RT5797B
3A, 1MHz, 6V CMCOT Synchronous Step-Down Converter
General Description
Features
The RT5797B is a high efficiency synchronous step-
⚫
Efficiency Up to 95%
down DC-DC converter. Its input voltage range is from
⚫
RDSON 100m HS / 70m LS
2.7V to 6V and provides an adjustable regulated output
⚫
VIN Range 2.7V to 6V
voltage from 0.6V to 3.4V while delivering up to 3A of
⚫
VREF 0.6V with 1% Accuracy at 25C
output current.
⚫
CMCOT™
compensation allows the transient response to be
optimized over a wide range of loads and output
capacitors. The RT5797B is available in the WDFN-8L
2x2 package.
Design
for
Best
Low-ESR (MLCC) COUT
switches increase efficiency and eliminate the need for
Constant-On-time (CMCOT) operation with internal
Loop
Transient Response, Robust Loop Stability with
The internal synchronous low on-resistance power
an external Schottky diode. The Current Mode
Control
⚫
Soft-Start 1.2ms
Applications
⚫
STB, Cable Modem, & xDSL Platforms
⚫
LCD TV Power Supply & Metering Platforms
⚫
General Purpose Point of Load (POL)
Ordering Information
Marking Information
RT5797B
Package Type
QW : WDFN-8L 2x2 (W-Type)
RT5797BLGQW
2S : Product Code
W : Date Code
Lead Plating System
G : Green (Halogen Free and Pb Free)
2SW
UVP Option
H : Hiccup
L : Latched-Off
RT5797BHGQW
2T : Product Code
W : Date Code
Note :
2TW
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.
Simplified Application Circuit
RT5797B
LX
VIN
VIN
CIN
April
2022
VOUT
EN
R1
FB
PG
SGND PGND
R2
Copyright © 2022 Richtek Technology Corporation. All rights reserved.
DS5797B-06
L
COUT
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1
RT5797B
Pin Configuration
FB
PG
VIN
PGND
1
2
3
4
PGND
(TOP VIEW)
9
8
7
6
5
SGND
EN
LX
NC
WDFN-8L 2x2
Functional Pin Description
Pin No.
Pin Name
Pin Function
1
FB
Feedback voltage input. An external resistor divider from the output to GND,
tapped to the FB pin, sets the output voltage.
2
PG
Power good indicator. The output of this pin is an open-drain with external pull-up
resistor. PG is pulled up when the FB voltage is within 90%, otherwise it is LOW.
3
VIN
Supply voltage input. The RT5797B operates from a 2.7V to 6V input.
4, 9
PGND
(Exposed Pad)
Power ground. The exposed pad must be soldered to a large PCB and connected
to PGND for maximum power dissipation.
5
NC
No internal connection.
6
LX
Switch node.
7
EN
Enable control input.
8
SGND
Signal GND.
Copyright © 2022 Richtek Technology Corporation. All rights reserved.
www.richtek.com
2
is a registered trademark of Richtek Technology Corporation.
DS5797B-06
April
2022
RT5797B
Functional Block Diagram
EN
VIN
UVLO
Shut Down
Control
OTP
-
FB
VREF
Error
Amplifier
Ton
Comparator
+
+
RC
CCOMP
-
Logic
Control
LX
VIN
Driver
Current
Limit
Detector
LX
GND
+
Current
Sense
-
LX
PG
Copyright © 2022 Richtek Technology Corporation. All rights reserved.
DS5797B-06
April
2022
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
3
RT5797B
Operation
The RT5797B is a synchronous low voltage step-down
Over Current Protection (OCP)
converter that can support the input voltage range from
The RT5797B provides over current protection by
2.7V to 6V and the output current can be up to 3A. The
detecting low side MOSFET valley inductor current. If
RT5797B uses a constant on-time, current mode
the sensed valley inductor current is over the current
architecture. In normal operation, the high side P-
limit threshold (3.7A typ.), the OCP will be triggered.
MOSFET is turned on when the switch controller is set
When OCP is tripped, the RT5797B will keep the over
by the comparator and is turned off when the Ton
current threshold level then cause the UV protection.
comparator resets the switch controller.
Low side MOSFET peak current is measured by internal
Thermal Shutdown (OTP)
RSENSE. The error amplifier EA adjusts COMP voltage
The device implements an internal thermal shutdown
by comparing the feedback signal (VFB) from the output
function when the junction temperature exceeds 150C.
voltage with the internal 0.6V reference. When the load
The thermal shutdown forces the device to stop
current increases, it causes a drop in the feedback
switching when the junction temperature exceeds the
voltage relative to the reference, then the COMP
thermal shutdown threshold. Once the die temperature
voltage rises to allow higher inductor current to match
decreases below the hysteresis of 20C, the device
the load current.
reinstates the power up sequence.
