DS7250AB 02

®
RT7250A/B
2A, 17V, 340/800kHz Synchronous Step-Down Converter
General Description
Features
The RT7250A/B is a high efficiency, monolithic
synchronous step-down DC/DC converter that can operate
at 340kHz/800kHz, while delivering up to 2A output current
from a 4V to 17V input supply. The RT7250A/B's current
mode architecture allows the transient response to be
optimized. Cycle-by-cycle current limit provides protection
against shorted outputs and soft-start eliminates input
current surge during start-up. Fault conditions also include
output under voltage protection, output over voltage
protection and thermal shutdown. The low current (<5μA)
shutdown mode provides output disconnection, enabling
easy power management in battery-powered systems. The
RT7250A/B is available in a SOP-8 (Exposed Pad)
package.

4V to 17V Input Voltage Range

2A Output Current
Internal N-MOSFETs
Current Mode Control
Fixed Frequency Operation : 340kHz/800kHz
Output Adjustable from 0.8V to 12V
Up to 95% Efficiency
Internal Compensation
Stable with Low ESR Ceramic Output Capacitors
Cycle-by-Cycle Over Current Protection
Input Under Voltage Lockout
Output Under Voltage Protection
Output Over Voltage Protection
Power Good Indicator
Thermal Shutdown Protection
RoHS Compliant and Halogen Free













Ordering Information

RT7250A/B
Package Type
SP: SOP-8 (Exposed Pad-Option 1)
Lead Plating System
Z : ECO (Ecological Element with
Halogen Free and Pb free)



Note :
Richtek products are :
RoHS compliant and compatible with the current require-
Industrial and Commercial Low Power Systems
Computer Peripherals
LCD Monitors and TVs
Green Electronics/Appliances
Point of Load Regulation for High-Performance DSPs,
FPGAs, and ASICs
Marking Information
RT7250AZSP
ments of IPC/JEDEC J-STD-020.



A : 340kHz
B : 800kHz

Applications
Suitable for use in SnPb or Pb-free soldering processes.
RT7250AZSP : Product Number
RT7250A
ZSPYMDNN
YMDNN : Date Code
Pin Configurations
(TOP VIEW)
SW
8
VIN
2
BOOT
EN
3
4
GND
9
RT7250BZSP
NC
7
GND
6
PGOOD
5
FB
RT7250BZSP : Product Number
RT7250B
ZSPYMDNN
YMDNN : Date Code
SOP-8 (Exposed Pad)
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS7250A/B-02 November 2013
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1
RT7250A/B
Typical Application Circuit
RT7250A
VIN
4V to 17V
2 VIN
BOOT 3
CIN
10µF
CBOOT
10nF
SW 1
6 PGOOD
PGOOD
Chip Enable
7, 9 (Exposed Pad)
R1
110k
FB 5
4 EN
L
15µH
VOUT
3.3V
COUT
22µF x 2
R2
36k
GND
RT7250B
VIN
4V to 17V
2 VIN
BOOT 3
CIN
10µF
CBOOT
10nF
SW 1
6 PGOOD
PGOOD
Chip Enable
7, 9 (Exposed Pad)
R1
47k
FB 5
4 EN
L
6.8µH
VOUT
3.3V
COUT
22µF x 2
R2
15k
GND
Table 1. Recommended Component Selection
RT7250A
VOUT (V)
L (H)
R1 (k)
R2 (k)
COUT (F)
1.2
4.7
110
220
22 x 2
2.5
10
110
51
22 x 2
3.3
15
110
36
22 x 2
5
22
120
22
22 x 2
VOUT (V)
L (H)
R1 (k)
R2 (k)
COUT (F)
1.2
3.6
47
91
22 x 2
2.5
4.7
47
22
22 x 2
3.3
6.8
47
15
22 x 2
5
10
62
12
22 x 2
RT7250B
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
www.richtek.com
2
is a registered trademark of Richtek Technology Corporation.
DS7250A/B-02 November 2013
RT7250A/B
Functional Pin Description
Pin No.
Pin Name
Pin Function
1
SW
Switch Node. Connect to external L-C filter.
2
VIN
Input Supply Voltage. Must bypass with a suitably large ceramic capacitor.
3
BOOT
Bootstrap for High Side Gate Driver. Connect 0.01F or greater ceramic
capacitor from BOOT to SW pin.
4
EN
Chip Enable. A logic-high enables the converter; a logic-low forces the
RT7250A/B into shutdown mode, reducing the supply current to less than 5A.
Attach this pin to VIN with a 100k pull up resistor for automatic startup.
5
FB
Feedback Input Pin. For an adjustable output, connect an external resistive
voltage divider to this pin.
6
PGOOD
Power Good Indicator. The output of this pin is low if the output voltage is
12.5% less than the nominal voltage. Otherwise, it is an open drain.
Ground. The exposed pad must be soldered to a large PCB and connected to
GND for maximum power dissipation.
7,
GND
9 (Exposed Pad)
8
NC
No Internal Connection.
Function Block Diagram
VIN
Internal
Regulator
EN
Enable
Comparator
+
2.5V
5k
3V
1V
OSC
340kHz/800kHz
VA VCC
Slope Comp
+
Current Sense
Amplifier
Foldback
Control
VA
+
BOOT
OV
OV Comparator
0.4V
+
+
UV
-
-
UV Comparator
0.8V
FB
-
S
Q
R
Current
Comparator
Q
155m
SW
150m
+
Error Amp
PGOOD
Comparator
+
-
35pF 400k
1pF
GND
0.7V
FB
PGOOD
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS7250A/B-02 November 2013
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
3
RT7250A/B
Absolute Maximum Ratings










