XRP7664
2A 18V Synchronous Step-Down Converter
March 2013
Rev. 2.0.1
GENERAL DESCRIPTION
APPLICATIONS
The XRP7664 is a synchronous current-mode
PWM step down (buck) voltage regulator
capable of a continuous output current up to
2Amps. A wide 4.5V to 18V input voltage
range allows for single supply operations from
industry standard 5V and 12V power rails.
With a 340kHz constant operating frequency
and
integrated
high
and
low
side
100mΩ/100mΩ
MOSFETs,
the
XRP7664
reduces the overall component count and
solution
footprint.
Current-mode
control
provides fast transient response and cycle-bycycle current limit. An adjustable soft-start
prevents inrush current at turn-on, and in
shutdown mode the supply current drops to
0.1µA.
Built-in output over voltage (open load), over
temperature, cycle-by-cycle over current and
under voltage lockout (UVLO) protections
insure safe operations under abnormal
operating conditions.
The XRP7664 is a pin and function compatible
device to MP1482.
The XRP7664 is offered in a RoHS compliant,
“green”/halogen free 8-pin SOIC package.
Distributed Power Architectures
Point of Load Converters
Audio-Video Equipments
Medical & Industrial Equipments
FEATURES
2A Continuous Output Current
4.5V to 18V Wide Input Voltage
PWM Current Mode Control
340kHz Constant Operations
Up to 95% Efficiency
Adjustable Output Voltage
0.925V to 16V Range
±2% Accuracy
Programmable Soft-Start and Enable
Function
Built-in Thermal, Over Current, UVLO
and Output Over Voltage Protections
Pin/Function Compatible to MP1482
RoHS Compliant, “Green”/Halogen
Free 8-Pin SOIC Package
TYPICAL APPLICATION DIAGRAM
Fig. 1: XRP7664 Application Diagram
Exar Corporation
48720 Kato Road, Fremont CA 94538, USA
www.exar.com
Tel. +1 510 668-7000 – Fax. +1 510 668-7001
XRP7664
2A 18V Synchronous Step-Down Converter
ABSOLUTE MAXIMUM RATINGS
OPERATING RATINGS
These are stress ratings only and functional operation of
the device at these ratings or any other above those
indicated in the operation sections of the specifications
below is not implied. Exposure to absolute maximum
rating conditions for extended periods of time may affect
reliability.
Input Voltage VIN ....................................... 4.50V to 18V
Ambient Operating Temperature ................ -40°C to 85°C
Maximum Output Current.................................... 2A min
Thermal Resistance θJA .....................................105°C/W
Supply Voltage VIN ...................................... -0.3V to 20V
Switch Node Voltage VSW ......................................... 21V
Boost Voltage VBS ................................... -0.3 to VSW+6V
Enable Voltage VEN ......................................... -0.3 to VIN
All Other Pins .............................................. -0.3 to +6V
Junction Temperature .......................................... 150°C
Storage Temperature .............................. -65°C to 150°C
Lead Temperature (Soldering, 10 sec) ................... 260°C
ESD Rating (HBM - Human Body Model) .................... 2kV
ESD Rating (MM - Machine Model) ...........................200V
Moisture Sensitivity Level (MSL) ................................... 3
ELECTRICAL SPECIFICATIONS
Specifications are for an Operating Ambient Temperature of TA = 25°C only; limits applying over the full Ambient Operating
Temperature range are denoted by a “•”. Minimum and Maximum limits are guaranteed through test, design, or statistical
correlation. Typical values represent the most likely parametric norm at TA = 25°C, and are provided for reference purposes
only. Unless otherwise indicated, VIN = VEN = 12V, VOUT=3.3V.
Typ.
Max.
Units
Shutdown Supply Current
Parameter
0.1
10
µA
VEN≤0.75V
Quiescent Current
1.2
1.4
mA
VEN=3V, VFB=1V
0.925
0.943
V
0.1
µA
Feedback Voltage VFB
Min.
