NX7102
PRODUCTION DATA SHEET
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Analog Mixed Signal Group
One Enterprise, Aliso Viejo, CA, 949-380-6100, Fax: 949-215-4996
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3A High Voltage Synchronous Buck Converter
NX7102
Copyright 2010
Rev.1.6, 2015-02-20
D E S C R I P T I O N
NX7102 is a 340kHz fixed
frequency, current mode, PWM
synchronous buck (step-down) DC-
DC converter, capable of driving a 3A
load with high efficiency, excellent
line and load regulation. The device
integrates N-channel power MOSFET
switches with low on-resistance.
Current mode control provides fast
transient response and cycle-by-cycle
current limit.
The controller is equipped with
output over-voltage protection which
protects the IC under an 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 with
exposed pad package.
K E Y F E A T U R E S
3A 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)
NX7102
COMP(6)GND(4)
IN(2)
VIN
OUT
EN(7)
SS(8)
R3
10k
C3
5.6nF
COUT
2*22uF(10V,X5R)
CIN
2x10uF(25V,X5R)
C4 0.1u
C5
10nF L1
10uH
R1
26.1k
R2
10k
R4 100k
3.3V
12V
PAD
Figure 1 – 12V Input, 3.3V Output with Ceramic Cap
P A C K A G E O R D E R I N F O
TA (C)
Plastic SOIC 8 Pin
With Exposed Pad
DE
RoHS Compliant / Pb-free
-40 to 85
NX7102IDE
Note: Available in Tape & Reel. Append the letters “TR” to the part
number. (i.e. NX7102IDE-TR)
NX7102
PRODUCTION DATA SHEET
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Analog Mixed Signal Group
One Enterprise, Aliso Viejo, CA, 949-380-6100, Fax: 949-215-4996
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3A High Voltage Synchronous Buck Converter
NX7102
Copyright 2010
Rev.1.6, 2015-02-20
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) ............................................................................. -1V to (VIN + 1V)
EN ................................................................................................... -0.3V to (VIN + 0.3V)
BST ................................................................................................... -0.3V to (VSW + 6V)
COMP, FB, SS ................................................................................................. -0.3V to 6V
Maximum Operating Junction Temperature ............................................................... 150C
Storage Temperature Range .........................................................................-65C to 150C
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 2 I D E
X X X X
DE PACKAGE
(Top View)
DE PART MARKING
“xxxx” Denote Date Code and Lot Identification
RoHS / Pb-free 100% Matte Tin Pin Finish
T H E R M A L D A T A
DE
Plastic SOIC 8-Pin With Exposed Pad
THERMAL RESISTANCE-JUNCTION TO AMBIENT, JA
60C/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 VIN 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 2.7V enables the IC. Forcing this pin below 1.1V 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 9ms. To disable the soft-
start feature, leave SS unconnected.
NX7102
PRODUCTION DATA SHEET
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Analog Mixed Signal Group
One Enterprise, Aliso Viejo, CA, 949-380-6100, Fax: 949-215-4996
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3A High Voltage Synchronous Buck Converter
NX7102
Copyright 2010
Rev.1.6, 2015-02-20
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
NX7102
Units
Min
Typ
Max
Input Operating Voltage
VIN
4. 5
18
V
Maximum Output Current
IOUTMAX
3
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 = 5V, TA = 25C.
Parameter
Symbol
Test Conditions
NX7102
Units
Min
Typ
Max
Operating Current
Quiescent Current
IQ
VFB = 1V
1.25
1.4
mA
Shutdown Current
ISHDN
VEN = 0V
.02
1
µA
UVLO
VIN UVLO Threshold
VUVLO
VIN Rising
3.65
4.00
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 = 0.8V
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
5.2
A/V
Soft-Start
Soft-start Current
6
µA
Soft-start Time
TSS
CSS = 0.1µF
15
ms
Output Stage
High-side Switch On Resistance
RDSONH
90
120
150
mΩ
Low-side Switch On Resistance
RDSONL
70
100
130
mΩ
High-side Switch Leakage
Current
ILEAKH
VIN = 18V, VEN = 0V, VSW = 0V
0.1
10
µA
High-side Switch Current Limit
ILIMH
4.3
5.5
6.7
A
Low-side Switch Current Limit
ILIML
0.85
1.45
2.05
A
EN
EN shutdown Threshold
VENH
1.1
1.5
2
V
EN shutdown Threshold
Hysteresis
VENL
350
mV
NX7102
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3A High Voltage Synchronous Buck Converter
NX7102
Copyright 2010
Rev.1.6, 2015-02-20
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 = 25C.
