Purpose
The RT8279 is a Current mode operation step-down regulator with an internal power MOSFET. This document explains the function and use of the RT8279 evaluation board (EVB) and provides information to enable operation and modification of the evaluation board and circuit to suit individual requirements.
Introduction
General Product Description
The RT8279 is a step-down regulator with an internal power MOSFET. It achieves 5A of continuous output current over a wide input supply range with excellent load and line regulation. Current mode operation provides fast transient response and eases loop stabilization. For protection, the RT8279 provides cycle-by-cycle current limiting and thermal shutdown protection. An adjustable soft-start reduces the stress on the input source at start up. In shutdown mode, the regulator draws only 25μA of supply current. The RT8279 requires a minimum number of readily available external components, providing a compact solution. The RT8279 is available in the SOP-8 (Exposed Pad) package.
Product Features
- 5A Output Current
- Internal Soft-Start
- 110mΩ Internal Power MOSFET Switch
- Internal Compensation Minimizes External Parts Count
- High Efficiency up to 90%
- 25μA Shutdown Mode
- Fixed 500kHz Frequency
- Thermal Shutdown
- Cycle-by-Cycle Over Current Protection
- Wide 5.5V to 36V Operating Input Range
- Adjustable Output Voltage from 1.222V to 26V
- Available In an SOP-8 (Exposed Pad) Package
- RoHS Compliant and Halogen Free
Application
- Distributive Power Systems
- Battery Charger
- DSL Modems
- Pre-regulator for Linear Regulators
Evaluation Board
Please carefully inspect the EVB IC and external components, comparing them to the following Bill of Materials, to ensure that all components are installed and undamaged. If any components are missing or damaged during transportation, please contact the distributor or send e-mail to evb_service@richtek.com
Test Points
The EVB is provided with the test points and pin names listed in the table below.
|
Test point/Pin name
|
Signal
|
Comment (expected waveforms or voltage levels on test points)
|
|
VIN
|
Input voltage
|
Input voltage range = 5.5V to 36V
|
|
VOUT
|
Output voltage
|
Output voltage = 2.4V
|
|
SW
|
Switch Node
|
|
|
EN
|
Chip Enable Operation
|
The EN pin is externally pulled to High by adding a 100kΩ resistor (R4) from the VIN pin in this EVB setting. For another enable operation, pull the EN pin low (<0.4V) will shutdown the device, drive the EN pin to high (>1.4V, <5.5V) will turn on the device again.
|
|
GND
|
Ground
|
Ground
|
Power-up & Measurement Procedure
1. Connect input power (5.5V< VIN < 36V) and input ground to Vin and GND pins respectively.
2. Connect positive end and negative end of load to VOUT and GND of output pins respectively.
3. The output voltage of (VOUT) can be set by R1 and R2.
VOUT = VREF * (1+R1/R2)
where VREF = 1.222V (typ.)
Specification
|
Parameter
|
Symbol
|
Min
|
Typ.
|
Max
|
Units
|
|
Input Voltage Range
|
VIN
|
5.5
|
|
36
|
V
|
|
Output Voltage
|
VOUT
|
|
2.4
|
|
V
|
|
Oscillator Frequency
|
fOSC
|
425
|
500
|
575
|
kHz
|
|
Output Current
|
IOUT
|
|
|
5
|
A
|
|
Current Limit
|
ILIM
|
6
|
7.5
|
9
|
A
|
Schematic
BOM
|
Reference
|
Q'ty
|
P/N
|
Description
|
Package
|
Manufacture
|
|
U1
|
1
|
RT8279GSP
|
Step-down converter
|
SOP-8
|
RICHTEK
|
|
C1, C2
|
2
|
GRM32ER71H475K
|
4.7μF/50V/X7R
|
C-1210
|
MURATA
|
|
C3, C6, C11
|
3
|
C1608X7R1H104K080AA
|
0.1μF/±10%/50V/X7R
|
C-0603
|
TDK
|
|
C4, C5
|
2
|
GRM32ER61C226KE20
|
22μF/±10%/16V/X5R
|
C-1210
|
MURATA
|
|
C12
|
1
|
|
82pF
|
C-0603
|
|
|
L1
|
1
|
74437368068
|
6.8μH, 6A, ±20%, DCR = 23.3mΩ
|
10 x 10 x 3.8mm
|
WE-LHMI
|
|
D1
|
1
|
B550C
|
50V/5A
|
|
DIODES
|
|
R1, R2, R4
|
3
|
|
100k
|
R-0402
|
|
|
C8, R5
|
2
|
|
NC
|
|
|
PCB Layout
PCS Layout (1st layer)
PCS Layout (2nd layer)
PCS Layout (3rd layer)
PCS Layout (4th layer)
Step-Down Converter Efficiency Test
