Datasheet UC2849, UC3849 Datasheet (TEXAS INSTRUMENTS)

Download

Page 1

www.ti.com

Pinnumbersreferto24-pinpackages.

SECONDARY SIDE AVERAGE CURRENT MODE CONTROLLER

FEATURES DESCRIPTION

• Practical Secondary Side Control of Isolated

Power Supplies

• 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

UC2849 UC3849

SLUS360C – JULY 1995 – REVISED AUGUST 2007

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.

BLOCK DIAGRAM

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. Products conform to specifications per the terms of the Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters.

Page 2

www.ti.com

DIL-24, SOIC-24 (TopView)

NandDWPackages

QPackage

PLCC-28(TopView)

UC2849 UC3849

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

ABSOLUTE MAXIMUM RATINGS

Supply Voltage (V Output current source or sink 0.3 A Analog input voltages –0.3 to 7 ILIM, KILL, SEQ, ENBL, RUN –0.3 to 7 CLKSYN current source 12 RUN current sink 15 SEQ current sink 20 RDEAD current sink 20 Share bus voltage (voltage with respect to GND) 0 to 6.2 ADJ voltage (voltage with respect to GND) 0.9to 6.3 V VVEE (voltage with respect to GND) –1.5 Storage temperaturee –65 to 150 Junction temperature –65 to 150 ° C Lead temperature (soldering, 10 sec.) 300

(1) All voltages with respect to VEE except where noted; all currents are positive into, negative out of the specified terminal.

RECOMMENDED OPERATING CONDITIONS

Input voltage 8 20 V Sink/source output current 250 mA

(1)

VALUE UNIT

) 20 V

MIN MAX UNIT

Submit Documentation Feedback

Page 3

www.ti.com

SLUS360C – JULY 1995 – REVISED AUGUST 2007

RECOMMENDED OPERATING CONDITIONS (continued)

MIN MAX UNIT

Timing resistor (RT) 1 200 k Ω Timing capacitor (CT) 75 2000 pF

UC2849 UC3849

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; V 12 V, VEE = GND, Output no load, CT= 345 pF, RT = 4530 Ω , RDEAD = 511 Ω , R

PARAMETER TEST CONDITIONS MIN TYP MAX UNIT

Current Sense Amplifier

Ib 0.5 3 μ A

Avo 60 90 dB

(2)

GBW V

CMRR –0.2 < Vcm < 6.5 V 80 PSRR 10 V < VCC < 20 V 80

Current Error Amplifier

Ib 0.5 3 μ A V

Avo 60 90 dB

(2)

GBW V

CMRR –0.1 < Vcm < 6.5 V 80 PSRR 10 V < VCC < 20 V 80

Voltage Error Amplifier

Ib 0.5 3 μ A V

Avo 60 90 dB

(2)

GBW V

– ILIM Tested ILIM = 0.5 V, 1.0 V, 2.0 V –100 100 mV

CMRR –0.1 < Vcm < 6.5 V 80 PSRR 10 V < VCC < 20 V 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.

TA= 25 ° C 3 Over Temperature 5

Acl = 1, RIN= 1 k Ω , CC = 15 pF, f = 200 kHz

(3)

IO= 1 mA, voltage above VEE 0.5 IO= 0 mA 3.8 V IO= –1 mA 3.5

Acl = 1, RIN= 1 k Ω , CC = 15 pF, f = 200 kHz

(3)

IO= 1 mA, voltage above VEE 0.5 IO= 0 mA 3.8 V IO= –1 mA 3.5

f = 200 kHz 4.5 7 MHz IO= 175 μ A, voltage above VEE 0.3 0.6 ILIM > 3 V 2.85 3 3.15

CLKSYN

= 1 k Ω , TA= TJ.