(Note 1)
Supply Voltage, VIN -----------------------------------------------------------------------------------------------SW ---------------------------------------------------------------------------------------------------------------------< 10ns -----------------------------------------------------------------------------------------------------------------BOOT to SW --------------------------------------------------------------------------------------------------------All Other Pins -------------------------------------------------------------------------------------------------------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 19V
−0.3V to (VIN + 0.3V)
−5V to 25V
−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 ----------------------------------------------------------------------------------------- 4V to 17V
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
ISHDN
VEN = 0V
--
1
5
A
Supply Current
IOUT
VEN = 3V, VFB = 0.9V
--
0.6
1
mA
0.788
0.8
0.812
V
--
10
--
nA
--
155
--
m
--
150
--
m
Feedback Reference Voltage VFB
4V  VIN  17V
Feedback Current
IFB
VFB = 0.8V
High Side Switch On
RDS(ON)1
Resistance
Low Side Switch On
RDS(ON)2
Resistance
Upper Switch Current Limit
Min. Duty Cycle, VBOOTVSW = 4.8V
Maximum Loading = 2A
--
3.6
--
A
Lower Switch Current Limit
From Drain to Source
--
1
--
A
For RT7250A
300
340
380
For RT7250B
700
800
900
VFB = 0V, For RT7250A
--
95
--
VFB = 0V, For RT7250B
--
170
--
VFB = 0.7V, For RT7250A
--
93
--
VFB = 0.7V, For RT7250B
--
84
--
Oscillation Frequency
f OSC1
Short-Circuit Oscillation
Frequency
f OSC2
Maximum Duty Cycle
DMAX
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
www.richtek.com
4
kHz
kHz
%
is a registered trademark of Richtek Technology Corporation.
DS7250A/B-02 November 2013
RT7250A/B
Parameter
Symbol
Test Conditions
Minimum On Time
tON
Input Under Voltage Lockout
VUVLO
Threshold
Input Under Voltage Lockout
VUVLO
Threshold Hysteresis
EN Threshold
Voltage
Logic-High VIH
Logic-Low
VIL
EN Pull Low Current
VEN = 2V, VFB = 1V
Min
Typ
Max
Unit
--
100
--
ns
--
3.5
--
V
--
200
--
mV
2.5
--
--
--
--
0.4
--
1
--
A
V
Soft-Start Period
tSS
--
1
--
ms
Thermal Shutdown
Thermal Shutdown
Hysteresis
Power Good Threshold
Rising
Power Good Threshold
Hysteresis
Power Good Pull Down
Resistance
Output OVP Threshold
TSD
--
150
--
C
TSD
--
15
--
C
--
0.7
--
V
--
130
--
mV
--
12
--

