UC2849DW [ROCHESTER]
0.3A SWITCHING CONTROLLER, 550kHz SWITCHING FREQ-MAX, PDSO24, GREEN, PLASTIC, SOIC-24;
| 型号： | UC2849DW |
| 厂家： | 
Rochester Electronics |
| 描述： | 0.3A SWITCHING CONTROLLER, 550kHz SWITCHING FREQ-MAX, PDSO24, GREEN, PLASTIC, SOIC-24 开关 光电二极管 |
| 文件： | 总25页 (文件大小：1419K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
UC2849
UC3849
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SLUS360C–JULY 1995–REVISED AUGUST 2007
SECONDARY SIDE AVERAGE CURRENT MODE CONTROLLER
FEATURES
DESCRIPTION
•
Practical Secondary Side Control of Isolated
Power Supplies
The UC3849 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 sense amplifier. The outputs of the
voltage error amplifier and current sense amplifier
differentially drive a high bandwidth, integrating
current error amplifier. The sawtooth waveform at the
current error amplifier output is the amplified and
inverted inductor current sensed through the resistor.
This inductor current down-slope compared to the
PWM ramp achieves slope compensation, which
gives an accurate and inherent fast transient
response to changes in load.
•
•
•
•
1 MHz Operation
Differential AC Switching Current Sensing
Accurate Programmable Maximum Duty Cycle
Multiple Chips Can be Synchronized to
Fastest Oscillator
•
•
Wide Gain Bandwidth Product (70 MHz, Acl
>10) Current Error and Current Sense
Amplifiers
Up to Ten Devices Can Easily Share a
Common Load
BLOCK DIAGRAM
Pin numbers refer to 24-pin packages.
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas
Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
PRODUCTION DATA information is current as of publication date.
Copyright © 1995–2007, Texas Instruments Incorporated
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
UC2849
UC3849
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SLUS360C–JULY 1995–REVISED AUGUST 2007
DESCRIPTION (cont.)
The UC3849 features load share, oscillator synchronization, undervoltage lockout, and programmable output
control. Multiple chip operation can be achieved by connecting up to ten UC3849 chips in parallel. The SHARE
bus and CLKSYN bus provide load sharing and synchronization to the fastest oscillator respectively. The
UC3849 is an ideal controller to achieve high power, secondary side average current mode control.
CONNECTION DIAGRAMS
DIL-24, SOIC-24 (Top View)
N and DW Packages
PLCC-28 (Top View)
Q Package
ABSOLUTE MAXIMUM RATINGS(1)
VALUE
20
UNIT
V
Supply Voltage (VCC
)
Output current source or sink
Analog input voltages
0.3
A
–0.3 to 7
–0.3 to 7
12
V
ILIM, KILL, SEQ, ENBL, RUN
CLKSYN current source
RUN current sink
15
mA
SEQ current sink
20
RDEAD current sink
20
Share bus voltage (voltage with respect to GND)
ADJ voltage (voltage with respect to GND)
VVEE (voltage with respect to GND)
Storage temperaturee
0 to 6.2
0.9to 6.3
–1.5
V
–65 to 150
–65 to 150
300
Junction temperature
°C
Lead temperature (soldering, 10 sec.)
(1) All voltages with respect to VEE except where noted; all currents are positive into, negative out of the specified terminal.
RECOMMENDED OPERATING CONDITIONS
MIN
MAX
UNIT
Input voltage
8
20
V
Sink/source output current
250
mA
2
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SLUS360C–JULY 1995–REVISED AUGUST 2007
RECOMMENDED OPERATING CONDITIONS (continued)
MIN
1
MAX
200
UNIT
kΩ
Timing resistor (RT)
Timing capacitor (CT)
75
2000
pF
ELECTRICAL CHARACTERISTICS(1)
Unless otherwise stated these specifications apply for TA = –40°C to 85°C for UC2849; and 0°C to 70°C for UC3849; VCC
