NSC LMZ10500

LMZ10500
650mA SIMPLE SWITCHER® Nano Module with 5.5V
Maximum Input Voltage
8 Pin LLP-Footprint Package
System Performance
(Quick Overview Links: VOUT = 1.2V, 1.8V, 2.5V, 3.3V)
Typical Efficiency at VIN = 3.6V
100
90
SE08A 8 Pin Package
3.0 x 2.5 x 1.2 mm (0.118 x 0.098 x 0.047 in)
RoHS Compliant
Electrical Specifications
■
■
■
■
EFFICIENCY (%)
30161631
Up to 650mA output current
Input voltage range 2.7V to 5.5V
Output voltage range 0.6V to 3.6V
Efficiency up to 95%
80
70
60
50
VOUT = 1.2V
VOUT = 1.8V
VOUT = 2.5V
VOUT = 3.3V
40
30
20
0.0
Key Features
0.2 0.3 0.4 0.5
LOAD CURRENT (A)
0.6
0.7
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Integrated inductor
Miniature form factor (3.0 mm x 2.5 mm x 1.2 mm)
8-pin LLP footprint
-40°C to 125°C junction temperature range
Adjustable output voltage
2.0MHz fixed PWM switching frequency
Integrated compensation
Soft start function
Current limit protection
Thermal shutdown protection
Input voltage UVLO for power-up, power-down, and
brown-out conditions
■ Only 5 external components — resistor divider and 3
ceramic capacitors
Applications
■ Point of load conversions from 3.3V and 5V rails
■ Space constrained applications
■ Low output noise applications
Performance Benefits
Small solution size
Low output voltage ripple
Easy component selection and simple PCB layout
High efficiency reduces system heat generation
Output Voltage Ripple
VIN = 5.0V, VOUT = 1.8V, IOUT = 650mA
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Radiated EMI (CISPR22)
VIN = 5.0V, VOUT = 1.8V, IOUT = 650mA
80
RADIATED EMISSIONS (dBμV/m)
■
■
■
■
■
■
■
■
■
■
■
■
■
■
■
0.1
Emissions
CISPR 22 Class B Limit
CISPR 22 Class A Limit
70
60
50
40
30
20
10
0
0
200
400
600
800
FREQUENCY (MHz)
1000
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© 2011 National Semiconductor Corporation
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650mA SIMPLE SWITCHER® Nano Module with 5.5V Maximum Input Voltage
October 5, 2011
LMZ10500
Connection Diagram
30161620
NS Package Number SE08A
Order Information
Order Number
Package Marking (Note)
Supplied As
LMZ10500SEE
XVS SX
250 units, Tape-and-Reel
LMZ10500SE
XVS SX
1000 units, Tape-and-Reel
LMZ10500SEX
XVS SX
3000 units, Tape-and-Reel
Note: The actual physical placement of the package marking will vary from part to part. The package marking “X” designates the date code. “V” is a NSC internal
code for die traceability. Both will vary in production. “S” designates device type as switcher and “SX” identifies the device (part number).
Pin Descriptions
Pin #
Name
1
EN
Enable Input. Set this digital input higher than 1.2V for normal operation. For shutdown, set low. Pin is
internally pulled up to VIN and can be left floating for always-on operation.
Description
2
VCON
Output voltage control pin. Connect to analog voltage from resisitve divider or DAC/controller to set the
VOUT voltage. VOUT = 2.5 x VCON. Connect a small (470pF) capacitor from this pin to SGND to provide
noise filtering.
3
FB
4
SGND
Ground for analog and control circuitry. Connect to PGND at a single point.
5
VOUT
Output Voltage. Connected to one terminal of the integrated inductor. Connect output filter capacitor
between VOUT and PGND.
6
PGND
Power ground for the power MOSFETs and gate-drive circuitry.
7
VIN
8
VREF
PAD
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Feedback of the error amplifier. Connect directly to output capacitor to sense VOUT.
Voltage supply input. Connect ceramic capacitor between VIN and PGND as close as possible to these
two pins. Typical capacitor values are between 4.7µF and 22µF.
2.35V voltage reference output. Typically connected to VCON pin through a resistive divider to set the
output voltage.
The 3 pads underneath the module are not internally connected to any node. These pads should be
connected to the ground plane for improved thermal performance.