--
125
--
%VREF
--
10
--
s
Output OVP Propagation
Delay
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 © 2013 Richtek Technology Corporation. All rights reserved.
DS7250A/B-02 November 2013
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
5
RT7250A/B
Typical Operating Characteristics
Efficiency vs. Output Current
Efficiency vs. Output Current
100
100
90
90
80
VOUT = 5V
VOUT = 3.3V
VOUT = 1.2V
70
60
Efficiency (%)
Efficiency (%)
80
50
40
30
20
70
VOUT = 5V
VOUT = 3.3V
VOUT = 1.2V
60
50
40
30
20
10
10
RT7250A, VIN = 12V
0
0.01
0.1
1
RT7250B, VIN = 12V
0
0.01
10
0.1
Output Current (A)
Output Voltage vs. Output Current
3.35
3.35
3.34
3.34
3.33
3.33
Output Voltage (V)
Output Voltage (V)
10
Output Current (A)
Output Voltage vs. Output Current
3.32
3.31
3.30
3.29
3.28
3.27
3.32
3.31
3.30
3.29
3.28
3.27
3.26
3.26
RT7250A, VIN = 12V, VOUT = 3.3V
3.25
RT7250B, VIN = 12V, VOUT = 3.3V
3.25
0.0
0.4
0.8
1.2
1.6
2.0
0.0
0.4
0.8
Output Current (A)
1.2
1.6
2.0
Output Current (A)
Reference Voltage vs. Temperature
Reference Voltage vs. Temperature
1.00
1.00
0.95
0.95
Reference Voltage (V)
Reference Voltage (V)
1
0.90
0.85
0.80
0.75
0.70
0.90
0.85
0.80
0.75
0.70
0.65
0.65
RT7250A, VIN = 12V, IOUT = 0A
RT7250B, VIN = 12V, IOUT = 0A
0.60
0.60
-50
-25
0
25
50
75
100
Temperature (°C)
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
www.richtek.com
6
125
-50
-25
0
25
50
75
100
125
Temperature (°C)
is a registered trademark of Richtek Technology Corporation.
DS7250A/B-02 November 2013
RT7250A/B
Frequency vs. Input Voltage
860
350
850
345
Frequency (kHz)1
Frequency (kHz)1
Frequency vs. Input Voltage
355
340
335
330
325
320
840
830
820
810
800
790
315
RT7250A, VOUT = 3.3V, IOUT = 0.3A
RT7250B, VOUT = 3.3V, IOUT = 0.3A
310
780
4
6
8
10
12
14
16
18
4
6
8
Frequency vs. Temperature
14
16
18
900
875
Frequency (kHz)1
375
Frequency (kHz)1
12
Frequency vs. Temperature
400
350
325
300
275
850
825
800
775
750
725
RT7250A, VOUT = 3.3V, IOUT = 0.3A
250
RT7250B, VOUT = 3.3V, IOUT = 0.3A
700
-50
-25
0
25
50
75
100
125
-50
-25
0
25
50
75
100
125
Temperature (°C)
Temperature (°C)
Quiescent Current vs. Input Voltage
Quiescent Current vs. Input Voltage
1000
900
950
850
Quiescent Current (μA)
Quiescent Current (μA)
10
Input Voltage (V)
Input Voltage (V)
800
750
700
650
900
850
800
750
700
650
RT7250B, VEN = 3.3V, VFB = 0.85V
RT7250A, VEN = 3.3V, VFB = 0.85V
600
600
4
6
8
10
12
14
16
Input Voltage (V)
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS7250A/B-02 November 2013
18
4
6
8
10
12
14
16
18
Input Voltage (V)
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
7
RT7250A/B
Quiescent Current vs. Temperature
0.90
0.85
0.85
Quiescent Current (mA)
Quiescent Current (mA)
Quiescent Current vs. Temperature
0.90
0.80
0.75
0.70
0.65
0.80