UV Comparator
Maximum Duty Cycle
If the feedback voltage (VFB) is lower than threshold
voltage 0.2V, the UV comparator's output will go high
The maximum duty cycle (70%, min.) can be calculated
and the switch controller will turn off the high side
max.) and switching frequency (1.2MHz, max.).
MOSFET. The output under voltage protection is
DMAX = 1 - ( tOFF_MIN + tD ) x fSW
designed to operate in Hiccup mode for RT5797BH,
Where tOFF_MIN is minimum off time, tD is dead time and
Latch mode for RT5797BL.
fSW is switching frequency.
PGOOD Comparator
If input voltage and output voltage are closed, RT5797B
When the feedback voltage (VFB) is higher than
threshold voltage 0.54V, the PGOOD open drain output
will be high impedance. The internal PG MOSFET is
typical 100. The PGOOD signal delay time from EN is
about 2ms.
by minimum off time (180ns, max.), dead time (60ns,
operates at high duty cycle. Once the operational duty
cycle is larger than the maximum duty cycle (70%, min.),
RT5797B keeps minimum off time (180ns, max.) and
deadtime (60ns, max.), then the output voltage starts to
drop. The input voltage at which the devices enter
dropout changes depending on the input voltage, output
Enable Comparator
voltage, switching frequency, load current, and the
A logic-high enables the converter; a logic-low forces
efficiency of the design.
the IC into shutdown mode.
tOFF_MIN
180ns
Soft-Start (SS)
An internal current source charges an internal capacitor
High-Side
MOSFET
to build the soft-start ramp voltage. The VFB voltage will
Deadtime
30ns
track the internal ramp voltage during soft-start interval.
Deadtime
30ns
The typical soft-start time is 1.2ms.
Low-Side
MOSFET
Copyright © 2022 Richtek Technology Corporation. All rights reserved.
www.richtek.com
4
is a registered trademark of Richtek Technology Corporation.
DS5797B-06
April
2022
RT5797B
Absolute Maximum Ratings
(Note 1)
⚫
Supply Input Voltage --------------------------------------------------------------------------------------------- −0.3V to 6.5V
⚫
VIN to SW ----------------------------------------------------------------------------------------------------------- −0.3V to 6.5V
⚫
VIN to SW (t 10ns) --------------------------------------------------------------------------------------------- −4.5V to 9V
⚫
Switch Voltage, SW ---------------------------------------------------------------------------------------------- −0.3V to 6.5V
SW (t 10ns) ------------------------------------------------------------------------------------------------------ −4.5V to 9V
⚫
Others Pins -------------------------------------------------------------------------------------------------------- −0.3V to 6.5V
⚫
Power Dissipation, PD @ TA = 25C
WDFN-8L 2x2 ------------------------------------------------------------------------------------------------------ 2.19W
⚫
Package Thermal Resistance
(Note 2)
WDFN-8L 2x2, JA ------------------------------------------------------------------------------------------------ 45.5C/W
⚫
Lead Temperature (Soldering, 10 sec.) ---------------------------------------------------------------------- 260C
⚫
Junction Temperature -------------------------------------------------------------------------------------------- −40C to 150C
⚫
Storage Temperature Range ----------------------------------------------------------------------------------- −65C to 150C
⚫
ESD Susceptibility
(Note 3)
HBM (Human Body Model) ------------------------------------------------------------------------------------- 2kV
Recommended Operating Conditions
(Note 4)
⚫
Supply Input Voltage --------------------------------------------------------------------------------------------- 2.7V to 6V
⚫
Ambient Temperature Range ---------------------------------------------------------------------------------- −40C to 85C
⚫
Junction Temperature Range ---------------------------------------------------------------------------------- −40C to 125C
Electrical Characteristics
(VIN = 3.6V, TA = 25C, unless otherwise specified)
Parameter
Symbol
Min
Typ
Max
Unit
2.7
--
6
V
0.594
0.6
0.606
V
VFB = 0.6V
--
--
0.1
A
Active ,VFB = 0.63V, Not Switching
--
300
--
Shutdown
--
--
1
Switching Leakage Current
--
--
1
A
Switching Frequency
--
1
--
MHz
Input Voltage
VIN
Feedback Reference Voltage
VREF
Feedback Leakage Current
IFB
DC Bias Current
Test Conditions
A
Switch On Resistance, Low
RNMOS
ISW = 0.3A
--
70
85
m
Switch On Resistance, High
RPMOS
ISW = 0.3A
--
100
125
m
Valley Current Limit
ILIM
3.03
3.7
4.6
A
Under-Voltage Lockout
Threshold
VUVLO
VDD Rising
--
2.25
2.5
V
VDD Falling
--
2
--
V
--
150
--
°C
Over-Temperature Threshold
Copyright © 2022 Richtek Technology Corporation. All rights reserved.
