10/96
BLOCK DIAGRAM
• Combined DAC/Voltage
Monitor and PWM Functions
• 4-Bit Digital-to-Analog
Converter (DAC)
• 1.0% DAC/Reference
• Low Offset X20 Current Sense
Amplifier
• 100kHz, 200kHz, 400kHz
Oscillator Frequency Options
• Foldback Current Limiting
• Overvoltage and Undervoltage
Fault Windows
• Undervoltage Lockout
• 2Ω Totem Pole Output
• Chip Disable Function
Pentium® Pro Controller
FEATURES DESCRIPTI ON
UDG-96106-1
UCC2880-4/-5/-6
UCC3880-4/-5/-6
PRELIMINARY
The UCC3880-4/-5/-6 combines high precision reference and voltage monitoring circuitry with average current mode PWM controller circuitry to power Intel
Pentium Pro and other high-end microprocessors with a minimum of external
components. The UCC3880-x converts 5VDC to an adjustable output, ranging
from 2.0VDC to 3.5VDC in 100mV steps with 1% DC system accuracy.
The chip incl udes a precision 5V reference which is capable of sourcing current to an external load. The output voltage of the DAC is derived from this
reference, and is programmed directly by Intel’ s VID pins (Table 1).
The accuracy of the DAC/reference combination is 1.0%. The overvoltage and
undervoltage comparators monitor the system output voltage and indicate
when it rises above or falls below its programmed value by more than 7.5%. A
second overvoltage protection comparator pulls the current amplifier output
voltage low to force zero duty cycle w hen the system output voltage exceeds
its designed value by more than 15%. This comparator also terminates the cycle. Undervoltage lockout circuitry assures the correct logic states at the outputs during powerup and powe rdown . Grounding the ENABLE pin forces the
GATE output low.
(continued)
UCC2880-4/-5/-6
UCC3880-4/-5/-6
CONNECTION DIAG RAM
SOIC-20 (Top View)
DW Package
ELECTRICAL CHARACTE RIST I CS:
Unless otherwise specified, VIN = 12V, VSENSE = 3.5V, VENBL = 5V, VD0 = VD1 = VD2
= VD3 = 0V, 0°C < T
A < 70°C, TA = TJ.
PARAMETER TEST CONDITIONS MIN TYP MAX UNITS
Undervol ta ge Lockout
VIN UVLO Turn-on Thr esh old 10.5 10. 8 V
VIN UVLO Turn-off Threshold 9.5 10 V
UVLO Threshold Hysteresis 500 mV
Supply Cur ren t
l
IN 3.5 mA
DAC/Reference
COMMAND Voltage Accu rac y 10.8V < VIN < 13.2V, I
VREF = 0mA –1 1 %
D0-D3 Voltage High DX Pin Floating 5 V
D0-D3 Input Bias Curre nt DX Pin Tied to GND –70 –20 µA
VREF Output Voltage 4.975 5 5.025 V
VREF Load Regulat io n I
VREF = 0mA to 5mA –10 0 mV
VREF Sourcing Current VREF = 0V 10 mA
OVP Comparator
Trip Point % Over COMMAND Volt age 10 15 20 %
Hystere s is 20 30 mV
VSENSE Input Bias Current OV, OVP, UV Combined –0.1 µA
Propagation Delay 1 µs
The voltage and current amplifiers have a 4MHz gain
bandwidth p roduct to satisfy high performance system requirements. The internal current sense amplifier permits
the use of a low val ue current sense resistor, minimizing
power loss. The oscillator frequency is fixed internally at
100kHz, 200kHz, or 400kHz, depending upon the option
selected. The foldback circuit reduces the converter short
circuit current limit to 50% of its nominal value when the
converter is short circuited. The gate driver is a 2Ω totem
pole output stage capable of driving an external MOSFET.
This device is available in 20-pin dual i n-line and surface
mount packa ges. The UCC2880-x is specifie d for operation from –25°C to 85°C, and the UCC3880-x is specified
for operation from 0°C to 70°C.
Pentium® Pro is a registered trademark of Intel Corporation.
DESCRIPTION (cont. )
Frequency
100kHz 200kHz 400kHz
UCC3880-4 X
UCC3880-5 X
UCC3880-6 X
Frequency Gain Table
ORDERING INFORMATION
Consult factory f or temper at ure ran ge or package opt ions
not shown.
2
ELECTRICAL CHARACTE RISTICS (cont.): Unless otherw ise specified, VIN = 12V, VSENSE = 3.5V, VENBL = 5V, VD0 =
VD1 = VD2 = VD3 = 0V, 0°C < T
A < 70°C, TA = TJ.
