UC2878DWPTR [ETC]
Voltage-Mode SMPS Controller ; 电压型开关电源控制器\n型号: | UC2878DWPTR |
厂家: | ETC |
描述: | Voltage-Mode SMPS Controller
|
文件: | 总12页 (文件大小:550K) |
中文: | 中文翻译 | 下载: | 下载PDF数据表文档文件 |
application
INFO
UC1875/6/7/8
UC2875/6/7/8
UC3875/6/7/8
available
Phase Shift Resonant Controller
FEATURES
DESCRIPTION
• Zero to 100% Duty Cycle Control
The UC1875 family of integrated circuits implements control of a bridge
power stage by phase-shifting the switching of one half-bridge with respect
to the other, allowing constant frequency pulse-width modulation in combi-
nation with resonant, zero-voltage switching for high efficiency performance
at high frequencies. This family of circuits may be configured to provide
control in either voltage or current mode operation, with a separate
over-current shutdown for fast fault protection.
• Programmable Output Turn-On Delay
• Compatible with Voltage or Current
Mode Topologies
• Practical Operation at Switching
Frequencies to 1MHz
A programmable time delay is provided to insert a dead-time at the turn-on
of each output stage. This delay, providing time to allow the resonant
switching action, is independently controllable for each output pair (A-B,
C-D).
• Four 2A Totem Pole Outputs
• 10MHz Error Amplifier
• Undervoltage Lockout
With the oscillator capable of operation at frequencies in excess of 2MHz,
overall switching frequencies to 1MHz are practical. In addition to the stan-
dard free running mode, with the CLOCKSYNC pin, the user may configure
these devices to accept an external clock synchronization signal, or may
lock together up to 5 units with the operational frequency determined by the
fastest device.
• Low Startup Current –150µA
• Outputs Active Low During UVLO
• Soft-Start Control
• Latched Over-Current Comparator
With Full Cycle Restart
Protective features include an undervoltage lockout which maintains all out-
puts in an active-low state until the supply reaches a 10.75V threshold.
1.5V hysteresis is built in for reliable, boot-strapped chip supply.
Over-current protection is provided, and will latch the outputs in the OFF
state within 70nsec of a fault. The current-fault circuitry implements
full-cycle restart operation.
• Trimmed Reference
BLOCK DIAGRAM
UDG-95073
07/99
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UC1875/6/7/8
UC2875/6/7/8
UC3875/6/7/8
DESCRIPTION (cont.)
Additional features include an error amplifier with band-
width in excess of 7MHz, a 5V reference, provisions for
soft-starting, and flexible ramp generation and slope com-
pensation circuitry.
Device
UVLO
Turn-On
UVLO
Turn-Off
Delay
Set
UC1875
UC1876
UC1877
UC1878
10.75
15.25V
10.75V
15.25V
9.25V
9.25V
9.25V
9.25V
Yes
Yes
No
These devices are available in 20-pin DIP, 28-pin
“bat-wing” SOIC and 28 lead power PLCC plastic pack-
ages for operation over both 0°C to 70°C and –25°C to
+85°C temperature ranges; and in hermetically sealed
cerdip, and surface mount packages for –55°C to +125°C
operation.
No
CONNECTION DIAGRAMS
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (VC, VIN) . . . . . . . . . . . . . . . . . . . . . . . . . . 20V
Output Current, Source or Sink
Dil-20 (Top View)
J or N Package
DC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.5A
Pulse (0.5µs). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3A
Analog I/0s
(Pins 1, 2, 3, 4, 5, 6, 7, 15, 16, 17, 18, 19) . . . . –0.3 to 5.3V
Storage Temperature Range . . . . . . . . . . . . . –65°C to +150°C
Junction Temperature. . . . . . . . . . . . . . . . . . . –55°C to +150°C
Lead Temperature (Soldering, 10 sec.) . . . . . . . . . . . . +300°C
Note: Pin references are to 20 pin packages. All voltages are
with respect to ground. Currents are positive into, neg-
ative out of, device terminals. Consult Unitrode
databook for information regarding thermal specifica-
tions and limitations of packages.
