PRODUCTION DATA SHEET
NX7101
Microsemi
Analog Mixed Signal Group
One Enterprise, Aliso Viejo, CA 92656 949-380-6100, fax 949-215-4996
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2A, High Voltage Synchronous Buck Regulator
D E S C R I P T I O N
The controller is equipped with output
over-voltage protection which protects the
IC under a open load condition.
Additional safety features include under
voltage lock-out (UVLO), programmable
soft-start and over-temperature protection
(OTP) to protect the circuit.
This IC is available in SOIC-8
package.
K E Y F E A T U R E S
2A Synchronous Step-down
Regulator
Operational Input Supply
Voltage Range: 4.5V-18V
Integrated Upper NMOS and
Lower NMOS
340kHz Switching Frequency
Input UVLO
Enable
Programmable External Soft-
Start
Cycle-By-Cycle Over-Current
Protection
Over Voltage Protection
Frequency Fold Back Under
Short Condition
A P P L I C A T I O N S
Set-Top Box
LCD TV’s
Notebook/Netbook
PoE Powered Devices
P R O D U C T H I G H L I G H T
FB(5)
SW(3)
BST(1)
NX7101
COMP(6)GND(4)
IN(2)
VIN
OUT
EN(7)
SS(8)
R3
10k
C3
3.9nF
COUT
2*22uF(6.3V,X5R)
CIN
2*10uF(25V,X5R)
C4 0.1u
C5
10nF L1
10uH
R1
26.1k
R2
10k
R4 100k
3.3V
12V
Figure 1 – NX7101 typical application
P A C K A G E O R D E R I N F O
TA (C)
Plastic SOIC 8 Pin
DM
RoHS Compliant / Pb-free
-40 to 85
NX7101IDM
Note: Available in Tape & Reel. Append the letters “TR” to the part
number. (i.e. NX7101IDM-TR)
PRODUCTION DATA SHEET
NX7101
Microsemi
Analog Mixed Signal Group
One Enterprise, Aliso Viejo, CA 92656 949-380-6100, fax 949-215-4996
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2A, High Voltage Synchronous Buck Regulator
A B S O L U T E M A X I M U M R A T I N G S
Supply Input Voltage (VIN) ........................................................................... -0.3V to 20V
Switch Voltage (SW) ..................................................................................................... 21V
EN .................................................................................................................. -0.3V to VIN
BST ................................................................................................... -0.3V to (VSW + 6V)
COMP, FB, SS ................................................................................................. -0.3V to 6V
Maximum Operating Junction Temperature .............................................................. 150°C
Storage Temperature Range ......................................................................... -65C to 150°C
Package Peak Temp. for Solder Reflow (40 seconds maximum exposure) ............... 260°C
Note: Exceeding these ratings could cause damage to the device. All voltages are with respect to
Ground. Currents are positive into, negative out of specified terminal.
P A C K A G E P I N O U T
4
3
2
1
5
6
7
8
BST
GND
SW
VIN
FB
COMP
EN
SS
M S C
7 1 0 1 I D M
X X X X
DM PACKAGE
(Top View)
DM PART MARKING
“xxxx” Denote Date Code and Lot Identification
RoHS / Pb-free 100% Matte Tin Pin Finish MSL3
T H E R M A L D A T A
DM
Plastic SOIC 8-Pin
THERMAL RESISTANCE-JUNCTION TO AMBIENT, JA
105C/W
Junction Temperature Calculation: TJ = TA + (PD x JA).
The JA numbers are guidelines for the thermal performance of the device/pc-board system. All of the
above assume no ambient airflow.
F U N C T I O N A L P I N D E S C R I P T I O N
Pin
Name
Description
1
BST
Bootstrap pin. A minimum 10nF bootstrap capacitor is connected between the BS pin and SW pin.
The voltage across the bootstrap capacitor drives the internal high side NMOS.
2
VIN
Supply input pin. A capacitor should be connected between the IN pin and GND pin to keep the input
voltage constant.
3
SW
Power switch output pin. This pin is connected to the inductor and bootstrap capacitor.
4
GND
Ground.
