L6728D

Manufacturer Part NumberL6728D
DescriptionIC CTLR PWM 1PH POWERGOOD 10DFN
ManufacturerSTMicroelectronics
L6728D datasheet
 


Specifications of L6728D

Pwm TypeVoltage ModeNumber Of Outputs1
Frequency - Max330kHzDuty Cycle80%
Voltage - Supply5 V ~ 12 VBuckYes
BoostNoFlybackNo
InvertingNoDoublerNo
DividerNoCukNo
IsolatedNoOperating Temperature-40°C ~ 125°C
Package / Case10-DFNFrequency-max330kHz
Lead Free Status / RoHS StatusLead free / RoHS Compliant  
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Features
Flexible power supply from 5 V to 12 V
Power conversion input as low as 1.5 V
0.8 V internal reference
0.8% output voltage accuracy
High-current integrated drivers
Power Good output
Sensorless and programmable OCP across
low-side R
DS(on)
OV / UV protection
VSEN disconnection protection
Oscillator internally fixed at 300 kHz
LSLess to manage pre-bias startup
Adjustable output voltage
Disable function
Internal soft-start
DFN10 package
Applications
Memory and termination supply
Subsystem power supply (MCH, IOCH, PCI,
etc.)
CPU and DSP power supply
Distributed power supply
General DC-DC converters
Table 1.
Device summary
Order codes
L6728D
L6728DTR
February 2010
Single-phase PWM controller with Power Good
Description
L6728D is a single-phase step-down controller
with integrated high-current drivers that provides
complete control logic and protection to simplify
the design of general DC-DC converters by using
a compact DFN10 package.
Device flexibility allows the management of
conversions with power input (V
1.5 V, and device supply voltage ranging from 5 V
to 12 V.
The L6728D provides a simple control loop with
voltage mode EA. The integrated 0.8 V reference
allows output voltages regulation with ±0.8%
accuracy over line and temperature variations.
The oscillator is internally fixed to 300 kHz.
The L6728D provides programmable dual level
overcurrent protection, as well as overvoltage and
undervoltage protection. Current information is
monitored across the low-side MOSFET R
eliminating the need for expensive and space-
consuming sense resistors.
A PGOOD output easily provides real-time
information on output voltage status, through the
VSEN dedicated output monitor.
Package
DFN10
Doc ID 16498 Rev 1
L6728D
DFN10
) as low as
IN
,
DS(on)
Packaging
Tube
Tape and reel
1/33
www.st.com
33

L6728D Summary of contents

  • Page 1

    ... Device flexibility allows the management of conversions with power input (V 1.5 V, and device supply voltage ranging from The L6728D provides a simple control loop with voltage mode EA. The integrated 0.8 V reference allows output voltages regulation with ±0.8% accuracy over line and temperature variations. ...

  • Page 2

    ... Low-side-less startup (LSLess Overcurrent protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 8.1 Overcurrent threshold setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 9 Output voltage setting and protections . . . . . . . . . . . . . . . . . . . . . . . . 15 10 Application details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 10.1 Compensation network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 10.2 Layout guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 11 Application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 11.1 Inductor design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 11.2 Output capacitor( 11.3 Input capacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 2/33 Doc ID 16498 Rev 1 L6728D ...

  • Page 3

    ... L6728D demonstration board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 12.1 Board description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 12.1.1 12.1.2 12.1.3 12.1.4 12.1 demonstration board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 13.1 Board description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 13.1.1 13.1.2 13.1.3 13.1.4 13.1.5 14 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 15 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Power input (Vin Output (Vout Signal input (Vcc Test points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Board characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Power input (Vin Output (Vout) ...

  • Page 4

    ... Typical application circuit and block diagram 1 Typical application circuit and block diagram 1.1 Application circuit Figure 1. Typical application circuit of the L6728D 12V CC C DEC PGOOD L6728D L6728A Reference Schematic 1.2 Block diagram Figure 2. Block diagram of the L6728D VSEN PGOOD 4/ VCC 1 10 ...

  • Page 5

    ... Open drain output set free after SS has finished and pulled low when VSEN is outside the 10 PGOOD relative window. Pull voltage equal or lower than VCC. If not used it can be left floating. Pin description and connection diagram L6728D Function R drop to measure the output current. This pin is also used by the DS(on) Doc ID 16498 Rev 1 resistor greater than 5 kΩ ...

  • Page 6

    ... Thermal resistance junction-to-case th(JC) T Maximum junction temperature MAX T Storage temperature range STG T Junction temperature range J P Maximum power dissipation at T TOT 6/33 Parameter = 25 °C A Doc ID 16498 Rev 1 L6728D Value Unit 45 °C/W 5 °C/W 150 °C -40 to 150 °C -40 to 125 °C 2.25 W ...