0.907
Feedback Overvoltage Threshold
Feedback Bias Current
1.1
-0.1
Conditions
V
VFB=1V
Error Amplifier Voltage Gain AEA
(Note 1)
400
V/V
Error Amplifier
Transconductance GEA
800
µA/V
COMP to Current Sense
Transconductance GCS
3.5
A/V
High-Side switch On Resistance
RDSONH (Note 2)
100
mΩ
ISW=0.2A&0.7A
Low-Side switch On Resistance
RDSONL (Note 2)
100
mΩ
ISW=-0.2A&-0.7A
High-Side switch Leakage
Current
0.1
µA
VIN=18V, VEN=0V, VSW=0V
High-Side Switch Current Limit
2.7
Low-Side Switch Current Limit
Oscillator Frequency FOSC1
3.5
280
340
90
Maximum Duty Cycle DMAX
90
Minimum Duty Cycle DMIN
2.2
EN Enable Threshold Voltage
Hysteresis (Note 1)
UVLO Threshold
© 2013 Exar Corporation
A
1.4
Short Circuit Oscillator
Frequency FOSC2
EN Enable Threshold
10
2.5
A
400
kHz
%
VFB=0.85V
0
%
VFB=1V
2.7
V
210
3.65
4.00
From Drain to Source
kHz
mV
4.25
2/12
V
VIN Rising
Rev. 2.0.1
XRP7664
2A 18V Synchronous Step-Down Converter
Parameter
Min.
UVLO Hysteresis
Soft-start Current
Soft-start Time (Note 1)
Thermal Shutdown (Note 1)
Thermal Shutdown Hysteresis
(Note 1)
Typ.
Max.
0.20
Units
Conditions
V
6
µA
15
ms
160
°C
30
°C
CSS=0.1µF
Note 1: Guaranteed by design.
Note 2: RDSON=(VSW1-VSW2)/(ISW1-ISW2)
BLOCK DIAGRAM
Fig. 2: XRP7664 Block Diagram
PIN ASSIGNMENT
Fig. 3: XRP7664 Pin Assignment (SOIC-8)
© 2013 Exar Corporation
3/12
Rev. 2.0.1
XRP7664
2A 18V Synchronous Step-Down Converter
PIN DESCRIPTION
Name
Pin Number
Description
BS
1
Bootstrap pin.
Connect a 0.01µF or greater bootstrap capacitor between the BS pin and the SW pin.
The voltage across the bootstrap capacitor drives the internal high-side power MOSFET.
IN
2
Power input pin.
A capacitor should be connected between the IN pin and GND pin to keep the input
voltage constant.
SW
3
Power switch output pin.
This pin is connected to the inductor and the bootstrap capacitor.
GND
4
Ground signal pin.
5
Feedback pin.
An external resistor divider connected to FB programs the output voltage. If the
feedback pin exceeds 1.1V the over-voltage protection will trigger. If the feedback
voltage drops below 0.3V the oscillator frequency is lowered to achieve short-circuit
protection.
COMP
6
Compensation pin.
This is the output of transconductance error amplifier and the input to the current
comparator. It is used to compensate the control loop. Connect an RC network form this
pin to GND.
EN
7
Control input pin.
Forcing this pin above 2.7V enables the IC. Forcing this pin below 0.75V shuts down the
IC. Pull up to VIN with 100kΩ resistor for automatic startup.
SS
8
Soft-start control input pin.
Connect a capacitor from SS to GND to set the soft-start period. A 0.1µF capacitor sets
the soft start period to 15ms. To disable the soft-start feature, leave SS unconnected.
FB
ORDERING INFORMATION
Part Number
XRP7664IDTR-F
XRP7664EVB
Temperature
Range
Marking
XRP7664I
YYWWF
X
XRP7664 Evaluation Board
-40°C≤TA≤+85°C
Packing
Quantity
Package
SOIC-8
Note 1
Note 2
2.5K/Tape & Reel RoHS Compliant
Halogen Free
“YY” = Year – “WW” = Work Week – “X” = Lot Number; when applicable.
© 2013 Exar Corporation
4/12
Rev. 2.0.1
XRP7664
2A 18V Synchronous Step-Down Converter
TYPICAL PERFORMANCE CHARACTERISTICS
All data taken at VIN = 12V, VOUT=3.3V, TJ = TA = 25°C, unless otherwise specified - Schematic and BOM from Application
Information section of this datasheet.
