NSC LMZ14202H

LMZ14202H
2A SIMPLE SWITCHER® Power Module for High Output
Voltage
Easy to use 7 pin package
Performance Benefits
■
■
■
■
High efficiency reduces system heat generation
Low radiated EMI (EN 55022 Class B compliant) (Note 5)
No compensation required
Low package thermal resistance
System Performance
Efficiency VOUT = 12V
30135530
TO-PMOD 7 Pin Package
10.16 x 13.77 x 4.57 mm (0.4 x 0.542 x 0.18 in)
θJA = 16°C/W, θJC = 1.9°C/W
RoHS Compliant
■
■
■
■
Up to 2A output current
Input voltage range 6V to 42V
Output voltage as low as 5V
Efficiency up to 97%
95
EFFICIENCY (%)
Electrical Specifications
100
90
85
80
VIN = 15V
VIN = 24V
VIN = 30V
VIN = 36V
VIN = 42V
75
70
0.0
Key Features
precision enable
Protection against inrush currents
Input UVLO and output short circuit protection
– 40°C to 125°C junction temperature range
Single exposed pad and standard pinout for easy
mounting and manufacturing
■ Low output voltage ripple
■ Pin-to-pin compatible family:
LMZ14203H/2H/1H (42V max 3A, 2A, 1A)
LMZ14203/2/1 (42V max 3A, 2A, 1A)
LMZ12003/2/1 (20V max 3A, 2A, 1A)
■ Fully enabled for Webench® Power Designer
■
■
■
■
2.5
2.0
1.5
1.0
0.5
VIN = 15V
VIN = 24V
VIN = 42V
0.0
-20
Intermediate bus conversions to 12V and 24V rail
Time critical projects
Space constrained / high thermal requirement applications
Negative output voltage applications
0 20 40 60 80 100 120 140
AMBIENT TEMPERATURE (°C)
30135532
Radiated Emissions (EN 55022 Class B)
RADIATED EMISSIONS (dBμV/m)
■
■
■
■
30135507
80
Applications
2.0
Thermal Derating VOUT = 12V, θJA = 16°C/W
OUTPUT CURRENT (A)
■ Integrated shielded inductor
■ Simple PCB layout
■ Flexible startup sequencing using external soft-start and
0.5
1.0
1.5
OUTPUT CURRENT (A)
Emissions (Evaluation Board)
EN 55022 Limit (Class B)
70
60
50
40
30
20
10
0
0
200
400
600
800
FREQUENCY (MHz)
1000
30135525
SIMPLE SWITCHER® is a registered trademark of National Semiconductor Corporation
© 2011 National Semiconductor Corporation
301355
www.national.com
LMZ14202H 2A SIMPLE SWITCHER® Power Module for High Output Voltage
January 21, 2011
LMZ14202H
Simplified Application Schematic
30135501
Connection Diagram
30135502
Top View
7-Lead TO-PMOD
Ordering Information
Order Number
Package Type
NSC Package Drawing
Supplied As
LMZ14202HTZ
TO-PMOD-7
TZA07A
250 Units on Tape and Reel
LMZ14202HTZX
TO-PMOD-7
TZA07A
500 Units on Tape and Reel
LMZ14202HTZE
TO-PMOD-7
TZA07A
45 Units in a Rail
Pin Descriptions
Pin
Name Description
1
VIN
Supply input — Additional external input capacitance is required between this pin and the exposed pad (EP).
2
RON
On time resistor — An external resistor from VIN to this pin sets the on-time and frequency of the application. Typical
values range from 100k to 700k ohms.
3
EN
4
GND
5
SS
Soft-Start — An internal 8 µA current source charges an external capacitor to produce the soft-start function.
6
FB
Feedback — Internally connected to the regulation, over-voltage, and short-circuit comparators. The regulation
reference point is 0.8V at this input pin. Connect the feedback resistor divider between the output and ground to set
the output voltage.
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Enable — Input to the precision enable comparator. Rising threshold is 1.18V.
Ground — Reference point for all stated voltages. Must be externally connected to EP.
2
7
EP
Name Description
VOUT Output Voltage — Output from the internal inductor. Connect the output capacitor between this pin and the EP.
EP
Exposed Pad — Internally connected to pin 4. Used to dissipate heat from the package during operation. Must be
electrically connected to pin 4 external to the package.
3
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LMZ14202H
Pin
LMZ14202H
ESD Susceptibility(Note 2)
For soldering specifications:
see product folder at www.national.com and
www.national.com/ms/MS/MS-SOLDERING.pdf
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
VIN, RON to GND
EN, FB, SS to GND
Junction Temperature
Storage Temperature Range
Operating Ratings
-0.3V to 43.5V
-0.3V to 7V
150°C
-65°C to 150°C
± 2 kV
(Note 1)
VIN
EN
Operation Junction Temperature
6V to 42V
0V to 6.5V
−40°C to 125°C
Electrical Characteristics
Limits in standard type are for TJ = 25°C only; limits in boldface type apply over the
junction temperature (TJ) range of -40°C to +125°C. Minimum and Maximum limits are guaranteed through test, design or statistical
correlation. Typical values represent the most likely parametric norm at TJ = 25°C, and are provided for reference purposes only.
