L6911E
L6911E
5 BIT PROGRAMMABLE STEP DOWN CONTROLLER WITH SYNCHRONOUS RECTIFICATION
■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 8.5 : 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 OUTPUT VOLTAGE
■OVERVOLTAGE PROTECTION AND MONITOR
■OVERCURRENT PROTECTION REALIZED USING THE UPPER MOSFET'S RdsON
■200KHz INTERNAL OSCILLATOR
■OSCILLATOR EXTERNALLY ADJUSTABLE FROM 50KHz TO 1MHz
■SOFT START AND INHIBIT FUNCTIONS
APPLICATIONS
■POWER SUPPLY FOR ADVANCED MICROPROCESSOR CORE
■DISTRIBUTED POWER SUPPLY
BLOCK DIAGRAM
SO-20
ORDERING NUMBERS: L6911E
L6911ETR (Tape and Reel)
DESCRIPTION
The device is a power supply controller specifically designed to provide a high performance DC/DC conversion for high current microprocessors. A precise 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 reference assures 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 mosfet as long as the overvoltage is detected. In case of over-current detection, the soft start capacitor is discharged an the system works in HICCUP mode.
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Vcc 5V to12V |
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Vin 5V to12V |
PGOOD |
VCC |
OCSET |
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SS |
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BOOT |
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MONITOR and |
UGATE |
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PROTECTION |
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OVP |
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Vo |
RT |
OSC |
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PHASE |
1.050V to 1.825V |
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VD0 |
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LGATE |
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VD1 |
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PGND |
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VD2 |
D/A |
- |
GND |
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VD3 |
+ |
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VD4 |
+ |
PWM |
VSEN |
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- |
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VFB |
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E/A |
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D98IN957 |
COMP |
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November 2001 |
1/20 |
L6911E
ABSOLUTE MAXIMUM RATINGS
Symbol |
Parameter |
Value |
Unit |
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Vcc |
Vcc to GND, PGND |
15 |
V |
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VBOOT-VPHASE |
Boot Voltage |
15 |
V |
VHGATE-VPHASE |
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15 |
V |
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OCSET, PHASE, LGATE |
-0.3 to Vcc+0.3 |
V |
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ROSC, SS, FB, PGOOD, VSEN |
7 |
V |
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COMP, OVP |
6.5 |
V |
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PIN CONNECTION
VSEN |
1 |
20 |
RT |
OCSET |
2 |
19 |
OVP |
SS/INH |
3 |
18 |
VCC |
VID0 |
4 |
17 |
LGATE |
VID1 |
5 |
16 |
PGND |
VID2 |
6 |
15 |
BOOT |
VID3 |
7 |
14 |
UGATE |
VID4 |
8 |
13 |
PHASE |
COMP |
9 |
12 |
PGOOD |
FB |
10 |
11 |
GND |
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D98IN958 |
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THERMAL DATA
Symbol |
Parameter |
Value |
Unit |
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Rth j-amb |
Thermal Resistance Junction to Ambient |
110 |
°C / W |
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Tmax |
Maximum junction temperature |
150 |
°C |
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Tstorage |
Storage temperature range |
-40 to 150 |
°C |
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TJ |
Junction temperature range |
0 to 125 |
°C |
2/20
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L6911E |
PIN FUNCTION |
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Name |
Description |
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1 |
VSEN |
Connected to the output voltage is able to manage over-voltage conditions and the PGOOD signal. |
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2 |
OCSET |
A resistor connected from this pin and the upper Mos Drain sets the current limit protection. |
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The internal 200mA current generator sinks a current from the drain through the external resistor. |
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The Over-Current threshold is due to the following equation: |
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IO CSET Þ ROCS ET |
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IP = ------------------------------------------------ |
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RDSon |
3 |
SS/INH |
The soft start time is programmed connecting an external capacitor from this pin and GND. The |
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internal current generator forces through the capacitor 10mA. |
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This pin can be used to disable the device forcing a voltage lower than 0.4V |
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4 - 8 |
VID0 - 4 |
Voltage Identification Code pins. These input are internally pulled-up and TTL compatible. They are |
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used to program the output voltage as specified in Table 1 and to set the overvoltage and power |
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good thresholds. |
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Connect to GND to program a ‘0’ while leave floating to program a ‘1’. |
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9 |
COMP |
This pin is connected to the error amplifier output and is used to compensate the voltage control |
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feedback loop. |
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10 |
FB |
This pin is connected to the error amplifier inverting input and is used to compensate the voltage |
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control feedback loop. |
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11 |
GND |
All the internal references are referred to this pin. Connect it to the PCB signal ground. |
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12 |
PGOOD |
This pin is an open collector output and is pulled low if the output voltage is not within the above |
