ST L6911E User Manual
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5 BIT PROGRAMMABLE STEP DOWN CONTROLLER
■
OPERATING SUPPL Y IC VOLTAGE FROM 5V
TO 12V BUSES
■
UP TO 1.3A GATE CURRENT CAPABILITY
■
TTL-COMP A T I BLE 5 BIT P ROGR AMMABLE
OUTPUT CO MPLIANT WITH VRM 8.5 :
1.050V TO 1.825V WITH 0.025V BINARY
STEPS
■
VOLTAGE MODE PWM CONTROL
■
EXCELLENT OUTPUT ACCURACY: ±1%
OVER LINE AND TEMPERATURE
VARIATIONS
■
VERY FAST LOAD TRANSIENT RESPONSE:
FROM 0% TO 100% DUTY CYCLE
■
POWER GOOD OU T PUT VO LTA GE
■
OVERVOLTAGE PROTECTION AND
MONITOR
■
OVERCURRENT PROTECTION REALIZED
USING THE UPPER MOSFE T'S R d sON
■
200KHz INTERNAL OSCILLATOR
■
OSCILLATOR EXTERNALLY ADJUST ABLE
FROM 50KHz TO 1MHz
■
SOFT START AND INHIBIT FUNCTIONS
APPLICATIONS
■
POWER SUPPLY FOR ADVANCED
MICROPROCESSOR CORE
■
DISTRIBUTED PO WE R SUPP LY
L6911E
WITH SYNCHRONOUS RECTIFICATION
SO-20
ORDERING NUMBERS: L6911E
DESCRIPTION
The device is a power supply controller specifically
designed to provide a high performance DC/DC conversion for high cur rent m icr oprocess ors. A precis e 5
bit digital to analog converter (DAC) allows to adjust
the output voltage from 1.050 to 1.825 with 25mV binary steps.
The high precision internal r eference ass ures the selected output voltage to be within ±1%. 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
overcurrent and load over-voltage. An external SCR
is triggered to crowbar the input supply in case of
hard overvoltage. An internal crowbar is also provided turning on the low side mosf et as long as the overvoltage is detected. In case of ove r-current detection,
the soft start capacitor is discharged an the system
works in HICCUP mode.
L6911ETR
(Tape and Reel)
BLOCK DIAGRAM
November 2001
PGOOD
OVP
VD0
VD1
VD2
VD3
VD4
D98IN957
Vcc 5V to12V
VCC OCSET
SS
RT
D/A
MONITOR and
PROTECTION
OSC
+
E/A
COMP
+
PWM
BOOT
UGATE
PHASE
LGATE
PGND
GND
VSEN
VFB
Vin 5V to12V
1.050V to 1.825V
Vo
1/20
L6911E
ABSOLUTE MAXIMUM RATINGS
Symbol Parameter Value Unit
Vcc Vcc to GND, PGND 15 V
V
BOOT-VPHASE
V
HGATE-VPHASE
PIN CONNECTION
Boot Voltage 15 V
15 V
OCSET, PHASE, LGATE -0.3 to Vcc+0.3 V
ROSC, SS, FB, PGOOD, VSEN 7 V
COMP, OVP 6.5 V
VSEN
OCSET
SS/INH
VID0
VID1
VID2
VID3
VID4
COMP PGOOD
FB GND
2
3
4
5
6
7
8
9
10
D98IN958
20
19
18
17
16
15
14
13
12
11
RT1
OVP
VCC
LGATE
PGND
BOOT
UGATE
PHASE
THERMA L D ATA
Symbol Parameter Value Unit
Rth j-amb Thermal Resistance Junction to Ambient 110 °
Tmax Maximum junction temperature 150 °
Tstorage Storage temperature range -40 to 150 °
2/20
T
J
Junction temperature range 0 to 125 °
C / W
C
C
C
L6911E
g
g
g
g
g
PIN FUNCTION
N Name Description
1 VSEN Connected to the output voltage is able to manage over-voltage conditions and the PGOOD signal.
2 OCSET A resistor connected from this pin and the upper Mos Drain sets the current limit protection.
The internal 200µA current
The Over-Current threshold is due to the followin
enerator sinks a current from the drain through the external resistor.
equation:
I
I
------------------------------------------------=
P
Þ
OCSETROCSET
R
DSon
3 SS/INH
The soft start time is pro
internal current
enerator forces through the capacitor 10µA.
rammed connecting an external capacitor from this pin and GND. The
This pin can be used to disable the device forcing a voltage lower than 0.4V
4 - 8 VID0 - 4 Voltage Identification Code pins. These input are internally pulled-up and TTL compatible. They are
used to program the output voltage as specified in Table 1 and to set the overvoltage and power
good thresholds.