5
FB
Feedback pin. This pin is connected to an external resistor divider to program the system output
voltage. When the FB pin voltage exceeds 20% of the nominal regulation value of 0.925V, the over
voltage protection is triggered. When the FB pin voltage is below 0.3V, the oscillator frequency is
lowered to realize short circuit protection.
6
COMP
Compensation pin. This pin is the output of the transconductance error amplifier and the input to the
current comparator. It is used to compensate the control loop. Connect a series RC network from this
pin to GND. In some cases, an additional capacitor from this pin to GND pin is required.
7
EN
Control input pin. Forcing this pin above 2V enables the IC. Forcing this pin below 0.75V shuts down
the IC. When the IC is in shutdown mode, all functions are disabled to decrease the supply current
below 1μA.
8
SS
Soft-start control input pin. 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 15ms. To disable the soft-start
feature, leave SS unconnected.
PRODUCTION DATA SHEET
NX7101
Microsemi
Analog Mixed Signal Group
One Enterprise, Aliso Viejo, CA 92656 949-380-6100, fax 949-215-4996
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2A, High Voltage Synchronous Buck Regulator
R E C O M M E N D E D O P E R A T I N G C O N D I T I O N S
Parameter
Symbol
NX7101
Units
Min
Typ
Max
Input Operating Voltage
VIN
4. 5
18
V
Maximum Output Current
IOUTMAX
2
A
Operating Ambient Temperature
TA
-40
85
°C
E L E C T R I C A L C H A R A C T E R I S T I C S
Unless otherwise specified, the following specifications apply for VIN = VEN =12V, VOUT = 3.3V, TA = 25°C.
Parameter
Symbol
Test Conditions
NX7101
Units
Min
Typ
Max
Operating Current
Quiescent Current
IQ
VFB = 1V, VEN = 3V
0.86
1.25
1.4
mA
Shutdown Current
ISHDN
VEN = 0V
0.1
10
µA
UVLO
VIN UVLO Threshold
VUVLO
VIN Rising
3.65
4.0
4.25
V
Hysteresis
VHYS
0.2
V
Feedback
Feedback Voltage
VFB
TA = -40°C to 85°C
0.907
0.925
0.943
V
Feedback Bias Current
IFB
VFB = 1V
-0.1
0.1
µA
Oscillator
Internal Oscillator Frequency
FOSC1
280
340
400
kHz
Short Circuit Oscillator Frequency
FOSC2
100
kHz
Maximum Duty Cycle
DMAX
VFB = 0.85V
90
%
Minimum Duty Cycle
DMIN
VFB = 1V
0
%
Error Amplifier
Error Amplifier Transconductance
GEA
800
µA/V
Voltage Gain(1)
AEA
400
V/V
Current Sensing Gain
Current Sensing Gain
GCS
3.5
A/V
Soft-Start
Soft-start Current
VSS = 0V
6
µA
Soft-start Time(1)
TSS
CSS = 0.1µF
15
ms
Output Stage
High-side Switch On Resistance
RDSONH
ISW = 0.2A/ 0.7A
85
115
145
mΩ
Low-side Switch On Resistance
RDSONL
ISW = -0.2A/ -0.7A
75
105
135
mΩ
High-side Switch Leakage Current
ILEAKH
VIN = 18V, VEN = 0V, VSW = 0V
0.1
10
uA
High-side Switch Current Limit
ILIMH
2.7
3.5
A
Low-side Switch Current Limit
ILIML
From Drain to Source
1.4
A
EN
EN Shutdown Threshold Voltage
VEN
1.1
1.5
2
V
EN Shutdown Threshold Voltage
Hysteresis (1)
VENH
350
mV
EN Lockout Threshold Voltage
2.2
2.5
2.7
V
EN Lockout Hysteresis
210
mV
PRODUCTION DATA SHEET
NX7101
Microsemi
Analog Mixed Signal Group
One Enterprise, Aliso Viejo, CA 92656 949-380-6100, fax 949-215-4996
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2A, High Voltage Synchronous Buck Regulator
E L E C T R I C A L C H A R A C T E R I S T I C S ( C O N T )
Unless otherwise specified, the following specifications apply for VIN = VEN =12V, VOUT = 5V, TA = 25°C.