DS5797B-06
April
2022
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
5
RT5797B
Parameter
Enable Input
Voltage
Symbol
Test Conditions
Min
Typ
Max
Unit
Logic-High
VIH
1.5
--
--
Logic-Low
VIL
--
--
0.4
Rising
--
90
--
Falling
--
85
--
--
--
100
--
1.2
--
ms
--
120
--
ns
70
--
--
%
--
1.8
--
k
PG Pin Threshold
(relative to VOUT)
PG Open-Drain Impedance
(PG = low)
Soft-Start Time
TSS
Minimum Off Time
Maximum Duty Cycle
DMAX
(Note 5)
Output Discharge Switch On
Resistance
V
%
Note 1. Stresses beyond those listed under “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. JA is measured at TA = 25C on a high effective thermal conductivity four-layer test board per JEDEC 51-7.
Note 3. Devices are ESD sensitive. Handling precautions are recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
Note 5. Guaranteed by design.
Copyright © 2022 Richtek Technology Corporation. All rights reserved.
www.richtek.com
6
is a registered trademark of Richtek Technology Corporation.
DS5797B-06
April
2022
RT5797B
Typical Application Circuit
VIN
3
CIN
22μF
R3
100k
7
2
CFF*
RT5797B
6
LX
VIN
L
CFF*
EN
R1
VOUT
COUT
22μF x 2
1
FB
PG
SGND PGND
8
4, 9 (Exposed Pad)
R2
: Optional for performance fine-tune
Table 1. Suggested Component Values
VOUT (V)
R1 (k)
R2 (k)
CIN (F)
L (H)
COUT (F)
3.3
90
20
22
1.5
22 x2
1.8
100
50
22
1.5
22 x2
1.5
100
66.6
22
1.5
22 x2
1.2
100
100
22
1.5
22 x2
1.05
100
133
22
1.5
22 x2
1
100
148
22
1.5
22 x2
Copyright © 2022 Richtek Technology Corporation. All rights reserved.
DS5797B-06
April
2022
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
7
RT5797B
Typical Operating Characteristics
Efficiency vs. Output Current
100
90
90
80
80
70
Efficiency (%)
Efficiency (%)
Efficiency vs. Output Current
100
VIN = 5V, VOUT = 3.3V
60
VIN = 3.3V, VOUT = 1.2V
50
40
30
70
40
30
20
10
10
0
0.001
0
0.5
1
1.5
2
2.5
VIN = 3.3V, VOUT = 1.2V
50
20
0
VIN = 5V, VOUT = 3.3V
60
3
0.01
Output Current (A)
1
Output Voltage vs. Output Current
1.28
3.40
1.26
3.38
Output Voltage (V)
1.24
1.22
1.20
1.18
1.16
3.36
3.34
3.32
3.30
3.28
1.14
VIN = 3.3V, VOUT = 1.2V
VIN = 5V, VOUT = 3.3V
1.12
3.26
0
0.5
1
1.5
2
2.5
3
0
0.5
Output Current (A)
1
1.5
2
2.5
3
Output Current (A)
Output Voltage vs. Input Voltage
Output Voltage vs. Input Voltage
1.26
3.40
3.38
Output Voltage (V)
1.24
Output Voltage (V)
10
Output Current (A)
Output Voltage vs. Output Current
Output Voltage (V)
0.1
IOUT = 0A
1.22
1.20
1.18
IOUT = 2A
1.16
IOUT = 0A
3.36
3.34
3.32
IOUT = 2A
3.30
3.28
3.26
1.14
3.24
VIN = 2.5V to 5.5V, V OUT = 1.2V
1.12
2.5
3
3.5
4
4.5
5
Input Voltage (V)
Copyright © 2022 Richtek Technology Corporation. All rights reserved.
www.richtek.com
8
5.5
VIN = 4.5V to 5.5V, V OUT = 3.3V
3.22
4.5
4.6
4.7
4.8
4.9
5
5.1
5.2
5.3
5.4
5.5
Input Voltage (V)
is a registered trademark of Richtek Technology Corporation.
