RT8295A
2A, 23V, 340kHz Synchronous Step-Down Converter
General Description
The RT8295A is a high efficiency, monolithic synchronous
step-down DC/DC converter that can deliver up to 2A
output current from a 4.5V to 23V input supply. The
RT8295A's current mode architecture and external
compensation allow the transient response to be
optimized over a wide range of loads and output capacitors.
Cycle-by-cycle current limit provides protection against
shorted outputs and soft-start eliminates input current
surge during start-up. The RT8295A also provides under
voltage protection and thermal shutdown prptection. The
low current (<3μA) shutdown mode provides output
disconnection, enabling easy power management in
battery-powered systems. The RT8295A is available in a
SOP-8 (Exposed Pad) package.
Features
±
1.5% High Accuracy Feedback Voltage
4.5V to 23V Input Voltage Range
2A Output Current
Integrated N-MOSFET Switches
Current Mode Control
Fixed Frequency Operation : 340kHz
Adjustable Output from 0.8V to 20V
Up to 95% Efficiency
Programmable Soft-Start
Stable with Low-ESR Ceramic Output Capacitors
Cycle-by-Cycle Over Current Protection
Input Under Voltage Lockout
Output Under Voltage Protection
Thermal Shutdown Protection
RoHS Compliant and Halogen Free
Ordering Information
RT8295A
Package Type
SP : SOP-8 (Exposed Pad-Option 1)
Lead Plating System
G : Green (Halogen Free and Pb Free)
Z : ECO (Ecological Element with
Halogen Free and Pb free)
H : UVP Hiccup
L : UVP Latch-Off
Note :
Richtek products are :
RoHS compliant and compatible with the current require-
ments of IPC/JEDEC J-STD-020.
Suitable for use in SnPb or Pb-free soldering processes.
Applications
Wireless AP/Router
Set-Top-Box
Industrial and Commercial Low Power Systems
LCD Monitors and TVs
Green Electronics/Appliances
Point of Load Regulation of High-Performance DSPs
Pin Configurations
(TOP VIEW)
BOOT
VIN
SW
GND
2
3
4
8
SS
EN
COMP
FB
GND
9
7
6
5
Marking Information
RT8295AxGSP
RT8295AxGSP : Product Number
RT8295AxZSP
SOP-8 (Exposed Pad)
RT8295AxZSP : Product Number
RT8295Ax
GSPYMDNN
x : H or L
YMDNN : Date Code
RT8295Ax
ZSPYMDNN
x : H or L
YMDNN : Date Code
DS8295A-03 March 2011
www.richtek.com
1
RT8295A
Typical Application Circuit
V
IN
4.5V to 23V
C
IN
10µF
R
EN
100k
2 VIN
BOOT
RT8295A
SW 3
7 EN
8 SS
GND
1
C
BOOT
L
100nF 10µH
R1
75k
FB 5
COMP
6
C
C
3.3nF
R
C
13k
R2
24k
V
OUT
3.3V/2A
C
OUT
22µF x 2
C
SS
0.1µF
4, 9 (Exposed Pad)
C
P
Open
Table 1. Recommended Component Selection
V
OUT
(V) R1 (kΩ) R2 (kΩ) R
C
(kΩ) C
C
(nF) L (µH)
8
27
3
27
3.3
22
5
62
11.8
20
3.3
15
3.3
75
24
13
3.3
10
2.5
25.5
12
9.1
3.3
6.8
1.5
10.5
12
4.7
3.3
3.6
1.2
12
24
3.6
3.3
3.6
1
3
12
3
3.3
2
C
OUT
(µF)
22 x 2
22 x 2
22 x 2
22 x 2
22 x 2
22 x 2
22 x 2
Functional Pin Description
Pin No.
1
2
3
4,
9 (Exposed Pad)
5
Pin Name
BOOT
VIN
SW
GND
Pin Function
Bootstrap for high side gate driver. Connect a 0.1µF or greater ceramic
capacitor from BOOT to SW pins.
Input Supply Voltage, 4.5V to 23V. Must bypass with a suitably large ceramic
capacitor.
Phase Node. Connect this pin to an external L-C filter.
Ground. The exposed pad must be soldered to a large PCB and connected to
GND for maximum power dissipation.
Feedback Input. This pin is connected to the converter output. It is used to set
the output of the converter to regulate to the desired value via an internal
resistive voltage divider. For an adjustable output, an external resistive
voltage divider is connected to this pin.
Compensation Node. COMP is used to compensate the regulation control
loop. Connect a series RC network from COMP to GND. In some cases, an
additional capacitor from COMP to GND is required.
Chip Enable (Active High). A logic high enables the converter; a logic low
forces the RT8295A into shutdown mode reducing the supply current to less
than 3µA. Attach this pin to VIN with a 100kΩ pull up resistor for automatic
startup.
Soft-Start Control Input. SS controls the soft-start period. Connect a capacitor
from SS to GND to set the soft-start period. A 0.1µF capacitor sets the
soft-start period to 13.5ms.