Unless otherwise stated the following conditions apply: VIN = 24V, VOUT = 12V, RON = 249kΩ
Symbol
Parameter
Conditions
Min
(Note 3)
Typ
(Note 4)
Max
(Note 3)
Units
1.10
1.18
1.25
V
SYSTEM PARAMETERS
Enable Control
VEN
VEN-HYS
EN threshold trip point
VEN rising
EN threshold hysteresis
90
mV
Soft-Start
ISS
ISS-DIS
SS source current
VSS = 0V
8
SS discharge current
10
15
-200
µA
µA
Current Limit
ICL
Current limit threshold
DC average
VINUVLO
Input UVLO
EN pin floating
VIN rising
3.75
V
VINUVLO-HYST
Hysteresis
EN pin floating
VIN falling
130
mV
ON timer minimum pulse width
150
ns
OFF timer pulse width
260
ns
2.4
3.2
3.95
A
VIN UVLO
ON/OFF Timer
tON-MIN
tOFF
Regulation and Over-Voltage Comparator
VFB
VFB
VFB-OVP
In-regulation feedback voltage
In-regulation feedback voltage
VIN = 24V, VOUT = 12V VSS >+ 0.8V
TJ = -40°C to 125°C
IOUT = 10mA to 2A
0.782
0.803
0.822
V
VIN = 24V, VOUT = 12V VSS >+ 0.8V
TJ = 25°C
IOUT = 10mA to 2A
0.786
0.803
0.818
V
VIN = 36V, VOUT = 24V VSS >+ 0.8V
TJ = -40°C to 125°C
IOUT = 10mA to 2A
0.780
0.803
0.824
V
VIN = 36V, VOUT = 24V VSS >+ 0.8V
TJ = 25°C
IOUT = 10mA to 2A
0.787
0.803
0.819
V
Feedback over-voltage
protection threshold
0.92
V
5
nA
IFB
Feedback input bias current
IQ
Non Switching Input Current
VFB= 0.86V
1
mA
ISD
Shut Down Quiescent Current
VEN= 0V
25
μA
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4
Parameter
Min
(Note 3)
Conditions
Typ
(Note 4)
Max
(Note 3)
Units
Thermal Characteristics
TSD
TSD-HYST
θJA
θJC
Thermal Shutdown
Rising
165
°C
15
°C
4 layer Printed Circuit Board, 7.62cm x
7.62cm (3in x 3in) area, 1 oz Copper, No
air flow
16
°C/W
4 layer Printed Circuit Board, 6.35cm x
6.35cm (2.5in x 2.5in) area, 1 oz
Copper, No air flow
18.4
°C/W
No air flow
1.9
°C/W
8
mV PP
Thermal Shutdown Hysteresis
Junction to Ambient
Junction to Case
PERFORMANCE PARAMETERS
ΔVOUT
Output Voltage Ripple
VOUT = 5V, CO = 100µF 6.3V X7R
ΔVOUT/ΔVIN
Line Regulation
VIN = 16V to 42V, IOUT= 3A
.01
%
ΔVOUT/ΔIOUT
Load Regulation
VIN = 24V, IOUT = 0A to 2A
1.5
mV/A
η
Efficiency
VIN = 24V VOUT = 12V IOUT = 1A
93
%
η
Efficiency
VIN = 24V VOUT = 12V IOUT = 2A
92
%
Note 1: Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which operation of the
device is intended to be functional. For guaranteed specifications and test conditions, see the Electrical Characteristics.
Note 2: The human body model is a 100pF capacitor discharged through a 1.5 kΩ resistor into each pin. Test method is per JESD-22-114.
Note 3: Min and Max limits are 100% production tested at 25°C. Limits over the operating temperature range are guaranteed through correlation using Statistical
Quality Control (SQC) methods. Limits are used to calculate National’s Average Outgoing Quality Level (AOQL).
Note 4: Typical numbers are at 25°C and represent the most likely parametric norm.
Note 5: EN 55022:2006, +A1:2007, FCC Part 15 Subpart B: 2007.
5
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LMZ14202H
Symbol
Unless otherwise specified, the following conditions apply: VIN = 24V; Cin = 10uF X7R Ceramic; CO = 47uF; TAMB = 25°C.