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specified threshlds. |
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If not used may be left floating. |
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13 |
PHASE |
This pin is connected to the source of the upper mosfet and provides the return path for the high side |
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driver. This pin monitors the drop across the upper mosfet for the current limit. |
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14 |
UGATE |
High side gate driver output. |
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15 |
BOOT |
Bootstrap capacitor pin. Through this pin is supplied the high side driver and the upper mosfet. |
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Connect through a capacitor to the PHASE pin and through a diode to Vcc (catode vs boot). |
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16 |
PGND |
Power ground pin. This pin has to be connected closely to the low side mosfet source in order to |
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reduce the noise injection into the device |
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17 |
LGATE |
This pin is the lower mosfet gate driver output |
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18 |
VCC |
Device supply voltage. The operative supply voltage range is from 4.5 to 12V. |
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DO NOT CONNECT VIN TO 12V IF VCC IS 5V. |
19 |
OVP |
Over voltage protection. If the output voltage reach the 15% above the programmed voltage this pin |
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is driven high and can be used to drive an external SCR that crowbar the supply voltage. |
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If not used, it may be left floating. |
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20 |
RT |
Oscillator switching frequency pin. Connecting an external resistor from this pin to GND, the external |
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frequency is increased according to the equation: |
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5 × 106 |
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fS = 200kHz + -------------------- |
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RT (kW ) |
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Connecting a resistor from this pin to Vcc (12V), the switching frequency is reduced according to the |
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equation: |
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4 × 107 |
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fS = 200kHz – -------------------- |
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RT (kW) |
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If the pin is not connected, the switching frequency is 200KHz. |
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The voltage at this pin is fixed at 1.23V. Forcing a 50mA current into this pin, the built in oscillator |
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stops to switch. |
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3/20 |
L6911E
ELECTRICAL CHARACTERISTIC (Vcc=12V; T=25°C unless otherwise specified)
Symbol |
Parameter |
Test Condition |
Min |
Typ |
Max |
Unit |
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Vcc SUPPLY CURRENT |
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Icc |
Vcc Supply current |
UGATE and LGATE open |
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5 |
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mA |
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POWER- |
ON |
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Turn-On Vcc threshold |
VOCSET = 4.5V |
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4.6 |
V |
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Turn-Off Vcc threshold |
VOCSET = 4.5V |
3.6 |
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V |
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Rising VOCSET threshold |
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1.26 |
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V |
Iss |
Soft Start Current |
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10 |
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μA |
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OSCILLATOR |
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Free running frequency |
RT = OPEN |
180 |
200 |
220 |
KHz |
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Total Variation |
6 KΩ< RT to GND <200 KΩ |
-15 |
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15 |
% |
Vosc |
Ramp amplitude |
RT = OPEN |
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1.9 |
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Vp-p |
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REFERENCE AND DAC |
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DACOUT Voltage |
VID0, VID1,VID2, VID3, |
-1 |
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1 |
% |
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Accuracy |
VID25mV see Table1;Tamb=0 to |
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70°C |
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VID Pull-Up voltage |
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3.1 |
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V |
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ERROR |
AMPLIFIER |
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DC Gain |
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88 |
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dB |
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GBWP |
Gain-Bandwidth Product |
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15 |
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MHz |
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SR |
Slew-Rate |
COMP=10pF |
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10 |
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V/μS |
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GATE DRIVERS |
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IUGATE |
High Side Source |
VBOOT - VPHASE=12V, |
1 |
1.3 |
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A |
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Current |
VUGATE - VPHASE= 6V |
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RUGATE |
High Side Sink |
VBOOT-VPHASE=12V, |
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2 |
4 |
Ω |
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Resistance |
IUGATE = 300mA |