12 V, VEE = GND, Output no load, CT = 345 pF, RT = 4530Ω, RDEAD = 511Ω, RCLKSYN = 1 kΩ, TA = TJ.
=
PARAMETER
Current Sense Amplifier
Ib
TEST CONDITIONS
MIN
TYP
MAX
UNIT
0.5
3
3
5
μA
TA = 25°C
VIO
mV
Over Temperature
Avo
60
90
7
dB
(2)
GBW
Acl = 1, RIN = 1 kΩ, CC = 15 pF, f = 200 kHz(3)
IO = 1 mA, voltage above VEE
IO = 0 mA
4.5
MHz
VOL
0.5
3.8
3.5
80
80
V
VOH
IO = –1 mA
CMRR
–0.2 < Vcm < 6.5 V
dB
PSRR
10 V < VCC < 20 V
Current Error Amplifier
Ib
0.5
3
3
μA
mV
dB
VIO
20
Avo
GBW(2)
VOL
60
90
7
Acl = 1, RIN = 1 kΩ, CC = 15 pF, f = 200 kHz(3)
IO = 1 mA, voltage above VEE
IO = 0 mA
4.5
MHz
0.5
3.8
3.5
80
80
V
VOH
IO = –1 mA
CMRR
–0.1 < Vcm < 6.5 V
dB
PSRR
10 V < VCC < 20 V
Voltage Error Amplifier
Ib
0.5
2
3
5
μA
mV
dB
VIO
Avo
GBW(2)
60
90
7
f = 200 kHz
4.5
MHz
VOL
IO = 175 μA, voltage above VEE
ILIM > 3 V
0.3
3
0.6
3.15
100
V
VOH
2.85
VOH – ILIM
CMRR
PSRR
Tested ILIM = 0.5 V, 1.0 V, 2.0 V
–0.1 < Vcm < 6.5 V
10 V < VCC < 20 V
–100
mV
dB
80
80
(1) Unless otherwise specified all voltages are with respect to GND. Currents are positive into, negative out of the specified terminal.
(2) Ensured by design not 100% tested in production.
(3) If a closed loop gain greater than 1 is used, the possible GBW will increase by a factor of ACL + 10; where ACL is the closed loop gain.
3
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ELECTRICAL CHARACTERISTICS (continued)
Unless otherwise stated these specifications apply for TA = –40°C to 85°C for UC2849; and 0°C to 70°C for UC3849; VCC
12 V, VEE = GND, Output no load, CT = 345 pF, RT = 4530Ω, RDEAD = 511Ω, RCLKSYN = 1 kΩ, TA = TJ.
=
PARAMETER
2X Amplifier and Share Amplifier
V offset (b; y = mx + b)
GAIN (m; y = mx + b)
GBW(2)
TEST CONDITIONS
MIN
TYP
MAX
UNIT
20
mV
V
Slope with AVOUT = 1 V and 2 V
1.98
2.02
100
200
kHz
kΩ
RSHARE
VCC = 0, VSHARE/ISHARE
Negative supply is VEE, GND Open,
VAO = GND
Total offset
VOL
–75
0
75
mV
VAO = voltage amplifier Vol, volts above VEE
IO = 0 mA, ILIM = 3 V, VAO = voltage amp VOH
IO = –1mA, ILIM = 3 V, VAO = voltage amp VOH
0.05
5.7
0.45
6
0.6
6.3
6.3
V
VOH
5.7
6
Adjust Amplifier
VIO
gm
40
60
–1
1
80
mV
mS
IOUT= –10 μA to 10 μA, VOUT = 3.5 V, CADJ = 1 μF
IOUT = 0
0.9
0.85
5.7
1.1
1.15
6.3
VOL
IOUT = 50 μA
1
V
IOUT = 0 , VSHARE = 6.5 V
IOUT = –50 μA, VSHARE = 6.5 V
6
VOH
5.7
6
6.3
Oscillator
Frequency
450
80%
2
500
85%
2.5
550
90%
2.8
kHz
V
Max duty cycle
OSC range amplitude
Clock Driver/SYNC (CLKSYN)
VOL
0.02
3.6
3.2
25
0.2
V
VOH
RCLKSYN = 200 Ω
ISOURCE
RCLKSYN
mA
kΩ
V
VCC = 0, VCLKSYN/ICLKSYN
10
VTH
1.5
VREF Comparator
Turn-on threshold
Hysteresis
4.72
0.4
V
4
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ELECTRICAL CHARACTERISTICS (continued)
Unless otherwise stated these specifications apply for TA = –40°C to 85°C for UC2849; and 0°C to 70°C for UC3849; VCC