Power Dissipation VOUT = 5.0V TAMB = 25°C
100
3.0
95
2.5
POWER DISSIPATION (W)
EFFICIENCY (%)
Efficiency VOUT = 5.0V TAMB = 25°C
90
85
80
75
70
0.0
VIN = 8V
VIN = 12V
VIN = 24V
VIN = 36V
VIN = 42V
0.5
1.0
1.5
OUTPUT CURRENT (A)
VIN = 8V
VIN = 12V
VIN = 24V
VIN = 36V
VIN = 42V
2.0
1.5
1.0
0.5
0.0
2.0
0.0
0.5
1.0
1.5
OUTPUT CURRENT (A)
2.0
30135512
30135510
Power Dissipation VOUT = 12V TAMB = 25°C
100
3.0
95
2.5
POWER DISSIPATION (W)
EFFICIENCY (%)
Efficiency VOUT = 12V TAMB = 25°C
90
85
80
75
70
0.0
VIN = 15V
VIN = 24V
VIN = 30V
VIN = 36V
VIN = 42V
0.5
1.0
1.5
OUTPUT CURRENT (A)
VIN = 15V
VIN = 24V
VIN = 30V
VIN = 36V
VIN = 42V
2.0
1.5
1.0
0.5
0.0
2.0
0.0
0.5
1.0
1.5
OUTPUT CURRENT (A)
2.0
30135507
30135516
Efficiency VOUT = 15V TAMB = 25°C
Power Dissipation VOUT = 15V TAMB = 25°C
100
3.0
95
2.5
POWER DISSIPATION (W)
EFFICIENCY (%)
LMZ14202H
Typical Performance Characteristics
90
85
80
75
VIN = 24V
VIN = 30V
VIN = 36V
VIN = 42V
70
0.0
2.0
1.5
1.0
0.5
0.0
0.5
1.0
1.5
OUTPUT CURRENT (A)
2.0
0.0
30135509
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VIN = 24V
VIN = 30V
VIN = 36V
VIN = 42V
0.5
1.0
1.5
OUTPUT CURRENT (A)
2.0
30135550
6
3.0
95
2.5
POWER DISSIPATION (W)
EFFICIENCY (%)
Power Dissipation VOUT = 18V TAMB = 25°C
100
90
85
80
75
VIN = 24V
VIN = 30V
VIN = 36V
VIN = 42V
70
0.0
VIN = 24V
VIN = 30V
VIN = 36V
VIN = 42V
2.0
1.5
1.0
0.5
0.0
0.5
1.0
1.5
OUTPUT CURRENT (A)
2.0
0.0
0.5
1.0
1.5
OUTPUT CURRENT (A)
2.0
30135549
30135548
Power Dissipation VOUT = 24V TAMB = 25°C
3.0
95
2.5
POWER DISSIPATION (W)
EFFICIENCY (%)
Efficiency VOUT = 24V TAMB = 25°C
100
90
85
80
75
VIN = 28V
VIN = 30V
VIN = 36V
VIN = 42V
70
0.0
VIN = 28V
VIN = 30V
VIN = 36V
VIN = 42V
2.0
1.5
1.0
0.5
0.0
0.5
1.0
1.5
OUTPUT CURRENT (A)
2.0
0.0
0.5
1.0
1.5
OUTPUT CURRENT (A)
2.0
30135547
30135546
Power Dissipation VOUT = 30V TAMB = 25°C
100
3.0
95
2.5
POWER DISSIPATION (W)
EFFICIENCY (%)
Efficiency VOUT = 30V TAMB = 25°C
90
85
80
75
70
0.0
LMZ14202H
Efficiency VOUT = 18V TAMB = 25°C
VIN = 34V
VIN = 36V
VIN = 42V
0.5
1.0
1.5
OUTPUT CURRENT (A)
2.0
1.5
1.0
0.5
0.0
2.0
0.0
30135540
VIN = 34V
VIN = 36V
VIN = 42V
0.5
1.0
1.5
OUTPUT CURRENT (A)
2.0
30135539
7
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LMZ14202H
Power Dissipation VOUT = 5.0V TAMB = 85°C
100
3.0
95
2.5
POWER DISSIPATION (W)
EFFICIENCY (%)
Efficiency VOUT = 5.0V TAMB = 85°C
90
85
80
75
70
0.0
VIN = 8V
VIN = 12V
VIN = 24V
VIN = 36V
VIN = 42V
0.5
1.0
1.5
OUTPUT CURRENT (A)
VIN = 8V
VIN = 12V
VIN = 24V
VIN = 36V
VIN = 42V
2.0
1.5
1.0
0.5
0.0
2.0
0.0
0.5
1.0
1.5
OUTPUT CURRENT (A)
2.0
30135515
30135545
Power Dissipation VOUT = 12V TAMB = 85°C
3.0
95
2.5
POWER DISSIPATION (W)
EFFICIENCY (%)
Efficiency VOUT = 12V TAMB = 85°C
100
90
85
80
75
70
0.0
VIN = 15V
VIN = 24V
VIN = 30V
VIN = 36V
VIN = 42V
0.5
1.0
1.5
OUTPUT CURRENT (A)
VIN = 15V
VIN = 24V
VIN = 30V
VIN = 36V
VIN = 42V
2.0
1.5
1.0
0.5
0.0
2.0
0.0
0.5
1.0
1.5
OUTPUT CURRENT (A)
2.0
30135514
30135513
Power Dissipation VOUT = 15V TAMB = 85°C
100
3.0
95
2.5
POWER DISSIPATION (W)
EFFICIENCY (%)
Efficiency VOUT = 15V TAMB = 85°C
90
85
80
75
VIN = 24V
VIN = 30V
VIN = 36V
VIN = 42V
70
0.0
2.0
1.5
1.0
0.5
0.0
0.5
1.0
1.5
OUTPUT CURRENT (A)
2.0
0.0
30135542
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VIN = 24V
VIN = 30V
VIN = 36V
VIN = 42V
0.5
1.0
1.5
OUTPUT CURRENT (A)
2.0
30135541
8
3.0
95
2.5
POWER DISSIPATION (W)
EFFICIENCY (%)
Power Dissipation VOUT = 18V TAMB = 85°C
100
90
85
80
75
VIN = 24V
VIN = 30V
VIN = 36V
VIN = 42V
70
0.0
VIN = 24V
VIN = 30V
VIN = 36V
VIN = 42V
2.0
1.5
1.0
0.5
0.0
0.5
1.0
1.5
OUTPUT CURRENT (A)
2.0
0.0
0.5
1.0
1.5
OUTPUT CURRENT (A)
2.0
30135544
30135543
Power Dissipation VOUT = 24V TAMB = 85°C
3.0
95
2.5
POWER DISSIPATION (W)
EFFICIENCY (%)
Efficiency VOUT = 24V TAMB = 85°C
100
90
85
80
75
VIN = 28V
VIN = 30V
VIN = 36V
VIN = 42V
70
0.0
VIN = 28V
VIN = 30V
VIN = 36V
VIN = 42V
2.0
1.5
1.0
0.5
0.0
0.5
1.0
1.5
OUTPUT CURRENT (A)
2.0
0.0
0.5
1.0
1.5
OUTPUT CURRENT (A)
2.0
30135538
30135537
Power Dissipation VOUT = 30V TAMB = 85°C
100
3.0
95
2.5
POWER DISSIPATION (W)
EFFICIENCY (%)
Efficiency VOUT = 30V TAMB = 85°C
90
85
80
75
70
0.0
LMZ14202H
Efficiency VOUT = 18V TAMB = 85°C
VIN = 34V
VIN = 36V
VIN = 42V
0.5
1.0
1.5
OUTPUT CURRENT (A)