4.5 7 MHz

3 20 mV

4.5 7 MHz

2 5 mV

Submit Documentation Feedback

Page 4

www.ti.com

UC2849 UC3849

SLUS360C – JULY 1995 – REVISED AUGUST 2007

ELECTRICAL CHARACTERISTICS (continued)

PARAMETER TEST CONDITIONS MIN TYP MAX UNIT

2X Amplifier and Share Amplifier

V offset (b; y = mx + b) 20 mV GAIN (m; y = mx + b) Slope with AV

(2)

GBW R

Total offset –75 0 75 mV V

VCC = 0, V Negative supply is VEE, GND Open,

VAO = GND VAO = voltage amplifier Vol, volts above VEE 0.05 0.45 0.6 IO= 0 mA, ILIM = 3 V, VAO = voltage amp V IO= –1mA, ILIM = 3 V, VAO = voltage amp V

Adjust Amplifier

gm I

= –10 μ A to 10 μ A, V

OUT

= 0 0.9 1 1.1

OUT

= 50 μ A 0.85 1 1.15

OUT

= 0 , V

OUT

= –50 μ A, V

OUT

Oscillator

Frequency 450 500 550 kHz Max duty cycle 80% 85% 90% OSC range amplitude 2 2.5 2.8 V

Clock Driver/SYNC (CLKSYN)

SOURCE

CLKSYN

= 200 Ω 3.2

CLKSYN

= 0, V

VREF Comparator

Turn-on threshold 4.72 Hysteresis 0.4

= 1 V and 2 V 1.98 2.02 V

OUT

= 3.5 V, C

OUT

= 6.5 V 5.7 6 6.3

CLKSYN/ICLKSYN

= 1 μ F –1 mS

ADJ

CLKSYN

= 1 k Ω , TA= TJ.

100 kHz 200 k Ω

5.7 6 6.3 V

5.7 6 6.3

40 60 80 mV

0.02 0.2

3.6 V

25 mA 10 k Ω

1.5 V

Submit Documentation Feedback

Page 5

www.ti.com

SLUS360C – JULY 1995 – REVISED AUGUST 2007

ELECTRICAL CHARACTERISTICS (continued)

PARAMETER TEST CONDITIONS MIN TYP MAX UNIT

VCC Comparator

Turn-on threshold 7.9 8.3 9.5 Hysteresis 0.4

KILL Comparator

Voltage threshold 3 V

Sequence Comparator

Voltage threshold 2.5 SEQ SAT 0.25

ENABLE Comparator

Voltage threshold 2.5 RUN SAT 0.25

Reference

VREF V

Line regulation 10 < VCC < 20 3 15 Load regulation 0 < IO< 10 mA 3 15 Short circuit I VREF = 0 V 30 60 90 mA

Output Stage

Rise time CL= 100 pF 10 20 Fall time CL= 100 pF 10 20

Virtual Ground

-VEE 0.2 0.75 V

GND

Icc

Icc (run) 21 33 mA

TA= 25 ° C 4.95 5 5.05 VCC = 15 V 4.9 5.1

VCC > 11 V, IO= –10 mA 8.0 8.4 8.8 IO= –200 mA 7.8 IO= 200 mA 3.0 IO= 10 mA 0.5

VEE is externally supplied, GND is floating and used as signal GND

CLKSYN

= 1 k Ω , TA= TJ.

UC2849 UC3849

Submit Documentation Feedback

Page 6

www.ti.com

Frequency [

CHARGE

) T

DISCHARGE

Maximum Duty Cycle [

CHARGE

) T

DISCHARGE

UC2849 UC3849

SLUS360C – JULY 1995 – REVISED AUGUST 2007

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- μ F 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 k Ω 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 T The dead time is approximately T

The C

capacitance should be increased by approximately 40 pF to account for parasitic capacitance.

CHARGE

DISCHARGE

= R

• C

when the RDEAD resistor is used.

= 2 • RDEAD • CT.

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.

(1)

(2)

Submit Documentation Feedback

Page 7

www.ti.com

VREF

2 R

UC2849 UC3849

SLUS360C – JULY 1995 – REVISED AUGUST 2007

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 C approximately 40 pF to account for parasitic capacitance.

RT: This pin programs the charge time of the oscillator ramp. The charge current is

The charge time is approximately T The dead time is approximately T

CHARGE

DISCHARGE

≈ R

• C

when the RDEAD resistor is used.