12 V, VEE = GND, Output no load, CT = 345 pF, RT = 4530Ω, RDEAD = 511Ω, RCLKSYN = 1 kΩ, TA = TJ.
=
PARAMETER
VCC Comparator
TEST CONDITIONS
MIN
TYP
MAX
UNIT
Turn-on threshold
Hysteresis
7.9
8.3
0.4
9.5
V
V
V
KILL Comparator
Voltage threshold
Sequence Comparator
Voltage threshold
SEQ SAT
3
2.5
0.25
ENABLE Comparator
Voltage threshold
RUN SAT
2.5
V
V
0.25
Reference
TA = 25°C
4.95
4.9
5
5.05
5.1
15
VREF
VCC = 15 V
10 < VCC < 20
0 < IO < 10 mA
VREF = 0 V
Line regulation
Load regulation
Short circuit I
Output Stage
Rise time
3
3
mV
mA
15
30
60
90
CL = 100 pF
CL = 100 pF
10
10
20
20
ns
V
Fall time
VCC > 11 V, IO = –10 mA
IO = –200 mA
8.0
7.8
8.4
8.8
VOH
IO = 200 mA
3.0
0.5
VOL
IO = 10 mA
Virtual Ground
VEE is externally supplied, GND is floating and used as
signal GND
VGND-VEE
0.2
0.75
21
V
Icc
Icc (run)
33
mA
5
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Pin Descriptions
ADJ: The output of the transconductance (gm = –1 ms) amplifier adjusts the control voltage to maintain equal
current sharing. The chip sensing the highest output current will have its output clamped to 1 V. 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 6 V) its control voltage (VA+) until its load current is equal to the master.
The 60-mV input offset on the gm amplifier specifies that the unit sensing the highest load current is chosen as
the master. The 60-mV offset ensures by design to be greater than the inherent offset of the gm amplifier and
the buffer amplifier. While the 60-mV offset represents an error in current sharing, the gain of the current and 2X
amplifiers reduces it to only 30 mV. This pin needs a 1-μF capacitor to compensate the amplifier.to the master.
CA–: The inverting input 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 4 V. It is internally connected to the
inverting input of the PWM comparator.
CS–, CS+: The inverting and non-inverting inputs to the current sense amplifier. This amplifier is not internally
compensated so the user must compensate externally to attain the highest GBW for the application.
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 1.4 V. The CLKSYN
voltage is 3.6 V when the oscillator capacitor (CT) is being discharged, otherwise it is 0 V. If the recommended
synchronization circuit is not used, a 1 kΩ or lower value resistor from CLKSYN to GND may be needed to
increase fall time on CLKSYN pin.
CSO: The output of the current sense amplifier which is internally clamped to 4 V.
ENBL: The active low input with a 2.5-V threshold enables the output to switch. SEQ and RUN are driven low
when ENBL is above its 2.5-V threshold.
GND: The signal ground used for the voltage sense amplifier, current sense amplifier, current error amplifier,
voltage reference, 2X amplifier, and share amplifier. The output sink transistor is wired directly to this pin.
KILL: The active low input with a 3.0-V threshold stops the output from switching. Once this function is activated
RUN must be cycled low by driving KILL above 3.0 V and either resetting the power to the chip (VCC) or
resetting the ENBL signal.
ILIM: A voltage on this pin programs the voltage error amplifier’s Voh clamp. The voltage error amplifier output
represents the average output current. The Voh clamp consequently limits the output current. If ILIM is tied to
VREF, it defaults to 3.0 V. A voltage less than 3.0 V connected to ILIM clamps the voltage error amplifier at this
voltage and consequently limits the maximum output current.
