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PDF L6728H Data sheet ( Hoja de datos )
| Número de pieza | L6728H | |
| Descripción | Single-phase Switching DC-DC Controllers & Smart Regulators | |
| Fabricantes | ST Microelectronics | |
| Logotipo |  |
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L6728H
Single phase PWM controller with Power Good
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 RDS(on)
■ OV / UV protections
■ VSEN disconnection protection
■ Oscillator internally fixed at 300 kHz
■ LSless to manage pre-bias start-up
■ Adjustable output voltage
■ Disable function
■ Internal soft-start
■ DFN10 package
Applications
■ Memory and termination supply
■ Subsystem power supply (MCH, IOCH, PCI...)
■ CPU and DSP power supply
■ Distributed power supply
■ General DC-DC converters
DFN10
Description
L6728H is a single-phase step-down controller
with integrated high-current drivers that provides
complete control logic and protection to realize in
a simple way general DC-DC converters by using
a compact DFN10 package.
Device flexibility allows managing conversions
with power input VIN as low as 1.5 V and device
supply voltage ranging from 5 V to 12 V.
L6728H provides simple control loop with voltage
mode EA. The integrated 0.8 V reference allows
regulating output voltages with ±0.8% accuracy
over line and temperature variations. Oscillator is
internally fixed to 300 kHz.
L6728H provides programmable dual level over
current protection as well as over and under
voltage protection. Current information is
monitored across the low-side MOSFET RDS(on)
saving the use of expensive and space-
consuming sense resistors.
PGOOD output easily provides real-time
information on output voltage status, through
VSEN dedicated output monitor.
Table 1.
Device summary
Order codes
L6728H
L6728HTR
Package
DFN10
Packaging
Tube
Tape and reel
May 2009
Doc ID 15725 Rev 1
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Pin description and connection diagrams
2 Pin description and connection diagrams
Figure 3. Pin connection (top view)
L6728H
2.1 Pin descriptions
Table 2. Pins description
Pin n° Name
Function
1
BOOT
HS driver supply. Connect through a capacitor (100 nF) to the floating node (LS-Drain) pin
and provide necessary bootstrap diode from VCC.
HS driver return path, current-reading and adaptive-dead-time monitor. Connect to the LS
2 PHASE drain to sense RDS(on) 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.
3 UGATE HS driver output. Connect directly to HS MOSFET gate.
LGATE. LS driver output. Connect directly to LS MOSFET gate. OC. Over current threshold
set. During a short period of time following VCC rising over UVLO threshold, a 10 μA current
4
LGATE / OC
is sourced from this pin. Connect to GND with an ROCSET resistor greater than 5 kΩ to
program OC threshold. The resulting voltage at this pin is sampled and held internally as the
OC set point. Maximum programmable OC threshold is 0.55 V. A voltage greater than 0.6 V
activates an internal clamp and causes OC threshold to be set at the maximum value.
5
GND
All internal references, logic and drivers are connected to this pin. Connect to the PCB ground
plane.
6
VCC
Device and drivers power supply. Operative range from 5 V to 12 V. Filter with at least 1 nF
MLCC to GND.
COMP. Error amplifier output. Connect with an RF - CF // CP to FB to compensate the device
7 COMP / DIS control loop. DIS. The device can be disabled by pushing this pin lower than 0.75 V (typ).
Setting free the pin, the device enables again.
8
FB
Error amplifier inverting input. Connect with a resistor RFB to the output regulated voltage.
Output resistor divider may be used to regulate voltages higher than the reference.
Regulated voltage sense pin for OVP and UVP protections and PGOOD. Connect to the
9 VSEN output regulated voltage, or to the output resistor divider if the regulated voltage is higher than
the reference.
Open drain output set free after SS has finished and pulled low when VSEN is outside the
10 PGOOD relative window. Pull up to a voltage equal or lower than VCC. If not used it can be left
floating.
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7 Soft-start
Soft-start
L6728H 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 gradually increases the
internal reference from 0 V to 0.8 V in 4.5 ms (typ.), in closed loop regulation, linearly
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 the PWM logic and both the high side and low
side gates. This condition is latched, cycle VCC to recover.
The device begins soft start phase only when VCC power supply is above UVLO threshold
and over current threshold setting phase has been completed.
7.1 Low-side-less startup (LSLess)
In order to avoid any kind of negative undershoot and dangerous return from the load during
start-up, L6728H performs a special sequence in enabling LS driver to switch: during the
soft-start phase, the LS driver results disabled (LS = OFF) until the HS starts to switch. This
avoid 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 higher than the final one, the HS would never
start to switch. In this case, at the end of soft start time, LS is enabled and discharge 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 this turning ON the LS MOSFET in case of need.
Figure 4. LSLess startup (left) vs non-LSLess startup (right)
Doc ID 15725 Rev 1
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| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet L6728H.PDF ] | |
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