≈ 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.

capacitance should be increased by

(3)

Submit Documentation Feedback

Page 8

www.ti.com

[

2.5 V R

REF

OSCILLATOR

REF

1.4V

2.5V

3.4V

1.2V

CLKSYN

10kW

RDEAD

500 W

345pF

OSC

4.5k

2.5V

UC2849 UC3849

SLUS360C – JULY 1995 – REVISED AUGUST 2007

Circuit Block Description

PWM Oscillator

The oscillator block diagram with external connections is shown in Figure 1 . A resistor (R sets the linear charge current;

) connected to pin RT

Figure 1. Oscillator Block with External Connections

Submit Documentation Feedback

Page 9

www.ti.com

VAOCURRENTCOMMAND

3.4V

1.2V

3.6V

1.4V (THRESHOLD)

8.5V

0V

OSC

CLKSYN

OUT

MINIMUMOUTPUTLOWTIME

100

1 10 100 1k 10k 100k 1M

R -TW

C =345pF

READ=51

READ=5000

READ=511

1 10 100 1k 10k 100k 1M

R -TW

CT =345pF

1nF

2.2nF

4.7nF

READ=500 W

1000

10k

100

f-Frequency-Hz

UC2849 UC3849

SLUS360C – JULY 1995 – REVISED AUGUST 2007

The timing capacitor (C

) 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 • C

• 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 k Ω . 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.

Figure 2. Oscillator and PWM Output Waveform

Figure 3. Output Frequency Figure 4. Maximum Duty Cycle

Submit Documentation Feedback

Page 10

www.ti.com

100pF

CLKSYN

OSC1

OSC2

OSC3

OSC10

C L K S Y N

B U S

10kW

UC2849 UC3849

SLUS360C – JULY 1995 – REVISED AUGUST 2007

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 R regulated voltage being sensed is actually:

is used for load sharing. The unit which is the master will force V

ADJ

to 1.0 V. Therefore, the

ADJ

Figure 5. Oscillator Synchronization

Connection Diagram

Figure 6. Voltage and Current Sense VEE

Tied to GND

Submit Documentation Feedback

Page 11

www.ti.com

VSP * VSM +ǒVREF * V

ADJ

R1) R

ADJ

) V

ADJ

VSM + 0 V, V

ADJ

+ 1 V(master), VREF + 5 V

VSP + 4

ADJ

R1) R

ADJ

) 1 V

Phase

qm=50º

200

160

120

10 100 1k 10k 100k 1M

10M 100M

f-Frequency-Hz

Gain-dB

SLUS360C – JULY 1995 – REVISED AUGUST 2007

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 .

UC2849 UC3849

(4) (5)

(6)

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.

Submit Documentation Feedback

Page 12

www.ti.com

Frequency(0 dB) +

2pR

INV

COMP

20.8 + 20 log

UC2849 UC3849

SLUS360C – JULY 1995 – REVISED AUGUST 2007

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. R 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.

typically is 10 to 30 times larger than R1. This also attenuates the overall

ADJ

is the input resistance at the inverting terminal CS– C

INV

is the capacitance between CS– and CSO.

COMP

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.

(7)

(8)

Submit Documentation Feedback

Page 13

www.ti.com

200

160

120

10 100 1k 10k 100k 1M 10M 100M

f-Frequency-Hz

Phase

qm=70º

A -

V O

A =OpenLoopGain

A =-10

Gain-dB

Max I

LOAD

GAIN

ILIM

GCA +

VS f

OńL

GAIN

;

Figure 8. Current Sense Amplifier and

Curent Error Amplifier Bode Plot

UC2849 UC3849

SLUS360C – JULY 1995 – REVISED AUGUST 2007

The gain of the differential current sense amplifier (CS The maximum voltage across the shunt resistor (R the voltage across RS, V

, to be equal to the voltage error amplifier Voh, the current control loop keeps the

) is calculated by knowing the maximum load current.

GAIN

) divided by R

is the maximum load current. By amplifying

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.

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 (V

/L) to the oscillator ramp slope (V

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):

where CS

and R

GAIN

are defined by Equation 9 and Equation 10 ,

Vs is the oscillator peak to peak voltage, fs is the oscillator frequency, V

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.

(9)

(10)

• fS).

