L6911C
5 BIT PROGRAMMABLE STEP DOWN CONTROLLER
WITH SYNCHRONOUS RECTIFICATION
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APPLICATIONS
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POWER SUPPLY FOR ADVANCED
MICROPROCESSOR CORE
s
DISTRIBUTED POWER SUPPLY
s
HIGH POWER DC-DC REGULATORS
BLOCK DIAGRAM
Vcc 5 to 12V
PGOOD
VCC
OCSET
SS
BOOT
MONITOR and
PROTECTION
UGATE
OVP
RT
OSC
PHASE
LGATE
PGND
D/A
+
-
E/A
-
+
PWM
GND
VSEN
VFB
VD0
VD1
VD2
VD3
VD4
OPERATING SUPPLY IC VOLTAGE FROM 5V
TO 12V BUSES
UP TO 1.3A GATE CURRENT CAPABILITY
TTL-COMPATIBLE 5 BIT PROGRAMMABLE
OUTPUT COMPLIANT WITH VRM 8.4 :
1.3V TO 2.05V WITH 0.05V BINARY STEPS
2.1V TO 3.5V WITH 0.1V 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 OUTPUT VOLTAGE
OVERVOLTAGE PROTECTION AND
MONITOR
OVERCURRENT PROTECTION REALIZED
USING THE UPPER MOSFET'S R
dsON
200KHz INTERNAL OSCILLATOR
OSCILLATOR EXTERNALLY ADJUSTABLE
FROM 50KHz TO 1MHz
SOFT START AND INHIBIT FUNCTIONS
SO-20
ORDERING NUMBERS: L6911C
L6911CTR
(Tape and Reel)
b
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DESCRIPTION
The device is a power supply controller specifically de-
signed to provide a high performance DC/DC conver-
sion for high current microprocessors. A precise 5-bit
digital to analog converter (DAC) allows adjusting the
output voltage from 1.30V to 2.05V with 50mV binary
steps and from 2.10V to 3.50V with 100mV binary steps.
The high precision internal reference assures the se-
lected 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 overvoltage. An external SCR is
triggered to crowbar the input supply in case of hard
over-voltage. An internal crowbar is also provided
turning on the low side mosfet as long as the over-
voltage is detected. In case of over-current detection,
the soft start capacitor is discharged and the system
works in HICCUP mode.
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Vin 5V to12V
Vo
1.300V to 3.500V
D01IN1260
COMP
November 2001
1/20
L6911C
ABSOLUTE MAXIMUM RATINGS
Symbol
V
CC
V
BOOT
-V
PHASE
V
HGATE
-V
PHASE
OCSET, LGATE, PHASE
RT, SS, FB, PGOOD, VSEN, VID0-4
OVP, COMP
V
CC
to GND, PGND
Boot Voltage
Parameter
Value
15
15
15
-0.3 to Vcc+0.3
7
6.5
Unit
V
V
V
V
V
THERMAL DATA
Symbol
R
th j-amb
T
j
T
stg
T
J
Parameter
Thermal Resistance Junction to Ambient
Maximum junction temperature
Storage temperature range
Junction temperature range
PIN CONNECTION
(Top view)
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VSEN
1
2
3
4
5
6
7
8
9
OCSET
SS/INH
VID0
VID1
VID2
VID3
VID4
COMP
FB
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19
18
17
16
15
14
13
12
11
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P
Value
110
150
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Unit
°C/W
°C
°C
°C
V
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RT
OVP
VCC
LGATE
PGND
BOOT
UGATE
PHASE
PGOOD
GND
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P
-40 to 150
0 to 125
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D98IN958
2/20
L6911C
PIN FUNCTION
Pin
Num.
1
2
Name
VSEN
OCSET
Description
Connected to the output voltage is able to manage over-voltage conditions and the PGOOD
signal.
A resistor connected from this pin and the upper Mos Drain sets the current limit protection.
The internal 200µA current generator sinks a current from the drain through the external resistor.
The Over-Current threshold is due to the following equation:
I
OCSE T
⋅
R
O CS ET
I
P
= ---------------------------------------------
-
R
DS on
The soft start time is programmed connecting an external capacitor from this pin and GND. The
internal current generator forces through the capacitor 10µA.
This pin can be used to disable the device forcing a voltage lower than 0.4V
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’.
This pin is connected to the error amplifier output and is used to compensate the voltage control
feedback loop.
This pin is connected to the error amplifier inverting input and is used to compensate the voltage
control feedback loop.
All the internal references are referred to this pin. Connect it to the PCB signal ground.
This pin is an open collector output and is pulled low if the output voltage is not within the above
specified thresholds.
If not used may be left floating.
3
SS/INH
4-8
VID0 - 4
9
10
11
12
COMP
FB
GND
PGOOD
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13
PHASE
UGATE
BOOT
14
15
High side gate driver output.
16
17
PGND
LGATE
VCC
OVP
This pin is the lower mosfet gate driver output
18
19
20
RT
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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
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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 (cathode vs. boot).
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
Device supply voltage. The operative nominal supply voltage ranges from 5 to 12V.
DO NOT CONNECT V
IN
TO A VOLTAGE GREATER THAN V
CC
.