OSC: The oscillator ramp pin which has a capacitor (CT) to ground and a resistor (RDEAD) to the RDEAD pin
programs its maximum duty cycle by programming a minimum dead time. The ramp oscillates between 1.2 V to
3.4 V when an RDEAD resistor is used. The maximum duty cycle can be increased by connecting RDEAD to
OSC which changes the oscillator ramp to vary between 0.2 V and 3.5 V. In order to ensure zero duty cycle in
this configuration VEE should not be connected to GND.
The charge time is approximately TCHARGE = RT • CT when the RDEAD resistor is used.
The dead time is approximately TDISCHARGE = 2 • RDEAD • CT.
1
) T
Frequency [
T
CHARGE
DISCHARGE
(1)
(2)
T
CHARGE
) T
Maximum Duty Cycle [
T
CHARGE
DISCHARGE
The CT capacitance should be increased by approximately 40 pF to account for parasitic capacitance.
OUT: The output of the PWM driver. It has an upper clamp of 8.5 V. The peak current sink and source are 250
mA. All UVLO, SEQ, ENBL, and KILL logic either enable or disable the output driver.
6
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RDEAD: The pin that programs the maximum duty cycle by connecting a resistor between it and OSC. The
maximum duty cycle is decreased by increasing this resistor value which increases the discharge time. The
dead time, the time when the output is low, is 2 • RDEAD • CT. The CT capacitance should be increased by
approximately 40 pF to account for parasitic capacitance.
RT: This pin programs the charge time of the oscillator ramp. The charge current is
VREF
2 R
T
(3)
The charge time is approximately TCHARGE ≈ RT • CT when the RDEAD resistor is used.
The dead time is approximately TDISCHARGE ≈ 2 • RDEAD • CT.
RUN: This is an open collector logic output that signifies when the chip is operational. RUN is pulled high to
VREF through an external resistor when VCC is greater than 8.4 V, VREF is greater than 4.65 V, SEQ is greater
than 2.5 V, and KILL lower than 3.0 V. RUN connected to the VA+ pin and to a capacitor to ground adds an RC
rise time on the VA+ pin initiating a soft start.
SEQ: The sequence pin allows the sequencing of startup for multiple units. A resistor between VREF and SEQ
and a capacitor between SEQ and GND creates a unique RC rise time for each unit which sequences the output
startup.
SHARE: The nearly dc voltage representing the average output current. This pin is wired directly to all SHARE
pins and is the load share bus.
VA+, VA–: The inverting and non-inverting inputs to the voltage error amplifier.
VAO: The output of the voltage error amplifier. Its Voh is clamped with the ILIM pin.
VCC: The input voltage of the chip. The chip is operational between 8.4 V and 20 V.
VEE: The negative supply to the chip which powers the lower voltage rail for all amplifiers. The chip is
operational if VEE is connected to GND or if GND is floating. When voltage is applied externally to VEE, GND
becomes a virtual ground because of an internal diode between VEE and GND. The GND current flows through
the forward biased diode and out VEE. GND is always the signal ground from which the voltage reference and
all amplifier inputs are referenced.
VREF: The reference voltage equal to 5.0 V.
7
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Circuit Block Description
PWM Oscillator
The oscillator block diagram with external connections is shown in Figure 1. A resistor (RT) connected to pin RT
sets the linear charge current;
2.5 V
I
[
RT
R
T
V
REF
OSCILLATOR
2.5 V
RT
21
R
T
4.5 kW
V
REF
1.4 V
OSC
23
S
R
2.5 V
3.4 V
345 pF
500 W
20
CLKSYN
C
T
1.2 V
22
RDEAD
10 kW
Figure 1. Oscillator Block with External Connections
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The timing capacitor (CT) is linearly charged with the charge current forcing the OSC pin to charge to a 3.4-V
threshold. After exceeding this threshold, the RS flip-flop is set driving CLKSYN high and RDEAD low which
discharges CT. This discharge time with the RC time delay of 2 • CT • RDEAD is the minimum output low time.