SOIC-28, (Top View)
DWP Package
PLCC-28 (Top View)
QP Package
2
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UC1875/6/7/8
UC2875/6/7/8
UC3875/6/7/8
ELECTRICAL CHARACTERISTICS: Unless otherwise stated, –55°C < TA < 125°C for the UC1875/6/7/8, –25°C < TA <
85°C for the UC2875/6/7/8 and 0°C < TA < 70°C for the UC3875/6/7/8, VC = VIN = 12V, RFREQSET = 12kΩ, CFREQSET = 330pF,
R
SLOPE = 12kΩ, CRAMP = 200pF, CDELAYSET A-B = CDELAYSET C-D = 0.01µF, IDELAYSET A-B = IDELAYSET C-D = –500µA, TA = TJ.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX UNITS
Undervoltage Lockout
Start Threshold
UC1875/UC1877
10.75 11.75
15.25
V
V
V
V
UC1876/UC1878
UC1875/UC1877
UC1876/UC1878
UVLO Hysteresis
0.5
1.25
6.0
2.0
Supply Current
IIN Startup
VIN = 8V, VC = 20V, RSLOPE open, IDELAY = 0
VIN = 8V, VC = 20V, RSLOPE open, IDELAY = 0
150
10
600
100
40
µA
µA
IC Startup
IIN
30
mA
mA
IC
15
30
Voltage Reference
Output Voltage
Line Regulation
Load Regulation
Total Variation
Noise Voltage
Long Term Stability
Short Circuit Current
Error Amplifier
Offset Voltage
Input Bias Current
AVOL
TJ = +25°C
4.92
4.9
5
1
5
5.08
10
V
mV
mV
V
11 < VIN < 20V
IVREF = –10mA
20
Line, Load, Temperature
10Hz to 10kHz
5.1
50
2.5
60
µVrms
mV
mA
TJ = 125°C, 1000 hours
VREF = 0V, TJ = 25°C
5
0.6
60
15
3
mV
µA
1V < VE/AOUT < 4V
1.5V < VCM < 5.5V
11V < VIN < 20V
VE/AOUT = 1V
90
dB
CMRR
75
85
1
95
dB
PSRR
100
2.5
–1.3
4.7
0.5
11
dB
Output Sink Current
Output Source Current
Output Voltage High
Output Voltage Low
Unity Gain BW
Slew Rate
mA
mA
V
VE/AOUT = 4V
–0.5
5
IE/AOUT = –0.5mA
IE/AOUT = 1mA
4
0
7
6
1
V
MHz
V/µsec
11
3
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UC1875/6/7/8
UC2875/6/7/8
UC3875/6/7/8
ELECTRICAL CHARACTERISTICS: Unless otherwise stated, –55°C < TA < 125°C for the UC1875/6/7/8, –25°C < TA <
85°C for the UC2875/6/7/8 and 0°C < TA < 70°C for the UC3875/6/7/8, VC = VIN = 12V, RFREQSET = 12kΩ, CFREQSET = 330pF,
R
SLOPE = 12kΩ, CRAMP = 200pF, CDELAYSET A-B = CDELAYSET C-D = 0.01µF, IDELAYSET A-B = IDELAYSET C-D = –500µA, TA = TJ.
PARAMETER
TEST CONDITIONS
TJ = 25°C (Note 3)
MIN
TYP
MAX UNITS
PWM Comparator
Ramp Offset Voltage
Zero Phase Shift Voltage
PWM Phase Shift (Note1)
1.3
0.9
99.5
0.5
5
V
V
(Note 4)
0.55
98
0
VE/AOUT > (Ramp Peak + Ramp Offset)
VE/AOUT < Zero Phase Shift Voltage
VE/AOUT < 1V
102
2
%
%
Output Skew (Note 1)
Ramp to Output Delay
±20
100
125
nsec
nsec
nsec
UC3875/6/7/8 (Note 6)
65
UC1875/6/7/8, UC2875/6/7/8 (Note 6)
65
Oscillator
Initial Accuracy
TJ = 25°C
0.85
0.80
1
1.15
2
MHz
%
Voltage Stability
11V < VIN < 20V
Line, Temperature
TJ = 25°C
0.2
Total Variation
1.20
MHz
V
Sync Pin Threshold
Clock Out Peak
3.8
4.3
3.3
TJ = 25°C
V
Clock Out Low
TJ = 25°C
V
Oscillator (cont.)
