IC CTRLR PWM W/BOOTSTRAP SO-16N

L6725

Manufacturer Part NumberL6725
DescriptionIC CTRLR PWM W/BOOTSTRAP SO-16N
ManufacturerSTMicroelectronics
L6725 datasheet
 


Specifications of L6725

Pwm TypeVoltage ModeNumber Of Outputs1
Frequency - Max550kHzDuty Cycle100%
Voltage - Supply4.5 V ~ 18 VBuckYes
BoostNoFlybackNo
InvertingNoDoublerNo
DividerNoCukNo
IsolatedNoOperating Temperature-40°C ~ 85°C
Package / Case16-SOIC (3.9mm Width)Frequency-max550kHz
PackageSO16NFor Use With497-5867 - EVAL BOARD 20A 250KHZ L6725497-5500 - EVAL BOARD FOR L6725
Lead Free Status / RoHS StatusLead free / RoHS Compliant  
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Features
Input voltage range from 1.8V to 18V
Supply voltage range from 4.5V to 18V
Adjustable output voltage down to 0.6V with
±0.8% accuracy over line voltage and
temperature (0°C~125°C)
Fixed frequency voltage mode control
0% to 100% duty cycle
External input voltage reference
Soft-start and inhibit
Bootstrap anti-discharging system
High current embedded drivers
Predictive anti-cross conduction control
Programmable high-side and low-side R
sense over-current-protection
Sink current capability
Selectable switching frequency 250KHz/
500KHz
Power good and synch available with L6725A
Pre-bias start up capability
Over voltage protection
Thermal shut-down
Package: SO16N
Table 1.
Device summary
Order codes
L6725
L6725TR
L6725A
L6725ATR
June 2007
Voltage mode PWM controller
with bootstrap anti-discharging system
SO16N (Narrow)
Applications
DS(on)
Low voltage distributed DC-DC
Graphic cards
Package
SO16N
SO16N
SO16N
SO16N
Rev 5
L6725
L6725A
Packing
Tube
Tape & Reel
Tube
Tape & Reel
1/32
www.st.com
32

L6725 Summary of contents

  • Page 1

    ... Predictive anti-cross conduction control ■ Programmable high-side and low-side R sense over-current-protection ■ Sink current capability ■ Selectable switching frequency 250KHz/ 500KHz ■ Power good and synch available with L6725A ■ Pre-bias start up capability ■ Over voltage protection ■ Thermal shut-down ■ Package: SO16N Table 1. ...

  • Page 2

    ... Internal LDO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 5.3 Bypassing the LDO to avoid the voltage drop with low Vcc . . . . . . . . . . . . . 11 5.4 Internal and external references . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 5.5 Error amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 5.6 Soft start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 5.7 Driver section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 5.8 Monitoring and protections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 5.9 Hiccup mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 5.10 Thermal shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 2/32 L6725 - L6725A ...

  • Page 3

    ... Bootstrap anti-discharging system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 5.12.1 Fan's power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 6 Application details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 6.1 Inductor design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 6.2 Output capacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 6.3 Input capacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 6.4 Compensation network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 7 L6725 demoboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 7.1 20A board description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 7.2 5A board description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 8 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 9 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Contents 3/32 ...

  • Page 4

    ... SYNCH 4/32 Vcc=4.5V-14V Vcc = 14V - 18V OCH OCH VCCDR VCCDR LDO LDO Monitor Monitor OSC OSC - - L6725 - - + + 0. PWM PWM E/A E COMP COMP L6725 - L6725A Vin = 14V - 18V Vin=1.8V-14V BOOT BOOT HGATE HGATE PHASE PHASE LGATE LGATE PGND PGND GND GND V OUT ...

  • Page 5

    ... L6725 - L6725A 2 Electrical data 2.1 Maximum rating Table 2. Absolute maximum ratings Symbol GND and PGND, OCH Boot voltage BOOT - PHASE V V HGATE - PHASE V BOOT BOOT PHASE V PHASE PHASE Spike, transient < 50ns (F SS, FB, EAREF, OCL, LGATE, COMP, V OCH Pin Maximum withstanding voltage range Test Condition: CDF-AEC-Q100-002 " ...

  • Page 6

    ... External Reference/F CCDR = 80 -> V CCDR REF = 95% - 100 ->V CCDR REF ) from this pin to ground through the external resistor OCL ). The over-current threshold is given by the following equation: I VALLEY L6725 - L6725A FB SGND SYNCH/NC PGOOD/NC VCC VCCDR LGATE PGND = 250KHz SW = 0.6V/F = 500KHz SW = 0.6V/F ...

