®
RT8298A
6A, 24V, 600kHz Step-Down Converter with Synchronous
Gate Driver
General Description
Features
The RT8298A is a synchronous step-down DC/DC converter
with an integrated high side internal power MOSFET and
a gate driver for a low side external power MOSFET. It
can deliver up to 6A output current from a 4.5V to 24V
input supply. The RT8298A's current mode architecture
allows the transient response to be optimized over a wider
input voltage and load range. Cycle-by-cycle current limit
provides protection against shorted outputs and soft-start
eliminates input current surge during start-up. The
RT8298A is synchronizable to an external clock with
frequency ranging from 300kHz to 1.5MHz.
The RT8298A is available in SOP-8 (Exposed Pad)
packages.
Ordering Information
RT8298A
Package Type
SP : SOP-8 (Exposed Pad-Option 2)
Applications
Lead Plating System
G : Green (Halogen Free and Pb Free)
Note :
Richtek products are :
4.5V to 24V Input Voltage Range
6A Output Current
45mΩ
Ω Internal High Side N-MOSFET
Current Mode Control
600kHz Switching Frequency
Adjustable Output from 0.8V to 15V
Up to 95% Efficiency
Internal Compensation
Stable with Ceramic Capacitors
Synchronous External Clock : 300kHz to 1.5MHz
Cycle-by-Cycle Current Limit
Input Under Voltage Lockout
Output Under Voltage Protection
Power Good Indicator
Thermal Shutdown Protection
Force PWM Turn On
RoHS Compliant and Halogen Free
RoHS compliant and compatible with the current require-
Point of Load Regulator in Distributed Power System
Digital Set top Boxes
Personal Digital Recorders
Broadband Communications
Flat Panel TVs and Monitors
ments of IPC/JEDEC J-STD-020.
Suitable for use in SnPb or Pb-free soldering processes.
Simplified Application Circuit
VIN
VIN
RT8298A
BOOT
CIN
CBOOT
L
SW
VCC
BG
VOUT
Q1
R1
CVCC
COUT
FB
R2
Chip Enable
EN/SYNC
Copyright © 2014 Richtek Technology Corporation. All rights reserved.
DS8298A-00 July 2014
GND
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1
RT8298A
Marking Information
Pin Configurations
(TOP VIEW)
RT8298AGSP : Product Number
RT8298A
GSPYMDNN
YMDNN : Date Code
8
SW
BOOT
2
VCC
3
BG
4
GND
VIN
7
EN/SYNC
6
FB
5
GND
9
SOP-8 (Exposed Pad)
Functional Pin Description
Pin No.
Pin Name
Pin Function
1
SW
Switching Node. Output of the internal high side MOSFET. Connect this pin to
external low-side N-MOSFET, inductor and bootstrap capacitor.
2
BOOT
Bootstrap for High side Gate Driver. Connect a 1F ceramic capacitor between the
BOOT pin and SW pin.
3
VCC
BG Driver Bias Supply. Decouple with a 1F X5R/X7R ceramic capacitor between
the VCC pin and GND.
4
BG
Gate Driver Output. Connect this pin to the gate of the external low-side
N-MOSFET.
5,
GND
9 (Exposed Pad)
Ground. The exposed pad must be soldered to a large PCB and connected to GND
for maximum thermal dissipation.
FB
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 external resistive
divider. The feedback reference voltage is 0.808V typically.
7
EN/SYNC
Enable or External Frequency Synchronization Input. A logic-high (2V < EN <
5.5V) enables the converter; a logic-low forces the IC into shutdown mode
reducing the supply current to less than 3A. For external frequency
synchronization operation, the available frequency range is from 300kHz to
1.5MHz.
8
VIN
Power Input. The available input voltage range is from 4.5V to 24V. A 22F or
larger input capacitor is needed to reduce voltage spikes at the input.
