LMZ10501EVAL/NOPB - NATIONAL SEMICONDUCTOR

LMZ10501

LMZ10501 1A SIMPLE SWITCHER® Nano Module with 5.5V Maximum Input Voltage

Literature Number: SNVS677B

LMZ10501

October 5, 2011

1A SIMPLE SWITCHER® Nano Module with 5.5V Maximum

Input Voltage

8 Pin LLP-Footprint Package

30124731

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

■Up to 1A output current

■Input voltage range 2.7V to 5.5V

■Output voltage range 0.6V to 3.6V

■Efficiency up to 95%

Key Features

■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

System Performance

(Quick Overview Links: VOUT = 1.2V, 1.8V, 2.5V, 3.3V)

Typical Efficiency at VIN = 3.6V

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

100

EFFICIENCY (%)

LOAD CURRENT (A)

VOUT = 1.2V

VOUT = 1.8V

VOUT = 2.5V

VOUT = 3.3V

30124730

Output Voltage Ripple

VIN = 5.0V, VOUT = 1.8V, IOUT = 1A

30124733

Radiated EMI (CISPR22)

VIN = 5.0V, VOUT = 1.8V, IOUT = 1A

0 200 400 600 800 1000

RADIATED EMISSIONS (dBμV/m)

FREQUENCY (MHz)

Emissions (Evaluation Board)

EN 55022 Class B Limit

EN 55022 Class A Limit

30124732

1A SIMPLE SWITCHER® Nano Module with 5.5V Maximum Input Voltage

Connection Diagram

30124720

NS Package Number SE08A

Order Information

Order Number Package Marking (Note) Supplied As

LMZ10501SEE XVS SP 250 units, Tape-and-Reel

LMZ10501SE XVS SP 1000 units, Tape-and-Reel

LMZ10501SEX XVS SP 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 “SP” identifies the device (part number).

Pin Descriptions

Pin # Name Description

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.

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 Feedback of the error amplifier. Connect directly to output capacitor to sense VOUT.

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 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.

8 VREF 2.35V voltage reference output. Typically connected to VCON pin through a resistive divider to set the

output voltage.

PAD 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.

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LMZ10501

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, VREF to SGND −0.2V to +6.0V

PGND to SGND −0.2V to +0.2V

EN, FB, VCON (SGND −0.2V)

to (VIN +0.2V)

w/6.0V max

VOUT (PGND −0.2V)

to (VIN +0.2V)

w/6.0V max

Junction Temperature (TJ-MAX) +150°C

Storage Temperature Range −65°C to +150°C

Maximum Lead Temperature +260°C

ESD Susceptibility(Note 2) ±2kV

Operating Ratings (Note 1)

Input Voltage Range 2.7V to 5.5V

Recommended Load Current 0 mA to 1000 mA

Junction Temperature (TJ) Range −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

(Note 4)

Typ

(Note 5)

Max

(Note 4)Units

SYSTEM PARAMETERS

VREF x GAIN Reference voltage x VCON to

FB Gain

VIN = VEN = 5.5V, VCON = 1.44V 5.7575 5.875 5.9925 V

GAIN VCON to FB Gain VIN = 5.5V, VCON = 1.44V 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

IqDC 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)1125 1350 mA

FOSC Internal oscillator frequency 1.75 2.0 2.25 MHz

VIH,ENABLE Enable logic HIGH voltage 1.2 V

VIL,ENABLE Enable logic LOW voltage 0.5 V

TSD Thermal shutdown Rising Threshold 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

°C/W

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

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LMZ10501

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 Min Typ Max Units

ΔVOUT/VOUT Output Voltage Regulation Over

Line Voltage and Load Current

VOUT = 0.6V

ΔVIN =2.7V to 4.2V

ΔIOUT = 0A to 1A

±1.75 %

ΔVOUT/VOUT Output Voltage Regulation Over

Line Voltage and Load Current

VOUT = 1.5V

ΔVIN = 2.7V to 5.5V

ΔIOUT = 0A to 1A

±0.92 %

ΔVOUT/VOUT Output Voltage Regulation Over

Line Voltage and Load Current

VOUT = 3.6V

ΔVIN = 4.0V to 5.5V

ΔIOUT = 0A to 1A

±0.38 %

VREF TRISE Rise time of reference voltage EN = Low to High, VIN = 4.2V

VOUT = 2.7V, IOUT = 1A 10 µs

Peak Efficiency VIN = 5.0V, VOUT = 3.3V

IOUT = 200 mA 95

Full Load Efficiency VIN = 5.0V, VOUT = 3.6V

IOUT = 1000 mA 91

VOUT Ripple Output voltage ripple VIN = 5.0V, VOUT = 1.8V

IOUT = 1000 mA (Note 8) 10 mV pk-pk

Line

Transient Line transient response

VIN = 2.7V to 5.5V,

TR = TF= 10 µs,

VOUT = 1.8V, IOUT = 1000mA

30 mV pk-pk

Load

Transient Load transient response

VIN = 5.0V

TR = TF = 40 µs,

VOUT = 1.8V

IOUT = 100mA to 1000 mA

30 mV pk-pk

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LMZ10501

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: 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.

