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FB1

FB2

OUT

LM2696

CATCH

GND

BOOT

CBOOT

EXT

EXTV

AVIN

PVIN

AVIN

RON

PGOOD

LM2696

www.ti.com

SNVS375B –OCTOBER 2005–REVISED APRIL 2013

LM2696 3A, Constant On Time Buck Regulator

Check for Samples: LM2696

FEATURES

DESCRIPTION

The LM2696 is a pulse width modulation (PWM) buck

• Input Voltage Range of 4.5V–24V

regulator capable of delivering up to 3A into a load.

• Constant On-Time

The control loop utilizes a constant on-time control

• No Compensation Needed

scheme with input voltage feed forward. This provides

a topology that has excellent transient response

• Maximum Load Current of 3A

without the need for compensation. The input voltage

• Switching Frequency of 100 kHz–500 kHz

feed forward ensures that a constant switching

• Constant Frequency Across Input Range

frequency is maintained across the entire V

range.

• TTL Compatible Shutdown Thresholds

The LM2696 is capable of switching frequencies in

• Low Standby Current of 12 µA

the range of 100 kHz to 500 kHz. Combined with an

integrated 130 mΩ high side NMOS switch the

• 130 mΩ Internal MOSFET Switch

LM2696 can utilize small sized external components

and provide high efficiency. An internal soft-start and

APPLICATIONS

power-good flag are also provided to allow for simple

• High Efficiency Step-Down Switching

sequencing between multiple regulators.

Regulators

The LM2696 is available with an adjustable output in

• LCD Monitors

an exposed pad HTSSOP-16 package.

• Set-Top Boxes

Typical Application Circuit

Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of

Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.

2All trademarks are the property of their respective owners.

PRODUCTION DATA information is current as of publication date.

Products conform to specifications per the terms of the Texas

Instruments standard warranty. Production processing does not

necessarily include testing of all parameters.

Summary of content (28 pages)