2.0
1.5
1.0
0.5
0.0
2.0
0.0
30135536
VIN = 34V
VIN = 36V
VIN = 42V
0.5
1.0
1.5
OUTPUT CURRENT (A)
2.0
30135535
9
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2.5
2.0
2.0
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
Thermal Derating VOUT = 12V, θJA = 20°C/W
2.5
1.5
1.0
0.5
0.0
-20
VIN = 15V
VIN = 24V
VIN = 42V
VIN = 15V
VIN = 24V
VIN = 42V
1.5
1.0
0.5
0.0
0 20 40 60 80 100 120 140
AMBIENT TEMPERATURE (°C)
-20
0 20 40 60 80 100 120 140
AMBIENT TEMPERATURE (°C)
30135532
30135529
Thermal Derating VOUT = 24V, θJA = 20°C/W
2.5
2.5
2.0
2.0
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
Thermal Derating VOUT = 24V, θJA = 16°C/W
1.5
1.0
0.5
0.0
-20
VIN = 30V
VIN = 36V
VIN = 42V
VIN = 30V
VIN = 36V
VIN = 42V
1.5
1.0
0.5
0.0
0 20 40 60 80 100 120 140
AMBIENT TEMPERATURE (°C)
-20
0 20 40 60 80 100 120 140
AMBIENT TEMPERATURE (°C)
30135531
30135528
Thermal Derating VOUT = 30V, θJA = 16°C/W
Thermal Derating VOUT = 30V, θJA = 20°C/W
2.5
2.5
2.0
2.0
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
LMZ14202H
Thermal Derating VOUT = 12V, θJA = 16°C/W
1.5
1.0
0.5
0.0
-20
VIN = 34V
VIN = 36V
VIN = 42V
1.5
1.0
0.5
0.0
0 20 40 60 80 100 120 140
AMBIENT TEMPERATURE (°C)
-20
30135553
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VIN = 34V
VIN = 36V
VIN = 42V
0 20 40 60 80 100 120 140
AMBIENT TEMPERATURE (°C)
30135554
10
Line and Load Regulation TAMB = 25°C
OUTPUT VOLTAGE REGULATION (%)
THERMAL RESISTANCE θJA (°C/W)
40
0LFM (0m/s) air
225LFM (1.14m/s) air
500LFM (2.54m/s) air
Evaluation Board Area
35
30
25
20
15
10
5
0
0
10
20
30
40
BOARD AREA (cm2)
50
LMZ14202H
Package Thermal Resistance θJA
4 Layer Printed Circuit Board with 1oz Copper
0.20
0.15
0.10
0.05
0.00
-0.05
-0.10
-0.15
-0.20
0.0
60
VIN = 15V
VIN = 24V
VIN = 30V
VIN = 36V
VIN = 42V
0.5
1.0
1.5
OUTPUT CURRENT (A)
2.0
30135555
30135527
Output Ripple
VIN = 12V, IOUT = 2A, Ceramic COUT, BW = 200 MHz
Output Ripple
VIN = 24V, IOUT = 2A, Polymer Electrolytic COUT, BW = 200 MHz
30135505
30135504
Load Transient Response VIN = 24V VOUT = 12V
Load Step from 10% to 100%
Load Transient Response VIN = 24V VOUT = 12V
Load Step from 30% to 100%
30135503
30135506
11
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Switching Frequency vs. Power Dissipation
VOUT = 5V TAMB = 25°C
3.5
POWER DISSIPATION (W)
DC CURRENT LIMIT LEVEL (A)
4.5
4.0
3.5
3.0
Fsw = 250kHz
Fsw = 400kHz
Fsw = 600kHz
2.5
2.0
3.0
VIN = 12V
VIN = 24V
VIN = 36V
VIN = 42V
2.5
2.0
1.5
1.0
0.5
0.0
5
10
15 20 25 30 35
INPUT VOLTAGE (V)
40
45
200
300 400 500 600 700
SWITCHING FREQUENCY (kHz)
30135521
Switching Frequency vs. Power Dissipation
VOUT = 12V TAMB = 25°C
3.5
POWER DISSIPATION (W)
DC CURRENT LIMIT LEVEL (A)
4.5
4.0
3.5
3.0
Fsw = 250kHz
Fsw = 400kHz
Fsw = 600kHz
2.5
2.0
3.0
VIN = 15V
VIN = 24V
VIN = 36V
VIN = 42V
2.5
2.0
1.5
1.0
0.5
0.0
5
10
15 20 25 30 35
INPUT VOLTAGE (V)
40
45
200
300 400 500 600 700
SWITCHING FREQUENCY (kHz)
30135522
800
30135519
Current Limit vs. Input Voltage
VOUT = 24V TAMB = 25°C
Switching Frequency vs. Power Dissipation
VOUT = 24V TAMB = 25°C
4.5
POWER DISSIPATION (W)
3.5
4.0
3.5
3.0
Fsw = 250kHz
Fsw = 400kHz
Fsw = 600kHz
2.5
2.0
3.0
2.5
2.0
1.5
1.0
0.5
VIN = 30V
VIN = 36V
VIN = 42V
0.0
30
33
36
39
42
INPUT VOLTAGE (V)
45
200
30135523
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800
30135518
Current Limit vs. Input Voltage
VOUT = 12V TAMB = 25°C
DC CURRENT LIMIT LEVEL (A)
LMZ14202H
Current Limit vs. Input Voltage
VOUT = 5V TAMB = 25°C
300 400 500 600 700
SWITCHING FREQUENCY (kHz)
800
30135520
12
Radiated EMI of Evaluation Board, VOUT = 12V
RADIATED EMISSIONS (dBμV/m)
80
Emissions (Evaluation Board)
EN 55022 Limit (Class B)
70
60
50
40
30
20
10
0
0
30135556
200
400
600
800
FREQUENCY (MHz)
1000
30135525
Conducted EMI, VOUT = 12V
Evaluation Board BOM and 3.3µH 2x10µF LC line filter
CONDUCTED EMISSIONS (dBμV)
80
70
Emissions
CISPR 22 Quasi Peak
CISPR 22 Average
60
50
40
30
20
10
0
0.1
1
10
FREQUENCY (MHz)
100
30135524
13
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LMZ14202H
Startup
VIN = 24V IOUT = 2A
LMZ14202H
Application Block Diagram
30135508
falling threshold of 1.09V. The maximum recommended voltage into the EN pin is 6.5V. For applications where the midpoint of the enable divider exceeds 6.5V, a small zener can
