Richtek RT8015GSP, RT8015PSP Schematic [ru]
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RT8015
2A, 2MHz, Synchronous Step-Down Regulator
General Description
The RT8015 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 up to 2A of output current.
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.
RT8015 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.
Ordering Information
RT8015 
Package Type
SP : SOP-8 (Exposed Pad-Option 2)
Lead Plating System P : Pb Free
G : Green (Halogen Free and Pb Free)
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.
Features
•High Efficiency : Up to 95%
•Low RDS(ON) Internal Switches : 110mΩ
•Programmable Frequency : 300kHz to 2MHz
•No Schottky Diode Required
•0.8V Reference Allows Low Output Voltage
•Forced Continuous Mode Operation
•Low Dropout Operation : 100% Duty Cycle
•RoHS Compliant and 100% Lead (Pb)-Free
Applications
•Portable Instruments
•Battery-Powered Equipment
•Notebook Computers
•Distributed Power Systems
•IP Phones
•Digital Cameras
Pin Configurations
(TOP VIEW)
SHDN/RT |
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8 |
COMP |
GND |
2 |
GND |
7 |
FB |
LX |
3 |
9 |
6 |
VDD |
PGND |
4 |
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5 |
PVDD |
SOP-8 (Exposed Pad)
DS8015-03 March 2011 |
www.richtek.com |
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RT8015
Typical Application Circuit
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L1 |
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VIN |
RT8015 |
LX |
3 |
2.2uH |
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VOUT |
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5 PVDD |
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2.5V/2A |
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2.6V to 5.5V |
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R1 |
CIN |
6 VDD |
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7 |
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510k |
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FB |
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COUT |
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22uF |
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8 |
RCOMP 13k |
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22uF |
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4 PGND |
COMP |
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R2 |
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ROSC |
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CCOMP |
240k |
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1nF |
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332k |
1 SHDN/RT |
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GND |
2, |
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Exposed |
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Pad (9) |
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Note : Using all Ceramic Capacitors
Recommended Component for Different Output Voltage Applications
VOUT |
L1 (uH) |
COUT (uF) |
R1 (kΩ) |
R2 (kΩ) |
RCOMP (kΩ) |
CCOMP (nF) |
3.3V |
2.2 |
22 |
750 |
240 |
13 |
1 |
2.5V |
2.2 |
22 |
510 |
240 |
13 |
1 |
1.8V |
1.0 |
22 |
300 |
240 |
7.5 |
1.5 |
1.2V |
1.0 |
22 |
120 |
240 |
7.5 |
1.5 |
Functional Pin Description
Pin No. |
Pin Name |
Pin Function |
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1 |
SHDN/RT |
Oscillator Resistor Input. Connecting a resistor to ground from this pin sets the |
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switching frequency. Forcing this pin to V |
causes the device to be shut down. |
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DD |
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Signal Ground. All small-signal components and compensation components should |
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2, |
GND |
connect to this ground, which in turn connects to PGND at one point. The exposed |
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9 (Exposed Pad) |
pad must be soldered to a large PCB and connected to GND for maximum power |
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dissipation. |
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3 |
LX |
Internal Power MOSFET Switches Output. Connect this pin to the inductor. |
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4 |
PGND |
Power Ground. Connect this pin close to the (−) terminal of CIN and COUT. |
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5 |
PVDD |
Power Input Supply. Decouple this pin to PGND with a capacitor. |
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6 |
VDD |
Signal Input Supply. Decouple this pin to GND with a capacitor. Normally VDD is |
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equal to PVDD. |
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7 |
FB |
Feedback Pin. Receives the feedback voltage from a resistive divider connected |
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across the output. |
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Error Amplifier Compensation Point. The current comparator threshold increases |
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8 |
COMP |
with this control voltage. Connect external compensation elements to this pin to |
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stabilize the control loop. |
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DS8015-03 March 2011 |
2
RT8015
Function Block Diagram
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SHDN/RT |
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SD |
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ISEN |
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PVDD |
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OSC |
Slope |
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Com |
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COMP |
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0.8V |
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Output |
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OC |
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EA |
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Limit |
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FB |
Clamp |
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Int-SS |
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Driver |
LX |
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0.9V |
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Control |
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Logic |
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0.7V |
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NISEN |
PGND |
POR |
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NMOS I Limit |
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0.4V |
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VREF |
OTP |
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GND |
VDD |
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DS8015-03 March 2011 |
www.richtek.com |
3
RT8015
Operation
Main Control Loop
The RT8015 is a monolithic, constant-frequency, current mode step-down DC/DC converter. During normal operation, the internal top power switch (P-Channel 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-Channel MOSFET) turns on until either the bottom current limit is reached or the beginning of the next clock 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 2MHz. Power Good comparators will pull the PGOOD output low if the output voltage comes out of regulation by 12.5%. In an over-voltage condition, the top power MOSFET is turned off and the bottom power MOSFET is switched on until either the over-voltage condition clears or the bottom MOSFET's current limit is reached.