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LMZ10501

Typical Performance Characteristics

Unless otherwise specified the following conditions apply: VIN = 3.6V, TA = 25°C

Dropout Voltage vs Load Current and Input Voltage

0.0 0.2 0.4 0.6 0.8 1.0

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

DROPOUT VOLTAGE (V)

LOAD CURRENT (A)

VIN = 2.7V

VIN = 3.3V

VIN = 3.6V

VIN = 4.0V

30124749

Thermal Derating VOUT = 1.2V, θJA = 120°C/W

60 70 80 90 100 110 120 130

0.0

0.2

0.4

0.6

0.8

1.0

1.2

OUTPUT CURRENT (A)

AMBIENT TEMPERATURE (°C)

VIN = 3.3V

VIN = 3.6V

VIN = 5.0V

VIN = 5.5V

30124744

Thermal Derating VOUT = 1.8V, θJA = 120°C/W

60 70 80 90 100 110 120 130

0.0

0.2

0.4

0.6

0.8

1.0

1.2

OUTPUT CURRENT (A)

AMBIENT TEMPERATURE (°C)

VIN = 3.3V

VIN = 3.6V

VIN = 5.0V

VIN = 5.5V

30124743

Thermal Derating VOUT = 2.5V, θJA = 120°C/W

60 70 80 90 100 110 120 130

0.0

0.2

0.4

0.6

0.8

1.0

1.2

OUTPUT CURRENT (A)

AMBIENT TEMPERATURE (°C)

VIN = 3.3V

VIN = 3.6V

VIN = 5.0V

VIN = 5.5V

30124742

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LMZ10501

Thermal Derating VOUT = 3.3V, θJA = 120°C/W

60 70 80 90 100 110 120 130

0.0

0.2

0.4

0.6

0.8

1.0

1.2

OUTPUT CURRENT (A)

AMBIENT TEMPERATURE (°C)

VIN = 4.0V

VIN = 4.5V

VIN = 5.0V

VIN = 5.5V

30124741

Radiated EMI (CISPR22)

VIN = 5.0V, VOUT = 1.8V, IOUT = 1A

Default evaluation board BOM

0 200 400 600 800 1000

RADIATED EMISSIONS (dBμV/m)

FREQUENCY (MHz)

Emissions (Evaluation Board)

EN 55022 Class B Limit

EN 55022 Class A Limit

30124732

Conducted EMI

VIN = 5.0V, VOUT = 1.8V, IOUT = 1A

Default evaluation board BOM with additional 1µH 1µF LC

input filter

100m 1 10 100

CONDUCTED EMISSIONS (dBμV)

FREQUENCY (MHz)

Conducted Emissions

CISPR 22 Quasi Peak

CISPR 22 Average

30124750

Startup

30124734

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LMZ10501

1.2V

Schematic VOUT = 1.2V

30124722

Efficiency VOUT = 1.2V

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

100

EFFICIENCY (%)

LOAD CURRENT (A)

VIN = 2.7V

VIN = 3.3V

VIN = 3.6V

VIN = 5.0V

VIN = 5.5V

30124727

Output Ripple VOUT = 1.2V

30124755

Load Transient VOUT = 1.2V

30124757

Line and Load Regulation VOUT = 1.2V

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

1.20

1.21

1.22

1.23

1.24

OUTPUT VOLTAGE (V)

LOAD CURRENT (A)

VIN = 2.7V

VIN = 3.3V

VIN = 3.6V

VIN = 5.0V

VIN = 5.5V

30124737

DC Current Limit VOUT = 1.2V

2.5 3.0 3.5 4.0 4.5 5.0 5.5

1.0

1.1

1.2

1.3

1.4

1.5

DC CURRENT LIMIT (A)

INPUT VOLTAGE (V)

TA = 85°C

30124751

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LMZ10501

1.8V

Schematic VOUT = 1.8V

30124723

Efficiency VOUT = 1.8V

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

100

EFFICIENCY (%)

LOAD CURRENT (A)

VIN = 2.7V

VIN = 3.3V

VIN = 3.6V

VIN = 5.0V

VIN = 5.5V

30124726

Output Ripple VOUT = 1.8V

30124733

Load Transient VOUT = 1.8V

30124758

Line and Load Regulation VOUT = 1.8V

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

1.77

1.78

1.79

1.80

1.81

OUTPUT VOLTAGE (V)