Fig. 4: Efficiency versus output current
Fig. 5: RDSONH versus case temperature
Fig. 6: RDSONL versus case temperature
Fig. 7: Feedback voltage versus case temperature
Fig. 8: Quiescent current versus case temperature
Fig. 9: Output voltage versus output current
© 2013 Exar Corporation
5/12
Rev. 2.0.1
XRP7664
2A 18V Synchronous Step-Down Converter
Fig. 10: Output voltage ripple, IOUT=2A
Base Time 2µs/div
Fig. 11: Load transient (IOUT=1A to 2A)
Base Time 200µs/div
Fig. 12: Enable turn on (RLOAD=1.65Ω)
Base Time 10ms/div
Fig. 13: Enable turn off (RLOAD=1.6Ω)
Base Time 200µs/div
Fig. 14: Short-circuit protection, IOUT=2A
Base Time 40µs/div
Fig. 15: Short-circuit recovery, IOUT=2A
Base Time 40µs/div
© 2013 Exar Corporation
6/12
Rev. 2.0.1
XRP7664
2A 18V Synchronous Step-Down Converter
THEORY OF OPERATION
OVERCURRENT PROTECTION OCP
The OCP protects against accidental increase
in load current that can cause the regulator to
fail. The current of internal switch M1 is
monitored. If this current reaches 3.5A then
M1 is turned off until next switching cycle.
FUNCTIONAL DESCRIPTION
The XRP7664 is a synchronous, current-mode,
step-down regulator. It regulates input
voltages from 4.5V to 18V and supplies up to
2A of continuous load current. The XRP7664
uses current-mode control to regulate the
output voltage. The output voltage is
measured at FB through a resistive voltage
divider and input to a transconductance error
amplifier. The high-side switch current is
compared to the output of the error amplifier
to control the output voltage. The regulator
utilizes internal N-channel MOSFETs to stepdown the input voltage. A bootstrapping
capacitor connected between BS and SW acts
as a supply for high-side MOSFET. This
capacitor is charged from the internal 5V
supply when SW node is low. The XRP7664
has several powerful protection features
including OCP, OVP, OTP, UVLO and output
short-circuit.
SHORT-CIRCUIT PROTECTION
If there is short-circuit across the output, the
feedback voltage VFB will droop. If VFB drops
below 0.3V the XRP7664 will detect a shortcircuit condition and reduce the switching
frequency to 90kHz for system protection. The
regulator will restart once the short-circuit has
been removed.
OVERVOLTAGE PROTECTION OVP
The XRP7664 has internal OVP. When VOUT
exceeds the OVP threshold (when VFB exceeds
1.1V) the power switching will be turned off.
The XRP7664 will restart when overvoltage
condition is removed.
PROGRAMMABLE SOFT-START
OVER-TEMPERATURE PROTECTION OTP
The soft-start time is fully programmable via
CSS capacitor, placed between the SS and
GND pin. The CSS is charged by a 6µA
constant-current source, generating a ramp
signal fed into non-inverting input of the error
amplifier. This ramp regulates the voltage on
comp pin during the regulator startup, thus
realizing soft-start. Calculate the required CSS
from:
If the junction temperature exceeds 160°C the
OTP circuit is triggered, turning off the internal
control circuit and switched M1 and M2. When
junction temperature drops below 130°C the
XRP7664 will restart.
APPLICATION INFORMATION
SETTING THE OUTPUT VOLTAGE
Where:
Use an external resistor divider to set the
output voltage. Program the output voltage
from:
tss is the required soft-start time
VFB is the feedback voltage (0.925V nominal)
ENABLE FUNCTION
Where:
The XRP7664 is enabled by raising the voltage
on the EN pin above 2.5V nominally. Connect
the EN pin to the VIN via a 100kΩ resistor for
automatic start-up. Shutdown is achieved by
pulling the EN pin voltage below 1.1V
nominally.
© 2013 Exar Corporation
R1 is the resistor between VOUT and FB
R2 is the resistor between FB and GND
(nominally 10kΩ)
0.925V is the nominal feedback voltage.
7/12
Rev. 2.0.1
XRP7664
2A 18V Synchronous Step-Down Converter
capacitance,
usually
the
overriding
requirement is current load-step transient. If
the unloading transient (i.e., when load
transitions from a high to a low current) is
met, then usually the loading transient (when
load transitions from a low to a high current)
is met as well. Therefore calculate the COUT
based on the unloading transient requirement
from:
OUTPUT INDUCTOR
Select the output inductor for inductance L, DC
current rating IDC and saturation current rating
ISAT. IDC should be larger than regulator output
current. ISAT, as a rule of thumb, should be
50% higher than the regulator output current.
Since the regulator is rated at 2A then IDC≥2A
and ISAT≥3A. Calculate the inductance from:
Where:
Where:
ΔIL is peak-to-peak inductor current ripple
nominally set to 30%-40% of IOUT
L is the inductance calculated in the preceding
step
fS is nominal switching frequency (340kHz)
IHigh is the value of load-step prior to
unloading. This is nominally set equal to
regulator current rating (2A).
