Datasheet UC1875, UC1876, UC1877, UC1878, UC2875 Datasheet (UNITRODE)

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Phase Shift Resonant Controller
FEATURES
Zero to 100% Duty Cycle Control
Programmable Output Turn-On Delay
Compatible with Voltage or Current
Mode Topologies Practical Operation at Switching
Frequencies to 1MHz Four 2A Totem Pole Outputs
10MHz Error Amplifier
Undervoltage Lockout
Low Startup Current –150µA
Outputs Active Low During UVLO
Soft-Start Control
Latched Over-Current Comparator
With Full Cycle Restart
Trimmed Reference
BLOCK DIAGRAM
DESCRIPTION
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.
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).
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.
Protective features include an undervoltage lockout which maintains all out­puts 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.
application
INFO
available
UC1875/6/7/8 UC2875/6/7/8 UC3875/6/7/8
-
-
07/99
UDG-95073
Page 2
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.
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.
UC1875/6/7/8 UC2875/6/7/8 UC3875/6/7/8
-
-
-
Device UVLO
Turn-On
UC1875 10.75 9.25V Yes UC1876 15.25V 9.25V Yes UC1877 10.75V 9.25V No UC1878 15.25V 9.25V No
UVLO
Turn-Off
Delay
Set
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (VC, VIN) . . . . . . . . . . . . . . . . . . . . . . . . . . 20V
Output Current, Source or Sink
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, neg­ative out of, device terminals. Consult Unitrode databook for information regarding thermal specifica­tions and limitations of packages.
SOIC-28, (Top View) DWP Package
CONNECTION DIAGRAMS
Dil-20 (Top View) J or N Package
PLCC-28 (Top View) QP Package
2
Page 3
UC1875/6/7/8 UC2875/6/7/8 UC3875/6/7/8
ELECTRICAL CHARACTERISTICS:
85°C for the UC2875/6/7/8 and 0°C < T R
SLOPE
= 12kΩ, C
RAMP
= 200pF, C
DELAYSET A-B=CDELAYSET C-D
Unless otherwise stated, –55°C < TA< 125°C for the UC1875/6/7/8, –25°C < TA<
< 70°C for the UC3875/6/7/8, VC = VIN = 12V, R
A
= 0.01µF, I
DELAYSET A-B=IDELAYSET C-D
FREQSET
= 12kΩ,C
FREQSET
= –500µA, TA=TJ.
= 330pF,
PARAMETER TEST CONDITIONS MIN TYP MAX UNITS
Undervoltage Lockout
Start Threshold UC1875/UC1877 10.75 11.75 V
UC1876/UC1878 15.25 V
UVLO Hysteresis UC1875/UC1877 0.5 1.25 2.0 V
UC1876/UC1878 6.0 V
Supply Current
I
Startup VIN = 8V, VC = 20V, R
IN
Startup VIN = 8V, VC = 20V, R
I
C
I
IN
I
C
SLOPE SLOPE
open, I open, I
= 0 150 600 µA
DELAY
= 0 10 100 µA
DELAY
30 40 mA 15 30 mA
Voltage Reference
Output Voltage T
= +25°C 4.92 5 5.08 V
J
Line Regulation 11 < VIN < 20V 1 10 mV Load Regulation I
= –10mA 5 20 mV
VREF
Total Variation Line, Load, Temperature 4.9 5.1 V Noise Voltage 10Hz to 10kHz 50 µVrms Long Term Stability T Short Circuit Current VREF = 0V, T
= 125°C, 1000 hours 2.5 mV
J
= 25°C 60 mA
J
Error Amplifier
Offset Voltage 515mV Input Bias Current 0.6 3 µA AVOL 1V < V CMRR 1.5V < V
< 4V 60 90 dB
E/AOUT
< 5.5V 75 95 dB
CM
PSRR 11V < VIN < 20V 85 100 dB Output Sink Current V Output Source Current V Output Voltage High I Output Voltage Low I
E/AOUT E/AOUT
= 1V 1 2.5 mA
E/AOUT
= 4V –1.3 –0.5 mA
E/AOUT
= –0.5mA 4 4.7 5 V
= 1mA 0 0.5 1 V Unity Gain BW 7 11 MHz Slew Rate 611 V/µsec
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UC1875/6/7/8 UC2875/6/7/8 UC3875/6/7/8
ELECTRICAL CHARACTERISTICS:
85°C for the UC2875/6/7/8 and 0°C < T R
SLOPE
= 12kΩ, C
RAMP
= 200pF, C
DELAYSET A-B=CDELAYSET C-D
Unless otherwise stated, –55°C < TA< 125°C for the UC1875/6/7/8, –25°C < TA<
< 70°C for the UC3875/6/7/8, VC = VIN = 12V, R
A
= 0.01µF, I
DELAYSET A-B=IDELAYSET C-D
FREQSET
= 12kΩ,C
FREQSET
= –500µA, TA=TJ.