6
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DS8298A-00 July 2014
RT8298A
Function Block Diagram
VIN
VCC
VCC
Internal
Regulator
OSC
Enable
Comparator
+
1.7V
-
EN/SYNC
5k
Slope
Current Sense
Compensator Amplifier
+
-
Foldback
Control
3V
RSENSE
VCC
OTP
BOOT
UV Comparator
VCC
0.4V
+
-
0.808V
15pF
FB
54pF
SW
Current
Signal
6nA
VSS
45m
Switch
Controller
+
+EA
-
COMP
+
-
Current
Comparator
BG
Driver
BG
300k
1pF
Operation
The RT8298A is a synchronous high voltage Buck
Converter that can support the input voltage range from
4.5V to 24V and the output current can be up to 6A. The
RT8298A uses a constant frequency, current mode
architecture. In normal operation, the high side N-MOSFET
is turned on when the Switch Controller is set by the
oscillator (OSC) and is turned off when the current
comparator resets the Switch Controller. While the NMOSFET is turned off, the external low side N-MOSFET
is turned on by BG Driver with 5V driving voltage from
Internal Regulator (VCC) until next cycle begins.
High side MOSFET peak current is measured by internal
RSENSE. The Current Signal is where Slope Compensator
works together with sensing voltage of RSENSE. The error
amplifier EA adjusts COMP voltage by comparing the
feedback signal (VFB) from the output voltage with the
internal 0.808V reference. When the load current
increases, it causes a drop in the feedback voltage relative
to the reference, the COMP voltage then rises to allow
higher inductor current to match the load current.
UV Comparator : If the feedback voltage (VFB) is lower
than threshold voltage 0.4V, the UV Comparator's output
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will go high and the Switch Controller will turn off the high
side MOSFET. The output under voltage protection is
designed to operate in Hiccup mode.
Oscillator (OSC) : The internal oscillator runs at nominal
frequency 600kHz and can be synchronized by an external
clock in the range between 300kHz and 1.5MHz from EN/
SYNC pin.
Enable Comparator : Internal 5kΩ resistor and Zener diode
are used to clamp the input signal to 3V. A 1.7V reference
voltage is for EN logic-high threshold voltage. The EN pin
can be connected to VIN through a 100kΩ resistor for
automatic startup.
Foldback Control : When VFB is lower than 0.7V, the
oscillation frequency will be proportional to the feedback
voltage.
Soft-Start (SS) : An internal current source (6nA) charges
an internal capacitor (15pF) to build the soft-start ramp
voltage (VSS). The VFB voltage will track the internal ramp
voltage during soft-start interval. The typical soft-start time
is 2ms.
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RT8298A
Absolute Maximum Ratings
(Note 1)
Supply Input Voltage, VIN -----------------------------------------------------------------------------------------Switching Voltage, SW -------------------------------------------------------------------------------------------SW (AC) < 20ns ----------------------------------------------------------------------------------------------------BOOT to SW --------------------------------------------------------------------------------------------------------All Other Voltage ---------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C
SOP-8 (Exposed Pad) --------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2)
SOP-8 (Exposed Pad), θJA ---------------------------------------------------------------------------------------SOP-8 (Exposed Pad), θJC --------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------Junction Temperature ----------------------------------------------------------------------------------------------Storage Temperature Range -------------------------------------------------------------------------------------ESD Susceptibility (Note 3)
HBM (Human Body Model) ---------------------------------------------------------------------------------------MM (Machine Model) -----------------------------------------------------------------------------------------------
Recommended Operating Conditions
–0.3V to 26V
–0.3V to (VIN + 0.3V)
–5V to 30V
–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
(Note 4)
Supply Input Voltage, VIN ------------------------------------------------------------------------------------------ 4.5V to 24V
Junction Temperature Range -------------------------------------------------------------------------------------- −40°C to 125°C
Ambient Temperature Range -------------------------------------------------------------------------------------- −40°C to 85°C
Electrical Characteristics
(VIN = 12V, TA = 25°C, unless otherwise specified)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
Shutdown Supply Current
VEN = 0V
--
1
--
A
Supply Current
VEN = 3V, VFB = 1V
--
0.9
--
mA
0.82
V
Feedback Reference Voltage
VREF
4.5V VIN 24V
Feedback Current
IFB
VFB = 0.8V
High-Side Switch On Resistance
RDS(ON)
BOOT SW = 4.8V
High-Side Switch Current Limit
0.796 0.808
--
10
--
nA
--
45
--
m
--
10
--
A
--
600
--
kHz
Oscillation Frequency
fOSC1
Short Circuit Oscillation Frequency
fOSC2
VFB = 0V
--
190
--
kHz
Maximum Duty Cycle
DMAX
VFB = 0.6V
--
90
--
%
Minimum On-Time
tON
VFB = 1V
--
100
--
ns
Input Under Voltage Lockout Threshold
VUVLO
4
4.2
4.4
V
Input Under Voltage Lockout Threshold
Hysteresis
VUVLO
--
400
--
mV
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DS8298A-00 July 2014
RT8298A
Parameter
EN Threshold
Voltage
Logic-High
Symbol
Test Conditions
VIH
Logic-Low
VIL
Min
Typ
Max
2
--
5.5
--
--
0.4
Unit
V
Sync Frequency Range
f Sync
0.3
--
1.5
MHz
EN Turn-Off Delay
tOFF
--
10
--
s
--
1
--
A
EN Pull Low Current
VEN = 2V
Thermal Shutdown
TSD
--
150
--
C
Thermal Shutdown Hysteresis
TSD
--
20
--
C
BG Driver Bias Supply Voltage
VCC
4.5
5
--
V
Gate Driver Sink Impedance
RSink
--
0.9
--
Gate Driver Source Impedance
RSource
--
3.3
--
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.
Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
Copyright © 2014 Richtek Technology Corporation. All rights reserved.
DS8298A-00 July 2014
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5
RT8298A
Typical Application Circuit
RT8298A
8
VIN
4.5V to 24V
VIN
BOOT
2
CIN
22µF
CBOOT
1µF
SW
3 VCC
BG
1
4
L
2.2µH
Q1
CVCC
1µF
R1
62k
FB
Chip Enable
VOUT
3.3V
7
EN/SYNC
GND
COUT
22µF x 3
6
R2
20k
5, 9 (Exposed Pad)
Table 1. Recommended Component Selection
VOUT (V)
R1 (k)
R2 (k)
L (H)
COUT (F)
1.2
62
127
1.5
22F x 3
1.8
62
50.5
1.5
22F x 3
2.5
62
30
2.2
22F x 3
3.3
62
20
2.2
22F x 3
5
93
18
2.8
22F x 3
8
120
13.5
3.6
22F x 3
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RT8298A
Typical Operating Characteristics
Output Voltage vs. Input Voltage
Efficiency vs. Output Current
3.33
100
90
3.32
VIN = 6V
VIN = 12V
VIN = 24V
70
60
Output Voltage (V)
Efficiency (%)
80
50
40
30
20
3.31
3.30
3.29
3.28
10
VIN = 4.5V to 24V, VOUT = 3.3V, IOUT = 0A
VOUT = 3.3V
3.27
0
0
1
2
3
4
5
4
6
6
8
10
Output Voltage vs. Temperature
16
18
20
22
24
Output Voltage vs. Output Current
3.40
3.40
3.38
3.38
3.36
3.36
Output Voltage (V)
Output Voltage (V)
14
Input Voltage (V)
Output Current (A)
3.34
3.32
3.30
3.28
3.26
3.24
3.34
3.32
3.30
3.28
VIN = 6V
VIN = 12V
VIN = 24V
3.26
3.24
3.22
3.22
VIN = 12V, VOUT = 3.3V, IOUT = 0A
3.20
VOUT = 3.3V
3.20
-50
-25
0
25
50
75
100
125
0
0.5
1
1.5
Temperature (°C)
2.5
3
3.5
4
4.5
5
5.5
6
Switching Frequency vs. Temperature
650
640
640
Switching Frequency (kHz)1
650
630
620
610
600
590
580
570
560
2
Output Current (A)
Switching Frequency vs. Input Voltage
Switching Frequency (kHz)1
12
630
620
610
600
590
580
570
560
VOUT = 3.3V, IOUT = 0A
VIN = 12V, VOUT = 3.3V, IOUT = 0A
550
550
4
6
8
10
12
14
16
18
20
22
Input Voltage (V)
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24
-50
-25
0
25
50
75
100
125
Temperature (°C)
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RT8298A
Current Limit vs. Temperature
Load Transient Response
12.0
Current Limit (A)
11.5
VOUT
(100mV/Div)
11.0
10.5
10.0
9.5
IOUT
(5A/Div)
9.0
8.5
VIN = 12V, VOUT = 3.3V, IOUT = 0A to 6A
VIN = 12V, VOUT = 3.3V
8.0
-50
-25
0
25
50
75
100
Time (250μs/Div)
125
Temperature (°C)
Load Transient Response
Output Ripple Voltage
VOUT
(10mV/Div)
VOUT
(100mV/Div)
VSW
(10V/Div)
IOUT
(5A/Div)
VIN = 12V, VOUT = 3.3V, IOUT = 3A to 6A
IL
(2A/Div)
VIN = 12V, VOUT = 3.3V, IOUT = 3A
Time (250μs/Div)
Time (1μs/Div)
Output Ripple Voltage
Power On from VIN
VOUT
(10mV/Div)
VIN
(5V/Div)
VSW
(10V/Div)
VOUT
(2V/Div)
IL
(5A/Div)
VIN = 12V, VOUT = 3.3V, IOUT = 6A
Time (1μs/Div)
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8
IL
(5A/Div)
VIN = 12V, VOUT = 3.3V, IOUT = 6A
Time (2.5ms/Div)
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RT8298A
Power On from EN