As an example, inductor values for several
common output voltages are shown in tables 1
and 2. Note that example inductors shown in
tables 1 and 2 are COOPER-Bussmann
shielded inductors. If the target application is
not sensitive to EMI then unshielded inductors
may be used.
VOUT(V) ΔIL(p-p)(A)
5.0
3.3
2.5
1.8
1.5
1.2
L(µH)
Inductor
Example
10
10
8.2
6.8
6.8
4.7
DR74-100-R
DR74-100-R
DR74-8R2-R
DR74-6R8-R
DR74-6R8-R
DR74-4R7-R
0.86
0.70
0.70
0.66
0.57
0.68
ILow is the value of load-step after unloading.
This is nominally set equal to 50% of regulator
current rating (1A).
Vtransient is the maximum permissible voltage
transient corresponding to the load step
mentioned above. Vtransient is typically specified
from 3% to 5% of VOUT.
ESR of the capacitor has to be selected such
that the output voltage ripple requirement
ΔVOUT, nominally 1% of VOUT, is met. Voltage
ripple ΔVOUT is mainly composed of two
components: the resistive ripple due to ESR
and capacitive ripple due to COUT charge
transfer. For applications requiring low voltage
ripple, ceramic capacitors are recommended
because of their low ESR which is typically in
the range of 5mΩ. Therefore ΔVOUT is mainly
capacitive. For ceramic capacitors calculate
the ΔVOUT from:
Table 1: Suggested Inductor Values
for VIN=12V and IOUT=2A
VOUT(V) ΔIL(p-p)(A)
3.3
2.5
1.8
1.5
1.2
L(µH)
Inductor
Example
4.7
4.7
4.7
4.7
4.7
DR74-4R7-R
DR74-4R7-R
DR74-4R7-R
DR74-4R7-R
DR74-4R7-R
0.70
0.78
0.72
0.66
0.57
Where:
Table 2: Suggested Inductor Values
for VIN=5V and IOUT=2A
ΔIL is from table 1 or 2
OUTPUT CAPACITOR COUT
COUT is the value calculated above
Select the output capacitor for voltage rating,
capacitance COUT and Equivalent Series
Resistance ESR. The voltage rating, as a rule
of thumb, should be at least twice the output
voltage. When calculating the required
fs is nominal switching frequency (340kHz)
© 2013 Exar Corporation
If tantalum or electrolytic capacitors are used
then ΔVOUT is essentially a function of ESR:
8/12
Rev. 2.0.1
XRP7664
2A 18V Synchronous Step-Down Converter
INPUT CAPACITOR CIN
1N4148
Select the input capacitor for voltage rating,
RMS current rating and capacitance. The
voltage rating should be at least 50% higher
than the regulator’s maximum input voltage.
Calculate the capacitor’s current rating from:
VIN = 5V
IN
BS
10nF
XRP7664
SW
Where:
IOUT is regulator’s maximum current (2A)
Fig. 16: Optional External Bootstrap Diode VIN=5V Fixed
D is duty cycle (D=VOUT/VIN)
1N4148
BS
Calculate the CIN capacitance from:
10nF
XRP7664
VOUT = 5V
or 3.3V
SW
COUT
Where:
ΔVIN is the permissible input voltage ripple,
nominally set at 1% of VIN
Fig. 17: Optional External Bootstrap Diode
where VOUT = 5V or 3.3V
OPTIONAL SCHOTTKY DIODE
LOOP COMPENSATION
An optional Schottky diode may be paralleled
between the GND pin and SW pin to improve
the regulator efficiency. Examples are shown
in Table 3.
Part Number
Voltage/Current
Rating
B130
SK13
30V/1A
30V/1A
MBRS130
30V/1A
XRP7664 utilizes current-mode control. This
allows
using
a
minimum
of
external
components to compensate the regulator. In
general only two components are needed: RC
and CC. Proper compensation of the regulator
(determining RC and CC) results in optimum
transient response. In terms of power supply
control theory, the goals of compensation are
to choose RC and CC such that the regulator
loop gain has a crossover frequency fc
between 15kHz and 34kHz. The corresponding
phase-margin should be between 45 degrees
and 65 degrees. An important characteristic of
current-mode buck regulator is its dominant
pole. The frequency of the dominant pole is
given by:
Vendor
Diodes, Inc.