2
Operating Ratings
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Input Voltage Range
Recommended Load Current
Junction Temperature (TJ) Range
VIN, VREF to SGND
PGND to SGND
EN, FB, VCON
VOUT
Junction Temperature (TJ-MAX)
Storage Temperature Range
Maximum Lead Temperature
ESD Susceptibility(Note 2)
−0.2V to +6.0V
−0.2V to +0.2V
(SGND −0.2V)
to (VIN +0.2V)
w/6.0V max
(PGND −0.2V)
to (VIN +0.2V)
w/6.0V max
+150°C
−65°C to +150°C
+260°C
±2kV
(Note 1)
2.7V to 5.5V
0 mA to 650mA
−40°C to +125°C
Thermal Properties
Junction-to-Ambient Thermal
120°C/W
Resistance (θJA), SE08A Package
(Note 3)
Electrical Characteristics
(Note 4) Specifications with standard typeface are for TJ = 25°C only; Limits in bold
face type apply over the operating junction temperature range TJ 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 = 3.6V, VEN = 1.2V.
Symbol
Parameter
Conditions
Min
Typ
(Note 4) (Note 5)
Max
(Note 4)
Units
SYSTEM PARAMETERS
VREF x GAIN
Reference voltage x VCON to VIN = VEN = 5.5V, VCON = 1.44V
FB Gain
5.7575
5.875
5.9925
V
GAIN
VCON to FB Gain
2.4375
2.5
2.5750
V/V
VINUVLO
VIN rising threshold
2.4
V
VINUVLO
VIN falling theshold
2.25
V
ISHDN
Shutdown supply current
VIN = 3.6V, VEN = 0.5V
(Note 6)
11
18
µA
Iq
DC bias current into VIN
VIN = 5.5V, VCON = 1.6V, IOUT = 0A
6.5
8.5
mA
RDROPOUT
VIN to VOUTresistance
IOUT = 200 mA
285
425
mΩ
I LIM
DC Output Current Limit
VCON = 0.24V
(Note 7)
FOSC
VIN = 5.5V, VCON = 1.44V
800
1000
mA
Internal oscillator frequency
1.75
2.0
VIH,ENABLE
Enable logic HIGH voltage
1.2
VIL,ENABLE
Enable logic LOW voltage
TSD
Thermal shutdown
150
°C
TSD-HYST
Thermal shutdown hysteresis
20
°C
DMAX
Maximum duty cycle
100
%
TON-MIN
Minimum on-time
50
ns
θJA
Package Thermal Resistance 20mm x 20mm board
2 layers, 2 oz copper, 0.5W, no
airlow
118
15mm x 15mm board
2 layers, 2 oz copper, 0.5W, no
airlow
132
10mm x 10mm board
2 layers, 2 oz copper, 0.5W, no
airlow
157
2.25
V
0.5
Rising Threshold
3
MHz
V
°C/W
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LMZ10500
Absolute Maximum Ratings (Note 1)
LMZ10500
System Characteristics
The following specifications are guaranteed by design providing the component values
in the Typical Application Circuit are used (CIN = COUT = 10 µF, 6.3V, 0603, TDK C1608X5R0J106K). These parameters are not
guaranteed by production testing. Unless otherwise stated the following conditions apply: TA = 25°C.
Symbol
Parameter
Conditions
ΔVOUT/VOUT Output Voltage Regulation Over VOUT = 0.6V
Line Voltage and Load Current ΔVIN =2.7V to 4.2V
Min
Typ
Max
Units
±1.23
%
±0.56
%
±0.24
%
EN = Low to High, VIN = 4.2V
VOUT = 2.7V, IOUT = 650 mA
10
µs
VIN = 5.0V, VOUT = 3.3V
IOUT = 200 mA
95
VIN = 5.0V, VOUT = 3.6V
IOUT = 650 mA
93
VIN = 5.0V, VOUT = 1.8V
IOUT = 650 mA (Note 8)
8
mV pk-pk
Line transient response
VIN = 2.7V to 5.5V,
TR = TF= 10 µs,
VOUT = 1.8V, IOUT = 650 mA
25
mV pk-pk
Load transient response
VIN = 5.0V
TR = TF = 40 µs,
VOUT = 1.8V
IOUT = 65mA to 650mA
25
mV pk-pk
ΔIOUT = 0A to 650mA
ΔVOUT/VOUT Output Voltage Regulation Over VOUT = 1.5V
Line Voltage and Load Current ΔVIN = 2.7V to 5.5V
ΔIOUT = 0A to 650mA
ΔVOUT/VOUT Output Voltage Regulation Over VOUT = 3.6V
Line Voltage and Load Current ΔVIN = 4.0V to 5.5V
ΔIOUT = 0A to 650 mA
VREF TRISE Rise time of reference voltage
Peak Efficiency
η
Full Load Efficiency
VOUT Ripple Output voltage ripple
Line
Transient
Load
Transient
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4
%
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: Junction-to-ambient thermal resistance (θJA) is based on 4 layer board thermal measurements, performed under the conditions and guidelines set forth
in the JEDEC standards JESD51-1 to JESD51-11. θJA varies with PCB copper area, power dissipation, and airflow.