Over voltage protection. If the output voltage reaches the 17% 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.
Oscillator switching frequency pin. Connecting an external resistor from this pin to GND, the
external frequency is increased according to the equation:
4.94
⋅
10
f
S
=
200kHz
+ -------------------------
R
T
(
kΩ
)
6
Connecting a resistor from this pin to Vcc (12V), the switching frequency is reduced according to
the equation:
4.306
⋅
10
f
S
=
200kHz
– ----------------------------
-
R
T
(
kΩ
)
If the pin is not connected, the switching frequency is 200KHz.
The voltage at this pin is fixed at 1.23V (typ). Forcing a 50µA current into this pin, the built in
oscillator stops to switch.
7
3/20
L6911C
ELECTRICAL CHARACTERISTCS
(V
CC
= 12V, T
amb
= 25°C unless otherwise specified)
Symbol
Parameter
Test Condition
Min.
Typ.
Max.
Unit
V
CC
SUPPLY CURRENT
Icc
Vcc Supply current
Turn-On Vcc threshold
Turn-Off Vcc threshold
Rising V
OCSET
threshold
I
SS
Soft start Current
UGATE and LGATE open
VOCSET=4.5V
VOCSET=4.5V
3.6
1.24
10
5
4.6
mA
V
V
V
µA
220
15
POWER-ON
OSCILLATOR
Free running frequency
Total Variation
∆V
osc
Ramp amplitude
R
T
= OPEN
6 KΩ < RT to GND < 200 KΩ
R
T
= OPEN
VID0, VID1, VID2, VID3, VID4
see Table1; Tamb = 0 to 70°C
-1
180
-15
200
1.9
REFERENCE AND DAC
DACOUT Voltage
Accuracy
VID Pull-Up voltage
ERROR AMPLIFIER
DC Gain
GBWP
SR
Gain-Bandwidth Product
Slew-Rate
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GATE DRIVERS
I
UGATE
High Side Source
Current
High Side Sink
Resistance
V
BOOT
- V
PHASE
=12V,
V
UGATE
- V
PHASE
= 6V
V
BOOT
-V
PHASE
=12V,
I
UGATE
= 300mA
R
UGATE
I
LGATE
Low Side Source
Current
Low Side Sink
Resistance
Vcc=12V, V
LGATE
= 6V
R
LGATE
Vcc=12V, I
LGATE
= 300mA
Output Driver Dead Time
Over Voltage Trip
(V
SEN
/DACOUT)
PROTECTIONS
V
SEN
Rising
I
OCSET
I
OVP
OCSET Current Source
OVP Sourcing Current
V
OCSET
= 4.5V
POWER GOOD
Upper Threshold
(V
SEN
/DACOUT)
Lower Threshold
(V
SEN
/DACOUT)
Hysteresis
(V
SEN
/DACOUT)
V
PGOOD
PGOOD Voltage Low
V
SEN
Rising
V
SEN
Falling
I
PGOOD
= -5mA
COMP=10pF
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KHz
%
Vp-p
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88
10
10
1.3
2
1.1
1.5
120
117
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1
V
A
4
Ω
A
3
Ω
%
dB
MHz
V/µS
PHASE connected to GND
ns
120
230
%
µA
mA
170
60
200
V
SEN
> OVP Trip, V
OVP
=0V
110
86
112
88
2
0.5
114
90
%
%
%
V
Upper and Lower threshold
4/20
L6911C
Table 1. VID Settings
VID4
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
VID3
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
VID2
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
VID0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
Output
Voltage (V)
1.30
1.35
1.40
1.45
1.50
1.55
1.60
1.65
1.70
1.75
1.80
1.85
1.90
1.95
2.00
2.05
VID4
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
VID3
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
VID2
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
VID1
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
Output
Voltage (V)
Output Off
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
Device Description
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The device is available in SO20 package.
Oscillator
4.94
⋅
10
f
S
=
200kH z
+ -------------------------
R
T
(
kΩ
)
6
The device is an integrated circuit realized in BCD technology. It provides complete 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 synchronous-rectified buck topology. The device works properly with Vcc rang-
ing from 5V to 12V and regulates the output voltage starting from a 1.26V power stage supply voltage (Vin). The
output voltage of the converter can be precisely regulated, programming the VID pins, from 1.3V to 2.05V with
50mV binary steps and from 2.1V to 3.5V with 100mV binary steps, with a maximum tolerance of ±1% over tem-
perature 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/µsec slew rate which permits high converter bandwidth for fast tran-
sient performance. The resulting PWM duty cycle ranges from 0% to 100%. The device protects against over-
current conditions entering in HICCUP mode. The device monitors the current by using the r
DS(ON)
of the upper
MOSFET which eliminates the need for a current sensing resistor.
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2.9
3.0
3.1
3.2
3.3
3.4
3.5
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The switching frequency is internally fixed to 200kHz. The internal oscillator generates the triangular waveform
for the PWM charging and discharging with a constant current an internal capacitor. The current delivered to the
oscillator is typically 50µA (Fsw=200KHz) and may be varied using an external resistor (R
T
) 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 sunk (forced) from (into) the pin.
In particular connecting it to GND the frequency is increased (current is sunk from the pin), according to the
following relationship:
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