(11)

Submit Documentation Feedback

Page 14

www.ti.com

1.0mF

ADJ

ILIM

OSC

VA-

VA+

RDEAD

VAO

CA-

CLKSYN

VEE

CAO

CS+

GND

OUT

CS-

CSO

VCC

RUN

ENBL

SEQ

VREF

KILL

500kW

345pF

5kW

10kW

2kW

0.1mF

20V

+20

R14, 10kW

C3, 100pF

R17, 10kW

R13, 1kW

R18, 5kW

15kW

10kW

R11, 1kW

R10, 10kW

C2 100pF

R12

10 kW

10kW

SENSE

UC2849 UC3849

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 V power supply using the UC3849 secondary side average current mode controller.

or the VI

ADJ

inputs. Figure 10 shows an isolated

SENSE

Figure 9. Open Loop Circuit

Submit Documentation Feedback

Page 15

www.ti.com

UC2849 UC3849

SLUS360C – JULY 1995 – REVISED AUGUST 2007

Figure 10. UC3849 Application Diagram

Submit Documentation Feedback

Page 16

PACKAGE OPTION ADDENDUM

www.ti.com

19-Jun-2007

PACKAGING INFORMATION

Orderable Device Status

(1)

Package

Type

Package Drawing

Pins Package

Qty

Eco Plan

UC2849DW ACTIVE SOIC DW 24 25 Green (RoHS &

no Sb/Br)

UC2849DWG4 ACTIVE SOIC DW 24 25 Green (RoHS &

no Sb/Br)

UC2849DWTRG4 ACTIVE SOIC DW 24 TBD Call TI Call TI

UC2849N ACTIVE PDIP N 24 15 Green (RoHS &

no Sb/Br)

UC2849NG4 ACTIVE PDIP N 24 15 Green (RoHS &

no Sb/Br)

UC3849DW ACTIVE SOIC DW 24 25 Green (RoHS &

no Sb/Br)

UC3849DWG4 ACTIVE SOIC DW 24 25 Green (RoHS &

no Sb/Br)

UC3849DWTR ACTIVE SOIC DW 24 2000 Green(RoHS &

no Sb/Br)

UC3849DWTRG4 ACTIVE SOIC DW 24 2000 Green(RoHS &

no Sb/Br)

UC3849NG4 ACTIVE PDIP N 24 TBD Call TI Call TI

UC3849Q ACTIVE PLCC FN 28 37 TBD Call TI Level-2-220C-1 YEAR

UC3849QTR ACTIVE PLCC FN 28 750 TBD Call TI Level-2-220C-1 YEAR

(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)

Lead/Ball Finish MSL Peak Temp

CU NIPDAU Level-2-260C-1 YEAR

CU NIPDAU N / A for Pkg Type

CU NIPDAU Level-2-260C-1 YEAR

(3)

(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.

Addendum-Page 1

Page 17

PACKAGE MATERIALS INFORMATION

www.ti.com

TAPE AND REEL INFORMATION

11-Mar-2008

*All dimensions are nominal

Device Package

UC3849DWTR SOIC DW 24 2000 330.0 24.4 10.85 15.8 2.7 12.0 24.0 Q1

UC3849QTR PLCC FN 28 750 330.0 24.4 12.95 12.95 5.0 16.0 24.0 Q1

Type

Package

Drawing

Pins SPQ Reel

Diameter

(mm)

Reel

Width

W1 (mm)

A0 (mm) B0 (mm) K0 (mm) P1

(mm)W(mm)

Pin1

Quadrant

Pack Materials-Page 1

Page 18

PACKAGE MATERIALS INFORMATION

www.ti.com

11-Mar-2008

*All dimensions are nominal

Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm)

UC3849DWTR SOIC DW 24 2000 346.0 346.0 41.0

UC3849QTR PLCC FN 28 750 346.0 346.0 41.0

Pack Materials-Page 2

Page 19

MECHANICAL DATA

MPDI006B – SEPTEMBER 2001 – REVISED APRIL 2002

N (R–PDIP–T24) PLASTIC DUAL–IN–LINE

1.222 (31,04) MAX

0.360 (9,14) MAX

0.070 (1,78) MAX

0.200 (5,08) MAX

0.020 (0,51) MIN

0.100 (2,54)

0.021 (0,53)

0.015 (0,38)

0.010 (0,25)

0.425 (10,80) MAX

Seating Plane

0.125 (3,18) MIN

0’–15’

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

Page 20

MECHANICAL DATA

MPDI008 – OCTOBER 1994

N (R-PDIP-T**) PLASTIC DUAL-IN-LINE PACKAGE

24 PIN SHOWN

0.560 (14,22)