Note 4: 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 5: Typical numbers are at 25°C and represent the most likely parametric norm.
Note 6: Shutdown current includes leakage current of the high side PFET.
Note 7: Current limit is built-in, fixed, and not adjustable.
Note 8: Ripple voltage should be measured across COUT on a well-designed PC board using the suggested capacitors.
5
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LMZ10500
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.
Unless otherwise specified the following conditions apply: VIN = 3.6V, TA = 25°C
Thermal Derating VOUT = 1.2V, θJA = 120°C/W
Dropout Voltage vs Load Current and Input Voltage
0.7
VIN = 2.7V
VIN = 3.3V
VIN = 3.6V
VIN = 4.0V
0.30
0.25
0.6
OUTPUT CURRENT (A)
DROPOUT VOLTAGE (V)
0.35
0.20
0.15
0.10
0.05
0.0
0.5
0.4
0.3
VIN = 3.3V
VIN = 3.6V
VIN = 5.0V
VIN = 5.5V
0.2
0.1
0.00
0.0
0.1
0.2 0.3 0.4 0.5
LOAD CURRENT (A)
0.6
0.7
60
70 80 90 100 110 120 130
AMBIENT TEMPERATURE (°C)
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Thermal Derating VOUT = 1.8V, θJA = 120°C/W
Thermal Derating VOUT = 2.5V, θJA = 120°C/W
0.7
0.7
0.6
0.6
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
LMZ10500
Typical Performance Characteristics
0.5
0.4
0.3
VIN = 3.3V
VIN = 3.6V
VIN = 5.0V
VIN = 5.5V
0.2
0.1
0.4
0.3
VIN = 3.3V
VIN = 3.6V
VIN = 5.0V
VIN = 5.5V
0.2
0.1
0.0
0.0
60
70 80 90 100 110 120 130
AMBIENT TEMPERATURE (°C)
60
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0.5
70 80 90 100 110 120 130
AMBIENT TEMPERATURE (°C)
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6
Radiated EMI (CISPR22)
VIN = 5.0V, VOUT = 1.8V, IOUT = 650mA
Default evaluation board BOM
0.7
80
RADIATED EMISSIONS (dBμV/m)
OUTPUT CURRENT (A)
0.6
0.5
0.4
0.3
VIN = 4.0V
VIN = 4.5V
VIN = 5.0V
VIN = 5.5V
0.2
0.1
0.0
60
LMZ10500
Thermal Derating VOUT = 3.3V, θJA = 120°C/W
70 80 90 100 110 120 130
AMBIENT TEMPERATURE (°C)
Emissions
CISPR 22 Class B Limit
CISPR 22 Class A Limit
70
60
50
40
30
20
10
0
0
30161641
200
400
600
800
FREQUENCY (MHz)
1000
30161632
Conducted EMI
VIN = 5.0V, VOUT = 1.8V, IOUT = 650mA
Default evaluation board BOM with additional 1µH 1µF LC
input filter
CONDUCTED EMISSIONS (dBμV)
80
70
Startup
Conducted Emissions
CISPR 22 Quasi Peak
CISPR 22 Average
60
50
40
30
20
10
30161634
0
100m
1
10
FREQUENCY (MHz)
100
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Schematic VOUT = 1.2V
Efficiency VOUT = 1.2V
100
EFFICIENCY (%)
90
80
70
60
50
VIN = 2.7V
VIN = 3.3V
VIN = 3.6V
VIN = 5.0V
VIN = 5.5V
40
30
20
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0.0
0.1
0.2 0.3 0.4 0.5
LOAD CURRENT (A)
0.6
0.7
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Output Ripple VOUT = 1.2V
Load Transient VOUT = 1.2V
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Line and Load Regulation VOUT = 1.2V
DC Current Limit VOUT = 1.2V
1.1
DC CURRENT LIMIT (A)
1.24
OUTPUT VOLTAGE (V)
LMZ10500
1.2V
1.23
1.22
VIN = 2.7V
VIN = 3.3V
VIN = 3.6V
VIN = 5.0V
VIN = 5.5V
1.21
1.20
0.0
0.1
0.2 0.3 0.4 0.5
LOAD CURRENT (A)
0.6
0.9
TA = 85°C
0.8
0.7
0.6
0.7
2.5
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1.0
3.0
3.5
4.0
4.5
5.0
INPUT VOLTAGE (V)
5.5
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8
LMZ10500
1.8V
Schematic VOUT = 1.8V
Efficiency VOUT = 1.8V
100
EFFICIENCY (%)
90
80