be added to limit this voltage.
The function of the RENT and RENB divider shown in the Application Block Diagram is to allow the designer to choose an
input voltage below which the circuit will be disabled. This implements the feature of programmable under voltage lockout.
This is often used in battery powered systems to prevent deep
discharge of the system battery. It is also useful in system
designs for sequencing of output rails or to prevent early turnon of the supply as the main input voltage rail rises at powerup. Applying the enable divider to the main input rail is often
done in the case of higher input voltage systems such as 24V
AC/DC systems where a lower boundary of operation should
be established. In the case of sequencing supplies, the divider
is connected to a rail that becomes active earlier in the powerup cycle than the LMZ14202H output rail. The two resistors
should be chosen based on the following ratio:
COT Control Circuit Overview
Constant On Time control is based on a comparator and an
on-time one shot, with the output voltage feedback compared
to an internal 0.8V reference. If the feedback voltage is below
the reference, the high-side MOSFET is turned on for a fixed
on-time determined by a programming resistor RON. RON is
connected to VIN such that on-time is reduced with increasing
input supply voltage. Following this on-time, the high-side
MOSFET remains off for a minimum of 260 ns. If the voltage
on the feedback pin falls below the reference level again the
on-time cycle is repeated. Regulation is achieved in this manner.
Design Steps for the LMZ14202H
Application
The LMZ14202H is fully supported by Webench® which offers the following:
• Component selection
• Electrical simulation
• Thermal simulation
• Build-it prototype board for a reduction in design time
RENT / RENB = (VIN-ENABLE/ 1.18V) – 1 (1)
The EN pin is internally pulled up to VIN and can be left floating for always-on operation. However, it is good practice to
use the enable divider and turn on the regulator when VIN is
close to reaching its nominal value. This will guarantee
smooth startup and will prevent overloading the input supply.
The following list of steps can be used to manually design the
LMZ14202H application.
• Select minimum operating VIN with enable divider resistors
• Program VO with divider resistor selection
• Program turn-on time with soft-start capacitor selection
• Select CO
• Select CIN
• Set operating frequency with RON
• Determine module dissipation
• Layout PCB for required thermal performance
OUTPUT VOLTAGE SELECTION
Output voltage is determined by a divider of two resistors
connected between VO and ground. The midpoint of the divider is connected to the FB input. The voltage at FB is
compared to a 0.8V internal reference. In normal operation
an on-time cycle is initiated when the voltage on the FB pin
falls below 0.8V. The high-side MOSFET on-time cycle causes the output voltage to rise and the voltage at the FB to
exceed 0.8V. As long as the voltage at FB is above 0.8V, ontime cycles will not occur.
The regulated output voltage determined by the external divider resistors RFBT and RFBB is:
ENABLE DIVIDER, RENT AND RENB SELECTION
The enable input provides a precise 1.18V reference threshold to allow direct logic drive or connection to a voltage divider
from a higher enable voltage such as VIN. The enable input
also incorporates 90 mV (typ) of hysteresis resulting in a
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VO = 0.8V x (1 + RFBT / RFBB) (2)
14
ESR:
RFBT / RFBB = (VO / 0.8V) - 1 (3)
The ESR of the output capacitor affects the output voltage
ripple. High ESR will result in larger VOUT peak-to-peak ripple
voltage. Furthermore, high output voltage ripple caused by
excessive ESR can trigger the over-voltage protection monitored at the FB pin. The ESR should be chosen to satisfy the
maximum desired VOUT peak-to-peak ripple voltage and to
avoid over-voltage protection during normal operation. The
following equations can be used:
ESRMAX-RIPPLE ≤ VOUT-RIPPLE / ILR P-P(7)
where ILR P-P is calculated using equation (19) below
These resistors should be chosen from values in the range of
1 kΩ to 50 kΩ.