  • Page 7

    ... Supply voltage pin. The operative supply voltage range is from 4.5V to 14V. CC PGOOD In L6725 this pin is N.C. With L6725A this pin is an open collector output and it is pulled low if the output voltage is not (L6725A) 13 within the specified thresholds (90%-110%). If not used it may be left floating. Pull-up N ...

  • Page 8

    ... Ramp Amplitude OSC Output Voltage V Output Voltage FB 8/32 Test condition SS to GND HG = open open, PH=open V = 1.7V OCH V = 1.7V OCH V =5.5V to 18V 1mA to 100mA 0.5V L6725 - L6725A Min Typ Max Unit 8.5 10 4.0 4.2 4.4 V 3.6 3.8 4.0 V 1.1 1.25 1.47 V 0.9 1.05 1 ...

  • Page 9

    ... L6725 - L6725A Table 5. Electrical characteristics Symbol Parameter Error Amplifier R EAREF Input Resistance EAREF I I.I. bias current FB Ext Ref Clamp V Error amplifier offset OFFSET G Open Loop Voltage Gain V GBWP Gain-Bandwidth Product SR Slew-Rate Gate drivers R High Side Source Resistance HGATE_ON R High Side Sink Resistance ...

  • Page 10

    ... L6725 - L6725A 5 Device description The controller provides complete control logic and protection for flexible and cost-effective DC- DC converters designed to drive N-Channel MOSFETs in a synchronous rectified buck topology. The output voltage of the converter can be precisely regulated down to 600mV with a maximum tolerance of ±0.8%, when the internal reference is used. The device allows also using an external reference ( ...

  • Page 11

    ... L6725 - L6725A 5.3 Bypassing the LDO to avoid the voltage drop with low Vcc ≈ the internal LDO works in dropout with an output resistance of about 1Ω. The CC maximum LDO output current is about 100mA and so the output voltage drop is 100mV, to avoid this the LDO can be bypassed. ...

  • Page 12

    ... After that it becomes 10µA until the final charge value of approximately 4V (see Figure 5. Soft-Start phase. Vss 12/32 are above their turn-ON thresholds (V IN 0.5V L6725 - L6725A is monitored by the OCH pin) IN with an internal current generator. The SS Figure 5.). Vcc Vin 4 ...

  • Page 13

    ... L6725 - L6725A L6725:The output of the error amplifier is clamped with this voltage (VSS) until it reaches the programmed value. L6725A:The reference of the error amplifier is clamped with this voltage (VSS) until it reaches the programmed value. No switching activity is observable if V MOSFETs are OFF. When reaches 1.1V (i.e. the oscillator triangular wave inferior limit) even the high-side SS MOSFET begins to switch and the output voltage starts to increase ...

  • Page 14

    ... SS pin reaches 0.5V the soft-start phase restarts (see 14/32 ), maintaining fast switching transitions. The low-side driver is DSON Table 4: Pin functions): L6725 - L6725A Figure 8). LGate FB Figure 9). ...

  • Page 15

    ... L6725 - L6725A 5.9 Hiccup mode Figure 9. Constant current and Hiccup Mode during an OCP. During the soft-start phase the OCP provides a constant-current-protection. If during the T the OCH comparator triggers an over current the high-side MOSFET(s) is immediately turned OFF (after the masking time and the internal delay) and returned on at the next pwm cycle. The limit of this protection is that the T because during the masking time the peak-current-protection is disabled ...

  • Page 16

    ... If, during synchronization between two (or more) L6725A, it's important to know in advance which the master is, it's timely to set its switching frequency at least 15% higher than the slave. Using an external clock signal ...

  • Page 17

    ... Often only the speed of the MOTOR is controlled by varying the voltage applied to the input terminal and there's no control on the torque because the current is not directly controlled. In order to vary the MOTOR speed the output voltage of the converter must be varied. The L6725 has a dedicated pin called EAREF (see the related section) that allows providing an external reference to the non-inverting input of the error-amplifier ...

  • Page 18

    ... Minimizing the response time can minimize the output capacitor size. 18/32 − Vin Vout Vout ≅ ⋅ L ∆ ⋅ Fsw I Vin L is the input voltage and L6725 - L6725A ) between 20% and 30% of the L (2) is the output voltage. OUT Vin=12V, L=1uH Vin=12V, L=2uH Vin=5V, L=500nH Vin=5V, L=1.5uH 4 ...

  • Page 19

    ... Vout COUT Where D is the maximum duty cycle value that in the L6725 is 100%. Usually the voltage MAX drop due to the ESR is the biggest one while the drop due to the capacitor discharge is almost negligible. Moreover the ESR value also affects the voltage static ripple, that is: 6 ...

