LTC3613 - 24V, 15A Monolithic Step Down Regulator with ...

LTC3613

FEATURES

24V, 15A Monolithic Step Down Regulator with Differential Output Sensing

DESCRIPTION

n Wide VIN Range: 4.5V to 24V; VOUT Range: 0.6V to 5.5V at up to 15A

n 0.67% Output Voltage Accuracy n Controlled On-Time Valley Current Mode Architecture,

Excellent Current Sharing Capability n Frequency Programmable from 200kHz to 1MHz

and Synchronizable to External Clock n RSENSE or Inductor DCR Current Sensing With

Accurate Current Limit n Fast Transient Response n Differential Output Voltage Sensing Allowing 500mV

Common Mode Remote Ground n tON(MIN) = 65ns; tOFF(MIN) = 105ns n Overvoltage Protection and Current Limit Foldback n Power Good Output Voltage Monitor n Voltage Tracking Start-Up n External VCC Input for Bypassing Internal LDO n Micropower Shutdown: IQ = 15A n 7mm ? 9mm 56-pin QFN Package

APPLICATIONS

n Distributed Power System n Point-of-Load Converters n Servers

The LTC?3613 is a monolithic synchronous step-down switching regulator capable of regulating outputs from 0.6V to 5.5V with up to 15A output current. The controlled on-time constant frequency valley current mode architecture allows for both fast transient response and constant frequency switching in steady-state operation, independent of VIN, VOUT and load. This also provides excellent current sharing capability.

Differential output voltage sensing along with a precision internal reference combine to offer ?0.67% output regulation, even if the output ground reference deviates from local ground by 500mV. The switching frequency can be programmed from 200kHz to 1MHz with an external resistor. The switching frequency is also phase synchronizable to an external clock in applications where switching noise/ EMI reduction is crucial.

Very low tON and tOFF times allow for near 0% and near 100% duty cycles, respectively. Voltage tracking soft start-up is provided for tracking and sequencing applications. Safety features include output overvoltage protection, programmable current limit with foldback, and power good monitoring.

L, LT, LTC, LTM, OPTI-LOOP, Linear Technology and the Linear logo are registered trademarks and Hot Swap and No RSENSE is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents including 5481178, 5487554, 6580258, 6304066, 6476589, 6774611.

TYPICAL APPLICATION

High Efficiency High Power Step-Down Converter

INTVCC

PVIN SVIN

100k

0.1F 47pF

LTC3613

PGOOD

VOUT

RUN VRNG

SENSE? SENSE+

MODE/PLLIN SW EXTVCC

TRACK/SS BOOST

270pF 21k 115k

ITH

RT SGND

INTVCC PGND VOSNS+ VOSNS?

3613 TA01

VIN

+

4.5V TO 24V

0.1F

82F

10

1000pF 10

0.47H 1.5m

0.1F

15k

10k

4.7F

+

VOUT 1.5V 15A

330F ?2

EFFICIENCY (%)

Efficiency and Power Loss vs Load Current

100

3.5

90 PULSE-SKIPPING MODE 3.0

80

70

2.5

60

FORCED

2.0

50

CONTINUOUS

40

MODE

1.5

30

20

10

0 0.01

1.0

VIN = 12V 0.5

VOUT = 1.5V

0

0.1

1

10

LOAD CURRENT (A)

3613 TA01a

POWER LOSS (W)

3613fa

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LTC3613

ABSOLUTE MAXIMUM RATINGS

(Note 1)

Supply Voltage (PVIN, SVIN)....................... ?0.3V to 24V Boost Voltage ............................................ ?0.3V to 30V SW Voltage ................................................ ?0.3V to 24V INTVCC, EXTVCC, (BOOST-SW), MODE /PLLIN, VRNG, PGOOD, RUN Voltages....................... ?0.3V to 6V VOSNS+, VOSNS? Voltages ........ ?0.6V to (INTVCC + 0.3V) VOUT, SENSE+, SENSE? Voltages ................. ?0.6V to 6V RT, ITH Voltages ..................... ?0.3V to (INTVCC + 0.3V) TRACK/SS Voltages..................................... ?0.3V to 5V Operating Junction Temperature Range (Notes 2, 4)............................................ ?40?C to 125?C Storage Temperature Range .................. ?65?C to 150?C