DS5797B-06
April
2022
RT5797B
Switching Frequency vs. Input Voltage
1.5
0.64
1.4
Switcing Frequency (MHz)1
Reference Voltage (V)
Reference Voltage vs. Input Voltage
0.65
0.63
0.62
0.61
0.60
0.59
0.58
0.57
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.56
0.6
0.55
0.5
2.5
3
3.5
4
4.5
5
IOUT = 0.6A
2.5
5.5
3
3.5
4.5
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
5
5.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
VEN = 0V
VEN = 0V
0.0
0.0
2.5
3
3.5
4
4.5
5
-50
5.5
-25
0
50
75
100
125
Quiescent Current vs. Temperature
Quiescent Current vs. Input Voltage
400
380
380
360
360
Quiescent Current (µA)
400
340
320
300
280
260
240
220
25
Temperature (°C)
Input Voltage (V)
Quiescent Current (µA)
4.5
Shutdown Currrent vs. Temperature
5.0
Shutdown Current (μA)1
Shutdown Current (µA)1
Shutdown Current vs. Input Voltage
5.0
0.5
4
Input Voltage (V)
Input Voltage (V)
VFB = 0.63V, LX no switch
200
340
320
300
280
260
240
220
VIN = 5V
200
2.5
3
3.5
4
4.5
5
Input Voltage(V)
Copyright © 2022 Richtek Technology Corporation. All rights reserved.
DS5797B-06
April
2022
5.5
-50
-25
0
25
50
75
100
125
Temperature (°C)
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
9
RT5797B
Current Limit vs. Temperature
5
4
4
Inductor Current (A)
Inductor Current (A)
Current Limit vs. Input Voltage
5
3
2
1
3
2
1
VOUT = 1.2V
VOUT = 1.2V
0
0
2.5
3
3.5
4
4.5
5
5.5
-50
-25
0
Input Voltage(V)
UVLO vs. Temperature
50
75
100
125
Enable Voltage vs. Temperature
2.5
1.4
2.4
1.2
Enable Voltage (V)
2.3
Input Voltage (V)
25
Temperature (°C)
Turn On
2.2
2.1
2.0
1.9
Turn Off
1.8
1.0
Enable On
0.8
Enable Off
0.6
0.4
1.7
0.2
1.6
VIN = 3.3V
VEN = 3.3V
0.0
1.5
-50
-25
0
25
50
75
100
-50
125
25
50
75
100
125
VOUT
(100mV/Div)
VOUT
(100mV/Div)
IOUT
(2A/Div)
VIN = 3.3V, VOUT = 1.2V, IOUT = 0A to 3A
Time (100μs/Div)
Copyright © 2022 Richtek Technology Corporation. All rights reserved.
www.richtek.com
10
0
Load Transient Response
Load Transient Response
IOUT
(2A/Div)
-25
Temperature (°C)
Temperature (°C)
VIN = 3.3V, VOUT = 1.2V, IOUT = 1A to 3A
Time (100μs/Div)
is a registered trademark of Richtek Technology Corporation.
DS5797B-06
April
2022
RT5797B
Voltage Ripple
Voltage Ripple
VIN = 3.3V, VOUT = 1.2V, IOUT = 1A
VIN = 5V, VOUT = 3.3V, IOUT = 1A
VOUT
VOUT
(10mV/Div)
(10mV/Div)
VLX
(2V/Div)
VLX
(2V/Div)
Time (1μs/Div)
Time (1μs/Div)
Power On from EN
Power Off from EN
VEN
(2V/Div)
VEN
(2V/Div)
VPGOOD
(2V/Div)
VPGOOD
(2V/Div)
VOUT
VOUT
(1V/Div)
(1V/Div)
IOUT
IOUT
(1A/Div)
(1A/Div)
VIN = 3.3V, VOUT = 1.2V, IOUT = 0A
VIN = 3.3V, VOUT = 1.2V, IOUT = 0A
Time (500μs/Div)
Time (10ms/Div)
Power On from VIN
Power Off from VIN
VIN
(3V/Div)
VIN
(3V/Div)
VOUT
(700mV/Div)
VOUT
(700mV/Div)
VLX
VLX
(5V/Div)
(5V/Div)
IOUT
IOUT
(3A/Div)
(3A/Div)
VIN = 5V, VOUT = 1.2V, IOUT = 3A
Time (2ms/Div)
Copyright © 2022 Richtek Technology Corporation. All rights reserved.