= 330pF,
PARAMETER TEST CONDITIONS MIN TYP MAX UNITS
PWM Comparator
Ramp Offset Voltage T
= 25°C (Note 3) 1.3 V
J
Zero Phase Shift Voltage (Note 4) 0.55 0.9 V PWM Phase Shift (Note1) V
V
Output Skew (Note 1) V
> (Ramp Peak + Ramp Offset) 98 99.5 102 %
E/AOUT
< Zero Phase Shift Voltage 0 0.5 2 %
E/AOUT
< 1V 5 ±20 nsec
E/AOUT
Ramp to Output Delay UC3875/6/7/8 (Note 6) 65 100 nsec
UC1875/6/7/8, UC2875/6/7/8 (Note 6) 65 125 nsec
Oscillator
Initial Accuracy T
= 25°C 0.85 1 1.15 MHz
J
Voltage Stability 11V < VIN < 20V 0.2 2 % Total Variation Line, Temperature 0.80 1.20 MHz Sync Pin Threshold T Clock Out Peak T Clock Out Low T
= 25°C 3.8 V
J
= 25°C 4.3 V
J
= 25°C 3.3 V
J
Oscillator (cont.)
Clock Out Pulse Width R Maximum Frequency R
CLOCKSYNC FREQSET
= 3.9k 30 100 nsec
= 5k 2 MHz
Ramp Generator/Slope Compensation
Ramp Current, Minimum I Ramp Current, Maximum I
SLOPE SLOPE
= 10µA, V = 1mA, V
FREQSET
FREQSET
= VREF –11 –14 µA
= VREF –0.8 –0.95 mA Ramp Valley 0V Ramp Peak - Clamping Level R
FREQSET
= 100k 3.8 4.1 V
Current Limit
Input Bias V
+ = 3V 2 5 µA
CS
Threshold Voltage 2.4 2.5 2.6 V Delay to Output UC3875/6/7/8 85 125 nsec
UC1875/6/7/8, UC2875/6/7/8 85 150 nsec
Soft-Start/Reset Delay
Charge Current V Discharge Current V
SOFTSTART SOFTSTART
= 0.5V –20 –9 –3 µA
= 1V 120 230 µA Restart Threshold 4.3 4.7 V Discharge Level 300 mV
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UC1875/6/7/8 UC2875/6/7/8 UC3875/6/7/8
ELECTRICAL CHARACTERISTICS:
85°C for the UC2875/6/7/8 and 0°C < T R
SLOPE
= 12kΩ, C
RAMP
= 200pF, C
DELAYSET A-B=CDELAYSET C-D
Unless otherwise stated, –55°C < TA< 125°C for the UC1875/6/7/8, –25°C < TA<
< 70°C for the UC3875/6/7/8, VC = VIN = 12V, R
A
= 0.01µF, I
DELAYSET A-B=IDELAYSET C-D
FREQSET
PARAMETER TEST CONDITIONS MIN TYP MAX UNITS
Output Drivers
Output Low Level I
Output High Level I
= 50mA 0.2 0.4 V
OUT
= 500mA 1.2 2.6 V
I
OUT
= –50mA 1.5 2.5 V
OUT
= –500mA 1.7 2.6 V
I
OUT
Delay Set (UC1875 and UC1876 only)
Delay Set Voltage I Delay Time I
= –500µA 2.3 2.4 2.6 V
DELAY
= –250µA (Note 5) (UC3875/6/7/8,
DELAY
UC2875/6/7/8)
= –250µA (Note 5) (UC1875/6/7/8) 150 250 600 nsec
I
DELAY
Note 1: Phase shift percentage (0% = 0°, 100% = 180°) is defined as fined in Figure 1. At 0% phase shift,
is the output skew.
θ=
200
T
, where is the phase shift, and and T are de
Φ%
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.
Note 5: Delay time can be programmed via resistors from the delay set pins to ground.Delay time
I
DELAY
=
R
DELAY
The recommended range for I
DELAY
is 25 A I
DELAY
1mA
Delay set voltage
Note 6: Ramp delay to output time is defined in Fig.2.
= 12kΩ,C
FREQSET
= 330pF,
= –500µA, TA=TJ.
150 250 400 nsec
12.–
62 5 10
I
DELAY
sec. Where
-
Duty Cycle = t/T Period = T T
(A to C) = T
DHL
(B to D) = Φ
DHL
Phase Shift, Output Skew & Delay Time Definitions
Figure 1
UDG-95074
UDG-95075
Figure 2
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Page 6
PIN FUNCTIONAL DESCRIPTIONS
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.
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.
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 initi­ated. 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 be­fore the SOFTSTART pin begins to rise -- this condition will not prematurely deliver power to the load.
FREQSET (oscillator frequency set pin): A resistor and a capacitor from FREQSET to GND will set the oscil lator frequency.
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.
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.
GND (signal ground): All voltages are measured with respect to GND. The timing capacitor, on the FREQSET
UC1875/6/7/8 UC2875/6/7/8 UC3875/6/7/8
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.
-
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.
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.
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
RC
SLOPE RAMP
Current mode control may be achieved with a minimum amount of external circuitry, in which case this pin pro­vides slope compensation.
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
-
ues of R
SLOPE
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.