LOAD CURRENT (A)

VIN = 2.7V

VIN = 3.3V

VIN = 3.6V

VIN = 5.0V

VIN = 5.5V

30124738

DC Current Limit VOUT = 1.8V

2.5 3.0 3.5 4.0 4.5 5.0 5.5

1.0

1.1

1.2

1.3

1.4

1.5

DC CURRENT LIMIT (A)

INPUT VOLTAGE (V)

TA = 85°C

30124752

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LMZ10501

2.5V

Schematic VOUT = 2.5V

30124724

Efficiency VOUT = 2.5V

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

100

EFFICIENCY (%)

LOAD CURRENT (A)

VIN = 3.3V

VIN = 3.6V

VIN = 5.0V

VIN = 5.5V

30124728

Output Ripple VOUT = 2.5V

30124746

Load Transient VOUT = 2.5V

30124747

Line and Load Regulation VOUT = 2.5V

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

2.50

2.51

2.52

2.53

OUTPUT VOLTAGE (V)

LOAD CURRENT (A)

VIN = 3.3V

VIN = 3.6V

VIN = 5.0V

VIN = 5.5V

30124739

DC Current Limit VOUT = 2.5V

2.5 3.0 3.5 4.0 4.5 5.0 5.5

1.0

1.1

1.2

1.3

1.4

1.5

DC CURRENT LIMIT (A)

INPUT VOLTAGE (V)

TA = 85°C

30124753

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LMZ10501

3.3V

Schematic VOUT = 3.3V

30124725

Efficiency VOUT = 3.3V

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

100

EFFICIENCY (%)

LOAD CURRENT (A)

VIN = 3.6V

VIN = 4.0V

VIN = 4.5V

VIN = 5.0V

VIN = 5.5V

30124729

Output Ripple VOUT = 3.3V

30124756

Load Transient VOUT = 3.3V

30124759

Line and Load Regulation VOUT = 3.3V

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

3.22

3.24

3.26

3.28

3.30

OUTPUT VOLTAGE (V)

LOAD CURRENT (A)

VIN = 3.6V

VIN = 4.0V

VIN = 4.5V

VIN = 5.0V

VIN = 5.5V

30124740

DC Current Limit VOUT = 3.3V

2.5 3.0 3.5 4.0 4.5 5.0 5.5

1.0

1.1

1.2

1.3

1.4

1.5

DC CURRENT LIMIT (A)

INPUT VOLTAGE (V)

TA = 85°C

30124754

Block Diagram

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LMZ10501

30124704

FIGURE 1. Functional Block Diagram

Overview

The LMZ10501 SIMPLE SWITCHER® nano module is an

easy-to-use step-down DC-DC solution capable of driving up

to 1A 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 inte-

grated inductor. The LMZ10501 operates in fixed 2.0MHz

PWM (Pulse Width Modulation) mode, and is designed to de-

liver 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 volt-

age of the LMZ10501 can also be dynamically adjusted be-

tween 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.

CIRCUIT OPERATION

The LMZ10501 is a synchronous Buck power module using

a PFET for the high side switch and an NFET for the syn-

chronous 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 sig-

nal is averaged using a low pass filter formed by the integrated

inductor and an output capacitor. The output voltage is equal

to the average of the duty-cycle modulated rectangular signal.

In PWM mode, the switching frequency is constant. The en-

ergy 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 com-

pared with the slope compensated output of the error ampli-

fier. 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 in-

crease 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 in-

ductor 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.

INPUT UNDER VOLTAGE DETECTION

The LMZ10501 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.

SHUTDOWN MODE

To shutdown the LMZ10501, pull the EN pin low (<0.5V). In

the shutdown mode all internal circuits are turned OFF.

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LMZ10501

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 con-

tinues to rise, operation will start once VIN exceeds the under-

voltage 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 rat-

ings of the device.

INTERNAL SYNCHRONOUS RECTIFICATION

The LMZ10501 uses an internal NFET as a synchronous rec-

tifier to minimize the switch voltage drop and increase effi-

ciency. 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.

CURRENT LIMIT

The LMZ10501 current limit feature protects the module dur-

ing 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 1.7A (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-by-

cycle 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.

STARTUP BEHAVIOR AND SOFTSTART

The LMZ10501 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 increas-

ing the PFET current limit threshold to the final operating

value as the output voltage ramps during startup. The maxi-

mum allowed current in the inductor is stepped up in a stair-

case 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 fig-

ure and allows for a smooth VOUT ramp up.