PIN CONFIGURATION

TOP VIEW

PVIN 1 PVIN 2 PVIN 3 PVIN 4 PVIN 5 PVIN 6 PVIN 7 PVIN 8 PVIN 9 SW 10

BOOST 11

SGND 12

PGOOD 13 SNS+ 14 SNS? 15

SGND 16

PVIN

SW

57

58

SGND 59

56 PVIN 55 PVIN 54 PVIN 53 PVIN 52 NC 51 SW 50 SW 49 SW 48 SW 47 SW 46 SW 45 SW

44 PGND 43 PGND 42 PGND 41 PGND 40 PGND 39 PGND 38 PGND 37 PGND 36 PGND 35 SW 34 INTVCC 33 INTVCC 32 SVIN 31 MODE/PLLIN 30 EXTVCC 29 SGND

SGND 17 VOUT 18 SGND 19 VOSNS? 20 VOSES+ 21 TRACK/SS 22

ITH 23 VRNG 24

RT 25 RUN 26

NC 27 SGND 28

WKH PACKAGE 56-LEAD (7mm ? 9mm) MULTIPAD QFN

TJMAX = 125?C, JA = 29?C/W

ORDER INFORMATION

LEAD FREE FINISH

TAPE AND REEL

PART MARKING*

PACKAGE DESCRIPTION

TEMPERATURE RANGE

LTC3613EWKH#PBF

LTC3613EWKH#TRPBF LTC3613WKH

56-Lead (7mm ? 9mm) Plastic QFN

?40?C to 125?C

LTC3613IWKH#PBF

LTC3613IWKH#TRPBF LTC3613WKH

56-Lead (7mm ? 9mm) Plastic QFN

?40?C to 125?C

Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.

For more information on lead free part marking, go to: For more information on tape and reel specifications, go to:

3613fa

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LTC3613

ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the specified operating

junction temperature range, otherwise specifications are at TA = 25?C. SVIN = 15V, VFB = VOSNS+ ? VOSNS?, unless otherwise noted. (Note 4)

SYMBOL

PARAMETER

CONDITIONS

MIN TYP MAX UNITS

Main Control Loop

VIN

Input Voltage Operating Range

VOUT

Output Voltage Operating Range

IQ

Input DC Supply Current

Normal

Shutdown Supply Current

MODE/PLLIN = INTVCC RUN = 0V

l 4.5 l 0.6

24

V

5.5

V

2

4

mA

15

25

A

VREG

Regulated Differential Feedback Voltage

ITH = 1.2V (Note 3)

(VOSNS+ ? VOSNS?)

TA = 25?C

TA = 0?C to 85?C

TA = ?40?C to 125?C

0.5985 0.6 0.6015

V

l 0.596 0.6 0.604

V

l 0.594 0.6 0.606

V

Regulated Differential Feedback Voltage Over Line, Load and Common Mode

VVIONSN=S4?.5=V?t5o002m4VV,

ITH = 0.5V (Note 3)

to

1.9V,

(VOSNS+ ? VOSNS?)

TA = 0?C to 85?C

l 0.594 0.6 0.606

V

TA = ?40?C to 125?C

l 0.591 0.6 0.609

V

tON(MIN)

Minimum On-Time

65

ns

tOFF(MIN)

Minimum Off-Time

105

ns

gm(EA)

Error Amplifier Transconductance

ITH = 1.2V (Note 3)

l 1.4

1.7

2

mS

VSENSE(MAX) VSENSE(MIN) VSENSE(CM)

Valley Current Sense Threshold, VSENSE+ ? VSENSE?, Peak Current = Valley + Ripple