Power Off from VIN
VIN
(5V/Div)
VEN
(5V/Div)
VOUT
(2V/Div)
VOUT
(2V/Div)
IL
(5A/Div)
IL
(5A/Div)
VIN = 12V, VOUT = 3.3V, IOUT = 6A
VIN = 12V, VOUT = 3.3V, IOUT = 6A
Time (5ms/Div)
Time (2.5ms/Div)
Power Off from EN
External SYNC
Clock
(5V/Div)
VEN
(5V/Div)
VLX
(10V/Div)
VOUT
(2V/Div)
IL
(5A/Div)
VOUT
(5V/Div)
IL
(5A/Div)
VIN = 12V, VOUT = 3.3V, IOUT = 6A
Time (5ms/Div)
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VIN = 12V, VOUT = 3.3V, IOUT = 6A, Clock = 800kHz
Time (500ns/Div)
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RT8298A
Application Information
Output Voltage Setting
the device again. For external timing control, the EN pin
can also be externally pulled high by adding a REN resistor
and CEN capacitor from the VIN pin (see Figure 3).
The resistive divider allows the FB pin to sense the output
voltage as shown in Figure 1.
EN
VIN
VOUT
REN
EN
RT8298A
CEN
R1
GND
FB
RT8298A
R2
Figure 3. Enable Timing Control
GND
Figure 1. Output Voltage Setting
The output voltage is set by an external resistive voltage
divider according to the following equation :
VOUT = VREF 1 R1
R2
Where VREF is the feedback reference voltage (0.808V
typ.).
An external MOSFET can be added to implement digital
control on the EN pin, as shown in Figure 4. In this case,
a 100kΩ pull-up resistor, REN, is connected between VIN
pin and the EN pin. MOSFET Q2 will be under logic control
to pull down the EN pin.
VIN
REN
100k
GND
Connect a 1μF low ESR ceramic capacitor between the
BOOT pin and SW pin. This capacitor provides the gate
driver voltage for the high side MOSFET.
It is recommended to add an external bootstrap diode
between an external 5V and BOOT pin for efficiency
improvement when input voltage is lower than 5.5V or duty
ratio is higher than 65% .The bootstrap diode can be a
low cost one such as IN4148 or BAT54. The external 5V
can be a 5V fixed input from system or a 5V output of the
RT8298A. Note that the external boot voltage must be
lower than 5.5V.
5V
Figure 4. Digital Enable Control Circuit
The chip starts to operate when VIN rises to 4.2V (UVLO
threshold). During the VIN rising period, if an 8V output
voltage is set, VIN is lower than the VOUT target value and
it may cause the chip to shut down. To prevent this
situation, a resistive voltage divider can be placed between
the input voltage and ground and connected to the EN pin
to adjust enable threshold, as shown in Figure 5. For
example, the setting VOUT is 8V and VIN is from 0V to
12V, when VIN is higher than 10V, the chip is triggered to
enable the converter. Assume REN1 = 50kΩ. Then,
REN2 =
BOOT
1µF
SW
Figure 2. External Bootstrap Diode
Chip Enable Operation
The EN pin is the chip enable input. Pulling the EN pin
low (
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