  • Page 7

    ... L6728D 4 Electrical specifications 4.1 Absolute maximum ratings Table 4. Absolute maximum ratings Symbol VCC to GND to PHASE GND BOOT, UGATE to GND; t < 200 ns to GND V PHASE to GND; t < 200 GND LGATE FB, COMP, VSEN to GND PGOOD to GND 4.2 Electrical characteristics Table 5. Electrical characteristics Symbol ...

  • Page 8

    ... VCC = 5 V Sourced from LGATE pin, during OC setting phase. V rising LGATE/OC VSEN rising un-latch, VSEN falling VSEN falling Sourced from VSEN VSEN rising VSEN falling PGOOD Doc ID 16498 Rev 1 L6728D Min. Typ. Max. Unit 1.5 A Ω 1.1 1.5 A Ω 0.65 μ ...

  • Page 9

    ... PGOOD in a compact DFN10 3x3 mm package. The L6728D is designed to operate from supply. The output voltage can be precisely regulated to as low as 0.8 V with ±0.8% accuracy over line and temperature variations. The switching frequency is internally set to 300 kHz. ...

  • Page 10

    ... Power dissipation The L6728D embeds high current MOSFET drivers for both high side and low side MOSFETs therefore important to consider the power that the device is going to dissipate in driving them, in order to avoid overcoming the maximum junction operating temperature ...

  • Page 11

    ... L6728D External gate resistors help the device to dissipate the switching power since the same power P is shared between the internal driver impedance and the external resistor, SW resulting in a general cooling of the device. Doc ID 16498 Rev 1 Driver section 11/33 ...

  • Page 12

    ... Low-side-less startup (LSLess) In order to avoid any kind of negative undershoot and dangerous return from the load during startup, the L6728D performs a special sequence in enabling the LS driver to switch: during the soft-start phase, the LS driver is disabled (LS = OFF) until the HS starts to switch. This prevents the dangerous negative spike on the output voltage which can happen if starting over a pre-biased output ...

  • Page 13

    ... The low side R DS(on) node when the LS MOSFET is turned on with the programmed OCP threshold voltages, internally held. If the monitored voltage is higher than these thresholds, an overcurrent event is detected. For maximum safety and load protection, the L6728D implements a dual-level overcurrent protection system: st ● 1 level threshold: This is the user externally-set threshold ...

  • Page 14

    ... Overcurrent protection 8.1 Overcurrent threshold setting The L6728D allows easy programming 550 mV, simply by adding a resistor (R level threshold is automatically set accordingly. During a short period of time (about 5 ms) following VCC rising over UVLO threshold, an internal 10 µA current (I across R . This voltage drop is sampled and internally held by the device OCSET overcurrent threshold. The OC setting procedure’ ...

  • Page 15

    ... L6728D 9 Output voltage setting and protections The L6728D is capable of precisely regulating an output voltage as low as 0 fact, the device is equipped with a fixed 0.8 V internal reference that guarantees the output regulated voltage remains within a ±0.8% tolerance over line and temperature variations (excluding output resistor divider tolerance, when present). ...

  • Page 16

    ... OSC _ + PWM COMPARATOR ERROR AMPLIFIER V REF + can be fixed by choosing the correct R 0dB shows an asymptotic bode plot of a type III compensation. Doc ID 16498 Rev 1 depending on the L OUT C OUT ESR and EA output with transfer OUT /2π. To achieve a good phase margin, SW L6728D OUT / ...

  • Page 17

    ... L6728D Figure 6. Example of type III compensation open loop EA gain closed loop gain compensation open loop converter gain ● Open loop converter singularities --------------------------------- - LC 2π ESR ● Compensation network singularities frequencies ------------------------------ Z1 2π ---------------------------------------------------- - Z2 2π ------------------------------------------------- - P1 2π ------------------------------ - P2 2π place the poles and zeroes of the compensation network, the following suggestions can ...

  • Page 18

    ... Check the phase margin obtained (it should be greater than 45°) and repeat if necessary. 10.2 Layout guidelines The L6728D provides control functions and high current integrated drivers to implement high-current step-down DC-DC converters. In this type of application, a good layout is very important. The first priority when placing components for these applications must be reserved for the power section, minimizing the length of each connection and loop as much as possible ...

  • Page 19

    ... It is then suggested in this cases to limit this extra charge by adding a small resistor in series to the bootstrap diode. Figure 8. Driver turn-on and turn-off paths LS DRIVER VCC LGATE GND V IN UGATE C IN PHASE L6728D LGATE GND LS MOSFET GATE INT Doc ID 16498 Rev 1 ...