70
60
50
VIN = 2.7V
VIN = 3.3V
VIN = 3.6V
VIN = 5.0V
VIN = 5.5V
40
30
20
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0.0
0.1
0.2 0.3 0.4 0.5
LOAD CURRENT (A)
0.6
0.7
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Output Ripple VOUT = 1.8V
Load Transient VOUT = 1.8V
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Line and Load Regulation VOUT = 1.8V
DC Current Limit VOUT = 1.8V
1.3
DC CURRENT LIMIT (A)
OUTPUT VOLTAGE (V)
1.81
1.80
1.79
VIN = 2.7V
VIN = 3.3V
VIN = 3.6V
VIN = 5.0V
VIN = 5.5V
1.78
1.77
0.0
0.1
0.2 0.3 0.4 0.5
LOAD CURRENT (A)
0.6
1.2
1.1
1.0
0.9
0.7
2.5
0.7
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TA = 85°C
0.8
3.0
3.5
4.0
4.5
5.0
INPUT VOLTAGE (V)
5.5
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Schematic VOUT = 2.5V
Efficiency VOUT = 2.5V
100
EFFICIENCY (%)
90
80
70
60
50
VIN = 3.3V
VIN = 3.6V
VIN = 5.0V
VIN = 5.5V
40
30
20
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0.0
0.1
0.2 0.3 0.4 0.5
LOAD CURRENT (A)
0.6
0.7
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Output Ripple VOUT = 2.5V
Load Transient VOUT = 2.5V
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Line and Load Regulation VOUT = 2.5V
DC Current Limit VOUT = 2.5V
1.3
DC CURRENT LIMIT (A)
2.53
OUTPUT VOLTAGE (V)
LMZ10500
2.5V
2.52
2.51
2.50
VIN = 3.3V
VIN = 3.6V
VIN = 5.0V
VIN = 5.5V
2.50
0.0
0.1
0.2 0.3 0.4 0.5
LOAD CURRENT (A)
0.6
1.1
1.0
0.9
TA = 85°C
0.8
0.7
2.5
0.7
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1.2
3.0
3.5
4.0
4.5
5.0
INPUT VOLTAGE (V)
5.5
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10
LMZ10500
3.3V
Schematic VOUT = 3.3V
Efficiency VOUT = 3.3V
100
EFFICIENCY (%)
90
80
70
60
50
VIN = 3.6V
VIN = 4.0V
VIN = 4.5V
VIN = 5.0V
VIN = 5.5V
40
30
20
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0.0
0.1
0.2 0.3 0.4 0.5
LOAD CURRENT (A)
0.6
0.7
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Output Ripple VOUT = 3.3V
Load Transient VOUT = 3.3V
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Line and Load Regulation VOUT = 3.3V
DC Current Limit VOUT = 3.3V
1.1
DC CURRENT LIMIT (A)
OUTPUT VOLTAGE (V)
3.30
3.28
3.26
VIN = 3.6V
VIN = 4.0V
VIN = 4.5V
VIN = 5.0V
VIN = 5.5V
3.24
3.22
0.0
0.1
0.2 0.3 0.4 0.5
LOAD CURRENT (A)
0.6
1.0
0.9
TA = 85°C
0.8
0.7
0.6
0.7
2.5
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3.0
3.5
4.0
4.5
5.0
INPUT VOLTAGE (V)
5.5
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LMZ10500
Block Diagram
30161604
FIGURE 1. Functional Block Diagram
The LMZ10500 SIMPLE SWITCHER® nano module is an
easy-to-use step-down DC-DC solution capable of driving up
to 650mA load in space-constrained applications. Only an input capacitor, an output capacitor, a small VCON filter capacitor, and two resistors are required for basic operation. The
nano module comes in 8-pin LLP footprint package with an
integrated inductor. The LMZ10500 operates in fixed 2.0MHz
PWM (Pulse Width Modulation) mode, and is designed to deliver power at maximum efficiency. The output voltage is
typically set by using a resistive divider between the built-in
reference voltage VREF and the control pin VCON. The VCON
pin is the positive input to the error amplifier. The output voltage of the LMZ10500 can also be dynamically adjusted between 0.6V and 3.6V by driving the VCON pin externally.
