UNITRODE UC1826, UC2826, UC3826 Technical data
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Secondary Side Average Current Mode Controller
UC1826
UC2826
UC3826
FEATURES
• Practical Secondary Side Control of
Isolated Power Supplies
• 1MHz Operation
• Tailored Loop Bandwidth Provides
Excellent Noise Immunity
• Voltage Feedforward Provides
Superior T ransient Response
• Accurate Programmable Maximum
Duty Cycle
• Multiple Chips Can be Synchronized
to Fastest Oscillator
• Wide Gain Bandwidth Product
(70MHz, Acl>10) Current Error
Amplifier
• Up to Ten Devices Can Easily Share
a Common Load
BLOCK DIAGRAM
DESCRIPTION
The UC1826 family of average current mode controllers accurately
accomplishes secondary side average current mode control.The secondary side output voltage is regulated by sensing the output voltage
and differentially sensing the AC switching current.The sensed output
voltage drives a voltage error amplifier.The AC switching current, monitored by a current sense resistor, drives a high bandwidth, low offset
current error amplifier. The output of the voltage error amplifier can be
used to drive the current amplifier which filters the measured inductor
current. Fast transient response is accomplished by utilizing voltage
feedforward in generating the PWM ramp.
The UC1826 features load share, oscillator synchronization, undervoltage lockout, and programmable output control. Multiple chip operation
can be achieved by connecting up to ten UC1826 chips in parallel.The
SHARE bus and CLKSYN bus provide load sharing and synchronization to the fastest oscillator respectively.With its tailored bandwidth, the
UC1826 provides excellent noise immunity and is an ideal controller to
achieve high power, secondary side average current mode control.
Pin Numbers refer to 24-pin packages.
7/95
UDG-95013
UC1826
UC2826
UC3826
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (VCC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20V
Output Current Source or Sink . . . . . . . . . . . . . . . . . . . . . .0.3A
Analog Input Voltages . . . . . . . . . . . . . . . . . . . . . . .−0.3V to 7V
ILIM, KILL, SEQ, ENBL, RUN, PWRSEN, PWROK . . . .−0.3V to 7V
CLKSYN Current Source . . . . . . . . . . . . . . . . . . . . . . . . .20mA
RUN Current Sink . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20mA
SEQ Current Sink . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20mA
RDEAD Current Sink . . . . . . . . . . . . . . . . . . . . . . . . . . . .20mA
RAMP Current Sink . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20mA
Share Bus Voltage (voltage with respect to GND) . . .0V to 6.2V
ADJ Voltage (voltage with respect to GND) . . . . . .0.9V to 6.3V
VEE (voltage with respect to GND) . . . . . . . . . . . . . . . . . .−1.5V
CONNECTION DIAGRAMS
DIL-24,SOIC-24,TSSOP-24 (Top View)
J or N,DW,PW Packages
Storage Temperature . . . . . . . . . . . . . . . . . . . .−65°C to +150°C
Junction Temperature . . . . . . . . . . . . . . . . . . .−65°C to +150°C
Lead Temperature (Soldering, 10 sec.) . . . . . . . . . . . . .+300°C
All voltages with respect to VEE except where noted;all currents
are positive into, negative out of the specified terminal.
Consult Packaging Section of Databook for thermal limitations
and considerations of packages.
RECOMMENDED OPERATING CONDITIONS
Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8V to 20V
Sink/Source Output Current . . . . . . . . . . . . . . . . . . . . . .250mA
Timing Resistor RT . . . . . . . . . . . . . . . . . . . . . . . . . .1k to 200k
Timing Capacitor CT . . . . . . . . . . . . . . . . . . . . . . . .75pF to 2nF
PLCC-28 (Top View)
Q Package
ELECTRICAL CHARACTERISTICSUnless otherwise stated these specifications apply for TA = −55°Cto+125°C for
UC1826;−40°C to +85°C for UC2826;and 0°C to +70°C for UC3826;VCC = 12V, VEE = GND, Output no load, CT = 345pF,
RT = 4kΩ, RDEAD = 1000Ω, CRAMP = 345pF, RRAMP = 35.2kΩ, RCLKSYN = 1k, TA =TJ.
PARAMETER TEST CONDITIONS MIN TYP MAX UNITS
Current Error Amplifier
Ib 0.5 3 µA
Vio TA = +25°C 0.75 3 mV
Over Temperature 5 mV
Avo 60 90 dB
GBW (Note 2) Acl = 10, RIN = 1k, CC = 15pF, f = 200kHz (Note 1) 45 70 MHz
Vol IO = 1mA, Voltage above VEE 0.5 V
Voh IO = 0mA 3.8 V
IO = −1mA 3.5 V
Voltage Error Amplifier
Ib 0.5 3 µA
Vio 5mV
Avo 60 90 dB
2
UC1826
UC2826
UC3826
ELECTRICAL CHARACTERISTICS (cont.)Unless otherwise stated these specifications apply for TA = −55°Cto
+125°C for UC1826;−40°C to +85°C for UC2826;and 0°C to +70°C for UC3826;VCC = 12V, VEE = GND, Output no load, CT =
345pF, RT = 4kΩ, RDEAD = 1000Ω, CRAMP = 345pF, RRAMP = 35.2kΩ, RCLKSYN = 1k, TA = TJ.
PARAMETER TEST CONDITION MIN TYP MAX UNITS
Voltage Error Amplifier (cont.)