A feed-forward capacitor is placed in parallel with RFBT to improve load step transient response. Its value is usually determined experimentally by load stepping between DCM and
CCM conduction modes and adjusting for best transient response and minimum output ripple.
A table of values for RFBT , RFBB , and RON is included in the
simplified applications schematic.
ESRMAX-OVP < (VFB-OVP - VFB) / (ILR P-P x AFB )(8)
where AFB is the gain of the feedback network from VOUT to
VFB at the switching frequency.
SOFT-START CAPACITOR, CSS, SELECTION
Programmable soft-start permits the regulator to slowly ramp
to its steady state operating point after being enabled, thereby
reducing current inrush from the input supply and slowing the
output voltage rise-time to prevent overshoot.
Upon turn-on, after all UVLO conditions have been passed,
an internal 8uA current source begins charging the external
soft-start capacitor. The soft-start time duration to reach
steady state operation is given by the formula:
As worst case, assume the gain of AFB with the CFF capacitor
at the switching frequency is 1.
The selected capacitor should have sufficient voltage and
RMS current rating. The RMS current through the output capacitor is:
I(COUT(RMS)) = ILR P-P / √12 (9)
tSS = VREF x CSS / Iss = 0.8V x CSS / 8uA (4)
INPUT CAPACITOR, CIN, SELECTION
The LMZ14202H module contains an internal 0.47 µF input
ceramic capacitor. Additional input capacitance is required
external to the module to handle the input ripple current of the
application. This input capacitance should be located as close
as possible to the module. Input capacitor selection is generally directed to satisfy the input ripple current requirements
rather than by capacitance value. Worst case input ripple current rating is dictated by the equation:
This equation can be rearranged as follows:
CSS = tSS x 8 μA / 0.8V (5)
Use of a 4700pF capacitor results in 0.5ms soft-start duration.
This is a recommended value. Note that high values of CSS
capacitance will cause more output voltage droop when a
load transient goes across the DCM-CCM boundary. Use
equation 18 below to find the DCM-CCM boundary load current for the specific operating condition. If a fast load transient
response is desired for steps between DCM and CCM mode
the softstart capacitor value should be less than 0.018µF.
I(CIN(RMS)) ≊ 1 / 2 x IO x √ (D / 1-D) (10)
where D ≊ VO / VIN
As the soft-start input exceeds 0.8V the output of the power
stage will be in regulation. Note that the following conditions
will reset the soft-start capacitor by discharging the SS input
to ground with an internal 200 μA current sink:
• The enable input being “pulled low”
• Thermal shutdown condition
• Over-current fault
• Internal VINUVLO
(As a point of reference, the worst case ripple current will occur when the module is presented with full load current and
when VIN = 2 x VO).
Recommended minimum input capacitance is 10uF X7R ceramic with a voltage rating at least 25% higher than the
maximum applied input voltage for the application. It is also
recommended that attention be paid to the voltage and temperature deratings of the capacitor selected. It should be
noted that ripple current rating of ceramic capacitors may be
missing from the capacitor data sheet and you may have to
contact the capacitor manufacturer for this rating.
If the system design requires a certain maximum value of input ripple voltage ΔVIN to be maintained then the following
equation may be used.
OUTPUT CAPACITOR, CO, SELECTION
None of the required output capacitance is contained within
the module. At a minimum, the output capacitor must meet
the worst case RMS current rating of 0.5 x ILR P-P, as calculated in equation (17). Beyond that, additional capacitance will
reduce output ripple so long as the ESR is low enough to permit it. A minimum value of 10 μF is generally required. Experimentation will be required if attempting to operate with a
minimum value. Low ESR capacitors, such as ceramic and
polymer electrolytic capacitors are recommended.
CIN ≥ IO x D x (1–D) / fSW-CCM x ΔVIN(11)
If ΔVIN is 1% of VIN for a 24V input to 12V output application
this equals 240 mV and fSW = 400 kHz.
CIN≥ 2A x 12V/24V x (1– 12V/24V) / (400000 x 0.240 V)
CIN≥ 5.2μF
CAPACITANCE:
The following equation provides a good first pass approximation of CO for load transient requirements:
Additional bulk capacitance with higher ESR may be required
to damp any resonant effects of the input capacitance and
parasitic inductance of the incoming supply lines.
As an example, for 2A load step, VIN = 24V, VOUT = 12V,
VOUT-TRAN = 50mV:
ON TIME, RON, RESISTOR SELECTION
Many designs will begin with a desired switching frequency in
mind. As seen in the Typical Performance Characteristics
section, the best efficiency is achieved in the 300kHz-400kHz
CO≥ISTEP x VFB x L x VIN/ (4 x VO x (VIN — VO) x VOUT-TRAN)
(6)
CO≥ 2A x 0.8V x 15μH x 24V / (4 x 12V x ( 24V — 12V) x
50mV)
15
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LMZ14202H
CO≥ 20μF
Rearranging terms; the ratio of the feedback resistors for a
desired output voltage is:
the amplitude of the inductor ripple current (ILR). ILR can be
calculated with:
fSW(CCM) ≊ VO / (1.3 x 10-10 x RON) (12)
ILR P-P=VO x (VIN- VO) / (15µH x fSW x VIN) (19)
This can be rearranged as
Where VIN is the maximum input voltage and fSW is determined from equation 12.