OSC continues to discharge until it reaches a 1.2 -V threshold and resets the RS flip-flop which repeats the
charging sequence as shown in Figure 2. Equations to approximate frequency and maximum duty cycle are
listed under the OSC pin description. Figure 3 and Figure 4 graphs show measured variation of frequency and
maximum duty cycle with varying RT, CT, and RDEAD component values.
As shown in Figure 5, several oscillators are synchronized to the highest free running frequency by connecting
100-pF capacitors in series with each CLKSYN pin and connecting the other side of the capacitors together
forming the CLKSYN bus. The CLKSYN bus is then pulled down to ground with a resistance of approximately 10
kΩ. Referring to Figure 1, the synchronization threshold is 1.4 V. The oscillator blanks any synchronization pulse
that occurs when OSC is below 2.5 V. This allows units, once they discharge below 2.5 V, to continue through
the current discharge and subsequent charge cycles whether or not other units on the CLKSYN bus are still
synchronizing. This requires the frequency of all free running oscillators to be within 40% of each other to assure
synchronization.
VAO CURRENT COMMAND
3.4 V
OSC
1.2 V
3.6 V
1.4 V (THRESHOLD)
CLKSYN
MINIMUM OUTPUT LOW TIME
8.5 V
OUT
0 V
Figure 2. Oscillator and PWM Output Waveform
100
10k
1000
100
C
= 345 pF
T
READ = 500 W
CT = 345 pF
1 nF
2.2 nF
75
READ = 51
READ = 511
4.7 nF
50
10
1
25
0
READ = 5000
1
10
100
1k
- W
10k 100k
1M
1
10
100
1k
- W
10k
100k
1M
R
T
R
T
Figure 3. Output Frequency
Figure 4. Maximum Duty Cycle
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Grounds, Voltage Sensing and Current Sensing
The voltage is sensed directly at the load. Proper load sharing requires the same sensed voltage for each power
supply connected in parallel. Referring to Figure 6, the positive sense voltage (VSP) connects to the voltage
error amplifier inverting terminal (VA–), the return lead for the on-chip reference is used as the negative sense
(VSM). The current is sensed across the shunt resistor, RS.
Figure 6 shows one recommended voltage and current sensing scheme when VEE is connected to GND. The
signal ground is the negative sense point for the output voltage and the positive sense point for the output
current. The voltage offset on the current sense amplifier is not needed if VEE is separated from GND. VEE is
the negative supply for the current sense amplifier. When it is separated from GND, it extends the current sense
amplifier's common mode input voltage range to include VEE which is approximately –0.7 V below ground. The
resistor RADJ is used for load sharing. The unit which is the master will force VADJ to 1.0 V. Therefore, the
regulated voltage being sensed is actually:
100 pF
CLKSYN
20
OSC1
C
L
K
S
Y
N
100 pF
100 pF
100 pF
CLKSYN
20
20
20
OSC2
OSC3
B
U
S
CLKSYN
CLKSYN
OSC10
10 kW
Figure 5. Oscillator Synchronization
Connection Diagram
Figure 6. Voltage and Current Sense VEE
Tied to GND
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R
ǒ Ǔ) V
ADJ
VSP * VSM + ǒVREF * V
Ǔ
ADJ
ADJ
R1 ) R
ADJ
(4)
(5)
VSM + 0 V, V
+ 1 V(master), VREF + 5 V
ADJ
R
ǒ Ǔ) 1 V
ADJ
VSP + 4
R1 ) R
ADJ
(6)
The ADJ pin voltage on the slave chips will increase forcing their load currents to increase to match the master.
The ac frequency response of the voltage error amplifier is shown in Figure 7.
200
160
120
Phase
80
40
A
VO
qm = 50º
0
10 M 100 M
10
100
1 k
10 k 100 k 1 M
f - Frequency - Hz
Figure 7. AC Frequency Response of the
Voltage Error Amplifier
Startup and Shutdown
Isolated power up can be accomplished using the UCC1889. Application Note U-149 is available for additional
information.