Clock Out Pulse Width
Maximum Frequency
Ramp Generator/Slope Compensation
Ramp Current, Minimum
Ramp Current, Maximum
Ramp Valley
RCLOCKSYNC = 3.9kΩ
RFREQSET = 5kΩ
30
100
–14
4.1
nsec
MHz
2
ISLOPE = 10µA, VFREQSET = VREF
–11
µA
mA
V
ISLOPE = 1mA, VFREQSET = VREF
–0.8 –0.95
0
Ramp Peak - Clamping Level
Current Limit
RFREQSET = 100kΩ
3.8
V
Input Bias
V
CS+ = 3V
2
5
µA
V
Threshold Voltage
Delay to Output
2.4
2.5
85
85
2.6
125
150
UC3875/6/7/8
nsec
nsec
UC1875/6/7/8, UC2875/6/7/8
Soft-Start/Reset Delay
Charge Current
VSOFTSTART = 0.5V
VSOFTSTART = 1V
–20
120
4.3
–9
230
4.7
300
–3
µA
µA
V
Discharge Current
Restart Threshold
Discharge Level
mV
4
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UC1875/6/7/8
UC2875/6/7/8
UC3875/6/7/8
ELECTRICAL CHARACTERISTICS: Unless otherwise stated, –55°C < TA < 125°C for the UC1875/6/7/8, –25°C < TA <
85°C for the UC2875/6/7/8 and 0°C < TA < 70°C for the UC3875/6/7/8, VC = VIN = 12V, RFREQSET = 12kΩ, CFREQSET = 330pF,
R
SLOPE = 12kΩ, CRAMP = 200pF, CDELAYSET A-B = CDELAYSET C-D = 0.01µF, IDELAYSET A-B = IDELAYSET C-D = –500µA, TA = TJ.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX UNITS
Output Drivers
Output Low Level
I
OUT = 50mA
0.2
1.2
1.5
1.7
0.4
2.6
2.5
2.6
V
V
V
V
IOUT = 500mA
IOUT = –50mA
IOUT = –500mA
Output High Level
Delay Set (UC1875 and UC1876 only)
Delay Set Voltage
I
DELAY = –500µA
2.3
2.4
2.6
V
Delay Time
IDELAY = –250µA (Note 5) (UC3875/6/7/8,
150
250
400
nsec
UC2875/6/7/8)
IDELAY = –250µA (Note 5) (UC1875/6/7/8)
150
250
600
nsec
200
Note 1: Phase shift percentage (0% = 0°, 100% = 180°) is defined as θ =
Φ%, where is the phase shift, and and T are de-
T
fined in Figure 1. At 0% phase shift, is the output skew.
Note 2: Delay time is defined as delay = T (1/2–(duty cycle)), where T is defined in Fig. 1.
Note 3: Ramp offset voltage has a temperature coefficient of about –4mV/°C.
Note 4: Zero phase shift voltage has a temperature coefficient of about –2mV/°C.
62.5• 10–12
Note 5: Delay time can be programmed via resistors from the delay set pins to ground. Delay time
Delay set voltage
sec. Where
IDELAY
I
=
The recommended range for I
is 25 A I
1mA
DELAY
DELAY
DELAY
RDELAY
Note 6: Ramp delay to output time is defined in Fig. 2.
