Richtek RT7277GSP Schematic [ru]
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®
RT7277
3A, 18V, 700kHz ACOTTM Synchronous Step-Down Converter
General Description
The RT7277 is a synchronous step-downDC/DC converter withAdvanced Constant On-Time (ACOTTM) mode control. It achieves high power density to deliver up to 3A output current from a 4.5V to 18V input supply. The proprietary ACOTTM mode offers an optimal transient response over a wide range of loads and all kinds of ceramic capacitors, which allows the device to adopt very low ESR output capacitors for ensuring performance stabilization. In addition, RT7277 keeps an excellent constant switching frequency under line and load variation and the integrated synchronous power switches with the ACOTTM mode operation provides high efficiency in whole output current load range. Cycle-by-cycle current limit provides an accurate protection by a valley detection of low side MOSFET and external soft-start setting eliminates input current surge during startup. Protection functions also include output under voltage protection, output over voltage protection, and thermal shutdown.
Marking Information
RT7277 |
RT7277GSP : Product Number |
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YMDNN : Date Code |
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GSPYMDNN |
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Features
zACOTTM Mode Enables Fast Transient Response
z4.5V to 18V Input Voltage Range
z3A Output Current
z60mΩ Internal Low Site N-MOSFET
zAdvanced Constant On-Time Control
zSupport All Ceramic Capacitors
zUp to 95% Efficiency
z700kHz Switching Frequency
zAdjustable Output Voltage from 0.765V to 8V
zAdjustable Soft-Start
zCycle-by-Cycle Current Limit
zInput Under Voltage Lockout
zThermal Shutdown
zRoHS Compliant and Halogen Free
Applications
zIndustrial and Commercial Low Power Systems
zComputer Peripherals
zLCD Monitors and TVs
zGreen Electronics/Appliances
zPoint of Load Regulation for High-Performance DSPs, FPGAs, and ASICs
Simplified Application Circuit
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RT7277 |
L1 |
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VIN |
VIN |
SW |
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VOUT |
C1 |
C2 |
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C6 |
C7 |
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BOOT |
C3 |
R1 |
Chip Enable |
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EN |
FB |
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SS |
PVCC |
VPVCC |
R2 |
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C5 |
GND |
C4 |
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Copyright ©2013 Richtek Technology Corporation. All rights reserved. |
is a registered trademark of Richtek Technology Corporation. |
DS7277-01 March 2013 |
www.richtek.com |
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RT7277
Ordering Information
RT7277 
Package Type
SP : SOP-8 (Exposed Pad-Option 2)
Lead Plating System
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.
Pin Configurations
(TOP VIEW)
EN |
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8 |
VIN |
FB |
2 |
7 |
BOOT |
PVCC |
3 |
GND |
SW |
6 |
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SS |
4 |
9 |
GND |
5 |
SOP-8 (Exposed Pad)
Functional Pin Description
Pin No. |
Pin Name |
Pin Function |
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1 |
EN |
Enable Input. A logic-high enables the converter; a logic-low forces the IC into |
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shutdown mode reducing the supply current to less than 10μA. |
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Feedback Input. It is used to regulate the output of the converter to a set value via |
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2 |
FB |
an external resistive voltage divider. The feedback threshold voltage is 0.765V |
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typically. |
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3 |
PVCC |
Internal Regulator Output. Connect a 1μF capacitor to GND to stabilize output |
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voltage. |
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Soft-Start Control Input. SS controls the soft-start period. Connect a capacitor from |
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4 |
SS |
SS to GND to set the soft-start period. A 3.9nF capacitor sets the soft-start period of |
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VOUT to 2.6ms. |
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5, 9 |
GND |
Ground. The Exposed pad should be soldered to a large PCB and connected to |
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(Exposed Pad) |
GND for maximum thermal dissipation. |
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6 |
SW |
Switch Node. Connect this pin to an external L-C filter. |
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7 |
BOOT |
Bootstrap Supply for High Side Gate Driver. Connect a 0.1μF or greater ceramic |
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capacitor from BOOT to SW pins. |
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8 |
VIN |
Power Input. The input voltage range is from 4.5V to 18V. Must bypass with a |
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suitably large ( ≥10μF x 2) ceramic capacitor. |
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Copyright ©2013 Richtek Technology Corporation. All rights reserved. |
is a registered trademark of Richtek Technology Corporation. |
www.richtek.com |
DS7277-01 March 2013 |
2 |
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RT7277
Function Block Diagram
PVCC |
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BOOT |
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Internal |
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VIN |
Regulator |
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PVCC |
Over Current |
PVCC |
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VIBIAS |
VREF |
Protection |
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UGATE |
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Switch |
Driver |
SW |
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Controller |
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PVCC |
Ripple |
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LGATE |
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Gen. |
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GND |
2µA |
+ |
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SW |
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SS |
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- |
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FB |
- |
FB |
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Comparator |
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On-Time |
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EN |
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EN |
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Operation
In normal operation, the high side N-MOSFET is turned on when the FB Comparator sets the Switch Controller, and it is turned off when On-Time Controller resets the Switch Controller. While the high sideN-MOSFET is turned off, the low side N-MOSFET is turned on and waits for the FB Comparator to set the beginning of next cycle.
The FB Comparator sets the Switch Controller by comparing the feedback signal (FB) from output voltage with the internal 0.765V reference. When load transient induces VOUT drop, the FB voltage will be less than its threshold voltage. This means that the high sideN-MOSFET will turn on again immediately after minimum off-time expired. The switching frequency will vary during the transient period thus can provide a very fast transient response. After the load transient finished, the RT7277 will be back to steady state with a constant switching frequency.