The UC3849 offers several features that enhance startup and shutdown. Soft start is accomplished by
connecting RUN to VA+ and a capacitor to ground. The resulting RC rise time on the VA+ pin initiates a soft
start. It can also be accomplished by connecting RUN to ILIM. When RUN is low it commands zero load current,
assuring a soft start. The undervoltage lockout (UVLO) is a logical AND of ENBL < 2.5 V, SEQ > 2.5 V, VCC >
8.4 V and VREF > 4.65 V. The block diagram shows that the thresholds are set by comparators. By placing an
RC divider on the SEQ pin, the enabling of multiple chips can be sequenced with different RC time constants.
Similarly, different RC time constants on the ENBL pins can sequence shutdown. The UVLO keeps the output
from switching; however the internal reference starts up with VCC less than 8.4 V. The KILL input shuts down
the switching of the chip. This can be used in conjunction with an overvoltage comparator for overvoltage
protection. In order to restart the chip after KILL has been initiated, the chip must be powered down and then
back up. A pulse on the ENBL pin also accomplishes this without actually removing voltage to the VCC pin.
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Load Sharing
Load sharing is accomplished similar to the UC1907. The sensed current for the UC3849 has an ac component
that is amplified and then averaged. The voltage error amplifier output is the current command signal
representing the average output load current. The ILIM pin programs the upper clamp voltage of this amplifier
and consequently the maximum load current. A gain of 2 amplifier connected between the voltage error amplifier
output and the share amplifier input increases the current share resolution and noise margin. The average
current is used as an input to a source only load share buffer amplifier. The output of this amplifier is the current
share bus. The device with the highest sensed current will have the highest voltage on the current share bus
and consequently act as the master. The 60-mV input offset ensures that the unit sensing the highest load
current is chosen as the master.
The adjust amplifier is used by the remaining (slave) devices to adjust their respective references high in order
to balance each device's load current. The master's ADJ pin will be at its 1.0-V clamp and connected back to the
non-inverting voltage error amplifier input through a high value resistor. This requires the user to initially
calculate the control voltage with the ADJ pin at 1.0 V.
VREF can be adjusted 150 mV to 300 mV which compensates for 5% unit to unit reference mismatch and
external resistor mismatch. RADJ typically is 10 to 30 times larger than R1. This also attenuates the overall
variation of the ADJ clamp of 1 V ±100 mV by a factor of 10 to 30, contributing only a 3 mV to 10 mV additional
delta to VREF. Refer to the UC3907 Application Note U-130 for further information on parallel power supply load
sharing.
Current Control Loop
The current sense amplifier (CSA) is designed specifically for the task of sensing and amplifying the inductor
ripple current at frequencies up to 1 MHz. The CSA's input offset voltage (VIO) is trimmed to less than 1 mV to
minimize error of the average current signal. This amplifier is not internally compensated allowing the user to
optimally choose the zero crossing bandwidth.on on parallel power supply load sharing.
1
C
Frequency(0 dB) +
2pR
INV
COMP
(7)
RINV is the input resistance at the inverting terminal CS– CCOMP is the capacitance between CS– and CSO.
Although it is only unity gain stable for a GBW of 7 MHz, the amplifier is typically configured with a differential
gain of at least 10, allowing the amplifier to operate at 70 MHz with sufficient phase margin. A closed loop gain
of 10 attenuates the output by 20.8 dB to the inverting terminal assuring stability. The amplifier’s gain fed back
into the inverting terminal is less than unity at 7 MHz, where the phase margin begins to roll off. See Figure 8 for
typical Bode plot.
1
11
20.8 + 20 log
(8)
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200
160
120
80
A
= Open Loop Gain
VO
Phase
A
= -10
40
0
VC
A
- b
V O
qm = 70º
10
100
1 k
10 k 100 k 1 M
f - Frequency - Hz
10 M 100 M
Figure 8. Current Sense Amplifier and
Curent Error Amplifier Bode Plot
The gain of the differential current sense amplifier (CSGAIN) is calculated by knowing the maximum load current.