Parameter
Symbol
Test Conditions
NX7101
Units
Min
Typ
Max
Protection
Over Voltage Protection Threshold
VFBOV
1.1
V
FB Short Circuit Protection
0.23
0.3
0.41
V
Thermal Shutdown Threshold
TOTSD
160
°C
Thermal Shutdown Hysteresis
THYS
30
°C
Notes:
1) Guaranteed by design, not tested.
S I M P L I F I E D B L O C K D I A G R A M
VIN
SW
GND
Driver
Current
Sensing
EN
Osc
340k/90k
PWM
LOGIC
Bias
1.5V SD
Soft Start
FB
COMP
Low Side
Current Limit
FB UVLO
0.3V
0.925V
Slope
Compensation
UVLO
SD Thermal
shutdown
VCC
UVLO
Regulator
SS
BST
1.1V
EN
2.5V
Figure 2 – Simplified Block Diagram
PRODUCTION DATA SHEET
NX7101
Microsemi
Analog Mixed Signal Group
One Enterprise, Aliso Viejo, CA 92656 949-380-6100, fax 949-215-4996
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2A, High Voltage Synchronous Buck Regulator
A P P L I C A T I O N C I R C U I T
FB(5)
SW(3)
BST(1)
NX7101
COMP(6)GND(4)
IN(2)
VIN
OUT
EN(7)
SS(8)
C6
330pF
COUT
1000uF,170mohm
CIN
10uF/25V
C4 0.1u
C5
10nF L1
22uH
R1
41.2k
R2
9.3k
R4 100k
Figure 3 – 12V Input, 5V Output with Electrolytic Cap
FB(5)
SW(3)
BST(1)
NX7101
COMP(6)GND(4)
IN(2)
VIN
OUT
EN(7)
SS(8)
R3
18k
C3
3.9nF
COUT
2*22uF(10V,X5R)
CIN
10uF/25V
C4 0.1u
C5
10nF L1
15uH
R1
41.2k
R2
9.3k
R4 100k
Figure 4 – 12V Input, 5V Output with Ceramic Cap
PRODUCTION DATA SHEET
NX7101
Microsemi
Analog Mixed Signal Group
One Enterprise, Aliso Viejo, CA 92656 949-380-6100, fax 949-215-4996
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2A, High Voltage Synchronous Buck Regulator
T Y P I C A L W A V E F O R M S @ 2 5 ° C ( R E F E R T O F I G U R E 1 )
Figure 5. DC Operation at 2A
Figure 7. Input power recycling
Figure 6. Transient Response
Figure 8. Output short operation
PRODUCTION DATA SHEET
NX7101
Microsemi
Analog Mixed Signal Group
One Enterprise, Aliso Viejo, CA 92656 949-380-6100, fax 949-215-4996
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2A, High Voltage Synchronous Buck Regulator
T Y P I C A L W A V E F O R M S @ 2 5 ° C ( R E F E R T O F I G U R E 3 )
Figure 9. EN and soft start
82.00%
84.00%
86.00%
88.00%
90.00%
92.00%
94.00%
0500 1000 1500 2000 2500
IOUT(mA)
Efficiency(%)
Figure 10. Efficiency vs. IOUT(VIN=12V,VOUT=5V)
PRODUCTION DATA SHEET
NX7101
Microsemi
Analog Mixed Signal Group
One Enterprise, Aliso Viejo, CA 92656 949-380-6100, fax 949-215-4996
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2A, High Voltage Synchronous Buck Regulator
T H E O R Y O F O P E R A T I O N
DETAIL DESCRIPTION
The NX7101 is a current-mode, PWM synchronous step-
down DC-DC converter with 340kHz fixed working
frequency. It can convert input voltages from 4.75V to 18V
down to an output voltage as low as 0.925V, and supply up
to 2A load current.
The NX7101 has two internal N-MOSFETs to step down the
voltage. The inductor current is determined by sensing the
internal high-side MOSFET current. The output of current
sense amplifier is summed with the slope compensation
signal to avoid subharmonic oscillation at duty cycles greater
than 50%. The combined signal is then compared with the
error amplifier output to generate the PWM signal.