If the output current IO is determined by assuming that IO =
IL, the higher and lower peak of ILR can be determined. Be
aware that the lower peak of ILR must be positive if CCM operation is required.
RON ≊ VO / (1.3 x 10 -10 x fSW(CCM) (13)
The selection of RON and fSW(CCM) must be confined by limitations in the on-time and off-time for the COT control section.
The on-time of the LMZ14202H timer is determined by the
resistor RON and the input voltage VIN. It is calculated as follows:
tON = (1.3 x
10-10
POWER DISSIPATION AND BOARD THERMAL
REQUIREMENTS
For a design case of VIN = 24V, VOUT = 12V, IOUT = 2A,
TAMB (MAX) = 85°C , and TJUNCTION = 125°C, the device must
see a maximum junction-to-ambient thermal resistance of:
x RON) / VIN (14)
The inverse relationship of tON and VIN gives a nearly constant
switching frequency as VIN is varied. RON should be selected
such that the on-time at maximum VIN is greater than 150 ns.
The on-timer has a limiter to ensure a minimum of 150 ns for
tON. This limits the maximum operating frequency, which is
governed by the following equation:
θJA-MAX < (TJ-MAX - TAMB(MAX)) / PD
This θJA-MAX will ensure that the junction temperature of the
regulator does not exceed TJ-MAX in the particular application
ambient temperature.
To calculate the required θJA-MAX we need to get an estimate
for the power losses in the IC. The following graph is taken
form the Typical Performance Characteristics section and
shows the power dissipation of the LMZ14202H for VOUT =
12V at 85°C TAMB.
fSW(MAX) = VO / (VIN(MAX) x 150 nsec) (15)
This equation can be used to select RON if a certain operating
frequency is desired so long as the minimum on-time of 150
ns is observed. The limit for RON can be calculated as follows:
RON ≥ VIN(MAX) x 150 nsec / (1.3 x 10 -10) (16)
If RON calculated in (13) is less than the minimum value determined in (16) a lower frequency should be selected. Alternatively, VIN(MAX) can also be limited in order to keep the
frequency unchanged.
Additionally, the minimum off-time of 260 ns (typ) limits the
maximum duty ratio. Larger RON (lower FSW) should be selected in any application requiring large duty ratio.
Power Dissipation VOUT = 12V TAMB = 85°C
3.0
POWER DISSIPATION (W)
LMZ14202H
switching frequency range. The following equation can be
used to calculate the RON value.
Discontinuous Conduction and Continuous Conduction
Modes
At light load the regulator will operate in discontinuous conduction mode (DCM). With load currents above the critical
conduction point, it will operate in continuous conduction
mode (CCM). When operating in DCM the switching cycle
begins at zero amps inductor current; increases up to a peak
value, and then recedes back to zero before the end of the
off-time. Note that during the period of time that inductor current is zero, all load current is supplied by the output capacitor.
The next on-time period starts when the voltage on the FB pin
falls below the internal reference. The switching frequency is
lower in DCM and varies more with load current as compared
to CCM. Conversion efficiency in DCM is maintained since
conduction and switching losses are reduced with the smaller
load and lower switching frequency. Operating frequency in
DCM can be calculated as follows:
2.0
1.5
1.0
0.5
0.0
0.0
0.5
1.0
1.5
OUTPUT CURRENT (A)
2.0
30135513
Using the 85°C TAMB power dissipation data PD for VIN = 24V
and VOUT = 12V is estimated to be 1.8W. The necessary θJAMAX can now be calculated.
θJA-MAX < (125°C - 85°C) / 1.8W
fSW(DCM)≊VO x (VIN-1) x 15μH x 1.18 x 1020 x IO / (VIN–VO) x
RON2 (17)
θJA-MAX < 22.2°C/W
To achieve this thermal resistance the PCB is required to dissipate the heat effectively. The area of the PCB will have a
direct effect on the overall junction-to-ambient thermal resistance. In order to estimate the necessary copper area we can
refer to the following Package Thermal Resistance graph.
This graph is taken from the Typical Performance Characteristics section and shows how the θJA varies with the PCB area.
In CCM, current flows through the inductor through the entire
switching cycle and never falls to zero during the off-time. The
switching frequency remains relatively constant with load current and line voltage variations. The CCM operating frequency can be calculated using equation 12 above.
The approximate formula for determining the DCM/CCM
boundary is as follows:
IDCB≊VOx (VIN–VO) / ( 2 x 15μH x fSW(CCM) x VIN) (18)
The inductor internal to the module is 15μH. This value was
chosen as a good balance between low and high input voltage
applications. The main parameter affected by the inductor is
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2.5
VIN = 15V
VIN = 24V
VIN = 30V
VIN = 36V
VIN = 42V
16
THERMAL RESISTANCE θJA (°C/W)
40
consist of a localized top side plane that connects to the GND
exposed pad (EP).
2. Have a single point ground.
The ground connections for the feedback, soft-start, and enable components should be routed to the GND pin of the
device. This prevents any switched or load currents from
flowing in the analog ground traces. If not properly handled,
poor grounding can result in degraded load regulation or erratic output voltage ripple behavior. Provide the single point
ground connection from pin 4 to EP.
3. Minimize trace length to the FB pin.
Both feedback resistors, RFBT and RFBB, and the feed forward
capacitor CFF, should be located close to the FB pin. Since
the FB node is high impedance, maintain the copper area as
small as possible. The traces from RFBT, RFBB, and CFF should
be routed away from the body of the LMZ14202H to minimize
noise pickup.