  • Page 20

    ... ESR. The DC Gain of the ESR divided by the peak-to-peak oscillator voltage (R5, C18 and C19). The compensation network has to provide a FB /10) and the highest gain in DC conditions to minimize the SW L6725 - L6725A at the PHASE node. This waveform is depending on the L-C LC OUT . OSC IN ...

  • Page 21

    ... L6725 - L6725A ● Modulator singularity frequencies: ω LC ● Compensation network singularity frequencies: ω ω ● Compensation network design: – Put the gain R ω – Place Z1 ω – Place Z2 ω – Place P1 ω – Place P2 – Check the loop gain considering the error amplifier open loop gain. ...

  • Page 22

    ... L6725 demoboard realizes in a four layer PCB a step-down DC/DC converter and shows the operation of the device in a general purpose application. The input voltage can range from 4.5V to 14V and the output voltage is at 3.3V. The module can deliver an output current in excess of 20A ...

  • Page 23

    ... L6725 - L6725A Table 6. Demoboard part list Reference Value R1 1kΩ R2 1kΩ R3 4K7 N.C. R7 2KΩ R8 10Ω R9 1KΩ R10 2.2Ω R11 2.2Ω R12 N.C. C1 4.7nF C2 47nF C3 1nF C4 100nF C5 100nF C6 N.C. C7 100nF C8 4.7uF 20V C9 1nF C10 1uF C11 ...

  • Page 24

    ... 24/32 Series 744318180 CDEP134-2R7MC-H HPI_13 T640 SPM12550T-1R0M220 FDA1254 HCF1305-1R0 HC5-1R0 Series C4532X5R1E156M C3225X5R0J107M 25PS100MJ12 ECJ4YB0J107M 500KHz 12V L6725 - L6725A Inductor Value (µH) Saturation Current (A) 1.8 2.7 1.4 1 2.2 1.15 1.3 Capacitor value(µF) Rated voltage (V) 15 100 100 100 6.3 25 6.3 ...

  • Page 25

    ... L6725 - L6725A Figure 18. PCB Layout: top layer Figure 19. PCB Layout: power ground layer Figure 20. PCB Layout: signal-ground layer Demoboard 25/32 ...

  • Page 26

    ... L6725 demoboard realizes in a two layer PCB a step-down DC/DC converter and shows the operation of the device in a general purpose application. The input voltage can range from 4.5V to 14V and the output voltage is at 3.3V. The module can deliver an output current in excess of 5A ...

  • Page 27

    ... L6725 - L6725A Table 9. Demoboard part list Reference Value C15 N.C. C16-19 2X 330uF 2,7uH L1 DO3316P-272HC D1 STPS1L30M D3 N.C. STS8DNH3LL Q1 (Dual Mosfet) U1 L6725 Figure 21. Demoboard efficiency Manufacturer / / Coilcraft Demoboard Package Supplier / / / ST (poscap) SMD ST DO216AA SO8 ST SO16N 27/32 ...

  • Page 28

    ... Demoboard Figure 22. Demoboard layout Figure 23. Demoboard layout 28/32 L6725 - L6725A ...

  • Page 29

    ... L6725 - L6725A 8 Package mechanical data In order to meet environmental requirements, ST offers these devices in ECOPACK These packages have a Lead-free second level interconnect . The category of second Level Interconnect is marked on the package and on the inner box label, in compliance with JEDEC Standard JESD97. The maximum ratings related to soldering conditions are also marked on the inner box label ...

  • Page 30

    ... L6725 - L6725A inch Min Typ Max 0.069 0.009 0.063 0.018 0.010 0.020 0.394 0.244 0.050 0.350 0.157 0.208 0.050 0.024 ...

  • Page 31

    ... L6725 - L6725A 9 Revision history Table 11. Revision history Date Revision 20-Dec-2005 30-May-2006 26-Jun-2006 5-Oct-2006 28-Jun-2007 1 Initial release. 2 New template, thermal data updated 3 Note page 5 deleted 4 Added new orderable L6725A, and 5A demoboard 5 Extended operative range Revision history Changes 31/32 ...

  • Page 32

    ... Australia - Belgium - Brazil - Canada - China - Czech Republic - Finland - France - Germany - Hong Kong - India - Israel - Italy - Japan - Malaysia - Malta - Morocco - Singapore - Spain - Sweden - Switzerland - United Kingdom - United States of America 32/32 Please Read Carefully: © 2007 STMicroelectronics - All rights reserved STMicroelectronics group of companies www.st.com L6725 - L6725A ...