PARAMETER TEST CONDIT IONS MI N TYP MAX UNIT S
OV Comparator
Trip Point % Over COMMAND Voltage ( Not e 1) 7.6 10 %
Return Point % Over COMMAND Voltage ( Not e 1) 5 7.4 %
Hystere sis 20 30 mV
PWRGOOD Equiva lent Resist ance VSENSE = 2.0V 470 Ω
Propagation Delay 1 µs
UV Comparator
Trip Point % Over COMMAND Voltage ( Not e 1) –10 –7.6 %
Return Point % Over COMMAND Voltage ( Not e 1) –7.4 – 5 %
Hystere sis 20 30 mV
Propagation Delay 1 µs
Enable Pi n
Pull-up Cur ren t V
ENBL = 2.5V –50 –20 µA
Voltage Error Amplifier
Input Offset Voltage V
COMP = 3.5V 0.0 mV
Input Bias Current V
CM = 3.0V –0.0 2 0 µA
Open Loo p Ga in 1V < V
COMP < 4V 90 dB
Common Mode Rejection Rat i o 2V < V
COMP < 3.5V 90 dB
Power Supply Reject ion Rat i o 10.8V < VIN < 15 V 85 dB
Output Sourcing Current V
VFB = 2V, VCOMMAND = VCOMP = 2.5V –0.5 mA
Output Sinking Current V
VFB = 3V, VCOMMAND = VCOMP = 2.5V 2.0 mA
Gain Bandwidth Product F = 100kHz 3 MHz
Current Sense Amplifier
Gain 20 V/V
Input Resistance 5kΩ
Common Mode Rejection Rat i o 0V < V
CM < 4.5V 60 dB
Power Supply Reject ion Rat i o 10.8V < VIN < 15 V 80 dB
Output Sourcing Current V
IS– = 2V, VISOUT = VIS+ = 2.5V –0.5 mA
Output Sinking Current V
IS– = 3V, VISOUT = VIS+ = 2.5V 6.0 mA
–3dB Freque ncy At GAIN = 20 1.75 MHz
Current Amplifier
Input Offset Voltage V
CM = 3.0V 10 mV
Input Bias Current V
CM = 3.0V 0.15 µA
Open Loo p Ga in 1V < V
CAO < 3V 90 dB
Output Voltage High VCOMP = 3V, VCAM = 2.5V 3.2 V
Common Mode Rejection Rat i o 1.5V < V
CM < 4.9V 80 dB
Power Supply Reject ion Rat i o 10.8V < VIN < 15 V 80 dB
Output Sourcing Current V
CAM = 2V, VCAO = VCOMP = 2.5V –0.5 mA
Output Sinking Current V
CAM = 3V, VCAO = VCOMP = 2.5V 2.0 mA
Gain Bandwidth Product F = 100kHz 3.5 MHz
UCC2880-4/-5/-6
UCC3880-4/-5/-6
3
UCC2880-4/-5/-6
UCC3880-4/-5/-6
PIN DESCRIPTIONS (cont.)
CAM (Current Amplifier Inverting Input): The average
load current feedback from ISOUT is applied through a
resistor to thi s pin. The current loop compensation network is also connected to this pin (see CAO below).
CAO (Current Amplifier Outp u t): The current loop compensation network is connected between this pin and
CAM. The voltage on this pin is the input to the PWM
comparator and regulates the o utput voltage o f the system. The GATE output is disabl ed (held low) unless the
voltage on this pin exceeds 1V, allowing the PWM to
force zero duty cycle when necessary. The PWM forces
maximum duty cycle when the voltage on CAO exceeds
the oscillator peak voltage (3V). A 3.2V clamp circuit prevents the CAO voltage from rising excessively past the
oscillator peak voltage for excellent transient response.
COMMAND (Digital-to-Analog Converter Output Voltage): This pin is the output of the 4-bit digital-to-analog
converter (DAC) and the noninverting input of the voltage
amplifier. The voltage on this pin sets the switching regulator output voltage. Setting all input control codes low
produces 3.5V at COMMAND; setting all codes high produces 2.0V at COMMAND. The DAC LSB step size (i.e.
resolution) is 100mV (See Table 1). The COMMAND
source impedance is typicall y 1.2kΩ and must therefore
drive only high impedance inputs if accuracy is to be
maintained. Bypass COMMAND with a 0.01µF, low ESR,
low ESL capacitor for best circuit noise immunity.
COMP (Voltage Amplifier Output): The system voltage
compensation network is applied between COMP and
VFB.
D0 - D3 (DAC Digital Input Control Codes): These are
the DAC digital input control codes, with D0 representing
the least significant bit (LSB) and D3, the most significant
bit (MSB). A bit is set low by being connected to GND. A
ELECTRICAL CHARACTE RISTICS (cont.):
Unless otherwise specified, VIN = 12V, VSENSE = 3.5V, V ENBL = 5V, VD0 =
VD1 = VD2 = VD3 = 0V, 0°C < T
A < 70°C, TA = TJ.