Duty Cycle = t/T
Period = T
(A to C) = T
UDG-95074
T
(B to D) = Φ
DHL
DHL
UDG-95075
Phase Shift, Output Skew & Delay Time Definitions
Figure 1
Figure 2
5
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UC1875/6/7/8
UC2875/6/7/8
UC3875/6/7/8
PIN FUNCTIONAL DESCRIPTIONS
pin, any bypass capacitor on the VREF pin, bypass ca-
pacitors on VIN and the ramp capacitor, on the RAMP
pin, should be connected directly to the ground plane
near the signal ground pin.
CLOCKSYNC (bi-directional clock and synchroniza-
tion pin): Used as an output, this pin provides a clock
signal. As an input, this pin provides a synchronization
point. In its simplest usage, multiple devices, each with
their own local oscillator frequency, may be connected to-
gether by the CLOCKSYNC pin and will synchronize on
the fastest oscillator. This pin may also be used to syn-
chronize the device to an external clock, provided the ex-
ternal signal is of higher frequency than the local
oscillator. A resistor load may be needed on this pin to
minimize the clock pulse width.
OUTA-OUTD (outputs A-D): The outputs are 2A to-
tem-pole drivers optimized for both MOSFET gates and
level-shifting transformers. The outputs operate as pairs
with a nominal 50% duty-cycle. The A-B pair is intended
to drive one half-bridge in the external power stage and
is syncronized with the clock waveform. The C-D pair will
drive the other half-bridge with switching phase shifted
with respect to the A-B outputs.
E/AOUT (error amplifier output): This is is the gain
stage for overall feedback control. Error amplifier output
voltage levels below 1 volt will force 0° phase shift. Since
the error amplifier has a relatively low current drive capa-
bility, the output may be overridden by driving with a suffi-
ciently low impedance source.
PWRGND (power ground): VC should be bypassed with
a ceramic capacitor from the VC pin to the section of the
ground plane that is connected to PWRGND. Any re-
quired bulk reservoir capacitor should parallel this one.
Power ground and signal ground may be joined at a sin-
gle point to optimize noise rejection and minimize DC
drops.
CS+ (current sense): The non-inverting input to the cur-
rent-fault comparator whose reference is set internally to
a fixed 2.5V (separate from VREF). When the voltage at
this pin exceeds 2.5V the current-fault latch is set, the
outputs are forced OFF and a SOFT-START cycle is initi-
ated. If a constant voltage above 2.5V is applied to this
pin the outputs are disabled from switching and held in a
low state until the CS+ pin is brought below 2.5V. The
outputs may begin switching at 0 degrees phase shift be-
fore the SOFTSTART pin begins to rise -- this condition
will not prematurely deliver power to the load.
RAMP (voltage ramp): This pin is the input to the PWM
comparator. Connect a capacitor from here to GND. A
voltage ramp is developed at this pin with a slope:
SenseVoltage
dV
=
dT RSLOPE • CRAMP
Current mode control may be achieved with a minimum
amount of external circuitry, in which case this pin pro-
vides slope compensation.
FREQSET (oscillator frequency set pin): A resistor
and a capacitor from FREQSET to GND will set the oscil-
lator frequency.
Because of the 1.3V offset between the ramp input and
the PWM comparator, the error amplifier output voltage
can not exceed the effective ramp peak voltage and duty
cycle clamping is easily achievable with appropriate val-
DELAYSET A-B, DELAYSET C-D (output delay con-
trol): The user programmed current flowing from these
pins to GND set the turn-on delay for the corresponding
output pair. This delay is introduced between turn-off of
one switch and turn-on of another in the same leg of the
bridge to provide a dead time in which the resonant
switching of the external power switches takes place.
Separate delays are provided for the two half-bridges to
accommodate differences in the resonant capacitor
charging currents.
ues of RSLOPE and CRAMP
.
SLOPE (set ramp slope/slope compensation): A resis-
tor from this pin to VCC will set the current used to gen-
erate the ramp. Connecting this resistor to the DC input
line voltage will provide voltage feed-forward.
SOFTSTART (soft start): SOFTSTART will remain at
GND as long as VIN is below the UVLO threshold.