Frequency Synchronization
The internal oscillator of the RT8011 can be synchronized to an external clock connected to the SYNC pin. The frequency of the external clock can be in the range of 300kHz to 2MHz. For this application, the oscillator timing resistor should be chosen to correspond to a frequency that is about 20% lower than the synchronization frequency.
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.
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The output voltage will then be determined by the input voltage minus the voltage drop across the internal P-Channel MOSFET and the inductor.
Low Supply Operation
The RT8015 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 RT8015 is used at 100% duty cycle with low input voltages to ensure that thermal limits are not exceeded.
Slope Compensation and Inductor Peak Current
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 RT8015, however, separated inductor current signals are used to monitor over current condition. This keeps the maximum output current relatively constant regardless of duty cycle.
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.
DS8015-03 March 2011
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RT8015 |
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Absolute Maximum Ratings |
(Note 1) |
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• Supply Input Voltage, VDD, PVDD --------------------------------------------------------------------------- |
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−0.3V to 6V |
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• LX Pin Switch Voltage ------------------------------------------------------------------------------------------ |
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−0.3V to (PVDD+ 0.3V) |
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• Other I/O Pin Voltages ------------------------------------------------------------------------------------------ |
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−0.3V to (VDD + 0.3V) |
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• LX Pin Switch Current------------------------------------------------------------------------------------------- |
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4A |
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• Power Dissipation, PD @ TA = 25°C |
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SOP-8 (Exposed Pad) ----------------------------------------------------------------------------------------- |
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1.33W |
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• Package Thermal Resistance (Note 2) |
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SOP-8 (Exposed Pad), θJA ------------------------------------------------------------------------------------ |
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75°C/W |
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SOP-8 (Exposed Pad), θJC ------------------------------------------------------------------------------------ |
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15°C/W |
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• Junction Temperature ------------------------------------------------------------------------------------------- |
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150°C |
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• Lead Temperature (Soldering, 10 sec.)---------------------------------------------------------------------- |
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260°C |
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• Storage Temperature Range ----------------------------------------------------------------------------------- |
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−65°C to 150°C |
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• ESD Susceptibility (Note 3) |
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HBM (Human Body Mode) ------------------------------------------------------------------------------------- |
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2kV |
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MM (Machine Mode) -------------------------------------------------------------------------------------------- |
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200V |
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Recommended Operating Conditions (Note 4) |
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• Supply Input Voltage -------------------------------------------------------------------------------------------- |
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2.6V to 5.5V |
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• Junction Temperature Range ---------------------------------------------------------------------------------- |
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−40°C to 125°C |
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• Ambient Temperature Range ---------------------------------------------------------------------------------- |
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−40°C to 85°C |
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Electrical Characteristics |
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(VDD = 3.3V, TA = 25°C, unless otherwise specified) |
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Parameter |
Symbol |
Test Conditions |
Min |
Typ |
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Max |
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Unit |
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Input Voltage Range |
VDD |
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2.6 |
-- |
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5.5 |
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V |
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Feedback Reference Voltage |
VREF |
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0.784 |
0.8 |
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0.816 |
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V |
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DC Bias Current |
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Active , VFB = 0.78V, Not Switching |
-- |
460 |
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-- |
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μA |
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Shutdown |
-- |
-- |
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1 |
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μA |
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Output Voltage Line Regulation |
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VIN = 2.7V to 5.5V |
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0.04 |
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-- |
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%/V |
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Output Voltage Load Regulation |
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0A < ILOAD < 2A |
-- |
0.25 |
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-- |
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% |
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Error Amplifier |
gm |
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-- |
800 |
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-- |
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us |
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Transconductance |
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Current Sense Transresistance |
RT |
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-- |
0.4 |
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-- |
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Ω |
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Power Good Range |
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-- |
±12.5 |
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±15 |
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% |
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Power Good Pull-Down |
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-- |
-- |
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120 |
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Ω |
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Resistance |
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Switching Frequency |
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ROSC = 332k |
0.8 |
1 |
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1.2 |
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MHz |
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Switching Frequency |
0.3 |
-- |
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2 |
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MHz |
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Sync Frequency Range |
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0.3 |
-- |
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2 |
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MHz |
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To be continued |
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DS8015-03 March 2011 |
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www.richtek.com |
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