Connect to GND to program a ‘0’ while leave floating to program a ‘1’.
9 COMP This pin is connected to the error amplifier output and is used to compensate the voltage control
feedback loop.
10 FB This pin is connected to the error amplifier inverting input and is used to compensate the voltage
control feedback loop.
11 GND All the internal references are referred to this pin. Connect it to the PCB signal ground.
12 PGOOD This pin is an open collector output and is pulled low if the output voltage is not within the above
specified threshlds.
If not used may be left floating.
13 PHASE This pin is connected to the source of the upper mosfet and provides the return path for the high side
driver. This pin monitors the drop across the upper mosfet for the current limit.
14 UGATE High side gate driver output.
15 BOOT Bootstrap capacitor pin. Through this pin is supplied the high side driver and the upper mosfet.
Connect through a capacitor to the PHASE pin and through a diode to Vcc (catode vs boot).
16 PGND Power ground pin. This pin has to be connected closely to the low side mosfet source in order to
reduce the noise injection into the device
17 LGATE This pin is the lower mosfet gate driver output
18 VCC Device supply voltage. The operative supply voltage range is from 4.5 to 12V.
DO NOT CONNECT V
TO 12V IF VCC IS 5V.
IN
19 OVP Over voltage protection. If the output voltage reach the 15% above the programmed voltage this pin
is driven high and can be used to drive an external SCR that crowbar the supply voltage.
If not used, it may be left floating.
20 RT Oscillator switching frequency pin. Connecting an external resistor from this pin to GND, the external
frequency is increased according to the equation:
6
510
⋅
f
S
200kHz
--------------------+=
R
kΩ()
T
Connecting a resistor from this pin to Vcc (12V), the switching frequency is reduced according to the
equation:
7
410
f
S
200kHz
--------------------–=
R
⋅
kΩ()
T
If the pin is not connected, the switching frequency is 200KHz.
The volta
e at this pin is fixed at 1.23V. Forcing a 50µA current into this pin, the built in oscillator
stops to switch.
3/20
L6911E
ELECTRICAL CHARACTERISTIC
(Vcc=12V; T=25°C unless otherwise specified)
Symbol Parameter Test Condition Min Typ Max Unit
Vcc SUPPLY CURRENT
Icc Vcc Supply current UGATE and LGATE open 5 mA
POWER-ON
Turn-On Vcc threshold V
Turn-Off Vcc threshold V
Rising V
threshold 1.26 V
OCSET
= 4.5V 4.6 V
OCSET
= 4.5V 3.6 V
OCSET
Iss Soft Start Current 10 µ
OSCILLATOR
Free running frequency RT = OPEN 180 200 220 KHz
∆
Vosc
Total Variation
6 KΩ< R
to GND <200 K
T
Ramp amplitude RT = OPEN 1.9 Vp-p
Ω -15 15 %
REFERENCE AND DAC
DACOUT Voltage
Accuracy
VID0, VID1,VID2, VID3,
VID25mV see Table1;Tamb=0 to
-1 1 %
70°C
VID Pull-Up voltage 3.1 V
ERROR AMPLIFIER
DC Gain 88 dB
GBWP G ain-Bandw idth Produ ct 15 MHz
SR Slew-Rate C OMP= 10pF 10
GATE DRIVERS
I
UGATE
R
UGATE
I
LGATE
High Side Source
Current
High Side Sink
Resistance
Low Side Source
- V
V
BOOT
V
- V
UGATE
V
BOOT-VPHASE
I
= 300mA
UGATE
Vcc=12V, V
PHASE
PHASE
LGATE
=12V,
= 6V
=12V,
= 6V
1 1.3 A
24Ω
0.9 1.1 A
Current
R
LGATE
Low Side Sink
Vcc=12V, I
LGATE
= 300mA
1.5 3 Ω
Resistance
Output Driver Dead Time PHASE connected to GND 120 nS
PROTECTIONS
Over Voltage Trip (V
SEN
/
V
Rising 117 120 %
SEN
DACOUT)
I
OCSET
I
OVP
OCSET Current Source V
OVP Sourcing Current V
= 4.5V 170 200 230 µ
OCSET
> OVP Trip, V
SEN
=0V 60 mA
OVP
POWER GOOD
V
Rising 108 110 112 %
SEN
V
Falling 88 90 92 %
SEN
Upper and Lower threshold 2 %
= -5mA 0.5 V
PGOOD
V
PGOOD
Upper Threshold
/DACOUT)
(V
SEN
Lower Threshold
(V
/DACOUT)
SEN
Hysteresis
(V
/DACOUT)
SEN
PGOOD Voltage Low I
A
V/µS
A
4/20
Table 1. VID Setting
VID4
(25mV)
VID3 VID2 VID1 VID0
00100
10100
00011
10011
00010
10010
00001
10001
00000
10000
01111
11111
01110
11110
01101
11101
Output
Voltage (V)
1.050
1.075
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
VID4
(25mV)
VID3 VID2 VID1 VID0
01100
11100
01011
11011
01010
11010
01001
11001
01000
11000
00111
10111
00110
10110
00101
10101
L6911E
Output
Voltage (V)
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
Device Description