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ILGATE |
Low Side Source |
Vcc=12V, VLGATE = 6V |
0.9 |
1.1 |
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A |
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Current |
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RLGATE |
Low Side Sink |
Vcc=12V, ILGATE = 300mA |
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1.5 |
3 |
Ω |
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Resistance |
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Output Driver Dead Time |
PHASE connected to GND |
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120 |
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nS |
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PROTECTIONS |
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Over Voltage Trip (VSEN/ |
VSEN Rising |
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117 |
120 |
% |
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DACOUT) |
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IOCSET |
OCSET Current Source |
VOCSET = 4.5V |
170 |
200 |
230 |
μA |
IOVP |
OVP Sourcing Current |
VSEN > OVP Trip, VOVP=0V |
60 |
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mA |
POWER |
GOOD |
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Upper Threshold |
VSEN Rising |
108 |
110 |
112 |
% |
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(VSEN/DACOUT) |
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Lower Threshold |
VSEN Falling |
88 |
90 |
92 |
% |
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(VSEN/DACOUT) |
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Hysteresis |
Upper and Lower threshold |
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2 |
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% |
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(VSEN/DACOUT) |
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VPGOOD |
PGOOD Voltage Low |
IPGOOD = -5mA |
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0.5 |
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V |
4/20
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L6911E |
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Table 1. VID Setting |
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VID4 |
VID3 |
VID2 |
VID1 |
VID0 |
Output |
VID4 |
VID3 |
VID2 |
VID1 |
VID0 |
Output |
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(25mV) |
Voltage (V) |
(25mV) |
Voltage (V) |
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0 |
0 |
1 |
0 |
0 |
1.050 |
0 |
1 |
1 |
0 |
0 |
1.450 |
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1 |
0 |
1 |
0 |
0 |
1.075 |
1 |
1 |
1 |
0 |
0 |
1.475 |
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0 |
0 |
0 |
1 |
1 |
1.100 |
0 |
1 |
0 |
1 |
1 |
1.500 |
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1 |
0 |
0 |
1 |
1 |
1.125 |
1 |
1 |
0 |
1 |
1 |
1.525 |
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0 |
0 |
0 |
1 |
0 |
1.150 |
0 |
1 |
0 |
1 |
0 |
1.550 |
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1 |
0 |
0 |
1 |
0 |
1.175 |
1 |
1 |
0 |
1 |
0 |
1.575 |
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0 |
0 |
0 |
0 |
1 |
1.200 |
0 |
1 |
0 |
0 |
1 |
1.600 |
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1 |
0 |
0 |
0 |
1 |
1.225 |
1 |
1 |
0 |
0 |
1 |
1.625 |
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0 |
0 |
0 |
0 |
0 |
1.250 |
0 |
1 |
0 |
0 |
0 |
1.650 |
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1 |
0 |
0 |
0 |
0 |
1.275 |
1 |
1 |
0 |
0 |
0 |
1.675 |
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0 |
1 |
1 |
1 |
1 |
1.300 |
0 |
0 |
1 |
1 |
1 |
1.700 |
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1 |
1 |
1 |
1 |
1 |
1.325 |
1 |
0 |
1 |
1 |
1 |
1.725 |
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0 |
1 |
1 |
1 |
0 |
1.350 |
0 |
0 |
1 |
1 |
0 |
1.750 |
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1 |
1 |
1 |
1 |
0 |
1.375 |
1 |
0 |
1 |
1 |
0 |
1.775 |
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0 |
1 |
1 |
0 |
1 |
1.400 |
0 |
0 |
1 |
0 |
1 |
1.800 |
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1 |
1 |
1 |
0 |
1 |
1.425 |
1 |
0 |
1 |
0 |
1 |
1.825 |
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Device Description
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 ranging 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 1.050V 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-current conditions entering in HICCUP mode.
The device monitors the current by using the rDS(ON) of the upper MOSFET which eliminates the need for a current 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 current an internal capacitor. The current delivered to the oscillator is tipically 50mA (Fsw=200KHz) and may be varied using an external resistor (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:
4.94 × 106 f = 200kHz + -------------------------
S RT (kW)
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
4.306 × 107 f = 200kHz + ----------------------------
S RT (kW)
15 × 107 f = 200kHz + --------------------
S RT (kW)
VCC = 12V
VCC = 5V
Switching frequency variations vs. RT are reported in Fig.1.
Note that forcing a 50mA current into this pin, the device stops switching because no current is delivered to the oscillator.
Figure 1.
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1 0 00 0 |
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1 00 0 |
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ce [kO h m ] |
10 0 |
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R e sista n |
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R T to G ND |
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1 0 |
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R T to VC C= 12V |
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R T to VC C= 5V |
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10 |
10 0 |
1 00 0 |
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Frequency [kH z] |
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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 DAC 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 precise point of the divider. The DAC output is delivered to an amplifier obtaining the VPROG voltage reference (i.e. the set-point of the error amplifier). Internal pull-ups are provided (realized with a 5mA 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 (VSS) reaches 0.5V the lower power MOS is turned on to discharge the output capacitor. As VSS reaches 1V (i.e. the oscillator triangular wave inferior limit) also the upper
6/20