Enable
Activate internal regulator once EN input level is higher than the target level. Force IC to enter shutdown mode when the EN input level is lower than 0.4V
Internal Regulator
Provide internal power for logic control and switch gate drivers.
On-Time Controller
Control on-time according to VIN and SW to obtain constant switching frequency.
Copyright ©2013 Richtek Technology Corporation. All rights reserved. |
is a registered trademark of Richtek Technology Corporation. |
DS7277-01 March 2013 |
www.richtek.com |
|
3 |
RT7277
Absolute Maximum Ratings |
(Note 1) |
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z Supply Voltage, VIN ----------------------------------------------------------------------------------------------- |
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−0.3V to 21V |
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z Switch Voltage, SW ----------------------------------------------------------------------------------------------- |
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−0.8V to (VIN + 0.3V) |
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<10ns ----------------------------------------------------------------------------------------------------------------- |
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−5V to 25V |
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z BOOT to SW, PVCC ---------------------------------------------------------------------------------------------- |
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−0.3V to 6V |
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z Other Pins Voltage ------------------------------------------------------------------------------------------------- |
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−0.3V to 21V |
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z Power Dissipation, PD @ TA = 25°C |
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SOP-8 (Exposed Pad) -------------------------------------------------------------------------------------------- |
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2.041W |
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z Package Thermal Resistance |
(Note 2) |
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SOP-8 (Exposed Pad), θJA --------------------------------------------------------------------------------------- |
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49°C/W |
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SOP-8 (Exposed Pad), θJC -------------------------------------------------------------------------------------- |
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15°C/W |
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z Junction Temperature Range ------------------------------------------------------------------------------------- |
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150°C |
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z Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------ |
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260°C |
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z Storage Temperature Range ------------------------------------------------------------------------------------- |
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−65°C to 150°C |
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z ESD Susceptibility (Note 3) |
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HBM (Human Body Model) --------------------------------------------------------------------------------------- |
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2kV |
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Recommended Operating Conditions |
(Note 4) |
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z Supply Voltage, VIN ----------------------------------------------------------------------------------------------- |
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4.5V to 18V |
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z Junction Temperature Range ------------------------------------------------------------------------------------- |
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−40°C to 125°C |
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z Ambient Temperature Range ------------------------------------------------------------------------------------- |
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−40°C to 85°C |
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Electrical Characteristics |
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(VIN = 12V, TA = 25°C, unless otherwise specified) |
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Parameter |
Symbol |
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Test Conditions |
Min |
Typ |
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Max |
Unit |
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Supply Current |
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Shutdown Current |
ISHDN |
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VEN = 0V |
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-- |
1.5 |
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10 |
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μA |
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Quiescent Current |
IQ |
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VEN = 3V, VFB = 1V |
-- |
0.7 |
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-- |
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mA |
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Logic Threshold |
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EN Voltage |
Logic-High |
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2 |
-- |
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18 |
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V |
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Logic-Low |
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-- |
-- |
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0.4 |
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VFB Voltage and Discharge Resistance |
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Feedback Threshold Voltage |
VFB |
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4.5V ≤ VIN ≤ 18V |
0.757 |
0.765 |
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0.773 |
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V |
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Feedback Input Current |
IFB |
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VFB = 0.8V |
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−0.1 |
0 |
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0.1 |
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μA |
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VPVCC Output |
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VPVCC Output Voltage |
VPVCC |
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6V ≤ VIN ≤ 18V, 0 < IPVCC < 5mA |
4.7 |
5.1 |
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5.5 |
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V |
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Line Regulation |
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6V ≤ VIN ≤ 18V, IPVCC = 5mA |
-- |
-- |
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20 |
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mV |
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Load Regulation |
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0 < IPVCC < 5mA |
-- |
-- |
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100 |
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mV |
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Output Current |
IPVCC |
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VIN = 6V, VPVCC = 4V |
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110 |
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-- |
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mA |
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Copyright ©2013 Richtek Technology Corporation. All rights reserved. |
is a registered trademark of Richtek Technology Corporation. |
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www.richtek.com |
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DS7277-01 March |
2013 |
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4 |
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RT7277
Parameter |
Symbol |
Test Conditions |
Min |
Typ |
Max |
Unit |
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RDS(ON) |
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Switch On |
High Side |
RDS(ON)_H |
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-- |
90 |
-- |
mΩ |
Resistance |
Low Side |
RDS(ON)_L |
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-- |
60 |
-- |
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Current Limit |
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Current Limit |
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ILIM |
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3.5 |
4.1 |
5.7 |
A |
Thermal Shutdown |
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Thermal Shutdown Threshold |
TSD |
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-- |
150 |
-- |
°C |
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Thermal Shutdown Hysteresis |
TSD |
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-- |
20 |
-- |
°C |
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On-Time Timer Control |
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On-Time |
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tON |
VIN = 12V, VOUT = 1.05V |
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145 |
-- |
ns |
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Minimum On-Time |
tON(MIN) |
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60 |
-- |
ns |
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Minimum Off-Time |
tOFF(MIN) |
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-- |
230 |
-- |
ns |
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Soft-Start |
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SS Charge Current |
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VSS = 0V |
1.4 |
2 |
2.6 |
μA |
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SS Discharge Current |
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VSS = 0.5V |
0.05 |
0.1 |
-- |
mA |
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UVLO |
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UVLO Threshold |
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VIN Rising to Wake up VPVCC |
3.55 |
3.85 |
4.15 |
V |
Hysteresis |
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-- |
0.3 |
-- |
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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. The PCB copper area of exposed pad is 70mm2.
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. |
is a registered trademark of Richtek Technology Corporation. |
DS7277-01 March 2013 |
www.richtek.com |
|
5 |