJ(MAX) and the thermal
resistance,
JA.
VIN
L1
D1
LX VCC SHDN
The derating curves in Figure 1 allows
6
4
2
3
GND
the designer to see the effect of rising ambient temperature
on the maximum power dissipation.
5
PGND GND FB
R1
R2
C2
VOUT
Figure 2. PCB Layout Guide
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RT8580
Outline Dimension
H
D
L
C
B
b
A
A1
e
Symbol
Dimensions In Millimeters
Dimensions In Inches
Min
Max
Min
Max
A
0.889
1.295
0.031
0.051
A1
0.000
0.152
0.000
0.006
B
1.397
1.803
0.055
0.071
b
0.250
0.560
0.010
0.022
C
2.591
2.997
0.102
0.118
D
2.692
3.099
0.106
0.122
e
0.838
1.041
0.033
0.041
H
0.080
0.254
0.003
0.010
L
0.300
0.610
0.012
0.024
SOT-23-6 Surface Mount Package
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.
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