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PDF L6727 Data sheet ( Hoja de datos )
| Número de pieza | L6727 | |
| Descripción | Single phase PWM controller | |
| Fabricantes | STMicroelectronics | |
| Logotipo |  |
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L6727
Single phase PWM controller
Feature
■ Flexible power supply from 5V to 12V
■ Power conversion input as low as 1.5V
■ 1% output voltage accuracy
■ High-current integrated drivers
■ Adjustable output voltage
■ 0.8V internal reference
■ Simple voltage mode control loop
■ Sensorless and programmable OCP across
Low-Side RdsON
■ Oscillator internally fixed at 300kHz
■ Internal Soft-Start
■ LS-LESS to manage pre-bias start-up
■ Disable function
■ OV / UV protection
■ FB disconnection protection
■ SO-8 package
Applications
■ Subsystem power supply (MCH, IOCH, PCI...)
■ Memory and termination supply
■ CPU & DSP power supply
■ Distributed power supply
■ General DC / DC converters
SO-8
Description
L6727 is a single-phase step-down controller with
integrated high-current drivers that provides
complete control logic, protections and reference
voltage to realize in an easy and simple way
general DC-DC converters by using a compact
SO-8 package.
Device flexibility allows managing conversions
with power input VIN as low as 1.5V and device
supply voltage in the range of 5V to 12V.
L6727 provides simple control loop with voltage-
mode error-amplifier. The integrated 0.8V
reference allows regulating output voltages with
±1% accuracy over line and temperature
variations. Oscillator is internally fixed to 300kHz.
L6727 provides programmable over current
protection as well as over and under voltage
protection. Current information is monitored
across the Low-Side mosfet RdsON saving the use
of expensive and space-consuming sense
resistors while output voltage is monitored
through FB pin.
FB disconnection protection prevents excessive
and dangerous output voltages in case of floating
FB pin.
Table 1. Device summary
Part Number
L6727
L6727TR
Package
SO-8
SO-8
Packaging
Tube
Tape & Reel
June 2007
Rev 3
1/22
www.st.com
1
1 page  
L6727
Pins description and connection diagrams
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2 Pins description and connection diagrams
Figure 3. Pins connection (top view)
BOOT
UGATE
GND
LGATE
18
27
3 L6727 6
45
PHASE
COMP / DIS / OC
FB
VCC
2.1
Pin descriptions
Table 2.
Pin #
Pins descriptions
Name
Function
HS Driver Supply.
1 BOOT Connect through a capacitor (100nF) to the floating node (LS-Drain) pin
and provide necessary bootstrap diode from VCC.
2 UGATE HS Driver Output. Connect to HS mosfet gate.
All internal references, logic and drivers are connected to this pin.
3 GND
Connect to the PCB ground plane.
4 LGATE LS Driver Output. Connect to LS mosfet gate.
Device and LS Driver power supply.
5 VCC
Operative range from 4.1V to 13.2V. Filter with at least 1µF MLCC to GND.
Error Amplifier Inverting Input.
6 FB Connect with a resistor RFB to the output regulated voltage. Additional
resistor ROS to GND may be used to regulate voltages higher than the
reference.
COMP. Error Amplifier Output. Connect with an RF - CF // CP to FB to
compensate the control-loop.
DIS. The device can be disabled by forcing this pin lower than 0.5V(typ). To
7
COMP / DIS
/ OC
disable the device, the external pull-down need to overcome 10mA of
COMP output current for about 15µs. Once disabled, COMP output current
drops to 20µA.
OC. Over current threshold set. Connect with an ROCSET resistor to VCC
(ONLY IF VCC is supplied by 5V bus) to program OC threshold. When
VCC > 5V, ROCSET need to be not-connected.
HS Driver return path, current-reading and adaptive-dead-time monitor.
8
PHASE
Connect to the LS drain to sense RdsON drop to measure the output
current. This pin is also used by the adaptive-dead-time control circuitry to
monitor when HS mosfet is OFF.
5/22
5 Page 
L6727
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6 Soft Start and Disable
Soft Start and Disable
L6727 implements a soft start to smoothly charge the output filter avoiding high in-rush
currents to be required from the input power supply. The device progressively increases the
internal reference from 0V to 0.8V in about 5.1ms, in closed loop regulation, gradually
charging the output capacitors to the final regulation voltage.
In the event of an over current triggering during soft start, the over current logic will override
the soft start sequence and will shut down both the high side and low side gates for the
internal soft start residual time (up to 2048 clock cycles) plus 2048 clock cycles, then it will
begin a new soft start.
The device begins soft start phase only when VCC power supply is above UVLO threshold
and over current threshold setting phase has been completed.
6.1 Low-Side-Less Start up (LSLess)
In order to manage start up over pre-biased output, L6727 performs a special sequence in
enabling LS driver to switch: during the soft-start phase, LS driver results disabled
(LS = OFF) until HS starts to switch. This avoids the dangerous negative spike on the output
voltage that can happen if starting over a pre-biased output.
If the output voltage is pre-biased to a voltage lower than the programmed one, neither HS
nor LS will turn on until the soft start ramp exceeds the output pre-bias voltage; then VOUT
will ramp up from there, without any drop or current return.
If the output voltage is pre-biased to a voltage higher than the programmed one, HS would
never start to switch. In this case, at the end of soft start time, LS is enabled and discharges
the output to the final regulation value.
This particular feature of the device masks the LS turn-on only from the control loop point of
view: protections by-pass LSLESS, turning ON the LS mosfet in case of need.
Figure 4. LSLess Startup (left) vs. Non-LSLess Startup (right)
11/22
11 Page | ||
| Páginas | Total 22 Páginas | |
| PDF Descargar | [ Datasheet L6727.PDF ] | |
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