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PDF L6917B Data sheet ( Hoja de datos )

Número de pieza L6917B
Descripción 5 BIT PROGRAMMABLE DUAL-PHASE CONTROLLER
Fabricantes STMicroelectronics 
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L6917B
5 BIT PROGRAMMABLE DUAL-PHASE CONTROLLER
s 2 PHASE OPERATION WITH
SYNCRHONOUS RECTIFIER CONTROL
s ULTRA FAST LOAD TRANSIENT RESPONSE
s INTEGRATED HIGH CURRENT GATE
DRIVERS: UP TO 2A GATE CURRENT
s TTL-COMPATIBLE 5 BIT PROGRAMMABLE
OUTPUT COMPLIANT WITH VRM 9.0
s 0.8% INTERNAL REFERENCE ACCURACY
s 10% ACTIVE CURRENT SHARING
ACCURACY
s DIGITAL 2048 STEP SOFT-START
s OVERVOLTAGE PROTECTION
s OVERCURRENT PROTECTION REALIZED
USING THE LOWER MOSFET'S RdsON OR A
SENSE RESISTOR
s 300 kHz INTERNAL OSCILLATOR
s OSCILLATOR EXTERNALLY ADJUSTABLE
UP TO 600kHz
s POWER GOOD OUTPUT AND INHIBIT
FUNCTION
s REMOTE SENSE BUFFER
s PACKAGE: SO-28
APPLICATIONS
s POWER SUPPLY FOR SERVERS AND
WORKSTATIONS
s POWER SUPPLY FOR HIGH CURRENT
MICROPROCESSORS
s DISTRIBUTED DC-DC CONVERTERS
SO-28
ORDERING NUMBERS:L6917BD
L6917BDTR (Tape & Reel)
DESCRIPTION
The device is a power supply controller specifically
designed to provide a high performance DC/DC con-
version for high current microprocessors.
The device implements a dual-phase step-down con-
troller with a 180° phase-shift between each phase.
A precise 5-bit digital to analog converter (DAC) al-
lows adjusting the output voltage from 1.100V to
1.850V with 25mV binary steps.
The high precision internal reference assures the se-
lected output voltage to be within ±0.8%. The high
peak current gate drive affords to have fast switching
to the external power mos providing low switching
losses.
The device assures a fast protection against load
over current and load over/under voltage. An internal
crowbar is provided turning on the low side mosfet if
an over-voltage is detected. In case of over-current,
the system works in Constant Current mode.
BLOCK DIAGRAM
PGOOD
ROSC / INH
2 PHASE
OSCILLATOR
DIGITAL
SOFT START
VID4
VID3
VID2
VID1
VID0
DAC
FBG
FBR
10k
10k
10k
10k
REMOTE
BUFFER
LOGIC
AND
PROTEC TIONS
VCC
VCC DR
CH1 OVER
CU RR EN T
CH2 OVER
CU RR EN T
IFB
ERR OR
AMPLIFIER
SGND
VCCD R
PWM1
-
+
CH 1 OVER
CU RR EN T
+TOTAL
CU RR EN T
AVG
CU RR EN T
<>
CURRENT
READ ING
CURRENT
READ ING
CH 2 OVER
CU RR EN T
+
-
PWM2
Vcc
HS
LS
LS
HS
BOOT1
UGATE1
PH AS E1
LGATE1
ISEN1
PGNDS1
PGND
PGNDS2
ISEN2
LGATE2
PH AS E2
UGATE2
BOOT2
September 2002
VSEN
FB
COMP
Vcc
1/33

1 page




L6917B pdf
Table 1. VID Settings
VID4
VID3
11
11
11
11
11
11
11
11
10
10
10
10
10
10
10
10
01
01
01
01
01
01
01
01
00
00
00
00
00
00
00
00
VID2
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
VID1
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
VID0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
L6917B
Output Voltage (V)
OUTPUT OFF
1.100
1.125
1.150
1.175
1.200
1.225
1.250
1.275
1.300
1.325
1.350
1.375
1.400
1.425
1.450
1.475
1.500
1.525
1.550
1.575
1.600
1.625
1.650
1.675
1.700
1.725
1.750
1.775
1.800
1.825
1.850
5/33

5 Page





L6917B arduino
L6917B
which the low-side mosfet is on (OFF Time). During this time, the reaction keeps the pin ISENx and PGNDSx
at the same voltage while during the time in which the reading circuitry is off, an internal clamp keeps these two
pins at the same voltage sinking from the ISENx pin the necessary current.
The proprietary current reading circuit allows a very precise and high bandwidth reading for both positive and
negative current. This circuit reproduces the current flowing through the sensing element using a high speed
Track & Hold transconductance amplifier. In particular, it reads the current during the second half of the OFF
time reducing noise injection into the device due to the mosfet turn-on (See fig. 4). Track time must be at least
200ns to make proper reading of the delivered current.
Figure 4. Current Reading Timing (Left) and Circuit (Right)
ILS1
ILS2
Total current
information
Track & Hold
LGATEX
ISENX
PGNDSX
Rg
IISENx
Rg
50µA
This circuit sources a constant 50µA current from the PGNDSx pin and keeps the pins ISENx and PGNDSx at
the same voltage. Referring to figure 4, the current that flows in the ISENx pin is then given by the following
equation:
IISENx = 50µA + -R----S----E---N----S----ER-----g---I-P----H----A----S---E-- = 50µ A + IINFOx
Where RSENSE is an external sense resistor or the rds,on of the low side mosfet and Rg is the transconductance
resistor used between ISENx and PGNDSx pins toward the reading points; IPHASE is the current carried by each
phase and, in particular, the current measured in the middle of the oscillator period
The current information reproduced internally is represented by the second term of the previous equation as
follow:
IINFOx
=
R-----S----E---N----S----E--------I-P----H----A----S---E--
Rg
Since the current is read in differential mode, also negative current information is kept; this allow the device to
check for dangerous returning current between the two phases assuring the complete equalization between the
phase's currents.
From the current information of each phase, information about the total current delivered (IFB = IINFO1 + IINFO2)
and the average current for each phase (IAVG = (IINFO1 + IINFO2)/2 ) is taken. IINFOX is then compared to IAVG
to give the correction to the PWM output in order to equalize the current carried by the two phases.
The transconductance resistor Rg has to be designed in order to have current information of 25µA per phase
at full nominal load; the over current intervention threshold is set at 140% of the nominal (IINFOx = 35µA).
According to the above relationship, the limiting current (ILIM) for each phase, which has to be placed at one half
of the total delivered maximum current, results:
ILIM
=
3----5----µ----A--------R-----g--
RSENSE
Rg = -I-L---I--M-----3---5-R---µ-S---A-E---N----S----E--
An over current is detected when the current flowing into the sense element is greater than 140% of the nominal
11/33

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