Diodes, Inc.
International
Rectifier
Table 3: Optional Schottky Diode
EXTERNAL BOOTSTRAP DIODE
A low-cost diode, such as 1N4148, is
recommended for higher efficiency when the
input voltage is 5V or the output is 5V or 3.3V.
Circuit configuration is shown in figures 16 and
17. The external bootstrap diode is also
recommended where duty cycle (VOUT/VIN) is
larger than 65%.
© 2013 Exar Corporation
where Rload is the output load resistance.
The uncompensated regulator has a constant
gain up to its pole frequency, beyond which
the gain decreases at -20dB/decade. The zero
9/12
Rev. 2.0.1
XRP7664
2A 18V Synchronous Step-Down Converter
arising from the output capacitor’s ESR is
inconsequential if ceramic COUT is used. This
simplifies the compensation. The RC and CC,
which are placed between the output of
XRP7664’s Error Amplifier and ground,
constitute a zero. The frequency of this
compensating zero is given by:
For the typical application circuit, RC=5.6kΩ
and CC=3.3nF provide a satisfactory
compensation. Please contact EXAR if you
need assistance with the compensation of your
particular circuit.
TYPICAL APPLICATIONS
Fig. 18: XRP7664 Typical Application Diagram - 12V to 3.3V Conversion
© 2013 Exar Corporation
10/12
Rev. 2.0.1
XRP7664
2A 18V Synchronous Step-Down Converter
PACKAGE SPECIFICATION
8-PIN SOIC
Unit: mm (inch)
© 2013 Exar Corporation
11/12
Rev. 2.0.1
XRP7664
2A 18V Synchronous Step-Down Converter
REVISION HISTORY
Revision
Date
1.0.0
11/02/2010
Initial release of data sheet
1.1.0
12/17/2010
RC(R3) changed from 2.2kΩ to 5.6kΩ - Updated schematics
Added the protection features to theory of operation
Added figures 16 and 17
1.2.0
10/13/2011
Added MSL level information
10/22/2012
Reformat of datasheet
Changed min operating input voltage from 4.75V to 4.5V
Updated Electrical Specifications parameter (quiescent current, feedback voltage, high
and low side switch on-resistance, oscillator frequency, EN shutdown threshold voltage
and hysteresis, EN lockout threshold voltage and hysteresis, UVLO threshold and
hysteresis, soft-start time)
Updated figure 2: XRP7664 block diagram
Updated Pin Description, EN pin description
Updated all Typical Performance Characteristics curves
3/29/2013
Updated Enable pin description
Deleted Electrical Specification parameters (shutdown supply current, EN shutdown
threshold voltage and hysteresis, EN lockout threshold voltage and hysteresis)
Added Electrical Specification parameters (EN enable threshold voltage and hysteresis)
Added “ENABLE FUNCTION” to the theory of operation section.
2.0.0
2.0.1
Description
FOR FURTHER ASSISTANCE
Email:
customersupport@exar.com
powertechsupport@exar.com
Exar Technical Documentation:
http://www.exar.com/TechDoc/default.aspx?
EXAR CORPORATION
HEADQUARTERS AND SALES OFFICES
48720 Kato Road
Fremont, CA 94538 – USA
Tel.: +1 (510) 668-7000
Fax: +1 (510) 668-7030
www.exar.com
NOTICE
EXAR Corporation reserves the right to make changes to the products contained in this publication in order to improve
design, performance or reliability. EXAR Corporation assumes no responsibility for the use of any circuits described herein,
conveys no license under any patent or other right, and makes no representation that the circuits are free of patent
infringement. Charts and schedules contained here in are only for illustration purposes and may vary depending upon a
user’s specific application. While the information in this publication has been carefully checked; no responsibility, however,
is assumed for inaccuracies.
EXAR Corporation does not recommend the use of any of its products in life support applications where the failure
malfunction of the product can reasonably be expected to cause failure of the life support system or to significantly affect
safety or effectiveness. Products are not authorized for use in such applications unless EXAR Corporation receives,
writing, assurances to its satisfaction that: (a) the risk of injury or damage has been minimized; (b) the user assumes
such risks; (c) potential liability of EXAR Corporation is adequately protected under the circumstances.
or
its
in
all
Reproduction, in part or whole, without the prior written consent of EXAR Corporation is prohibited.
© 2013 Exar Corporation
12/12
Rev. 2.0.1