Current mode control provides not only fast control loop
response but also cycle-by-cycle current limit protection.
When load current reaches its maximum output level when
the inductor peak current triggers the high-side NMOFET
current limit. If FB pin voltage drops below 0.3V, the
working frequency will be fold back to protect chip from
run-away.
When FB pin voltage exceeds 1.1V, the over voltage
protection is triggered. The high side MOSFET is turned off.
Once the OVP condition is gone, the chip will resume the
operation following soft-start.
PRODUCTION DATA SHEET
NX7101
Microsemi
Analog Mixed Signal Group
One Enterprise, Aliso Viejo, CA 92656 949-380-6100, fax 949-215-4996
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2A, High Voltage Synchronous Buck Regulator
A P P L I C A T I O N I N F O R M A T I O N
SYMBOL USED IN APPLICATION INFORMATION:
VIN - Input voltage
VOUT - Output voltage
IOUT - Output current
VRIPPLE - Output voltage ripple
FS - Working frequency
IRIPPLE - Inductor current ripple
DESIGN EXAMPLE
The following is typical application for NX7101, the
schematic is figure 1.
VIN = 12V
VOUT =3.3V
IOUT =2A
OUTPUT INDUCTOR SELECTION
The selection of inductor value is based on inductor ripple
current, power rating, working frequency and efficiency. A
larger inductor value normally means smaller ripple current.
However if the inductance is chosen too large, it results in slow
response and lower efficiency. Usually the ripple current
ranges from 20% to 40% of the output current. This is a design
freedom which can be determined by the design engineer
according to various application requirements. The inductor
value can be calculated by using the following equations:

IN OUT OUT
OUT RIPPLE IN S
RIPPLE OUTPUT
V - V V 1
LI V F
I k I
... (1)
where k is between 0.2 to 0.4.
In this design, k is set at 0.35 and 10µH inductor value is
chosen. In order to avoid output oscillation at light load, a
minimum 8.2µH inductor is required for all NX7101
application.
OUTPUT CAPACITOR SELECTION
Output capacitor is basically decided by the amount of the
output voltage ripple allowed during steady state (DC) load
condition as well as specification for the load transient. The
optimum design may require a couple of iterations to satisfy
both conditions.
The amount of voltage ripple during the DC load condition is
determined by equation (2).

RIPPLE
RIPPLE RIPPLE S OUT
I
V ESR I 8 F C
... (2)
Where ESR is the output capacitor’s equivalent series
resistance, COUT is the value of output capacitor.
Typically when large value capacitors are selected such as
Aluminum Electrolytic, POSCAP and OSCON types are
used, the amount of the output voltage ripple is dominated
by the first term in equation(2) and the second term can be
neglected.
If ceramic capacitors are chosen as output capacitors, both
terms in equation (2) need to be evaluated to determine the
overall ripple. Usually when this type of capacitor is
selected, the amount of capacitance per single unit is not
sufficient to meet the transient specification, which results
in the need for parallel configuration of multiple capacitors.
In this design two 22µF 6.3V X5R ceramic capacitors are
chosen as output capacitors.
INPUT CAPACITOR SELECTION
Input capacitors are usually a mix of high frequency
ceramic capacitors and bulk capacitors. Ceramic capacitors
bypass the high frequency noise, and bulk capacitors supply
current to the MOSFETs. Usually 1uF ceramic capacitor is
chosen to decouple the high frequency noise. The bulk
input capacitors are determined by the voltage rating and
RMS current rating. The RMS current in the input
capacitors can be calculated as:
RMS OUT
OUT
IN
I I D 1-D
V
DV
... (3)
In this design two 10µF 25V X5R ceramic capacitors are
chosen.
OUTPUT VOLTAGE CALCULATION
Output voltage is set by reference voltage and external
voltage divider. The reference voltage is fixed at 0.925V.
The divider consists of two ratioed resistors so that the
output voltage applied at the FB pin is 0.925V when the
output voltage is at the desired value. The following
equation and picture show the relationship between and
voltage divider.