VRNG = 2V, VFB = 0.57V VRNG = 0V, VFB = 0.57V VRNG = INTVCC, VFB = 0.57V

Minimum Current Sense Threshold,VSENSE+ ? VRNG = 2V, VFB = 0.63V

VSENSE?, Force Continuous Operation

VRNG = 0V, VFB = 0.63V

VRNG = INTVCC, VFB = 0.63V

SENSE+, SENSE? Voltage Range (Common

Mode)

l 80

100

120

mV

l 22

30

38

mV

l 39

50

61

mV

?50

mV

?15

mV

?25

mV

l ?0.5

5.5

V

ISENSE

SENSE+, SENSE? Input Bias Current

VSENSE(CM) = 0.6V VSENSE(CM) = 5V

?5

?50

nA

1

4

A

VRUN(TH)

RUN Pin On Threshold

VRUN Rising

l 1.1

1.2

1.3

V

VRUN(HYS)

RUN Pin Hysteresis

80

mV

ISS

Soft-Start Charging Current

VTRACKSS = 0V

1.0

A

UVLO

IVOSNS+ IVOSNS?

INTVCC Undervoltage Lockout INTVCC Undervoltage Lockout Release

VOSNS+ Input Bias Current

VOSNS? Input Bias Current

Falling Rising

VFB = 0.6V

VFB = 0.6V

l 3.4

3.65

4.0

V

l

4.2

4.5

V

?5

?25

nA

?15

?50

A

3613fa

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LTC3613

ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the specified operating

junction temperature range, otherwise specifications are at TA = 25?C. SVIN = 15V, VFB = VOSNS+ ? VOSNS?, unless otherwise noted. (Note 4)

SYMBOL

PARAMETER

CONDITIONS

MIN TYP MAX UNITS

Oscillator and Clock Synchronization

fOSC

Free Running Switching Frequency

CLKIH

Clock Input High Level Into Mode/PLLIN

CLKIL

Clock Input Low Level Into Mode/PLLIN

Internal VCC Regulator and External VCC

INTVCC

Internal VCC Voltage

INTVCC(%)

Internal VCC Load Regulation

EXTVCC(TH)

EXTVCC Switchover Voltage

EXTVCC(HYS)

EXTVCC Switchover Hysteresis

INTVCC

EXTVCC Voltage Drop

PGOOD Output

RT = 205k RT = 80.6k RT = 38.8k

6V < VIN < 24V ICC = 0mA to 50mA EXTVCC Rising

VEXTVCC = 5V. ICC = 50mA

175

200

225

kHz

450

500

550

kHz

900 1000 1100

kHz

2

V

0.5

V

5.1

5.3

5.55

V

?1

?2

%

4.4

4.6

4.75

V

200

mV

200

mV

PGDOV

PGDUV

PGDHYS VPGD(LO) tPGD(FALL) tPGD(RISE) RDS(ON) RDS(ON)

PGOOD Upper Threshold

PGOOD Lower Threshold

PGOOD Hysteresis PGOOD Low Voltage Delay from OV/UV Fault to PGOOD Falling

VFB Rising (With Respect to Regulated Feedback Voltage VREG)

VFB Falling (With Respect to Regulated Feedback Voltage VREG)

VFB Returning

IPGOOD = 5mA

(Note 5)

Delay from OV/UV Recovery to PGOOD Rising (Note 5)

Top Switch On-Resistance Bottom Switch On-Resistance

5

7.5

10

%

?10 ?7.5

?5

%

2

%

0.15

0.4

V

20

s

10

s

7.5

mohm

5.5

mohm

Note 1: Stresses beyond those listed under Absolute Maximum Ratings cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime.

Note 2: TJ is calculated from the ambient temperature, TA, and power dissipation, PD, as follows:

TJ = TA + (PD ? 29?C/W) (JA is simulated per JESD51-7 high effective thermal conductivity test board)

JC =1?C/W (JC is simulated when heat sink is applied at the bottom of the package.) Note 3: The LTC3613 is tested in a feedback loop that adjusts VFB = VOSNS+ ? VOSNS? to achieve a specified error amplifier output voltage (ITH).

Note 4: The LTC3613 is tested under pulsed load conditions such that TJ TA. The LTC3613E is guaranteed to meet specifications from 0?C to 125?C junction temperature. Specifications over the ?40?C to 125?C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. The LTC3613I is guaranteed over the full ?40?C to 125?C operating junction temperature range. Note that the maximum ambient temperature consistent with these specifications is determined by specific operating conditions in conjunction with board layout, the rated package thermal impedance and other environmental factors.