SOFTSTART will be pulled up to about 4.8V by an inter-
nal 9µA current source when VIN becomes valid (assum-
ing a non-fault condition). In the event of a current-fault
(CS+ voltage exceeding 2.5V), SOFTSTART will be
pulled to GND and them ramp to 4.8V. If a fault occurs
during the SOFTSTART cycle, the outputs will be imme-
diately disabled and SOFTSTART must charge fully prior
to resetting the fault latch.
EA– (error amplifier inverting input): This is normally
connected to the voltage divider resistors which sense
the power supply output voltage level.
EA+ (error amplifier non-inverting input): This is nor-
mally connected to a reference voltage used for compari-
son with the sensed power supply output voltage level at
the EA+ pin.
For paralleled controllers, the SOFTSTART pins may be
paralled to a single capacitor, but the charge currents will
be additive.
GND (signal ground): All voltages are measured with
respect to GND. The timing capacitor, on the FREQSET
6
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UC1875/6/7/8
UC2875/6/7/8
UC3875/6/7/8
PIN FUNCTIONAL DESCRIPTIONS (cont.)
NOTE: When VIN exceeds the UVLO threshold the sup-
ply current (IIN) will jump from about 100µA to a current
in excess of 20µA. If the UC1875 is not connected to a
well bypassed supply, it may immediately enter UVLO
again.
VC (output switch supply voltage): This pin supplies
power to the output drivers and their associated bias cir-
cuitry. Connect VC to a stable source above 3V for nor-
mal operation, above 12V for best performance. This
supply should be bypassed directly to the PWRGND pin
with low ESR, low ESL capacitors.
VREF: This pin is an accurate 5V voltage reference. This
output is capable of delivering about 60mA to peripheral
circuitry and is internally short circuit current limited.
VREF is disabled while VIN is low enough to force the
chip into UVLO. The circuit is also in UVLO until VREF
reaches approximately 4.75V. For best results bypass
VREF with a 0.1µF, low ESR, low ESL, capacitor to the
GND pin.
VIN (primary chip supply voltage): This pin supplies
power to the logic and analog circuitry on the integrated
circuit that is not directly associated with driving the out-
put stages. Connect VIN to a stable source above 12V
for normal operation. To ensure proper chip functionality,
these devices will be inactive until VIN exceeds the upper
undervoltage lockout threshold. This pin should by by-
passed directly to the GND pin with low ESR, low ESL
capacitors.
APPLICATIONS INFORMATION
UNDERVOLTAGE LOCKOUT SECTION
When power is applied to the circuit and VIN is below held low. When VIN exceeds the upper UVLO thresh-
old, the reference generator turns on. All else remains
in the shut-down mode until the output of the reference,
VREF, exceeds 4.75V.
the upper UVLO threshold, IIN will be below 600µA, the
reference generator will be off, the fault latch is reset,
the soft-start pin is discharged, and the outputs are ac-
tively
UDG-95076
OSCILLATOR
The high frequency oscillator may be either free-running operation, the frequency is set via an ex-
free-running
or
externally
synchronized.
For ternal resistor and capacitor to ground from the
FREQSET pin.
Simplified Oscillator Schematic
UDG-95077
UDG-95079
UDG-95078
7
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UC1875/6/7/8
UC2875/6/7/8
UC3875/6/7/8
APPLICATIONS INFORMATION (cont.)
SYNCHRONIZING THE OSCILLATOR
The CLOCKSYNC pin of the oscillator may be used to synchronize multiple UC1875 devices simply by connecting
the CLOCKSYNC of each UC1875 to the others:
1875/6/7/8s only
UDG-95080
All ICs will sync to chip with the fastest local oscillator.
R1 & RN may be needed to keep sync pulse narrow due to capacitance on line.
R1 & RN may also be needed to properly terminate RSYNC line.
Syncing to external TTL/CMOS
UDG-95081
ICs will sync to fastest chip or TTL clock if it is higher frequency.