The maximum voltage across the shunt resistor (RS) divided by RS is the maximum load current. By amplifying
the voltage across RS, VRS, to be equal to the voltage error amplifier Voh, the current control loop keeps the
load from exceeding its current limit. Voh is set at 3.0 V if ILIM is connected to VREF. The maximum current
limit clamp can be reduced by reducing the voltage at ILIM to less than 3.0 V as described in the ILIM pin
description.
V
RS
R
+
S
Max I
LOAD
(9)
V
ILIM
CS
+
GAIN
V
RS
(10)
The current error amplifier (CEA) also needs its loop compensated by the user with the same criteria as the
current sense amplifier. This amplifier is essentially the same wide bandwidth amplifier without the input offset
voltage trim. The zero crossing can also be approximately calculated with Equation 7. The gain bandwidth of the
current loop is optimized by matching the inductor downslope (VO/L) to the oscillator ramp slope (VS • fS).
Subharmonic oscillation problems are avoided by keeping the amplified inductor downslope less than the
oscillator ramp slope.
The following equation determines the current error amplifier gain (GCA):
V f
s
S
GCA +
;
ǒ Ǔ
V
R CS
S
GAIN
OńL
(11)
where CSGAIN and RS are defined by Equation 9 and Equation 10,
Vs is the oscillator peak to peak voltage,
fs is the oscillator frequency,
VO is the output voltage,
and L is the inductance.
Additional Information about average current mode control can be found in Unitrode Application Note U-140.
13
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UC2849
UC3849
www.ti.com
SLUS360C–JULY 1995–REVISED AUGUST 2007
Design Example
Figure 9 is an open loop test that lets the user test the circuit blocks discussed without having to build an entire
control loop. The pulse width can be varied by either the VADJ or the VISENSE inputs. Figure 10 shows an isolated
power supply using the UC3849 secondary side average current mode controller.
1
2
ADJ
ILIM
VA-
SHARE
OSC
24
23
22
21
20
19
18
17
16
15
14
13
C4
345pF
R6
15kW
+20
R1
500kW
3
RDEAD
RT
R7
10kW
R2
5kW
4
VA+
VAO
CA-
R9
10kW
+
20V
5
CLKSYN
VEE
C1
1.0mF
6
R10, 10kW
C2 100pF
7
CAO
CS+
CS-
GND
VISENSE
R11, 1kW
8
OUT
10kW
+
R13, 1kW
9
VCC
R14, 10kW
R12
10 kW
R3
2kW
10
11
12
CSO
ENBL
SEQ
RUN
C3, 100pF
R17, 10kW
C5
0.1mF
VREF
KILL
R4
10kW
R18, 5kW
C5
0.1mF
Figure 9. Open Loop Circuit
14
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UC2849
UC3849
www.ti.com
SLUS360C–JULY 1995–REVISED AUGUST 2007
Figure 10. UC3849 Application Diagram
15
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PACKAGE OPTION ADDENDUM
www.ti.com
27-Aug-2009
PACKAGING INFORMATION
Orderable Device
UC2849DW
Status (1)
ACTIVE
ACTIVE
ACTIVE
ACTIVE
ACTIVE
ACTIVE
ACTIVE
ACTIVE
Package Package
Pins Package Eco Plan (2) Lead/Ball Finish MSL Peak Temp (3)
Qty
Type
Drawing
SOIC
DW
24
24
24
24
24
24
24
24
25 Green (RoHS & CU NIPDAU Level-2-260C-1 YEAR
no Sb/Br)
UC2849DWG4
UC2849N
SOIC
PDIP
PDIP
SOIC
SOIC
SOIC
SOIC
DW
N
25 Green (RoHS & CU NIPDAU Level-2-260C-1 YEAR
no Sb/Br)
15 Green (RoHS & CU NIPDAU N / A for Pkg Type
no Sb/Br)
UC2849NG4
N
15 Green (RoHS & CU NIPDAU N / A for Pkg Type
no Sb/Br)
UC3849DW
DW
DW
DW
DW
25 Green (RoHS & CU NIPDAU Level-2-260C-1 YEAR
no Sb/Br)
UC3849DWG4
UC3849DWTR
UC3849DWTRG4
25 Green (RoHS & CU NIPDAU Level-2-260C-1 YEAR
no Sb/Br)
2000 Green (RoHS & CU NIPDAU Level-2-260C-1 YEAR
no Sb/Br)
2000 Green (RoHS & CU NIPDAU Level-2-260C-1 YEAR
no Sb/Br)
(1) The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in
a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check
http://www.ti.com/productcontent for the latest availability information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements
for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered
at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and
package, or 2) lead-based die adhesive used between the die and leadframe. The component is otherwise considered Pb-Free (RoHS
compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame
retardants (Br or Sb do not exceed 0.1% by weight in homogeneous material)
(3)
MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder
temperature.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is
provided. TI bases its knowledge and belief on information provided by third parties, and makes no representation or warranty as to the
accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and continues to take
reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on
incoming materials and chemicals. TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited
information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI
to Customer on an annual basis.