  • Page 20

    ... Figure 9. Inductor current ripple vs output voltage 20/33 OUT the input voltage and V IN shows the ripple current vs. the output voltage for different values of the = 5 V and Doc ID 16498 Rev 1 L6728D is the output OUT ...

  • Page 21

    ... L6728D 11.2 Output capacitor(s) The output capacitors are basic components to define the ripple voltage across the output and for the fast transient response of the power supply. They depend on the output voltage ripple requirements, as well as any output voltage deviation requirement during a load transient ...

  • Page 22

    ... A demonstration board demonstration board The L6728D demonstration board is constructed using a four-layer PCB, and is designed as a step-down DC-DC converter. The board demonstrates the operation of the device in a general-purpose application. The input voltage can range from buses and the output voltage is fixed at 1.25 V. The application can deliver an output current ...

  • Page 23

    ... L6728D Figure 13 demonstration board schematic Doc ID 16498 Rev demonstration board 23/33 ...

  • Page 24

    ... Resistor, 2K2, 1/16W, 1% Resistor, 3K9, 1/16W, 1% Resistor, 18K, 1/16W, 1% Resistor, 22K, 1/16W, 1% Resistor, 20K, 1/16W, 1% Inductor, 1.25 μH, T60-18, 6 turns Easymagnet AP106019006P-1R1M Diode, 1N4148 or BAT54 STD70N02L STD95NH02LT4 Controller, L6728D Doc ID 16498 Rev 1 Description Package Radial SMD0603 SMD1206 SMD0805 SMD1206 Radial SMD0603 ...

  • Page 25

    ... L6728D 12.1 Board description 12.1.1 Power input (Vin) This is the input voltage for the power conversion. The high-side drain is connected to this input. This voltage can range from 1 bus. If the voltage is between 4.5 V and can also supply the device (through the Vcc pin) and in this case the R16 (0 Ω ...

  • Page 26

    ... A demonstration board demonstration board The L6728D demonstration board is constructed using a two-layer PCB, and is designed as a step-down DC-DC converter. The board demonstrates the operation of the device in a general-purpose, low-current application. The input voltage can range from buses and the output voltage is fixed at 1.25 V. The application can deliver an output current in excess ...

  • Page 27

    ... L6728D Figure 17 demonstration board schematic GND Doc ID 16498 Rev demonstration board OUT OUT OUT OUT OUT OUT OUT OUT OUT OUT OUT OUT OUT OUT OUT OUT COMP 27/33 ...

  • Page 28

    ... Resistor, 3R3, 1/ Resistor, 0R, 1/ Resistor, 1R8, 1 Resistor, 15R, 1/ Resistor, 2K2, 1/ Resistor, 3K9, 1/ Resistor, 4K7, 1/ Resistor, 22K, 1/ Resistor, 10K, 1/ Inductor, 2.2 μH, WURTH 744324220LF Diode, BAT54 STS9D8NH3LL Controller, L6728D Doc ID 16498 Rev 1 L6728D Package SMD1206 SMD0603 SMD0805 SMD1206 SMD7343 SMD0603 SMD0603 SMD0603 SMD0805 ...

  • Page 29

    ... L6728D 13.1 Board description 13.1.1 Power input (Vin) This is the input voltage for the power conversion. The high-side drain is connected to this input. This voltage can range from 1 bus. If the voltage is between 4.5 V and can also supply the device (through the Vcc pin), and in this case the R16 (0 Ω ...

  • Page 30

    ... A demonstration board 13.1.5 Board characterization Figure 18 demonstration board efficiency 30/33 Doc ID 16498 Rev 1 L6728D ...

  • Page 31

    ... L6728D 14 Package mechanical data In order to meet environmental requirements, ST offers these devices in different grades of ® ECOPACK packages, depending on their level of environmental compliance. ECOPACK specifications, grade definitions and product status are available at: www.st.com. ® ECOPACK trademark. Table 8. DFN10 mechanical data Dim Figure 19. Package dimensions mm Min ...

  • Page 32

    ... Revision history 15 Revision history Table 9. Document revision history Date 03-Feb-2010 32/33 Revision 1 Initial release. Doc ID 16498 Rev 1 L6728D Changes ...

  • Page 33

    ... L6728D Information in this document is provided solely in connection with ST products. STMicroelectronics NV and its subsidiaries (“ST”) reserve the right to make changes, corrections, modifications or improvements, to this document, and the products and services described herein at any time, without notice. All ST products are sold pursuant to ST’s terms and conditions of sale. ...