PAGE 1
LM2696 www.ti.com SNVS375B – OCTOBER 2005 – REVISED APRIL 2013 LM2696 3A, Constant On Time Buck Regulator Check for Samples: LM2696 FEATURES DESCRIPTION • • • • • • • • • The LM2696 is a pulse width modulation (PWM) buck regulator capable of delivering up to 3A into a load. The control loop utilizes a constant on-time control scheme with input voltage feed forward. This provides a topology that has excellent transient response without the need for compensation.
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LM2696 SNVS375B – OCTOBER 2005 – REVISED APRIL 2013 www.ti.com Connection Diagram Top View SW 1 16 PVIN SW 2 15 PVIN SW 3 14 PVIN CBOOT 4 13 SD AVIN 5 12 RON EXTVCC 6 11 PGOOD FB 7 10 SS N/C 8 9 GND Figure 1.
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LM2696 www.ti.com SNVS375B – OCTOBER 2005 – REVISED APRIL 2013 ABSOLUTE MAXIMUM RATINGS (1) (2) (3) Voltages from the indicated pins to GND AVIN −0.3V to +26V PVIN −0.3V to (AVIN+0.3V) −0.3V to +33V CBOOT −0.3V to +7V CBOOT to SW −0.3V to +7V FB, SD, SS, PGOOD −65°C to +150°C Storage Temperature Range Junction Temperature +150°C Lead Temperature (Soldering, 10 sec.) 260°C Minimum ESD Rating 1.5 kV (1) Absolute Maximum Ratings indicate limits beyond which damage may occur to the device.
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LM2696 SNVS375B – OCTOBER 2005 – REVISED APRIL 2013 www.ti.com ELECTRICAL CHARACTERISTICS (continued) Specifications with standard typeface are for TJ = 25°C, and those in boldface type apply over the full Operating Temperature Range (TJ = −40°C to +125°C). Minimum and Maximum limits are specified 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 specified VIN = 12V.
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LM2696 www.ti.com SNVS375B – OCTOBER 2005 – REVISED APRIL 2013 TYPICAL PERFORMANCE CHARACTERISTICS IQ vs VIN 1.5 1.30 1.45 1.28 1.4 1.26 1.35 IQ (PA) IQ (mA) IQ vs Temp 1.32 1.24 1.22 1.3 1.25 1.2 1.2 1.18 1.15 1.16 1.1 1.14 1.05 1.12 -40 -20 0 20 40 60 1 4.5 80 100 120 7.5 10.5 13.5 16.5 19.5 22.5 TEMPERATURE (oC) Figure 2. Figure 3.
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LM2696 SNVS375B – OCTOBER 2005 – REVISED APRIL 2013 www.ti.com TYPICAL PERFORMANCE CHARACTERISTICS (continued) EXTVCC vs VIN EXTVCC vs Load Current 3.660 3.66 3.658 3.65 EXT VCC (V) EXTVCC (V) 3.656 3.654 3.652 3.650 3.64 3.63 3.648 3.646 3.644 4.5 3.62 10.5 13.5 16.5 19.5 22.5 7.5 0 24 10 20 66.5 1.256 66.3 1.255 66.1 TON . ION (Ps . PA) VFB (V) kON vs Temp 1.257 1.254 1.253 1.252 1.251 1.25 65.9 65.7 65.5 65.3 65.1 1.249 64.9 1.248 -40 -20 64.
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LM2696 www.ti.com SNVS375B – OCTOBER 2005 – REVISED APRIL 2013 TYPICAL PERFORMANCE CHARACTERISTICS (continued) Max and Min Duty-Cycle vs Freq (Min TON = 400 ns, Min TOFF = 200 ns) FET Resistance vs Temp 0.25 1.0 0.2 0.6 0.15 RDS_ON (:) DUTY CYCLE Max Duty Cycle 0.8 0.4 0.2 0.05 Min Duty Cycle 0.0 100 200 0.1 300 400 0 -40 -20 500 0 20 40 60 80 100 120 o TEMPERATURE ( C) FREQUENCY (kHz) Figure 14. Figure 15. RON Pin Voltage vs Temp Current Limit vs Temp 1 5.4 5.
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LM2696 SNVS375B – OCTOBER 2005 – REVISED APRIL 2013 www.ti.com BLOCK DIAGRAM LM2696 AVIN EXTVCC 3.65V INTERNAL LDO SD RON UVLO ON TIMER THERMAL SHUTDOWN 6V INTERNAL SUB REGULATOR Ron Q SS 1 PA CBOOT 1.25V SD PGOOD PVIN OFF TIMER Q DRIVER 94% x Vbg 1.25V LEVEL SHIFT UNDER-VOLTAGE COMPARATOR FB REGULATION COMPARATOR FB S Q R Q SW COMPLETE CURRENT LIMIT START OFF TIMER SD 4.
PAGE 9
LM2696 www.ti.com SNVS375B – OCTOBER 2005 – REVISED APRIL 2013 INTERNAL OPERATION UNDER-VOLTAGE COMPARATOR An internal comparator is used to monitor the feedback pin for sensing under-voltage output events. If the output voltage drops below the UVP threshold the power-good flag will fall. ON-TIME GENERATOR SHUTDOWN The on-time for the LM2696 is inversely proportional to the input voltage. This scheme of on-time control maintains a constant frequency over the input voltage range.
PAGE 10
LM2696 SNVS375B – OCTOBER 2005 – REVISED APRIL 2013 www.ti.com The switching frequency of the LM2696 is set by the resistor connected to the RON pin. This resistor controls the current flowing into the RON pin and is directly related to the on-time pulse. Connecting a resistor from this pin to PVIN allows the switching frequency to remain constant as the input voltage changes. In normal operation this pin is approximately 0.65V above GND.
PAGE 11
LM2696 www.ti.com SNVS375B – OCTOBER 2005 – REVISED APRIL 2013 To ensure stability, two constraints need to be met. These constraints are the voltage ripple at the feedback pin must be greater than some minimum value and the voltage ripple must be in phase with the switch pin. The ripple voltage necessary at the feedback pin may be estimated using the following relationship: ΔVFB > −0.057 • fSW + 35 where • • fSW is in kHz ΔVFB is in mV.
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LM2696 SNVS375B – OCTOBER 2005 – REVISED APRIL 2013 www.ti.com FEEDBACK RESISTORS The feedback resistors are used to scale the output voltage to the internal reference value such that the loop can be regulated. The feedback resistors should not be made arbitrarily large as this creates a high impedance node at the feedback pin that is more susceptible to noise. Typically, RFB2 is on the order of 1 kΩ.