For paralleled controllers, the SOFTSTART pins may be paralled to a single capacitor, but the charge currents will be additive.
6
and C
RAMP
.
-
-
-
-
-
-
-
-
-
-
Page 7
PIN FUNCTIONAL DESCRIPTIONS (cont.)
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.
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
UC1875/6/7/8 UC2875/6/7/8 UC3875/6/7/8
NOTE: When VIN exceeds the UVLO threshold the sup
-
ply current (I
-
in excess of 20µA. If the UC1875 is not connected to a well bypassed supply, it may immediately enter UVLO again.
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.
) will jump from about 100µA to a current
IN
-
When power is applied to the circuit and VIN is below the upper UVLO threshold, I
will be below 600µA, the
IN
reference generator will be off, the fault latch is reset, the soft-start pin is discharged, and the outputs are ac­tively
OSCILLATOR
The high frequency oscillator may be either free-running or externally synchronized. For
Simplified Oscillator Schematic
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.
UDG-95076
free-running operation, the frequency is set via an ex ternal resistor and capacitor to ground from the FREQSET pin.
-
-
UDG-95077
UDG-95079
UDG-95078
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Page 8
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 R1 & RN
may
be needed to keep sync pulse narrow due to capacitance on line.
may
also be needed to properly terminate R
SYNC
line.
Syncing to external TTL/CMOS
ICs will sync to fastest chip or TTL clock if it is higher frequency.
may
R & RN
Although each UC1875/6/7/8 has a local oscillator fre quency, the group of devices will synchronize to the fastest oscillator driving the CLOCKSYNC pin. This ar rangement allows the synchronizing connection be tween ICs to be broken without any local loss of functionality.
Synchronizing the device to an external clock signal may be accomplished with a minimum of external cir cuitry, as shown in the previous figure.
be needed for same reasons as above
-
Capacitive loading on the CLOCKSYNC pin will in crease the clock pulse width, and may adversely effect
-
system performance. Therefore, a resistor to ground
-
from the CLOCKSYNC pin is optional, but may be re quired to offset capacitive loading on this pin. These re sistors are shown in the oscillator schematics as R1, RN.
-
UDG-95081
-
-
-
8
Page 9
APPLICATIONS INFORMATION (cont.) DELAY BLOCKS AND OUTPUT STAGES
UC1875/6/7/8 UC2875/6/7/8 UC3875/6/7/8
In each of the output stages, transistors Q3 through Q6 form a high-speed totem-pole driver which will source or sink more than one amp peak with a total delay of approximately 30 nanoseconds. To ensure a low output level prior to turn-on, transistors Q7 through Q9 form a
self-biased driver to hold Q6 on prior to the supply reaching its turn-on threshold. This circuit is operable when the chip supply is zero. Q6 is also turned on and held low with a signal from the fault logic portion of the chip.
The delay providing the dead-time is accomplished with C1 which must discharge to V
before the output can
TH
go high. The time is defined by the current sources, I1, which is programmed by an external resistor, R
TD
. The
2.5V and the range of dead time control is from 50 to 200 nanoseconds. NOTE: There is no way to disable the delay circuitry, and the delay time must 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-95082
3 Winding Bifilar, AWG 30 Kynar Insulation
9
UDG-95083
Page 10
APPLICATIONS INFORMATION (cont.) FAULT/SOFT-START
UC1875/6/7/8 UC2875/6/7/8 UC3875/6/7/8
The fault control circuitry provides two forms of power shutdown:
• Complete turn-off of all four output power stages.
• Clamping the phase shift command to zero.
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
ceed while the phase-shift is advanced from zero to its nominal value with the time constant of the SOFT-START capacitor.
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.
-
-
UDG-95084
UDG-95085
10
Page 11
APPLICATIONS INFORMATION (cont.) SLOPE/RAMP PINS
UC1875/6/7/8 UC2875/6/7/8 UC3875/6/7/8
The ramp generator may be configured for the following control methods:
• Voltage Mode
• Voltage Feedforward
• Current Mode
• Current Mode with Slope Compensation
Voltage Mode Operation
The figure below shows a voltage-mode configuration. With R
SLOPE
form on C conventional voltage-mode control. If R
tied to a stable voltage source, the wave
will be a constant-slope ramp, providing
RAMP
SLOPE
is con nected to the power supply input voltage, a vari able-slope ramp will provide voltage feedforward.
1. Simple voltage mode operation achieved by placing R
SLOPE
between VIN
and SLOPE.
2. Voltage Feedforward achieved by plac­ing R
SLOPE
between supply voltage and
SLOPE pin of UC1875. RAMP
dV
dTVRC
Rslope
SLOPE RAMP
-
-
-
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
Page 12
IMPORTANT NOTICE
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TI warrants performance of its semiconductor products to the specifications applicable at the time of sale in accordance with TI’s standard warranty. Testing and other quality control techniques are utilized to the extent TI deems necessary to support this warranty . Specific testing of all parameters of each device is not necessarily performed, except those mandated by government requirements.
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Copyright 1999, Texas Instruments Incorporated
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