0.75
0.70
0.65
RT7250A, VIN = 12V, VEN = 3.3V, VFB = 0.85V
RT7250B, VIN = 12V, VEN = 3.3V, VFB = 0.85V
0.60
0.60
-50
-25
0
25
50
75
100
125
-50
-25
0
Temperature (°C)
4.0
RT7250A
3.8
3.6
3.2
3.0
VOUT = 1.2V
2.8
2.6
RT7250B
100
125
VOUT = 3.3V
3.2
3.0
2.8
2.6
2.4
2.2
2.2
2.0
VOUT = 1.2V
3.4
2.4
2.0
4
6
8
10
12
14
16
18
4
6
8
Input Voltage (V)
10
12
14
16
18
Input Voltage (V)
Current Limit vs. Temperature
3.9
75
3.6
VOUT = 3.3V
Current Limit (A)
Current Limit (A)
3.4
50
Current Limit vs. Input Voltage
Current Limit vs. Input Voltage
3.8
25
Temperature (°C)
Current Limit vs. Temperature
4.0
RT7250A
RT7250B
3.7
3.3
Current Limit (A)
Current Limit (A) 1
3.6
3.0
2.7
2.4
2.1
3.4
3.1
2.8
1.8
VIN = 12V, VOUT = 1.2V
1.5
-50
-25
0
25
50
75
100
Temperature (°C)
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
www.richtek.com
8
125
VIN = 12V, VOUT = 1.2V
2.5
-50
-25
0
25
50
75
100
125
Temperature (°C)
is a registered trademark of Richtek Technology Corporation.
DS7250A/B-02 November 2013
RT7250A/B
Load Transient Response
Load Transient Response
RT7250A
RT7250B
VOUT
(100mV/Div)
VOUT
(50mV/Div)
IOUT
(1A/Div)
IOUT
(1A/Div)
VIN = 12V, VOUT = 3.3V, IOUT = 0.1A to 2A
VIN = 12V, VOUT = 3.3V, IOUT = 0.1A to 2A
Time (1ms/Div)
Time (1ms/Div)
Switching
Switching
RT7250A
RT7250B
VSW
(10V/Div)
VSW
(10V/Div)
VOUT
(5mV/Div)
VOUT
(5mV/Div)
IL
(2A/Div)
IL
(2A/Div)
VIN = 12V, VOUT = 3.3V, IOUT = 2A
VIN = 12V, VOUT = 3.3V, IOUT = 2A
Time (5μs/Div)
Time (500ns/Div)
Power On from EN
Power On from EN
RT7250A
RT7250B, VIN = 12V, VOUT = 3.3V, IOUT = 2A
VEN
(5V/Div)
VEN
(5V/Div)
PGOOD
(5V/Div)
VOUT
(5V/Div)
PGOOD
(5V/Div)
VOUT
(5V/Div)
IOUT
(2A/Div)
IOUT
(2A/Div)
VIN = 12V, VOUT = 3.3V, IOUT = 2A
Time (500μs/Div)
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS7250A/B-02 November 2013
Time (500μs/Div)
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
9
RT7250A/B
Power Off from EN
Power Off from EN
RT7250A
RT7250B, VIN = 12V, VOUT = 3.3V, IOUT = 2A
VEN
(5V/Div)
VEN
(5V/Div)
PGOOD
(5V/Div)
PGOOD
(5V/Div)
VOUT
(5V/Div)
VOUT
(5V/Div)
IOUT
(2A/Div)
VIN = 12V, VOUT = 3.3V, IOUT = 2A
Time (100μs/Div)
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
www.richtek.com
10
IOUT
(2A/Div)
Time (100μs/Div)
is a registered trademark of Richtek Technology Corporation.
DS7250A/B-02 November 2013
RT7250A/B
Application Information
The RT7250A/B is a synchronous high voltage buck
converter that can support the input voltage range from
4V to 17V and the output current can be up to 2A.
Output Voltage Setting
The resistive divider allows the FB pin to sense the output
voltage as shown in Figure 1.
VOUT
R1
FB
R2
RT7250A/B
GND
Figure 1. Output Voltage Setting
The output voltage is set by an external resistive divider
according to the following equation :
R1 