PRODUCTION DATA SHEET
NX7101
Microsemi
Analog Mixed Signal Group
One Enterprise, Aliso Viejo, CA 92656 949-380-6100, fax 949-215-4996
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2A, High Voltage Synchronous Buck Regulator
A P P L I C A T I O N I N F O R M A T I O N
1
OUT REF 2
R
V =V (1+ )
R
... (4)
In this design R1 is 26.1k, R2 is 10k.
COMPENSATOR DESIGN
The NX7101 uses peak current mode control to provide fast
transient and simple compensation. The DC gain of close loop
can be estimated by the equation (5).
FB
EA CS LOAD OUT
V
Gain=A G R V
... (5)
Where AEA is error amplifier voltage gain 560V/V, GCS is
current sensing gain 3.5A/V, RLOAD is the load resistor.
The system itself has one pole P1, one zero Z1 and double pole
PDOUBLE at half of switching frequency FS.
The system pole P1 is set by output capacitor and output load
resistor. The calculation of this pole is given by the equation
(6).
P1 L OUT
1
F2 R C
... (6)
The system zero Z1 is set by output capacitor and ESR of
output capacitor. The calculation of this zero is given by the
equation (7).
Z1 ESR OUT
1
F=
2 R C
... (7)
The crossover frequency is recommended to be set at 1/10th of
switching frequency. In order to achieve this desired crossover
frequency and make system stable, the resistor R3 and the
capacitor C3 is needed in typical applications which use
ceramic capacitors as output capacitors.
The pole P2 set by output resistance of error amplifier and C3
is given by the equation (8).
EA
P2 EA 3
G
F=
2 A C
... (8)
Where GEA is error amplifier transconductance 800uA/V.
The zero Z2 set by R3 and C3 is given by the equation (9).
Z2 33
1
F=
2 R C
... (9)
When Aluminum Electrolytic capacitors are chosen as output
capacitors, the ESR zero is much lower and extra capacitor C6
from COMP pin to ground is needed to stabilize the system.
NX7101
Vout
Vref
FB
R1
R2
COMP
Figure 11 Voltage Divider
The pole P3 set by R3 and C6 is given by the equation (10).
P3 36
1
F=
2 R C
... (10)
The compensation values for typical output voltage
application are given in the table below.
VOUT
L
COUT
R3
C3
C6
1.8V
10µH
22µFx2
6k
3.9nF
None
2.5V
10µH
22µFx2
8k
3.9nF
None
3.3V
10µH
22µFx2
10k
3.9nF
None
5V
15µH
22µFx2
18k
3.9nF
None
2.5V
10µH
470µF AL.
30m ESR
85k
250pF
150pF
5V
15-
22µH
470µF AL.
30m ESR
150k
220nF
82pF
PRODUCTION DATA SHEET
NX7101
Microsemi
Analog Mixed Signal Group
One Enterprise, Aliso Viejo, CA 92656 949-380-6100, fax 949-215-4996
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2A, High Voltage Synchronous Buck Regulator
P A C K A G E D I M E N S I O N S
DM
Plastic SOIC 8 Pin
A
P
G
B
K
L
F
C
DJ
M
IM
MILLIMETERS
INCHES
MIN
MAX
MIN
MAX
A
4.700
5.100
0.185
0.201
B
3.800
4.000
0.150
0.157
G
1.270 BSC
0.050 BSC
P
5.800
6.200
0.228
0.244
C
1.350
1.750
0.053
0.069
D
0.330
0.510
0.013
0.020
K
0.100
0.300
0.004
0.012
L
0.320 BSC
0.013 BSC
J
0.190
0.250
0.007
0.010
F
0.450
0.800
0.017
0.031
M
-
8°
-
8°
PRODUCTION DATA SHEET
NX7101
Microsemi
Analog Mixed Signal Group
One Enterprise, Aliso Viejo, CA 92656 949-380-6100, fax 949-215-4996
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Rev. 1.7, 2014-06-24
2A, High Voltage Synchronous Buck Regulator
N O T E S
PRODUCTION DATA – Information contained in this document is proprietary to
Microsemi and is current as of publication date. This document may not be modified in
any way without the express written consent of Microsemi. Product processing does not
necessarily include testing of all parameters. Microsemi reserves the right to change the
configuration and performance of the product and to discontinue product at any time.