4. Make input and output bus connections as wide as
possible.
This reduces any voltage drops on the input or output of the
converter and maximizes efficiency. To optimize voltage accuracy at the load, ensure that a separate feedback voltage
sense trace is made to the load. Doing so will correct for voltage drops and provide optimum output accuracy.
5. Provide adequate device heat-sinking.
Use an array of heat-sinking vias to connect the exposed pad
to the ground plane on the bottom PCB layer. If the PCB has
a plurality of copper layers, these thermal vias can also be
employed to make connection to inner layer heat-spreading
ground planes. For best results use a 6 x 6 via array with
minimum via diameter of 10mils (254 μm) thermal vias spaced
59mils (1.5 mm). Ensure enough copper area is used for heatsinking to keep the junction temperature below 125°C.
0LFM (0m/s) air
225LFM (1.14m/s) air
500LFM (2.54m/s) air
Evaluation Board Area
35
30
25
20
15
10
5
0
0
10
20
30
40
BOARD AREA (cm2)
50
60
30135527
For θJA-MAX< 22.2°C/W and only natural convection (i.e. no air
flow), the PCB area will have to be at least 30cm2. This corresponds to a square board with approximately 5.5cm x
5.5cm (2.17in x 2.17in) copper area, 4 layers, and 1oz copper
thickness. Higher copper thickness will further improve the
overall thermal performance. Note that thermal vias should
be placed under the IC package to easily transfer heat from
the top layer of the PCB to the inner layers and the bottom
layer.
For more guidelines and insight on PCB copper area, thermal
vias placement, and general thermal design practices please
refer to Application Note AN-2020 (http://www.national.com/
an/AN/AN-2020.pdf).
PC BOARD LAYOUT GUIDELINES
PC board layout is an important part of DC-DC converter design. Poor board layout can disrupt the performance of a DCDC converter and surrounding circuitry by contributing to EMI,
ground bounce and resistive voltage drop in the traces. These
can send erroneous signals to the DC-DC converter resulting
in poor regulation or instability. Good layout can be implemented by following a few simple design rules.
Additional Features
OUTPUT OVER-VOLTAGE COMPARATOR
The voltage at FB is compared to a 0.92V internal reference.
If FB rises above 0.92V the on-time is immediately terminated. This condition is known as over-voltage protection (OVP).
It can occur if the input voltage is increased very suddenly or
if the output load is decreased very suddenly. Once OVP is
activated, the top MOSFET on-times will be inhibited until the
condition clears. Additionally, the synchronous MOSFET will
remain on until inductor current falls to zero.
CURRENT LIMIT
Current limit detection is carried out during the off-time by
monitoring the current in the synchronous MOSFET. Referring to the Functional Block Diagram, when the top MOSFET
is turned off, the inductor current flows through the load, the
PGND pin and the internal synchronous MOSFET. If this current exceeds ICL the current limit comparator disables the start
of the next on-time period. The next switching cycle will occur
only if the FB input is less than 0.8V and the inductor current
has decreased below ICL. Inductor current is monitored during
the period of time the synchronous MOSFET is conducting.
So long as inductor current exceeds ICL, further on-time intervals for the top MOSFET will not occur. Switching frequency is lower during current limit due to the longer off-time. It
should also be noted that DC current limit varies with duty
cycle, switching frequency, and temperature.
30135511
1. Minimize area of switched current loops.
From an EMI reduction standpoint, it is imperative to minimize
the high di/dt paths during PC board layout. The high current
loops that do not overlap have high di/dt content that will
cause observable high frequency noise on the output pin if
the input capacitor (Cin1) is placed at a distance away from
the LMZ14202H. Therefore place CIN1 as close as possible to
the LMZ14202H VIN and GND exposed pad. This will minimize the high di/dt area and reduce radiated EMI. Additionally, grounding for both the input and output capacitor should
17
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LMZ14202H
Package Thermal Resistance θJA 4 Layer Printed Circuit
Board with 1oz Copper
LMZ14202H
chronous MOSFET when its current reaches zero until the
next on-time. This circuit enables the DCM operating mode,
which improves efficiency at light loads.
THERMAL PROTECTION
The junction temperature of the LMZ14202H should not be
allowed to exceed its maximum ratings. Thermal protection is
implemented by an internal Thermal Shutdown circuit which
activates at 165 °C (typ) causing the device to enter a low
power standby state. In this state the main MOSFET remains
off causing VO to fall, and additionally the CSS capacitor is
discharged to ground. Thermal protection helps prevent
catastrophic failures for accidental device overheating. When
the junction temperature falls back below 145 °C (typ Hyst =
20 °C) the SS pin is released, VO rises smoothly, and normal
operation resumes.
PRE-BIASED STARTUP
The LMZ14202H will properly start up into a pre-biased output. This is startup situation is common in multiple rail logic
applications where current paths may exist between different
power rails during the startup sequence. The pre-bias level of
the output voltage must be less than the input UVLO set point.
This will prevent the output pre-bias from enabling the regulator through the high side MOSFET body diode.
ZERO COIL CURRENT DETECTION
The current of the lower (synchronous) MOSFET is monitored
by a zero coil current detection circuit which inhibits the syn-
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18
LMZ14202H
Physical Dimensions inches (millimeters) unless otherwise noted
7-Lead TZA Package
NS Package Number TZA07A
19
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LMZ14202H 2A SIMPLE SWITCHER® Power Module for High Output Voltage
Notes
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