PARAMETER TEST CONDITIONS MIN TYP MAX UNITS
Oscillator
Frequenc y (-4) 85 100 115 kHz
Frequenc y (-5) 200 kHz
Frequenc y (-6) 400 kHz
Frequenc y Change Wit h Voltage 10. 8V < VIN < 15V 1 %
Output Secti on
Maximum Duty Cycle 90 95 99 %
Output Low Voltage I
GATE = –100mA 0.20 V
Output High Voltage IGATE = 100mA 11.8 V
Rise Time C
GATE = 3.3nF 20 80 ns
Fall Time C
GATE = 3.3nF 15 80 ns
Output Impedance I
GATE = 100mA 2 Ω
I
GATE = –100mA 2 Ω
Foldback Curr ent Li mit
Clamp Level Measured at Voltage EA Output;
V
SENSE = VCOMMAND = 3V
4.4 V
V
COMMAND = 3V, VSENSE = 0 3.7 V
Note 1: This percenta ge is me asur ed wit h respect to the ideal CO MM AND volt age program med by the D0 - D3 pins.
Decimal
Code
D3 D2 D1 D0 COMMAND
Voltage
151111 2.0
141110 2.1
131101 2.2
121100 2.3
111011 2.4
101010 2.5
91001 2.6
81000 2.7
70111 2.8
60110 2.9
50101 3.0
40100 3.1
30011 3.2
20010 3.3
10001 3.4
00000 3.5
Table 1. Programming the COMMAND Voltage
4
UCC2880-4/-5/-6
UCC3880-4/-5/-6
PIN DESCRIPTIONS (cont.)
bit is set high by floating it, or connecting it to a 5V
source. Each control pin is pulled up to approximately 5V
by an internal 70µA current source.
ENBL (Chip Enable Pin): This input is used to disable
the GATE and PWRGOOD outputs. Grounding this pin
causes the GATE output to be held low; floating the pin or
pulling it up to 5V ensures normal operation. ENBL is
pulled up to 5V internally.
GATE (PWM Output, MOSFET Driver): This output provides a 2Ω totem pole driver. Use a series resistor of at
least 5Ω between this pin and the gate of the external
MOSFET to prevent excessive overshoot.
GND (Signal Ground): All voltages are mea sured with
respect to GND. Bypass capacitors on the VCC and
VREF pins should be connected directly to the ground
plane near the GND pin.
IS– (Current Sense Amplifier Inverting Input): This pin
is the inverting input to the current sense amplifier and is
connected to the low side of the average current sense
resistor.
IS+ (Current Sense Amplifier Noninverting Input):
This pin is the noninverting input to the current sense amplifier and is con nected to the high side of the average
current sense resistor.
ISOUT (Current Sense Amplifier Output): This pin is
the output of the current sense amplifier. The voltage on
this pin is (COMMAND + G
CSA • I • RSENSE), where
COMMAND is the voltage on the COMMAND pin, G
CSA
is the fixed gain of the current sense amplifier, equal to
20, I
is the current through the sense resistor, and
R
SENSE is the value of the average current sensing resis-
tor.
PGND (Power Ground): This pin provides a dedicated
ground for the o utput gate driver. The GND and PGND
pins should be connected externally using a short printed
circuit board trace close to the IC. Decouple VIN to
PGND with a low ESR capacitor ≥ 0.10µF.
PWRGOOD (Undervoltage/Lower Overvoltage Output): This pin is an open drain output which is driven low
to reset the microprocessor when VSENSE rises above
or falls below its nominal value by 7.5%. The on resistance of the open drain switch will be no higher than
470Ω. The OV and UV comparators’ hysteresis is fixed at
20mV independent of the COMMAND voltage.
VIN (Positive Supply Voltage): This p in supplies power
to the chip. Connect VIN to a stable voltage source of at
least 10.8V. The GATE and P WRGOOD outputs will be
held low until VCC exceeds the upper undervoltage lockout threshold. This pin should be bypassed directly to the
GND pin.
VFB (Voltage Amplifier Inverting Input): This input is
connected to COMP through a feedback network and to
the power supply output through a resistor or a divider
network.
VREF (Voltage Reference Output): This pin provides an
accurate 5V reference and is internally short circuit current limited. VREF powers the D/A converter and also
provides a threshold voltage for the UVLO comparator.
For best reference stability , bypass VREF directly to GND
with a low ESR, low ESL capacit or of at least 0.01µF.
VSENSE (Output Voltage Sensing Input): This pin is
connected to the system output voltage through a low
pass filter. When the voltage on VSENSE rises above or
falls below the COMMAND voltage by 7.5%, the
PWRGOOD output is driven low to reset the microprocessor. When the voltage on VSENSE rises above the
COMMAND voltage by 15 %, the OVP comparator pulls
the current amplifier output voltage below the oscillator
valley voltage to force zero duty cycle at the GATE output. This pin is also used by the foldback current limiting
circuitry.
