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SC1211VXSTR Datasheet(PDF) 8 Page - Semtech Corporation

Part # SC1211VXSTR
Description  High Speed, Combi-Sense짰, Synchronous MOSFET Driver for Mobile Applications
Download  11 Pages
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Manufacturer  SEMTECH [Semtech Corporation]
Direct Link  http://www.semtech.com
Logo SEMTECH - Semtech Corporation

SC1211VXSTR Datasheet(HTML) 8 Page - Semtech Corporation

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 2005 Semtech Corp.
www.semtech.com
POWER MANAGEMENT
SC1211VX
Applications Information
THEOR
THEOR
THEOR
THEOR
THEORY OF OPERA
Y OF OPERA
Y OF OPERA
Y OF OPERA
Y OF OPERATION
TION
TION
TION
TION
The SC1211VX is a high speed, Combi-Sense®, dual out-
put driver designed to drive top and bottom MOSFETs in
a synchronous Buck converter. It features adaptive de-
lay for shoot-through protection and VID-on-Fly opera-
tion; 5V gate drive voltage; and Virtual Phase Node for
Combi-Sense® solution. These drivers combined with
PWM controller SC2643VX form a multi-phase voltage
regulator for advanced microprocessors. A three-phase
voltage regulator with 19V input 60A output is shown in
the Typical Application Circuit section.
Startup and UVLO
Startup and UVLO
Startup and UVLO
Startup and UVLO
Startup and UVLO
To startup the driver, a supply voltage applied to VCC pin
of the SC1211VX. The top and bottom gates are held
low until VCC exceeds UVLO threshold of the driver, typi-
cally 4.2V. Then the top gate remains low and the bot-
tom gate is pulled high to turn on the bottom FET. Once
VIN exceeds UVLO threshold of the PWM controller, typi-
cally 7.5V, the soft-start begins and the PWM signal takes
fully control of the gate transitions.
Gat
Gat
Gat
Gat
Gate T
e T
e T
e T
e Transition and Shoo
ransition and Shoo
ransition and Shoo
ransition and Shoo
ransition and Shoot thr
t thr
t thr
t thr
t through Pr
ough Pr
ough Pr
ough Pr
ough Proooootttttection
ection
ection
ection
ection
Refer to the Timing Diagrams section, the rising edge of
the PWM input initiates the bottom FET turn-off and the
top FET turn-on. After a short propagation delay (tPDL_BG),
the bottom gate begins to fall (tF_BG). An adaptive circuit
in the SC1211VX monitors the bottom gate voltage to
drop below 1.4V. Then after a preset delay time (tPDH_TG)
is expired, the top gate turns on. The delay time is set to
be 20ns typically. This prevents the top FET from turning
on until the bottom FET is off. During the transition, the
inductor current is freewheeling through the body diode
of either bottom FET or top FET, upon the direction of
the inductor current. The phase node could be low
(ground) or high (VIN).
The falling edge of the PWM input controls the top FET
turn-off and the bottom FET turn-on. After a short propa-
gation delay (tPDL_TG), the top gate begins to fall (tF_TG).
As the inductor current is commutated from the top FET
to the body diode of the bottom FET, the phase node
begins to fall. The adaptive circuit in the SC1211VX de-
tects the phase node voltage. It holds the bottom FET
off until the phase node voltage has dropped below 1.0V.
This prevents the top and bottom FETs from conducting
simultaneously or shoot-through.
VID-on-Fly Operation
VID-on-Fly Operation
VID-on-Fly Operation
VID-on-Fly Operation
VID-on-Fly Operation
Certain new processors have required to changing the
VID dynamically during the operation, or refered as VID-
on-Fly operation. A VID-on-Fly can occur under light load
or heavy load conditions. At light load, it could force the
converter to sink current. Upon turn-off of the top FET,
the reversed inductor current has to be freewheeling
through the body diode of the top FET instead of the
bottom FET. As a result, the phase node voltage remains
high. The SC1211VX incorporates the ability by pulling
the bottom gate to high internally, which over rides the
adaptive circuit and turns the bottom FET on. The delay
time from the PWM falling egde to the bottom gate turn-
on is set at 200ns typically.
Virtual Phase Node for
Virtual Phase Node for
Virtual Phase Node for
Virtual Phase Node for
Virtual Phase Node for Combi-Sense
Combi-Sense
Combi-Sense
Combi-Sense
Combi-Sense®
Peak-Current-Mode control is widely employed in multi-
phase voltage regulators. It features phase current bal-
ance, fast transient response, and over current protec-
tion, etc. These are essential to low-voltage high-cur-
rent regulators designed for advanced microprocessors.
Usually, a costly current sensing resistor is required to
obtain the output inductor current information for the
peak current control. The Combi-Sense® technique fea-
tured by the SC1211VX is an approach to sense induc-
tor current without using sensing resistor.
The above circuit shows the concept of Combi-Sense®
technique. An internal totem pole (Qcst, Qcsb) gener-
ates a VPN (Virtual Phase Node) signal. This VPN follows
the DRN (or the Power Phase Node) with the same tim-
ing. A RC network (Rcs and Ccs) is connected between
Inductor Current Signal
Vout
Qcst
VIN
Rcs
C
SC1211VX
PGND
VIN
VPN
Lo
Q2
Qcsb
DRN
Q1
+
Co
Ccs


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