The device is an i ntegrated circuit r ealized in BCD technol ogy. It provides c omplete control logic and protections
for a high performance step-down DC-DC converter optimized for microprocessor power supply. It is designed
to drive N Channel Mosfets in a synch ronou s-rectified buc k topology . The devic e works proper ly with V cc ranging from 5V to 12V and regulates the output voltage starting from a 1.26V power stage s upply voltage (Vin). The
output voltage of the converter can be precisely regulated, programming the VID pins, from 1.050V to 1.825V
with 25mV binary steps, with a maximum tolerance of ±1% over temperature and line voltage variations. The
device provides voltage-mode control with fast transient response. It includes a 200kHz free-running oscillator
that is adjustable from 50kHz to 1MHz. The error amplifier features a 15MHz gain-bandwidth product and 10V/
ms slew rate which permits high converter bandwidth for fast transient performance. The resulting PWM duty
cycle ranges from 0% to 100%. The device protects against over -curr ent condi tions entering in H ICCUP mode.
The device moni tors the curr ent by us ing the r
of the upper MOSFET which eliminates the need for a cur-
DS(ON)
rent sensing resistor.
The device is available in SO20 package.
Oscillator
The switching frequency is internally fixed to 200kHz. The internal oscillator generates the triangular waveform
for the PWM charging and discharging with a constant c urrent an internal capacit or. The current deliver ed to the
oscillator is tipically 50
µ
A (Fsw=200KHz) and may be v ari ed usi ng an external r esistor ( RT) connected between
RT pin and GND or VCC. Since the RT pin is maintained at fixed voltage (typ. 1.235V), the frequency is varied
proportionally to the current sinked (forced) from (into) the pin.
In particular connecting it to GND the frequency is increased (current is sinked from the pin), according to the
following relationship:
6
⋅
4.94 10
f
S
200kHz
-------------------------+=
Ω()
R
k
T
Connecting RT to VCC=12V or to VCC=5V the frequency is reduced (current is forced into the pin), according
to the following relationships:
5/20
L6911E
f
S
f
S
200kHz
200kHz
⋅
4.306 10
---------------------------- -+=
R
k
T
⋅
15 10
--------------------+=
R
k
T
Ω()
Ω()
7
V
7
V
CC
CC
= 12V
= 5V
Switching frequency variations vs. R
µ
Note that forcing a 50
A current into this pin, the device stops switching because no current is delivered to the
are reported in Fig.1.
T
oscillator.
Figure 1.
10000
1000
100
Resistance [kOhm ]
10
10 100 1000
R T to G ND
R T to VCC= 1 2V
R T to VCC= 5 V
Frequency [kHz]
Digital to Analog Converter
The built-in digital to analog converter allows the adjustment of the output voltage from 1.050V to 1.825V with
25mV binary steps as shown in the previous table 1. The internal reference is trimmed to ensure the precision
of 1%.
The internal reference voltage for the regulation is programmed by the voltage identification (VID) pins. These
are TTL compatible inputs of an internal D AC that is realised by means of a series of resistors rpoviding a partition of the internal voltage reference. The VID code drives a multiplexer that selects a voltage on a precis e
point of the divider. The D AC output i s del ivered to an amplifier obtaining the VPROG voltage referenc e ( i.e. the
set-point of the error amplifier). Internal pull-ups are provided (realized with a 5
µ
A current generator); in this
way, to program a logic "1" it is enough to leave the pin floating, while to program a logic "0" it is enough to short
the pin to GND.
The voltage identification (VID) pin configuration also sets the power-good thresholds (PGOOD) and the overvoltage protection (OVP) thresholds.
Soft Start and Inhibit
At start-up a ramp is generated charging the external capacitor CSS by means of a 10µA constant current, as
shown in figure 2.
When the voltage across the soft start capacitor (V
charge the output capacitor. As V
6/20
reaches 1V (i.e. the oscillator triangular wave inferior limit) also the upper
SS
) reaches 0.5V the lower power MOS is turned on to dis-
SS
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