Note 5: Delay times are measured using 50% levels.

3613fa

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LTC3613

TYPICAL PERFORMANCE CHARACTERISTICS TA = 25?C unless otherwise noted

Transient Response: Forced Continuous Mode

Load Step: Forced Continuous Mode

Load Release: Forced Continuous Mode

VOUT 100mV/DIV

IL 10A/DIV

ILOAD 10A/DIV

40s/DIV LOAD TRANSIENT = 0A TO 15A VIN = 12V, VOUT = 1.5V FIGURE 10 CIRCUIT

VOUT 100mV/DIV

IL 10A/DIV

3613 G01

ILOAD 10A/DIV

10s/DIV LOAD STEP = 0A TO 15A VIN = 12V, VOUT = 1.5V FIGURE 10 CIRCUIT

VOUT 100mV/DIV

IL 10A/DIV

ILOAD 10A/DIV

3613 G02

10s/DIV

LOAD RELEASE = 15A TO 0A VIN = 12V, VOUT = 1.5V FIGURE 10 CIRCUIT

3613 G03

Transient Response: Pulse-Skipping Mode

Load Step: Pulse-Skipping Mode

Load Release: Pulse-Skipping Mode

VOUT 100mV/DIV

IL 10A/DIV

ILOAD 10A/DIV

VOUT 100mV/DIV

IL 10A/DIV

ILOAD 10A/DIV

40s/DIV

LOAD TRANSIENT = 500mA TO 15A VIN = 12V, VOUT = 1.5V FIGURE 10 CIRCUIT

3613 G04

10s/DIV

LOAD STEP = 500mA TO 15A VIN = 12V, VOUT = 1.5V FIGURE 10 CIRCUIT

VOUT 100mV/DIV

IL 10A/DIV

ILOAD 10A/DIV

3613 G05

10s/DIV

LOAD RELEASE = 15A TO 500mA VIN = 12V, VOUT = 1.5V FIGURE 10 CIRCUIT

3613 G06

Normal Soft Start-Up

Soft Start-Up into a Pre-Biased Output

Output Tracking

VIN 5V/DIV

TRACK/SS 500mV/DIV

VOUT 1V/DIV

VIN = 12V

4ms/DIV

VOUT = 1.5V

FIGURE 10 CIRCUIT

VIN 5V/DIV

TRACK/SS 500mV/DIV

VOUT 1V/DIV

VOUT PRE-BIASED TO 0.75V

3613 G07

VIN = 12V

2ms/DIV

VOUT = 1.5V

FIGURE 10 CIRCUIT

TRACK/SS 500mV/DIV

3613 G08

VOUT 1V/DIV

VIN = 12V

10ms/DIV

VOUT = 1.5V

FIGURE 10 CIRCUIT

3613 G09

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LTC3613 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25?C unless otherwise noted

Overcurrent Protection

LOAD-STEP TRIGGER 7.5A

VOUT 1V/DIV

VOUT DROOPS DUE TO

REACHING CURRENT LIMIT

ILOAD 10A/DIV

Short-Circuit Protection

SHORTCIRCUIT TRIGGER

SHORT-CIRCUIT REGION

VOUT 1V/DIV

ILOAD 10A/DIV

NOTE

Overvoltage Protection

VOUT 200mV/DIV

OVERVOLTAGE TRIGGER

IL 10A/DIV

SW 20V/DIV

OVERVOLTAGE REGION

VIN = 12V

4ms/DIV

VOUT = 1.5V

FIGURE 10 CIRCUIT

3613 G10

VIN = 12V

200s/DIV

VOUT = 1.5V

FIGURE 10 CIRCUIT

3613 G11

NOTE: INDUCTOR CURRENT REACHES CURRENT LIMIT BEFORE FOLDBACK AND DURING SHORT-CIRCUIT RECOVERY

VIN = 12V

20s/DIV

VOUT = 1.5V

FIGURE 10 CIRCUIT

NOTE: SW IS FORCED LOW

FOR EXTENDED PERIODS TO

REMOVE OVERVOLTAGE

3613 G12

VOUT ERROR (%)