Parameter
Symbol
Test Conditions
NX7102
Units
Min
Typ
Max
EN Lockout Threshold
2.2
2.5
2.7
EN Lockout Hysteresis
210
mV
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
Regualtor
SS
BST
1.3V
EN
2.5V
Figure 2 – Simplified Block Diagram
NX7102
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3A High Voltage Synchronous Buck Converter
NX7102
Copyright 2010
Rev.1.6, 2015-02-20
A P P L I C A T I O N C I R C U I T
FB(5)
SW(3)
BST(1)
NX7102
COMP(6)
GND(4)
IN(2)
VIN
OUT
EN(7)
SS(8)
C6
2200pF
COUT
1000uF,170mohm
CIN
2x(10uF,25V)
C4 0.1u
C5
10nF L1
22uH
R1
42.2k
R2
9.53k
PAD
R4 100k
Figure 3 – 12V Input, 5V Output with Electrolytic Cap
NX7102
PRODUCTION DATA SHEET
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One Enterprise, Aliso Viejo, CA, 949-380-6100, Fax: 949-215-4996
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3A High Voltage Synchronous Buck Converter
NX7102
Copyright 2010
Rev.1.6, 2015-02-20
FB(5)
SW(3)
BST(1)
NX7102
COMP(6)
GND(4)
IN(2)
VIN
OUT
EN(7)
SS(8)
R3
10k
C3
5.6nF
COUT
2*22uF(10V,X5R)
CIN
2*10uF(25V,X5R)
C4 0.1u
C5
10nF L1
10uH
R1
42.2k
R2
9.53k
PAD
R4 100k
Figure 4 – 12V Input, 5V Output with Ceramic Cap
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 5. DC Operation at 3A
Figure 6. Transient Response
NX7102
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3A High Voltage Synchronous Buck Converter
NX7102
Copyright 2010
Rev.1.6, 2015-02-20
Figure 7. Start up with no load
Figure 8. Input power recycling
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. Start into 2A resistive load
Figure 10. Output short operation
NX7102
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3A High Voltage Synchronous Buck Converter
NX7102
Copyright 2010
Rev.1.6, 2015-02-20
Figure 11. NX7102 Efficiency VS Load ( VIN=5V)
Figure 12. NX7102 Efficiency VS Load ( VIN=12V)
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0 500 1000 1500 2000 2500 3000
Efficiency
Load Current (mA)
VOUT=1V VOUT=1.8V
VOUT=2.5V VOUT=3.3V
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0 500 1000 1500 2000 2500 3000
Efficiency
Load Current (mA)
VOUT = 1V VOUT = 1.8V
VOUT = 2.5V VOUT = 3.3V
NX7102
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3A High Voltage Synchronous Buck Converter
NX7102
Copyright 2010
Rev.1.6, 2015-02-20
T H E O R Y O F O P E R A T I O N
DETAIL DESCRIPTION
The NX7102 is a current-mode, PWM synchronous step-
down DC-DC converter with 340kHz fixed working
frequency. It can convert input voltages from 4. 5V to 18V
down to an output voltage as low as 0.925V, and supply up
to 3A load current.
The NX7102 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 sub-harmonic 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 no 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 high-side NMOFET
current limit. If FB pin voltage drops below 0.3V, the
working frequency will be fold back to typically 100kHz 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.
The soft-start time is programmable through the SS pin in
order to have desired soft-start time
When the input voltage falls below the UVLO threshold, the
Lower Side MOSFET turns to discharge the output
capacitance.
NX7102
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3A High Voltage Synchronous Buck Converter
NX7102
Copyright 2010
Rev.1.6, 2015-02-20
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 NX7102, the
schematic is figure 1.
VIN = 12V
VOUT = 3.3V
IOUT = 3A
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 0.23 and 10μH inductor value is
chosen. In order to avoid output oscillation at light load, a
minimum 8.2μH inductor is required for all NX7102
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 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 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 10uF 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 the ratio of two 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.
NX7102
Vout
Vref
FB
R1
R2
COMP
Figure 13 Voltage Divider
The pole P3 set by R3 and C6 is given by the equation (10).
NX7102
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3A High Voltage Synchronous Buck Converter
NX7102
Copyright 2010
Rev.1.6, 2015-02-20
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 choose R1 26.1k, choose R2 10k.
COMPENSATOR DESIGN
The NX7102 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 5.2A/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 800μA/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.
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
8.2μH
22μFx2
4.02kΩ
5.6nF
None
2.5V
10μH
22μFx2
5.11kΩ
5.6nF
None
3.3V
10μH
22μFx2
6.49kΩ
5.6nF
None
5V
10μH
22μFx2
10kΩ
5.6nF
None
2.5V
10μH
470μF AL.
30m ESR
40.2kΩ
390pF
220pF
5V
10-15μH
470μF AL.
30m ESR
150kΩ
220pF
120pF
NX7102
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3A High Voltage Synchronous Buck Converter
NX7102
Copyright 2010
Rev.1.6, 2015-02-20
P A C K A G E D I M E N S I O N S
DE
Plastic SOIC 8 Pin With Exposed Pad
NX7102
PRODUCTION DATA SHEET
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Analog Mixed Signal Group
One Enterprise, Aliso Viejo, CA, 949-380-6100, Fax: 949-215-4996
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3A High Voltage Synchronous Buck Converter
NX7102
Copyright 2010
Rev.1.6, 2015-02-20
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.