DS5797B-06
April
2022
VIN = 5V, VOUT = 1.2V, IOUT = 3A
Time (2ms/Div)
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
11
RT5797B
Output Voltage vs. Temperature
1.280
Output Voltage (V)
1.260
1.240
1.220
1.200
VIN = 5V
1.180
VIN = 3.3V
1.160
1.140
1.120
-50
-25
0
25
50
75
100
125
Temperature (°C)
Copyright © 2022 Richtek Technology Corporation. All rights reserved.
www.richtek.com
12
is a registered trademark of Richtek Technology Corporation.
DS5797B-06
April
2022
RT5797B
Application Information
The RT5797B is a single-phase step-down converter. It
During soft-start, the internal soft-start capacitor
provides single feedback loop constant on-time, current
becomes charged and generates a linear ramping up
mode control with fast transient response. An internal
voltage across the capacitor. This voltage clamps the
0.6V reference allows the output voltage to be precisely
voltage at the FB pin, causing PWM pulse width to
regulated for low output voltage applications. A fixed
increase slowly and in turn reduce the input surge
switching frequency (1MHz) oscillator and internal
current. The internal 0.6V reference takes over the loop
compensation are integrated to minimize external
control once the internal ramping-up voltage becomes
component count. Protection features include over
higher than 0.6V.
current protection, under voltage protection and over
temperature protection.
Over Voltage Protection (OVP)
The RT5797BL provide over voltage protection function
Output Voltage Setting
when output voltage over 120%. The IC will be into
Connect a resistive voltage divider at the FB between
Latch-off mode.
VOUT and GND to adjust the output voltage. The output
voltage is set according to the following equation :
(
VOUT = VREF 1 + R1
R2
UVLO Protection
The RT5797B has input Under Voltage Lockout
)
protection (UVLO). If the input voltage exceeds the
UVLO rising threshold voltage (2.25V typ.), the
where VREF is the feedback reference voltage 0.6V
converter resets and prepares the PWM for operation.
(typ.).
If the input voltage falls below the UVLO falling
threshold voltage during normal operation, the device
VOUT
R1
will stop switching. The UVLO rising and falling
threshold voltage has a hysteresis to prevent noisecaused reset.
FB
R2
GND
Figure 1. Setting VOUT with a Voltage Divider
Chip Enable and Disable
The EN pin allows for power sequencing between the
controller bias voltage and another voltage rail. The
RT5797B remains in shutdown if the EN pin is lower
Input Capacitor Selection
High quality ceramic input decoupling capacitor, such
as X5R or X7R, with values greater than 22F are
recommended for the input capacitor. The X5R and
X7R ceramic capacitors are usually selected for power
regulator capacitors because the dielectric material has
less capacitance variation and more temperature
stability.
than 400mV. When the EN pin rises above the VEN trip
Voltage rating and current rating are the key parameters
point, the RT5797B begins a new initialization and soft-
when selecting an input capacitor. Generally, selecting
start cycle.
an input capacitor with voltage rating 1.5 times greater
than the maximum input voltage is a conservatively safe
Internal Soft-Start
design.
The RT5797B provides an internal soft-start function to
The input capacitor is used to supply the input RMS
prevent large inrush current and output voltage
overshoot when the converter starts up. The soft-start
(SS) automatically begins once the chip is enabled.
current, which can be approximately calculated using
the following equation :
IIN_RMS = ILOAD
Copyright © 2022 Richtek Technology Corporation. All rights reserved.
DS5797B-06
April
2022
VOUT
V
1− OUT
VIN
VIN
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
13
RT5797B
The next step is selecting a proper capacitor for RMS
where LIR is the ratio of the peak-to-peak ripple current
current rating. One good design uses more than one
to the average inductor current.
capacitor with low equivalent series resistance (ESR) in
Find a low loss inductor having the lowest possible DC
parallel to form a capacitor bank.
resistance that fits in the allotted dimensions. The core
The input capacitance value determines the input ripple
must be large enough not to saturate at the peak
voltage of the regulator. The input voltage ripple can be
inductor current (IPEAK) :
approximately calculated using the following equation :
IPEAK = ILOAD(MAX) + LIR ILOAD(MAX)
2
VIN =
IOUT(MAX) VOUT VOUT
1−
CIN fSW
VIN
VIN
Output Capacitor Selection
The output capacitor and the inductor form a low pass
filter in the Buck topology. In steady state condition, the
ripple current flowing into/out of the capacitor results in
ripple voltage. The output voltage ripple (VP-P) can be
calculated by the following equation :
1
VP_P = LIR ILOAD(MAX) ESR +
8
C
f
OUT
SW
When load transient occurs, the output capacitor
supplies the load current before the controller can
respond. Therefore, the ESR will dominate the output
voltage sag during load transient. The output voltage
undershoot (VSAG) can be calculated by the following
equation :
VSAG = ILOAD ESR
For a given output voltage sag specification, the ESR
value can be determined.