Output Regulation vs Input Voltage

0.5 VIN = 12V ILOAD = 5A FIGURE 10 CIRCUIT

0.3

Output Regulation vs Load Current

0.5 VIN = 12V ILOAD = 4A

0.3 FIGURE 10 CIRCUIT

VOUT ERROR (%)

0.1

0.1

?0.1

?0.1

?0.3

?0.3

?0.5 0

4

8 12 16 20 24

INPUT VOLTAGE (V)

3613 G13

Switching Frequency vs Input Voltage

2.0

1.5

1.0

0.5

0

?0.5

VIN = 12V ILOAD = 5A

FIGURE 10 CIRCUIT

?1.0

0

4

8 12 16

VIN (V)

20 24

3613 G16

NORMALIZED f (%)

?0.5 0

3

6

9

12

15

LOAD CURRENT (A)

3613 G14

Switching Frequency

vs Load Current

0.5 VIN = 12V ILOAD = 4A

0.3 FIGURE 10 CIRCUIT

0.1

?0.1

?0.3

?0.5 0

3

6

9

12

15

LOAD CURRENT (A)

3613 G17

NORMALIZED f (%)

6

NORMALIZED f (%)

NORMALIZED VOUT (%)

Output Regulation vs Temperature

0.2 VIN = 12V ILOAD = 0A VOUT NORMALIZED AT TA = 25?C

0.1 FIGURE 10 CIRCUIT

0

?0.1

?0.2 ?50 ?25 0 25 50 55 100 125 150 TEMPERATURE (?C)

3613 G15

Non-Synchronized Switching Frequency vs Temperature

1.0 VIN = 12V ILOAD = 0A

0.5 FREQUENCY NORMALIZED AT TA = 25?C FIGURE 10 CIRCUIT

0

?0.5

?1.0

?1.5

?2.0 ?50 ?25 0 25 50 75 100 125 150 TEMPERATURE (?C)

3613 G18

3613fa

LTC3613 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25?C unless otherwise noted

TRANSCONDUCTANCE (mS)

Error Amplifier Transconductance vs Temperature

1.80

1.75

1.70

1.65

1.60

1.55

1.50 ?50 ?25 0 25 50 75 100 125 150 TEMPERATURE (?C)

3613 G22

RUN Thresholds vs Temperature

1.6

1.4

SWITCHING REGION

1.2

1.0 STANDBY REGION

0.8

0.6

0.4

SHUTDOWN REGION

0.2

0 ?50 ?25

0 25 50 75 100 125 150 TEMPERATURE (?C)

3613 G25

UVLO THRESHOLDS (V)

CURRENT SENSE VOLTAGE (mV)

Current Sense Voltage vs ITH Voltage

120

100

80

60

40

20

0 ?20

?40

?60 0

VRNG = 0.6V VRNG = 0.9V VRNG = 1.3V VRNG = 1.6V VRNG = 2.0V

0.5

1

1.5

2

2.5

ITH VOLTAGE (V)

3613 G23

Input Undervoltage Lockout Thresholds vs Temperature

4.5

4.3

UVLO RELEASE

(INTVCC RISING)

4.1

3.9

UVLO LOCK

3.7

(INTVCC FALLING)

3.5

3.3 ?50 ?25 0 25 50 75 100 125 150 TEMPERATURE (?C)

3613 G26

CURRENT (A)

MAXIMUM CURRENT SENSE VOLTAGE (mV)

Maximum Current Sense Voltage vs Temperature

120

100

VRNG = 2V

80

60 VRNG = 1V

40

VRNG = 0.6V

20

0 ?50 ?25 0 25 50 75 100 125 150

TEMPERATURE (?C)

3613 G24

RUN and TRACK/SS Pull-Up Currents vs Temperature

1.8

1.6

RUN 1.4

1.2

TRACK/SS 1.0

0.8

0.6 ?50 ?25 0 25 50 75 100 125 150 TEMPERATURE (?C)

3613 G27

RUN PIN THRESHOLDS (V)

3613fa

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LTC3613

PIN FUNCTIONS

PVIN (Pins 1-9, 53-56, 57 Exposed Pad): Power Supply Inputs. These pins connect to the drain of the internal power MOSFETS. The PVIN exposed pad must be soldered to the circuit board for electrical contact and rated thermal performance. The supply voltage can range from 4.5V to 24V. The voltage on this pin is also used to adjust the TG on-time in order to maintain constant frequency operation.