Internal current limit based softstart function, current overload
protection, and thermal shutdown are also provided.
to the average of the duty-cycle modulated rectangular signal.
In PWM mode, the switching frequency is constant. The energy per cycle to the load is controlled by modulating the
PFET on-time, which controls the peak inductor current. In
current mode control architecture, the inductor current is compared with the slope compensated output of the error amplifier. At the rising edge of the clock, the PFET is turned ON,
ramping up the inductor current with a slope of (VIN - VOUT)/
L. The PFET is ON until the current signal equals the error
signal. Then the PFET is turned OFF and NFET is turned ON,
ramping down the inductor current with a slope of VOUT /L. At
the next rising edge of the clock, the cycle repeats. An increase of load pulls the output voltage down, resulting in an
increase of the error signal. As the error signal goes up, the
peak inductor current is increased, elevating the average inductor current and responding to the heavier load. To ensure
stability, a slope compensation ramp is subtracted from the
error signal and internal loop compensation is provided.
CIRCUIT OPERATION
The LMZ10500 is a synchronous Buck power module using
a PFET for the high side switch and an NFET for the synchronous rectifier switch. The output voltage is regulated by
modulating the PFET switch on-time. The circuit generates a
duty-cycle modulated rectangular signal. The rectangular signal is averaged using a low pass filter formed by the integrated
inductor and an output capacitor. The output voltage is equal
INPUT UNDER VOLTAGE DETECTION
The LMZ10500 implements an under voltage lock out (UVLO)
circuit to ensure proper operation during startup, shutdown
and input supply brownout conditions. The circuit monitors the
voltage at the VIN pin to ensure that sufficient voltage is
present to bias the regulator. If the under voltage threshold is
not met, all functions of the controller are disabled and the
controller remains in a low power standby state.
Overview
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12
LMZ10500
SHUTDOWN MODE
To shutdown the LMZ10500, pull the EN pin low (<0.5V). In
the shutdown mode all internal circuits are turned OFF.
EN PIN OPERATION
The EN pin is internally pulled up to VIN through a 790kΩ
(typ.) resistor. This allows the nano module to be enabled by
default when the EN pin is left floating. In such cases VIN will
set EN high when VIN reaches 1.2V. As the input voltage continues to rise, operation will start once VIN exceeds the undervoltage lockout (UVLO) threshold. To set EN high externally,
pull it up to 1.2V or higher. Note that the voltage on EN must
remain at less than VIN+ 0.2V due to absolute maximum ratings of the device.
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INTERNAL SYNCHRONOUS RECTIFICATION
The LMZ10500 uses an internal NFET as a synchronous rectifier to minimize the switch voltage drop and increase efficiency. The NFET is designed to conduct through its intrinsic
body diode during the built-in dead time between the PFET
on-time and the NFET on-time. This eliminates the need for
an external diode. The dead time between the PFET and
NFET connection prevents shoot through current from VIN to
PGND during the switching transitions.
FIGURE 2. Startup behavior of current limit based
softstart.
The soft start rate is also limited by the VCON ramp up rate.
The VCON pin is discharged internally through a pull down device before startup occurs. This is done to deplete any residual charge on the VCON filter capacitor and allow the VCON
voltage to ramp up from 0V when the part is started. The
events that cause VCON discharge are thermal shutdown, UVLO, EN low, or output short circuit detection. The minimum
recommended capacitance on VCON is 220pF and the maximum is 1nF. The duration of startup current limiting sequence
takes approximately 75µs. After the sequence is completed,
the feedback voltage is monitored for output short circuit
events.