FB
6
COMP
7
EN
8
SS
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2
DS8295A-03 March 2011
RT8295A
Function Block Diagram
VIN
Internal
Regulator
Shutdown
Comparator VA V
CC
1.2V
+
-
Lockout
Comparator
-
+
2.7V
V
CC
6µA
SS
0.8V
+
+EA
-
Oscillator
Foldback
Control
0.4V
+
-
UV
Comparator
Current Sense
Amplifier
Slope Comp
+
-
VA
BOOT
S
+
R
-
Current
Comparator
Q
Q
130mΩ
EN
5k
SW
130mΩ
3V
GND
FB
COMP
DS8295A-03 March 2011
www.richtek.com
3
RT8295A
Absolute Maximum Ratings
l
l
l
l
l
(Note 1)
−0.3V
to 25V
−0.3V
to (V
IN
+ 0.3V)
−0.3V
to 6V
−0.3V
to 6V
1.333W
75°C/W
15°C/W
260°C
150°C
−65°C
to 150°C
2kV
200V
l
l
l
l
l
Supply Voltage, V
IN
----------------------------------------------------------------------------------------------
Input Voltage, SW ------------------------------------------------------------------------------------------------
V
BOOT
−
V
SW
-------------------------------------------------------------------------------------------------------
All Other Pin Voltages -------------------------------------------------------------------------------------------
Power Dissipation, P
D
@ T
A
= 25°C
SOP-8 (Exposed Pad) -------------------------------------------------------------------------------------------
Package Thermal Resistance (Note 2)
SOP-8 (Exposed Pad),
θ
JA
--------------------------------------------------------------------------------------
SOP-8
(Εxposed
Pad),
θ
JC
-------------------------------------------------------------------------------------
Lead Temperature (Soldering, 10 sec.) -----------------------------------------------------------------------
Junction Temperature --------------------------------------------------------------------------------------------
Storage Temperature Range ------------------------------------------------------------------------------------
ESD Susceptibility (Note 3)
HBM (Human Body Mode) --------------------------------------------------------------------------------------
MM (Machine Mode) ---------------------------------------------------------------------------------------------
(Note 4)
Recommended Operating Conditions
l
l
l
Supply Voltage, V
IN
---------------------------------------------------------------------------------------------- 4.5V to 23V
Junction Temperature Range -----------------------------------------------------------------------------------
−40°C
to 125°C
Ambient Temperature Range -----------------------------------------------------------------------------------
−40°C
to 85°C
Electrical Characteristics
(V
IN
= 12V, T
A
= 25°C, unless otherwise specified)
Parameter
Shutdown Supply Current
Supply Current
Feedback Voltage
Error Amplifier
Transconductance
High Side Switch On
Resistance
Low Side Switch
On-Resistance
High Side Switch Leakage
Current
Upper Switch Current Limit
COMP to Current Sense
Transconductance
Oscillation Frequency
Short Circuit Oscillation
Frequency
Maximum Duty Cycle
Minimum On Time
Symbol
V
EN
= 0V
Test Conditions
Min
--
--
0.788
--
--
--
Typ
0.5
0.8
0.8
940
130
130
0
4.3
4
340
100
93
100
Max
3
1.2
0.812
--
--
--
10
--
--
380
--
--
--
Unit
µA
mA
V
µA/V
mΩ
mΩ
µA
A
A/V
kHz
kHz
%
ns
V
EN
= 3 V, V
FB
= 0.9V
V
FB
G
EA
R
DS(ON)1
R
DS(ON)2
V
EN
= 0V, V
SW
= 0V
Min. Duty Cycle, V
BOOT
−
V
SW
= 4.8V
G
CS
f
OSC1
f
OSC2
D
MAX
t
ON
V
FB
= 0V
V
FB
= 0.7V
4.5V
≤
V
IN
≤
23V
∆IC
=
±
10µA
--
--
--
300
--
--
--
To be continued
www.richtek.com
4
DS8295A-03 March 2011
RT8295A
Parameter
EN Input Threshold
Voltage
Logic-High
Logic-Low
Symbol
V
IH
V
IL
V
UVLO
∆V
UVLO
I
SS
t
SS
T
SD
V
SS
= 0V
C
SS
= 0.1µF
V
IN
Rising
Test Conditions
Min
2.7
--
3.8
--
--
--
--
Typ
--
--
4.2
320
6
13.5
150
Max
5.5
0.4
4.5
--
--
--
--
Unit
V
V
mV
µA
ms
°C
Input Under Voltage Lockout Threshold
Input Under Voltage Lockout Hysteresis
Soft-Start Current
Soft-Start Period
Thermal Shutdown
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.
θ
JA
is measured in natural convection at T
A
= 25°C on a high effective thermal conductivity four-layer test board of
JEDEC 51-7 thermal measurement standard. The measurement case position of
θ
JC
is on the exposed pad of the
package.
Note 3.
Devices are ESD sensitive. Handling precaution is recommended.
Note 4.
The device is not guaranteed to function outside its operating conditions.
DS8295A-03 March 2011
www.richtek.com
5
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