30124734

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 de-

vice before startup occurs. This is done to deplete any resid-

ual 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, UV-

LO, EN low, or output short circuit detection. The minimum

recommended capacitance on VCON is 220pF and the maxi-

mum 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.

OUTPUT SHORT CIRCUIT PROTECTION

In addition to cycle by cycle current limit, the LMZ10501 fea-

tures 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 START-

UP BEHAVIOR AND SOFTSTART section. After the startup

sequence is completed again, the feedback voltage is moni-

tored 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

LMZ10501 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.

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LMZ10501

30124745

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 capaci-

tor is also limited. This results in a smooth VOUT ramp up to

nominal voltage. However, using excessively large output ca-

pacitance 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 main-

tain 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

1A load applications. See the INPUT AND OUTPUT CAPAC-

ITOR SELECTION section for guidance on maximum capac-

itances for different output voltage settings.

HIGH DUTY CYCLE OPERATION

The LMZ10501 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 LMZ10501

input voltage is lowered, such that the off-time of the PFET

reduces to less than 35ns, the LMZ10501 doubles the switch-

ing period to extend the off-time for that VIN and maintain

regulation. If VIN is lowered even more, the off-time of the

PFET will reach the 35ns mark again. The LMZ10501 will then

reduce the frequency again, achieving less than 100% duty

cycle operation and maintaining regulation. As VIN is lowered

even more, the LMZ10501 will continue to scale down the

frequency, aiming to maintain at least 35ns off time. Eventu-

ally, 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.

30124760

FIGURE 4. High duty cycle operation and switching

frequency reduction.

THERMAL OVERLOAD PROTECTION

The junction temperature of the LMZ10501 should not be al-

lowed 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 stand-

by 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 re-

quire derating at elevated ambient temperature. See the Typ-

ical Performance Characteristics section for thermal derating

plots for various output voltages.

www.national.com 14

LMZ10501

Application Information

30124736

FIGURE 5. Typical Application Circuit

SETTING THE OUTPUT VOLTAGE

The LMZ10501 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 (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)(2)

After substitution,

VOUT = VREF x GAIN x RB/ (RB + RT)(3)

RT = ( GAIN x VREF / VOUT – 1 ) x RB(4)

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 accu-

racy. 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

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.

DYNAMIC OUTPUT VOLTAGE SCALING

The VCON pin on the LMZ10501 can be driven externally by a

DAC to scale the output voltage dynamically. The output volt-

age 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.

INTEGRATED INDUCTOR

The LMZ10501 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.

INPUT AND OUTPUT CAPACITOR SELECTION

The LMZ10501 is designed for use with low ESR multi-layer

ceramic capacitors (MLCC) for its input and output filters. Us-

ing a 10 µF 0603 or 0805 with 6.3V or 10V rating ceramic input

capacitor typically provides sufficient VIN bypass. Use of mul-

tiple 4.7 µF or 2.2µF capacitors can also be considered.

Ceramic capacitors with X5R and X7R temperature charac-

teristics 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.

15 www.national.com

LMZ10501

The optimum output capacitance value is application depen-

dent. Too small output capacitance can lead to instability due

to lower loop phase margin. On the other hand, if the output

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 pro-

tection 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 capaci-

tance 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 exces-

sive COUT values.

TABLE 1. Output Capacitance Range

Output

Voltage

Minimum

COUT

Suggested

COUT

Maximum

COUT

0.6V 4.7µF 10µF 47µF

1.0V 3.3µF 10µF 47µF

1.2V 3.3µF 10µF 47µF

1.8V 3.3µF 10µF 68µF

2.5V 3.3µF 10µF 100µF

3.3V 3.3µF 10µF 100µF

Use of multiple 4.7 µF or 2.2µF output capacitors can be con-

sidered 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 fre-

quency 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 ap-

plications 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.

www.national.com 16

LMZ10501

Board Layout Considerations

30124748

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 volt-

age properly, the board layout can mean the difference be-

tween passing or failing EMI regulations. In a Buck converter,

the most critical board layout path is between the input ca-

pacitor 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 LMZ10501 integrates the inductor and simplifies the DC-

DC converter board layout. Refer to the example layout in

Figure 6. There are a few basic requirements to achieve a

good LMZ10501 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 LMZ10501 are next to each other which makes the

input capacitor placement simple.

2. Place the VCON filter capacitor CVC and the RB RT resis-

tive divider as close as possible to the VCON and SGND

terminals.The CVC capacitor (not RB) should be the compo-

nent 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 www.national.com

LMZ10501

Physical Dimensions inches (millimeters) unless otherwise noted

NS Package Number SE08A

www.national.com 18

LMZ10501

Notes

19 www.national.com

LMZ10501

Notes

1A SIMPLE SWITCHER® Nano Module with 5.5V Maximum Input Voltage

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