OTHER QUALIFIED VERSIONS OF UC3849 :
Military: UC1849
•
NOTE: Qualified Version Definitions:
Addendum-Page 1
PACKAGE OPTION ADDENDUM
www.ti.com
27-Aug-2009
Military - QML certified for Military and Defense Applications
•
Addendum-Page 2
PACKAGE MATERIALS INFORMATION
www.ti.com
1-May-2009
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
Package Package Pins
Type Drawing
SPQ
Reel
Reel
A0 (mm)
B0 (mm)
K0 (mm)
P1
W
Pin1
Diameter Width
(mm) W1 (mm)
(mm) (mm) Quadrant
UC3849DWTR
SOIC
DW
24
2000
330.0
24.4
10.85
15.8
2.7
12.0
24.0
Q1
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
1-May-2009
*All dimensions are nominal
Device
Package Type Package Drawing Pins
SOIC DW 24
SPQ
Length (mm) Width (mm) Height (mm)
346.0 346.0 41.0
UC3849DWTR
2000
Pack Materials-Page 2
MECHANICAL DATA
MPDI006B – SEPTEMBER 2001 – REVISED APRIL 2002
N (R–PDIP–T24)
PLASTIC DUAL–IN–LINE
1.222 (31,04) MAX
24
13
0.360 (9,14) MAX
1
12
0.070 (1,78) MAX
0.200 (5,08) MAX
0.020 (0,51) MIN
0.425 (10,80) MAX
Seating Plane
0.125 (3,18) MIN
0.100 (2,54)
0.010 (0,25)
0’–15’
0.021 (0,53)
0.015 (0,38)
0.010 (0,25) NOM
4040051–3/D 09/01
NOTES: A. All linear dimensions are in inches (millimeters).
B. This drawing is subject to change without notice.
C. Falls within JEDEC MS–010
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
MECHANICAL DATA
MPDI008 – OCTOBER 1994
N (R-PDIP-T**)
PLASTIC DUAL-IN-LINE PACKAGE
24 PIN SHOWN
A
24
13
0.560 (14,22)
0.520 (13,21)
1
12
0.060 (1,52) TYP
0.200 (5,08) MAX
0.020 (0,51) MIN
0.610 (15,49)
0.590 (14,99)
Seating Plane
0.100 (2,54)
0.125 (3,18) MIN
0.010 (0,25) NOM
0°–15°
0.021 (0,53)
0.015 (0,38)
0.010 (0,25)
PINS **
M
24
28
32
40
48
52
DIM
1.270
1.450
1.650
2.090
2.450
2.650
A MAX
(32,26) (36,83) (41,91) (53,09) (62,23) (67,31)
1.230
1.410
1.610
2.040
2.390
2.590
A MIN
(31,24) (35,81) (40,89) (51,82) (60,71) (65,79)
4040053/B 04/95
NOTES: A. All linear dimensions are in inches (millimeters).
B. This drawing is subject to change without notice.
C. Falls within JEDEC MS-011
D. Falls within JEDEC MS-015 (32 pin only)
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
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