SW (Pins 10, 35, 45-51, 58 Exposed Pad): Switch Node Connection. The (?) terminal of the bootstrap capacitor, CB, connects to this node. This pin swings from a diode voltage below ground up to VIN. The SW exposed pad must be soldered to the circuit board for electrical contact and rated thermal performance.

BOOST (Pin 11): Boosted Driver Supply Connection. The (+) terminal of the bootstrap capacitor, CB, as well as the cathode of the Schottky diode, DB, connects to this node. This node swings from INTVCC ? VSCHOTTKY to VIN + INTVCC ? VSCHOTTKY.

SGND (Pins 12, 16, 17, 19, 28, 29, 59 Exposed Pad): Signal Ground Connection. The SGND exposed pad must be soldered to the circuit board for electrical contact and rated thermal performance. All small-signal components should be connected to the signal ground. Connect signal ground to power ground only at one point using a single PCB trace.

PGOOD (Pin 13): Power Good Indicator Output. This open-drain logic output is pulled to ground when the output voltage is outside of a ?7.5% window around the regulation point.

SENSE+ (Pin 14): Differential Current Sensing (+) Input. For RSENSE current sensing, Kelvin (4-wire) connect SENSE+ and SENSE? pins across the sense resistor. For DCR sensing, Kelvin connect SENSE+ and SENSE? pins across the sense filter capacitor.

SENSE? (Pin 15): Differential Current Sensing (?) Input. For RSENSE current sensing, Kelvin (4-wire) connect the SENSE+ and SENSE? pins across the sense resistor. For DCR sensing, Kelvin connect the SENSE+ and SENSE? pins across the sense filter capacitor.

VOUT (Pin 18): Output voltage sense for adjusting the on-time for constant frequency operation. Tying this pin to the local output (instead of the remote output) is recommended for most applications. This pin can be programmed as needed for achieving the steady-state on-time required for constant frequency operation.

VOSNS? (Pin 20): Differential Output Sensing (?) Input. Connect this pin to the negative terminal of the output capacitor. There is a bias current of 35A (typical) flowing out of this pin.

VOSNS+ (Pin 21): Differential Output Sensing (+) Input. Connect this pin to the feedback resistor divider between the positive and negative output capacitor terminals. In normal operation the LTC3613 will regulate the differential output voltage which is divided down to 0.6V by the feedback resistor divider.

TRACK/SS (Pin 22): External Tracking and Soft-Start Input. The LTC3613 regulates the differential feedback voltage (VOSNS+ - VOSNS?) to the smaller of 0.6V or the voltage on the TRACK/SS pin. An internal 1.0A pull-up current source is connected to this pin. A capacitor to ground at this pin sets the ramp time to the final regulated output voltage. Alternatively, another voltage supply connected through a resistor divider to this pin allows the output to track the other supply during start-up.

ITH (Pin 23): Current Control Voltage and Switching Regulator Compensation Point. The current sense threshold increases with this control voltage which ranges from 0V to 2.4V.

VRNG (Pin 24): Current Sense Voltage Range Input. The maximum allowed sense voltage between SENSE+ and SENSE? is equal to 0.05 ? VRNG. If VRNG is tied to SGND, the device operates with a maximum sense voltage of 30mV. If VRNG is tied to INTVCC, the device operates with a maximum sense voltage of 50mV.

RT (Pin 25): Switching Frequency Programming Pin. Connect an external resistor from RT to signal ground to program the switching frequency between 200kHz and 1MHz. An external clock applied to MODE/PLLIN must be within ?30% of this free-running frequency to ensure frequency lock.

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