CURRENT LIMIT
The LMZ10500 current limit feature protects the module during an overload condition. The circuit employs positive peak
current limit in the PFET and negative peak current limit in the
NFET switch. The positive peak current through the PFET is
limited to 1.2A (typ.). When the current reaches this limit
threshold the PFET switch is immediately turned off until the
next switching cycle. This behavior continues on a cycle-bycycle basis until the overload condition is removed from the
output. The typical negative peak current limit through the
NFET switch is -0.6A (typ.).
The ripple of the inductor current depends on the input and
output voltages. This means that the DC level of the output
current when the peak current limiting occurs will also vary
over the line voltage and the output voltage level. Refer to the
DC Output Current Limit plots in the Typical Performance
Characteristics section for more information.
OUTPUT SHORT CIRCUIT PROTECTION
In addition to cycle by cycle current limit, the LMZ10500 features a second level of short circuit protection. If the load pulls
the output voltage down and the feedback voltage falls to
0.375V, the output short circuit protection will engage. In this
mode the internal PFET switch is turned OFF after the current
limit comparator trips and the beginning of the next cycle is
inhibited for approximately 230µs. This forces the inductor
current to ramp down and limits excessive current draw from
the input supply when the output of the regulator is shorted.
The synchronous rectifier is always OFF in this mode. After
230µs of non-switching a new startup sequence is initiated.
During this new startup sequence the current limit is gradually
stepped up to the nominal value as illustrated in the STARTUP BEHAVIOR AND SOFTSTART section. After the startup
sequence is completed again, the feedback voltage is monitored for output short circuit. If the short circuit is still persistent
after the new startup sequence, switching will be stopped
again and there will be another 230µs off period. A persistent
output short condition results in a hiccup behavior where the
LMZ10500 goes through the normal startup sequence, then
detects the output short at the end of startup, terminates
switching for 230µs, and repeats this cycle until the output
short is released. This behavior is illustrated in the following
figure.
STARTUP BEHAVIOR AND SOFTSTART
The LMZ10500 features a current limit based soft start circuit
in order to prevent large in-rush current and output overshoot
as VOUT is ramping up. This is achieved by gradually increasing the PFET current limit threshold to the final operating
value as the output voltage ramps during startup. The maximum allowed current in the inductor is stepped up in a staircase profile for a fixed number of switching periods in each
step. Additionally, the switching frequency in the first step is
set at 450kHz and is then increased for each of the following
steps until it reaches 2MHz at the final step of current limiting.
This current limiting behavior is illustrated in the following figure and allows for a smooth VOUT ramp up.
13
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LMZ10500
regulation. If VIN is lowered even more, the off-time of the
PFET will reach the 35ns mark again. The LMZ10500 will then
reduce the frequency again, achieving less than 100% duty
cycle operation and maintaining regulation. As VIN is lowered
even more, the LMZ10500 will continue to scale down the
frequency, aiming to maintain at least 35ns off time. Eventually, as the input voltage decreases further, 100% duty cycle
is reached. This behavior of extending the VIN regulation
range is illustrated in the following plot.
30161645
FIGURE 3. Hiccup behavior with persistent output short
circuit.
Since the output current is limited during normal startup by
the softstart function, the current charging the output capacitor is also limited. This results in a smooth VOUT ramp up to
nominal voltage. However, using excessively large output capacitance or VCON capacitance under normal conditions can
prevent the output voltage from reaching 0.375V at the end
of the startup sequence. In such cases the module will maintain the described above hiccup mode and the output voltage
will not ramp up to final value. To cause this condition, one
would have to use unnecessarily large output capacitance for
650mA load applications. See the INPUT AND OUTPUT CAPACITOR SELECTION section for guidance on maximum
capacitances for different output voltage settings.
30161660
FIGURE 4. High duty cycle operation and switching
frequency reduction.
THERMAL OVERLOAD PROTECTION
The junction temperature of the LMZ10500 should not be allowed to exceed its maximum operating rating of 125°C.
Thermal protection is implemented by an internal thermal
shutdown circuit which activates at 150°C (typ). When this
temperature is reached, the device enters a low power standby state. In this state switching remains off causing the output
voltage to fall. Also, the VCON capacitor is discharged to
SGND. When the junction temperature falls back below 130
°C (typ) normal startup occurs and VOUT rises smoothly from
0V. Applications requiring maximum output current may require derating at elevated ambient temperature. See the Typical Performance Characteristics section for thermal derating
plots for various output voltages.