Another parameter that has influence on the output
voltage sag is the equivalent series inductance (ESL).
The rapid change in load current results in di/dt during
transient. Therefore, the ESL contributes to part of the
voltage sag. Using a capacitor with low ESL can obtain
better transient performance. Generally, using several
capacitors connected in parallel can have better
transient performance than using a single capacitor for
the same total ESR.
The calculation above serves as a general reference.
To further improve transient response, the output
inductor can be further reduced. This relation should be
considered along with the selection of the output
capacitor.
Inductor saturation current should be chosen over IC’s
current limit.
Thermal Considerations
For continuous operation, do not exceed absolute
maximum junction temperature. The maximum power
dissipation depends on the thermal resistance of the IC
package, PCB layout, rate of surrounding airflow, and
difference between junction and ambient temperature.
The maximum power dissipation can be calculated by
the following formula :
PD(MAX) = (TJ(MAX) − TA) / JA
where TJ(MAX) is the maximum junction temperature, T A
is the ambient temperature, and JA is the junction to
ambient thermal resistance.
For recommended operating condition specifications,
the maximum junction temperature is 125C. The
junction to ambient thermal resistance, JA, is layout
dependent. For WDFN-8L 2x2 package, the thermal
resistance, JA, is 45.5C/W on a standard four-layer
thermal test board. The maximum power dissipation at
TA = 25C can be calculated by the following formula :
PD(MAX) = (125C − 25C) / (45.5C/W) = 2.19W for
WDFN-8L 2x2 package
Inductor Selection
The maximum power dissipation depends on the
The switching frequency (on-time) and operating point
(% ripple or LIR) determine the inductor value as shown
operating ambient temperature for fixed TJ(MAX) and
thermal resistance, JA. The derating curve in Figure 2
below :
allows the designer to see the effect of rising ambient
L=
VOUT ( VIN − VOUT )
fSW LIR ILOAD(MAX) VIN
Copyright © 2022 Richtek Technology Corporation. All rights reserved.
www.richtek.com
14
temperature on the maximum power dissipation.
is a registered trademark of Richtek Technology Corporation.
DS5797B-06
April
2022
RT5797B
Maximum Power Dissipation (W)1
2.5
Four-Layer PCB
2.0
1.5
1.0
0.5
0.0
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 2. Derating Curve of Maximum Power
Dissipation
Copyright © 2022 Richtek Technology Corporation. All rights reserved.
DS5797B-06
April
2022
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
15
RT5797B
Outline Dimension
Symbol
Dimensions In Millimeters
Dimensions In Inches
Min
Max
Min
Max
A
0.700
0.800
0.028
0.031
A1
0.000
0.050
0.000
0.002
A3
0.175
0.250
0.007
0.010
b
0.200
0.300
0.008
0.012
D
1.950
2.050
0.077
0.081
D2
1.000
1.250
0.039
0.049
E
1.950
2.050
0.077
0.081
E2
0.400
0.650
0.016
0.026
e
L
0.500
0.300
0.020
0.400
0.012
0.016
W-Type 8L DFN 2x2 Package
Richtek Technology Corporation
14F, No. 8, Tai Yuen 1st Street, Chupei City
Hsinchu, Taiwan, R.O.C.
Tel: (8863)5526789
Richtek products are sold by description only. Richtek reserves the right to change the circuitry and/or specifications without notice at any time. Customers should
obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. Richtek cannot assume
responsibility for use of any circuitry other than circuitry entirely embodied in a Richtek product. Information furnished by Richtek is believed to be accurate and reliable.
However, no responsibility is assumed by Richtek or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result
from its use. No license is granted by implication or otherwise under any patent or patent rights of Richtek or its subsidiaries.
Copyright © 2022 Richtek Technology Corporation. All rights reserved.
www.richtek.com
16
is a registered trademark of Richtek Technology Corporation.
DS5797B-06
April
2022
工商网监
湘ICP备2023018690号