Current Limit
The short circuit current limit, I
SC, is set according to:
I
SC =
1.4V
R
SENSE • GCSA
where RSENSE is the average current sense resistor and
G
CSA is the current sense amplifier gain, where GCSA
equals 20. Example: Choose RSENSE to set the short circuit current limit at 16A using the UCC3880-5
R
SENSE =
1.4V
16A • 20
= 4.4mΩ
A lower resistance value may be needed if the AC ripple
current in the inductor is more than 20% of the full load
current.
Related Publication s
U-156 and U-157 are Unitrode Application Notes describing the operation of the UC3886 and the UC3886/
UC3910 together in a Pentium® Pro application.
APPLICATION INFORMATION
5
UCC3880 Configured for Powering the Pentium® Pro
TYPICAL APPLICATION
The UCC3 880-x is ideal for converting the 5.0V system bus i nto the required Pentium® Pro bus voltage.
UDG-96224
UCC2880-4/-5/-6
UCC3880-4/-5/-6
6
UNITRODE INTEGRA TED CIRCUITS
7 CONTINENTA L BLVD. • MERRIMACK, NH 03054
TEL. (603) 424-2410 • FAX (603) 424-3460
Pentium® Pro is a register ed tra dem ark of Intel Corpor at ion.
UCC2880-4/-5/-6
UCC3880-4/-5/-6
REF. DESCRIPTION PACKAGE
U1 Unitrode UCC3830DWP-5 DAC/PWM SOIC-20 Wide
C1 Sanyo 6MV1500GX, 1500 µF, 6. 3V, Aluminum Electrolyt ic 10x20mm Radial C an
C2 Sanyo 6MV1500GX, 1500 µF, 6. 3V, Aluminum Electrolyt ic 10x20mm Radial C an
C3 Sanyo 6MV1500GX, 1500 µF, 6. 3V, Aluminum Electrolyt ic 10x20mm Radial C an
C4 Sanyo 6MV1500GX, 1500 µF, 6. 3V, Aluminum Electrolyt ic 10x20mm Radial C an
C5 Sprague/Vishay 595D475X0016A2B, 4.7µF 16V Tantalum SPRAGUE Size A
C6 Sanyo 6MV1500GX, 1500 µF, 6. 3V, Aluminum Electrolyt ic 10x20mm Radial C an
C7 Sanyo 6MV1500GX, 1500 µF, 6. 3V, Aluminum Electrolyt ic 10x20mm Radial C an
C8 Sanyo 6MV1500GX, 1500 µF, 6. 3V, Aluminum Electrolyt ic 10x20mm Radial C an
C9 Sanyo 6MV1500GX, 1500 µF, 6. 3V, Aluminum Electrolyt ic 10x20mm Radial C an
C10 Sanyo 6MV1500G X, 1500µF, 6. 3V, Aluminum Electrolytic 10x20mm Radial Ca n
C11 Sprague 593D107X9010D2, 100µF, 6.3V Tantalum EIA Size D SMD
C12 0.10µF Ceramic 1206 SMD
C13 0.01µF Ceramic 0603 SMD
C14 0.01µF Ceramic 0603 SMD
C15 0.01µF Ceramic 0603 SMD
C16 1000pF Ceramic 0603 SMD
C17 0.10µF Ceramic 1206 SMD
C18 33pF NPO Ceramic 0603 SMD
C19 1500pF Ceramic 0603 SMD
C20 82pF NPO Ceramic 0603 SMD
C21 0.10µF Ceramic 1206 SMD
C22 0.10µF Ceramic 1206 SMD
CR1 Internationa l Rectifier 32CTQ 030 30V, 30A Schot tky Diode TO-220AB
L1 Micrometals T50- 52B, 10 Tu rns #16AW G, 4.5µH Toroid
Q1 International Rectifier I RL3103, 30V, 56A TO-220AB
R1 Dale/Vishay WSR-2 0.005Ω 1% SMD Power Packa ge
R2 10Ω, 5%, 1/16 Watt 0603 SMD
R3 8.2kΩ, 5%, 1/16 Watt 0603 SMD
R4 6.81kΩ, 1%, 1/16 Watt 0603 SMD
R5 3.92kΩ, 1%, 1/16 Watt 0603 SMD
R6 261kΩ, 1%, 1/16 Watt 0603 SMD
R7 100kΩ, 1%, 1/16 Watt 0603 SMD
R8 3.92kΩ, 1%, 1/16 Watt 0603 SMD
R9 10.5kΩ, 1%, 1/16 Watt 0603 SMD
Q1-HS AAVID 576802 TO-220 Heat Sink TO-220AB
CR1-HS AAVI D 577 002 TO-220 Heat Sink TO-220AB
PARTS LIST
7
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