HIGH DUTY CYCLE OPERATION
The LMZ10500 features a transition mode designed to extend
the output regulation range to the minimum possible input
voltage. As the input voltage decreases closer and closer to
VOUT, the off-time of the PFET gets smaller and smaller and
the duty cycle eventually needs to reach 100% to support the
output voltage. The input voltage at which the duty cycle
reaches 100% is the edge of regulation. When the LMZ10500
input voltage is lowered, such that the off-time of the PFET
reduces to less than 35ns, the LMZ10500 doubles the switching period to extend the off-time for that VIN and maintain
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14
LMZ10500
Application Information
30161636
FIGURE 5. Typical Application Circuit
trimmed so that this product is as close to the ideal 5.875V
value as possible, achieving high VOUT accuracy. See the
Electrical Specifications section for the VREF x GAIN product
tolerance limits.
SETTING THE OUTPUT VOLTAGE
The LMZ10500 provides a fixed 2.35V VREF voltage output.
As shown in Figure 5 above, a resistive divider formed by
RT and RB sets the VCON pin voltage level. The VOUT voltage
tracks VCON and is governed by the following relationship:
VOUT = GAIN x VCON
DYNAMIC OUTPUT VOLTAGE SCALING
The VCON pin on the LMZ10500 can be driven externally by a
DAC to scale the output voltage dynamically. The output voltage VOUT = 2.5V/V x VCON. When driving VCON with a source
different than VREF place a 1.5kΩ resistor in series with the
VCON pin. Current limiting the external VCON helps to protect
this pin and allows the VCON capacitor to be fully discharged
to 0V after fault conditions.
(1)
where GAIN is 2.5V/V from VCON to VFB.
This equation is valid for output voltages between 0.6V and
3.6V and corresponds to VCON voltage between 0.24V and
1.44V, respectively.
RT and RB Selection for Fixed VOUT
The parameters affecting the output voltage setting are the
RT, RB, and the product of the VREF voltage x GAIN. The
VREF voltage is typically 2.35V. Since VCON is derived from
VREF via RT and RB,
VCON = VREF x RB/ (RB + RT)
INTEGRATED INDUCTOR
The LMZ10500 uses a Low Temperature Co-fired Ceramic
(LTCC) type 2.6 µH inductor with over 1.2A DC current rating
and soft saturation profile for up to 2A. This inductor allows
for the 1.2mm overall package height providing an easy to
use, compact solution with reduced EMI.
(2)
After substitution,
VOUT = VREF x GAIN x RB/ (RB + RT)
(3)
RT = ( GAIN x VREF / VOUT – 1 ) x RB
(4)
INPUT AND OUTPUT CAPACITOR SELECTION
The LMZ10500 is designed for use with low ESR multi-layer
ceramic capacitors (MLCC) for its input and output filters. Using a 10 µF 0603 or 0805 with 6.3V or 10V rating ceramic input
capacitor typically provides sufficient VIN bypass. Use of multiple 4.7 µF or 2.2µF capacitors can also be considered.
Ceramic capacitors with X5R and X7R temperature characteristics are recommended for both input and output filters.
These provide an optimal balance between small size, cost,
reliability, and performance for space sensitive applications.
The DC voltage bias characteristics of the capacitors must be
considered when selecting the DC voltage rating and case
size of these components. The effective capacitance of an
MLCC is typically reduced by the DC voltage bias applied
across its terminals. For example, a typical 0805 case size
X5R 6.3V 10 µF ceramic capacitor may only have 4.8 µF left
in it when a 5.0V DC bias is applied. Similarly, a typical 0603
case size X5R 6.3V 10 µF ceramic capacitor may only have
2.4 µF at the same 5.0V DC. Smaller case size capacitors
may have even larger percentage drop in value with DC bias.
The optimum output capacitance value is application dependent. Too small output capacitance can lead to instability due
to lower loop phase margin. On the other hand, if the output
The ideal product of GAIN x VREF = 5.875V.
Choose RT to be between 80kΩ and 300kΩ. Then, RB can be
calculated using equation (5) below.