VOUT = VFB  1 

R2


Where VFB is the feedback reference voltage (0.8V typ.).
External Bootstrap Diode
Connect a 10nF 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 the 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 1N4148 or BAT54. The external 5V can be a 5V
fixed input from system or a 5V output of the RT7250A/B.
Note that the external boot voltage must be lower than
5.5V
5V
BOOT
RT7250A/B
10nF
SW
Figure 2. External Bootstrap Diode
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS7250A/B-02 November 2013
Over Voltage Protection (OVP)
The RT7250A/B provides Over Voltage Protection function
when output voltage over 125%. The internal MOS will be
turned off. The control will return to normal operation if
over voltage condition is removed.
Under Voltage Protection (UVP)
For the RT7250A/B, it provides Hiccup Mode Under
Voltage Protection (UVP). When the FB voltage drops
below 50% of the feedback reference voltage, the UVP
function will be triggered and the RT7250A/B will shut down
for a period of time and then recover automatically. The
Hiccup Mode UVP can reduce input current in short-circuit
conditions.
Inductor Selection
The inductor value and operating frequency determine the
ripple current according to a specific input and output
voltage. The ripple current ΔIL increases with higher VIN
and decreases with higher inductance.

V
 V
IL =  OUT  1 OUT 
VIN 
 f L  
Having a lower ripple current reduces not only the ESR
losses in the output capacitors but also the output voltage
ripple. High frequency with small ripple current can achieve
highest efficiency operation. However, it requires a large
inductor to achieve this goal. For the ripple current
selection, the value of ΔIL = 0.2(IMAX) will be a reasonable
starting point. The largest ripple current occurs at the
highest VIN. To guarantee that the ripple current stays
below the specified maximum, the inductor value should
be chosen according to the following equation :
 VOUT  
VOUT 
L= 
 1 

 f  IL(MAX)   VIN(MAX) 
Table 2. Suggested Inductors for Typical
Application Circuit
Component
Supplier
TDK
TDK
TAIYO
YUDEN
Series
Dimensions
(mm)
VLF10045
SLF12565
10 x 9.7 x 4.5
12.5 x 12.5 x 6.5
NR8040
8x8x4
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
11
RT7250A/B
CIN and COUT Selection
The input capacitance, C IN, is needed to filter the
trapezoidal current at the source of the high side MOSFET.
To prevent large ripple current, a low ESR input capacitor
sized for the maximum RMS current should be used. The
RMS current is given by :
V
IRMS = IOUT(MAX) OUT
VIN
VIN
1
VOUT
This formula has a maximum at VIN = 2VOUT, where IRMS =
IOUT/2. This simple worst-case condition is commonly used
for design because even significant deviations do not offer
much relief. Choose a capacitor rated at a higher
temperature than required. Several capacitors may also
be paralleled to meet size or height requirements in the
design. For the input capacitor, a 10μF low ESR ceramic
capacitor is recommended. For the recommended
capacitor, please refer to table 3 for more detail. The
selection of COUT is determined by the required ESR to
minimize voltage ripple. Moreover, the amount of bulk
capacitance is also a key for COUT selection to ensure
that the control loop is stable. Loop stability can be
checked by viewing the load transient response as
described in a later section. The output ripple, ΔVOUT , is
determined by :
1