PAGE 13
LM2696 www.ti.com SNVS375B – OCTOBER 2005 – REVISED APRIL 2013 AVIN CAPACITOR AVIN is the analog bias rail of the device. It should be bypassed externally with a small (1 µF) ceramic capacitor to prevent unwanted noise from entering the device. In a shutdown state the current needed by AVIN will drop to approximately 12 µA, providing a low power sleep state.
PAGE 14
LM2696 SNVS375B – OCTOBER 2005 – REVISED APRIL 2013 www.ti.com PGOOD RESISTOR The PGOOD resistor is used to pull the PGOOD pin high whenever a steady state operating range is achieved. This resistor needs to be sized to prevent excessive current from flowing into the PGOOD pin whenever the open drain FET is turned on. The recommendation is to use a 10 kΩ–100 kΩ resistor. This range of values is a compromise between rise time and power dissipation.
PAGE 15
LM2696 www.ti.com SNVS375B – OCTOBER 2005 – REVISED APRIL 2013 UNDER- & OVER-VOLTAGE CONDITIONS The LM2696 has a built in under-voltage comparator that controls PGOOD. Whenever the output voltage drops below the set threshold, the PGOOD open drain FET will turn on pulling the pin to ground. For an over-voltage event, there is no separate comparator to control PGOOD. However, the loop responds to prevent this event from occurring because the error comparator is essentially sensing an OVP event.
PAGE 16
LM2696 SNVS375B – OCTOBER 2005 – REVISED APRIL 2013 www.ti.com The last benefit of this scheme is when the short circuit is removed, and full load is re-applied, the part will automatically recover into the load. The variation in the off-time removes the constraints of other frequency fold back systems where the load would typically have to be reduced. NORMALIZED OUTPUT VOLTAGE 1.4 1.2 1.0 0.8 0.6 0.4 0.2 2.5 3 3.5 4 4.5 5 5.5 LOAD CURRENT (A) Figure 22.
PAGE 17
LM2696 www.ti.com SNVS375B – OCTOBER 2005 – REVISED APRIL 2013 Inductor Current IAVERAGE Time (s) DCM-CCM Boundary Inductor Current IPEAK Discontinuous Conduction Mode (DCM) Time (s) Switchnode Voltage VIN VOUT Discontinuous Conduction Mode (DCM) Time (s) Figure 23. Modes of Operation It can be seen that in DCM, whenever the inductor runs dry the SW node will become high impedance.
PAGE 18
LM2696 SNVS375B – OCTOBER 2005 – REVISED APRIL 2013 www.ti.com The output voltage is given by the following relationship: VOUT = VL = VAVERAGE - 1 'I R 1 VRIPPLE = VAVERAGE L ESR 2 2 (21) as discussed in the FEEDBACK RESISTORS section of this document. TRANSIENT RESPONSE Constant on-time architectures have inherently excellent transient line and load response. This is because the control loop is extremely fast.
PAGE 19
LM2696 www.ti.com SNVS375B – OCTOBER 2005 – REVISED APRIL 2013 PRE-BIAS LOAD STARTUP Should the LM2696 start into a pre-biased load the output will not be pulled low. This is because the part is asynchronous and cannot sink current. The part will respond to a pre-biased load by simply enabling PWM high or extending the off-time until regulation is achieved.
PAGE 20
LM2696 SNVS375B – OCTOBER 2005 – REVISED APRIL 2013 www.ti.com LM2696 VPGOOD PGOOD VSD EXTVCC SD CEXT CSD RON CBOOT RON VIN CIN CBY CAVIN CSS CBOOT AVIN SW PVIN GND L VOUT RFB1 DCATCH SS COUT FB RFB2 Figure 27. 5V-to-2.5V Voltage Applications Circuit Table 1. Bill of Materials (1) Designator Function Description Vendor Part Number CIN Input Cap 470 µF Sanyo 10MV470WX CBY Bypass Cap 0.1 µF Vishay VJ0805Y104KXAM CSS Soft-Start Cap 0.
PAGE 21
LM2696 www.ti.com SNVS375B – OCTOBER 2005 – REVISED APRIL 2013 LM2696 VPGOOD PGOOD EXTVCC SD VSD CEXT CSD RON CBOOT RON VIN CIN CBY CAVIN CSS CBOOT AVIN SW PVIN GND L VOUT Rff DCATCH SS RFB1 COUT FB Cff RFB2 Figure 28. 12V-to 3.3V Voltage Applications Circuit Table 2. Bill of Materials (1) Designator Function Description Vendor Part Number CIN Input Cap 560 µF Sanyo 35MV560WX CBY Bypass Cap 0.1 µF Vishay VJ0805Y104KXAM CSS Soft-Start Cap 0.
PAGE 22
LM2696 SNVS375B – OCTOBER 2005 – REVISED APRIL 2013 www.ti.com REVISION HISTORY Changes from Revision A (April 2013) to Revision B • 22 Page Changed layout of National Data Sheet to TI format ..........................................................................................................
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PACKAGE OPTION ADDENDUM www.ti.
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PACKAGE OPTION ADDENDUM www.ti.com 1-Nov-2013 continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals. TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
PAGE 25
PACKAGE MATERIALS INFORMATION www.ti.com 8-Apr-2013 TAPE AND REEL INFORMATION *All dimensions are nominal Device LM2696MXAX/NOPB Package Package Pins Type Drawing SPQ HTSSOP 2500 PWP 16 Reel Reel A0 Diameter Width (mm) (mm) W1 (mm) 330.0 12.4 Pack Materials-Page 1 6.95 B0 (mm) K0 (mm) P1 (mm) 8.3 1.6 8.0 W Pin1 (mm) Quadrant 12.
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PACKAGE MATERIALS INFORMATION www.ti.com 8-Apr-2013 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) LM2696MXAX/NOPB HTSSOP PWP 16 2500 367.0 367.0 35.
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MECHANICAL DATA PWP0016A MXA16A (Rev A) www.ti.
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