RB = ( VOUT / (5.875V – VOUT) ) x RT
(5)
Note that the resistance of RT should be ≥ 80kΩ. This ensures
that the VREF output current loading is not exceeded and the
reference voltage is maintained. The current loading on
VREF should not be greater than 30 µA.
OUTPUT VOLTAGE ACCURACY OPTIMIZATION
Each nano module is optimized to achieve high VOUT accuracy. Equation (1) shows that, by design, the output voltage
is a function of the VCON voltage and the gain from VCON to
VFB. The voltage at VCON is derived from VREF. Therefore, as
shown in equation (3), the accuracy of the output voltage is a
function of the VREF x GAIN product as well as the tolerance
of the RT and RB resistors. The typical VREF x GAIN product
by design is 5.875V. Each nano module's VREF voltage is
15
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LMZ10500
capacitor is too large, it may prevent the output voltage from
reaching the 0.375V required voltage level at the end of the
startup sequence. In such cases, the output short circuit protection can be engaged and the nano module will enter a
hiccup mode as described in the OUTPUT SHORT CIRCUIT
PROTECTION section. The table below sets the minimum
output capacitance for stability and maximum output capacitance for proper startup for various output voltage settings.
Note that the maximum COUT value in Table 1 assumes that
the filter capacitance on VCON is the maximum recommended
value of 1nF and the RT resistor value is less than 300kΩ.
Lower VCON capacitance can extend the maximum COUT
range. There is no great performance benefit in using excessive COUT values.
Use of multiple 4.7 µF or 2.2µF output capacitors can be considered for reduced effective ESR and smaller output voltage
ripple. In addition to the main output capacitor, small 0.1µF –
0.01µF parallel capacitors can be used to reduce high frequency noise.
PACKAGE CONSIDERATIONS
The nano module package includes an LTCC inductor on the
bottom and a micro SMD die mounted on top. The die has
exposed edges and can be sensitive to ambient light. For applications with direct high intensity ambient red, infrared, LED,
or natural light it is recommended to have the device shielded
from the light source to avoid abnormal behavior.
TABLE 1. Output Capacitance Range
Output
Voltage
Minimum
COUT
Suggested
COUT
Maximum
COUT
0.6V
4.7µF
10µF
33µF
1.0V
3.3µF
10µF
33µF
1.2V
3.3µF
10µF
33µF
1.8V
3.3µF
10µF
47µF
2.5V
3.3µF
10µF
68µF
3.3V
3.3µF
10µF
68µF
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16
LMZ10500
Board Layout Considerations
30161648
FIGURE 6. Example Top Layer Board Layout
The board layout of any DC-DC switching converter is critical
for the optimal performance of the design. Bad PCB layout
design can disrupt the operation of an otherwise good
schematic design. Even if the regulator still converts the voltage properly, the board layout can mean the difference between passing or failing EMI regulations. In a Buck converter,
the most critical board layout path is between the input capacitor ground terminal and the synchronous rectifier ground.
The loop formed by the input capacitor and the power FETs
is a path for the high di/dt switching current during each
switching period. This loop should always be kept as short as
possible when laying out a board for any Buck converter.
The LMZ10500 integrates the inductor and simplifies the DCDC converter board layout. Refer to the example layout in
Figure 6. There are a few basic requirements to achieve a
good LMZ10500 layout.
1. Place the input capacitor CIN as close as possible to
the VIN and PGND terminals. VIN (pin 7) and PGND (pin 6)
on the LMZ10500 are next to each other which makes the
input capacitor placement simple.
2. Place the VCON filter capacitor CVC and the RB RT resistive divider as close as possible to the VCON and SGND
terminals.The CVC capacitor (not RB) should be the component closer to the VCON pin, as shown in Figure 6. This allows
for better bypass of the control voltage set at VCON.
3. Run the feedback trace (from VOUT to FB) away from
noise sources.
4. Connect SGND to a quiet GND plane.
5. Provide enough PCB area for proper heatsinking. Refer
to the Electrical Characteristics table for example θJA values
for different board areas. Also, refer to AN-2020 for additional
thermal design hints.
Refer to the evaluation board application note (AN-2166) for
a complete board layout example.
17
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LMZ10500
Physical Dimensions inches (millimeters) unless otherwise noted
NS Package Number SE08A
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18
LMZ10500
Notes
19
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650mA SIMPLE SWITCHER® Nano Module with 5.5V Maximum Input Voltage
Notes
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