VOUT  IL ESR 

8fC
OUT

The output ripple will be highest at the maximum input
voltage since ΔIL increases with input voltage. Multiple
capacitors placed in parallel may be needed to meet the
ESR and RMS current handling requirement. Dry tantalum,
special polymer, aluminum electrolytic and ceramic
capacitors are all available in surface mount packages.
Special polymer capacitors offer very low ESR value.
However, it provides lower capacitance density than other
types. Although Tantalum capacitors have the highest
capacitance density, it is important to only use types that
pass the surge test for use in switching power supplies.
Aluminum electrolytic capacitors have significantly higher
ESR. However, it can be used in cost-sensitive applications
for ripple current rating and long term reliability
considerations. Ceramic capacitors have excellent low
ESR characteristics but can have a high voltage coefficient
and audible piezoelectric effects. The high Q of ceramic
capacitors with trace inductance can also lead to significant
ringing.
Higher values, lower cost ceramic capacitors are now
becoming available in smaller case sizes. Their high ripple
current, high voltage rating and low ESR make them ideal
for switching regulator applications. However, care must
be taken when these capacitors are used at input and
output. When a ceramic capacitor is used at the input
and the power is supplied by a wall adapter through long
wires, a load step at the output can induce ringing at the
input, VIN. At best, this ringing can couple to the output
and be mistaken as loop instability. At worst, a sudden
inrush of current through the long wires can potentially
cause a voltage spike at VIN large enough to damage the
part.
Table 3. Suggested Capacitors for CIN and COUT
Component Supplier
Part No.
Capacitance (μF)
Case Size
MURATA
GRM31CR61E106K
10
1206
TDK
C3225X5R1E106K
10
1206
TAIYO YUDEN
TMK316BJ106ML
10
1206
MURATA
GRM31CR60J476M
47
1206
TDK
C3225X5R0J476M
47
1210
TAIYO YUDEN
EMK325BJ476MM
47
1210
MURATA
GRM32ER71C226M
22
1210
TDK
C3225X5R1C226M
22
1210
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
www.richtek.com
12
is a registered trademark of Richtek Technology Corporation.
DS7250A/B-02 November 2013
RT7250A/B
1.4
Maximum Power Dissipation (W)1
Checking Transient Response
The regulator loop response can be checked by looking
at the load transient response. Switching regulators take
several cycles to respond to a step in load current. When
a load step occurs, VOUT immediately shifts by an amount
equal to ΔILOAD (ESR) also begins to charge or discharge
COUT generating a feedback error signal for the regulator
to return VOUT to its steady-state value. During this
recovery time, VOUT can be monitored for overshoot or
ringing that would indicate a stability problem.
Four-Layer PCB
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0
25
Thermal Considerations
For continuous operation, do not exceed the maximum
operation junction temperature 125°C. The maximum
power dissipation depends on the thermal resistance of
IC package, PCB layout, the rate of surroundings airflow
and temperature difference between junction to ambient.
The maximum power dissipation can be calculated by
following formula :
the junction to ambient thermal resistance.
For recommended operating condition specifications, the
maximum junction temperature is 125°C. The junction to
ambient thermal resistance, θJA, is layout dependent. For
SOP-8 (Exposed Pad) packages, the thermal resistance,
θJA, is 75°C/W on a standard JEDEC 51-7 four-layer
thermal test board. The maximum power dissipation at TA
= 25°C can be calculated by the following formula :
The maximum power dissipation depends on the operating
ambient temperature for fixed T J(MAX) and thermal
resistance, θJA. The derating curve in Figure 3 allows the
designer to see the effect of rising ambient temperature
on the maximum power dissipation.
100
125
Figure 3. Derating Curve of Maximum Power Dissipation
Layout Consideration
Follow the PCB layout guidelines for optimal performance
of the RT7250A/B

Keep the traces of the main current paths as short and
wide as possible.

Put the input capacitor as close as possible to the device
pins (VIN and GND).

SW node is with high frequency voltage swing and
should be kept at small area. Keep sensitive
components away from the SW node to prevent stray
capacitive noise pickup.

Place the feedback components to the FB pin as close
as possible.

The GND and Exposed Pad should be connected to a
strong ground plane for heat sinking and noise protection.
SW should be connected to
inductor by wide and short trace.
VOUT
Keep sensitive components
away from this trace.
PD(MAX) = (125°C − 25°C) / (75°C/W) = 1.333W for
SOP-8 (Exposed Pad) package
75
Ambient Temperature (°C)
PD(MAX) = (TJ(MAX) − TA) / θJA
Where T J(MAX) is the maximum operation junction
temperature, TA is the ambient temperature and the θJA is
50
COUT
L
CIN
Input capacitor must
be placed as close
to the IC as possible.
CBOOT
SW
8
VIN
2
BOOT
3
EN
4
GND
9
NC
7
GND
6
PGOOD
5
FB
R1
R2
SW
VOUT
GND
The resistor divider must be
connected as close to the
device as possible.
Figure 4. PCB Layout Guide
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS7250A/B-02 November 2013
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
13
RT7250A/B
Outline Dimension
H
A
M
EXPOSED THERMAL PAD
(Bottom of Package)
Y
J
X
B
F
C
I
D
Dimensions In Millimeters
Dimensions In Inches
Symbol
Min
Max
Min
Max
A
4.801
5.004
0.189
0.197
B
3.810
4.000
0.150
0.157
C
1.346
1.753
0.053
0.069
D
0.330
0.510
0.013
0.020
F
1.194
1.346
0.047
0.053
H
0.170
0.254
0.007
0.010
I
0.000
0.152
0.000
0.006
J
5.791
6.200
0.228
0.244
M
0.406
1.270
0.016
0.050
X
2.000
2.300
0.079
0.091
Y
2.000
2.300
0.079
0.091
X
2.100
2.500
0.083
0.098
Y
3.000
3.500
0.118
0.138
Option 1
Option 2
8-Lead SOP (Exposed Pad) Plastic 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.
www.richtek.com
14
DS7250A/B-02 November 2013