GBW (Note 2) f = 200kHz 7 MHz
Vol IO = 175mA, Volts above VEE 0.6 V
V oh ILIM = 3V 2.85 3 3.15 V
Voh-ILIM Tested ILIM = 0.5V, 1.0V, 2.0V −100 100 mV
2X Amplifier and Share Amplifier
V offset (b;y = mx + b) 20 mV
GAIN (m;y = mx + b) Slope with AVOUT = 1V and 2V 1.98 2.02 V
GBW (Note 2) 100 kHZ
RSHARE VCC = 0, VSHARE/ISHARE 200 kΩ
Total Offset Negative supply is VEE, GND Open,VAO = GND −75 0 75 mV
V ol VAO = V oltage Amp Vol, Volts above VEE 0.2 0.45 0.6 V
Voh IO = 0mA, ILIM = 3V, VA O = Voltage Amp V oh 5.7 6 6.3 V
IO = −1mA, ILIM = 3V, VAO = V oltage Amp V oh 5.7 6 6.3 V
Adjust Amplifier
Vio 40 60 80 mV
gm IO = −2µA to 2µA, CADJ = 0.1µF −0.1 −0.3 mS
Vol IOUT = 0 0.9 1 1.1 V
IOUT = 2µA 0.85 1 1.15 V
Voh IOUT = 0, VSHARE = 6.5V 5.7 6 6.3 V
IOUT =−2µA, VSHARE = 6.5V 5.7 6 6.3 V
Oscillator
Frequency 450 500 550 kHz
Max Duty Cycle 72 76 80 %
OSC Ramp Amplitude 2 2.2 2.4 V
Ramp Saturation IO = 10mA, OSC = 0V 0.44 0.8 V
Clock Driver/SYNC (CLKSYN)
Vol 0.02 0.2 V
Voh 3.6 V
RCLKSYN = 200Ω 3.5 V
ISOURCE 25 mA
RCLKSYN VCC = 0, VCLKSYN/ICLKSYN 10 k
VTH 1.5 V
VREF Comparator
T urn-on Threshold 4.65 V
Hysteresis 0.4 V
VCC Comparator
T urn-on Threshold 7.9 8.4 8.9 V
Hysteresis 0.4 V
PWR Sense Comparator
V oltage Threshold 1.25 V
Vol IO = 1mA 0.3 0.4 V
Voh IO =−100µA4V
KILL Comparator
V oltage Threshold 3V
3
UC1826
UC2826
UC3826
ELECTRICAL CHARACTERISTICS (cont.)Unless otherwise stated these specifications apply for TA = −55°Cto
+125°C for UC1826;−40°C to +85°C for UC2826;and 0°C to +70°C for UC3826;VCC = 12V, VEE = GND, Output no load, CT =
345pF, RT = 4kΩ, RDEAD = 1000Ω, CRAMP = 345pF, RRAMP = 35.2kΩ, RCLKSYN = 1k, TA = TJ.
PARAMETER TEST CONDITION MIN TYP MAX UNITS
Sequence Comparator
V oltage Threshold 2.5 V
SEQ SAT IO = 10mA 0.25 V
Enable Comparator
V oltage Threshold 2.5 V
RUN SAT IO = 10mA 0.2 V
Reference
VREF TA = 25°C 4.95 5 5.05 V
VCC = 15V 4.9 5.1 V
Line Regulation 10 < VCC < 20 3 15 mV
Load Regulation 0 < IO < 10mA 3 15 mV
Short Circuit I VREF = 0V 30 60 90 mA
Output Stage
Rise Time CL = 100pF 10 20 ns
Fall Time CL = 100pF 10 20 ns
Voh VCC > 11V, IO =−10mA 8.0 8.4 8.8 V
IO = −200mA 7.8 V
Vol IO = 200mA 3.0 V
IO = 10mA 0.5 V
Virtual Ground
V
GND − VEE VEE is externally supplied, GND is floating 0.2 0.75 V
and used as Signal GND.
Icc
Icc (run) 21 30 mA
Note 1: Guaranteed by design.Not 100% tested in production.
Note 2: Unless otherwise specified all voltages are with respect to GND.Currents are positive into, negative out of the
specified terminal.
PIN DESCRIPTIONS
ADJ: The output of the transconductance (gm = −0.1mS)
amplifier adjusts the control voltage to maintain equal current sharing.The chip sensing the highest output current
will have its output clamped to 1V. A resistor divider
between VREF and ADJ drives the control voltage (VA+)
for the voltage amplifier. Each slave unit’s ADJ voltage
increases (to a maximum of 6V) its control voltage (VA+)
until its load current is equal to the master.The 60mV
input offset on the gm amplifier guarantees that the unit
sensing the highest load current is chosen as the master.
The 60mV offset is guaranteed by design to be greater
than the inherent offset of the gm amplifier and the buffer
amplifier. While the 60mV offset represents an error in
current sharing, the gain of the current and 2X amplifiers
reduces it to only 30mV. The total current sense gain is
the current amplifier gain.This pin needs a 0.1µF capaci-
tor to compensate the amplifier.
CA-, CA+: The inverting and non-inverting inputs to the
current error amplifier. This amplifier needs a capacitor
between CA- and CAO to set its dominant pole.
CAO: The output of the current error amplifier which is
internally clamped to 4V.It is internally connected to the
inverting input of the PWM comparator.
CLKSYN: The clock and synchronization pin for the
oscillator. This is a bidirectional pin that can be used to
synchronize several chips to the fastest oscillator. Its
input synchronization threshold is 1.4V. The CLKSYN
voltage is 3.6V when the oscillator capacitor CT is being
discharged, otherwise it is 0V.
4
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