R & RN may be needed for same reasons as above
Although each UC1875/6/7/8 has a local oscillator fre- Capacitive loading on the CLOCKSYNC pin will in-
quency, the group of devices will synchronize to the crease the clock pulse width, and may adversely effect
fastest oscillator driving the CLOCKSYNC pin. This ar- system performance. Therefore, a resistor to ground
rangement allows the synchronizing connection be- from the CLOCKSYNC pin is optional, but may be re-
tween ICs to be broken without any local loss of quired to offset capacitive loading on this pin. These re-
functionality.
sistors are shown in the oscillator schematics as R1,
RN.
Synchronizing the device to an external clock signal
may be accomplished with a minimum of external cir-
cuitry, as shown in the previous figure.
8
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UC1875/6/7/8
UC2875/6/7/8
UC3875/6/7/8
APPLICATIONS INFORMATION (cont.)
DELAY BLOCKS AND OUTPUT STAGES
In each of the output stages, transistors Q3 through Q6 self-biased driver to hold Q6 on prior to the supply
form a high-speed totem-pole driver which will source reaching its turn-on threshold. This circuit is operable
or sink more than one amp peak with a total delay of when the chip supply is zero. Q6 is also turned on and
approximately 30 nanoseconds. To ensure a low output held low with a signal from the fault logic portion of the
level prior to turn-on, transistors Q7 through Q9 form a chip.
UDG-95082
The delay providing the dead-time is accomplished with 2.5V and the range of dead time control is
C1 which must discharge to VTH before the output can from 50 to 200 nanoseconds. NOTE: There is no way
go high. The time is defined by the current sources, I1, to disable the delay circuitry, and the delay time must
which is programmed by an external resistor, RTD. The be programmed.
voltage on the Delay Set pins is internally regulated to
OUTPUT SWITCH ORIENTATION
The four outputs of the UC1875/6/7/8 interface to the full bridge converter switches as shown below:
UDG-95083
3 Winding Bifilar, AWG 30 Kynar Insulation
9
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UC1875/6/7/8
UC2875/6/7/8
UC3875/6/7/8
APPLICATIONS INFORMATION (cont.)
FAULT/SOFT-START
The fault control circuitry provides two forms of power ceed while the phase-shift is advanced from zero to its
shutdown:
nominal value with the time constant of the
SOFT-START capacitor.
• Complete turn-off of all four output power stages.
• Clamping the phase shift command to zero.
The fault logic insures that a continuous fault will insti-
tute a low frequency “hiccup” retry cycle by forcing the
SOFT-START capacitor to charge through its full cycle
between each restart attempt.
Complete turn-off is ordered for an over-current fault or
a low supply voltage. When the SOFTSTART pin
reaches its low threshold, switching is allowed to pro-
UDG-95084
UDG-95085
10
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UC1875/6/7/8
UC2875/6/7/8
UC3875/6/7/8
APPLICATIONS INFORMATION (cont.)
SLOPE/RAMP PINS
The ramp generator may be configured for the following The figure below shows a voltage-mode configuration.
control methods:
With RSLOPE tied to a stable voltage source, the wave-
form on CRAMP will be a constant-slope ramp, providing
conventional voltage-mode control. If RSLOPE is con-
nected to the power supply input voltage, a vari-
able-slope ramp will provide voltage feedforward.
• Voltage Mode
• Voltage Feedforward
• Current Mode
• Current Mode with Slope Compensation
Voltage Mode Operation
1. Simple voltage mode operation
achieved by placing RSLOPE between VIN
and SLOPE.
2. Voltage Feedforward achieved by plac-
ing RSLOPE between supply voltage and
SLOPE pin of UC1875.
RAMP
VRslope
dV
≈
dT RSLOPE • CRAMP
UDG-95086
For current-mode control the ramp generator may be disabled by grounding the slope pin and using the ramp pin
as a direct current sense input to the PWM comparator.
UNITRODE CORPORATION
7 CONTINENTAL BLVD. • MERRIMACK, NH 03054
TEL. (603) 424-2410 • FAX (603) 424-3460
11
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