0.520 (13,21)

0.060 (1,52) TYP

0.200 (5,08) MAX

0.020 (0,51) MIN

0.100 (2,54)

0.021 (0,53)

0.015 (0,38)

0.010 (0,25)

PINS **

DIM

A MAX

A MIN

1.270

(32,26) (36,83)

1.230

(31,24)

1.450

1.410

(35,81)

0.125 (3,18) MIN

322824

1.650

(41,91)

1.610

(40,89)

Seating Plane

0.010 (0,25) NOM

2.090

2.040

(51,82)

2.450 2.650

(62,23)(53,09)

2.390

(60,71)

0.610 (15,49)

0.590 (14,99)

0°–15°

524840

(67,31)

2.590

(65,79)

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

4040053/B 04/95

Page 21

MECHANICAL DATA

MPLC004A – OCT OBER 1994

FN (S-PQCC-J**) PLASTIC J-LEADED CHIP CARRIER

20 PIN SHOWN

Seating Plane

0.004 (0,10)

E1E

NO. OF

PINS

D/E

MINMAXMIN

0.032 (0,81)

0.026 (0,66)

0.050 (1,27)

0.008 (0,20) NOM

D1/E1

MAX

D2/E2

MIN

0.180 (4,57) MAX

0.120 (3,05)

0.090 (2,29)

0.020 (0,51) MIN

D2/E2

0.021 (0,53)

0.013 (0,33)

0.007 (0,18)

MAX

20 28 44 52 68 84

NOTES: A. All linear dimensions are in inches (millimeters).

B. This drawing is subject to change without notice. C. Falls within JEDEC MS-018

0.385 (9,78)

0.485 (12,32)

0.685 (17,40)

0.785 (19,94)

0.985 (25,02)

1.185 (30,10)

0.395 (10,03)

0.495 (12,57)

0.695 (17,65)

0.795 (20,19)

0.995 (25,27)

1.195 (30,35)

0.350 (8,89)

0.450 (11,43)

0.650 (16,51)

0.750 (19,05)

0.950 (24,13)

1.150 (29,21)

0.356 (9,04)

0.456 (11,58)

0.656 (16,66)

0.756 (19,20)

0.958 (24,33)

1.158 (29,41)

0.141 (3,58)

0.191 (4,85)

0.291 (7,39)

0.341 (8,66)

0.441 (11,20)

0.541 (13,74)

0.169 (4,29)

0.219 (5,56)

0.319 (8,10)

0.369 (9,37)

0.469 (11,91)

0.569 (14,45)

4040005/B 03/95

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

Page 22

Page 23

IMPORTANT NOTICE

Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, modifications, enhancements, improvements, and other changes to its products and services at any time and to discontinue any product or service without notice. Customers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. All products are sold subject to TI’s terms and conditions of sale supplied at the time of order acknowledgment.

TI warrants performance of its hardware products to the specifications applicable at the time of sale in accordance with TI’s standard warranty. Testing and other quality control techniques are used to the extent TI deems necessary to support this warranty. Except where mandated by government requirements, testing of all parameters of each product is not necessarily performed.

TI assumes no liability for applications assistance or customer product design. Customers are responsible for their products and applications using TI components. To minimize the risks associated with customer products and applications, customers should provide adequate design and operating safeguards.

TI does not warrant or represent that any license, either express or implied, is granted under any TI patent right, copyright, mask work right, or other TI intellectual property right relating to any combination, machine, or process in which TI products or services are used. Information published by TI regarding third-party products or services does not constitute a license from TI to use such products or services or a warranty or endorsement thereof. Use of such information may require a license from a third party under the patents or other intellectual property of the third party, or a license from TI under the patents or other intellectual property of TI.

Reproduction of TI information in TI data books or data sheets is permissible only if reproduction is without alteration and is accompanied by all associated warranties, conditions, limitations, and notices. Reproduction of this information with alteration is an unfair and deceptive business practice. TI is not responsible or liable for such altered documentation. Information of third parties may be subject to additional restrictions.

Resale of TI products or services with statements different from or beyond the parameters stated by TI for that product or service voids all express and any implied warranties for the associated TI product or service and is an unfair and deceptive business practice. TI is not responsible or liable for any such statements.

TI products are not authorized for use in safety-critical applications (such as life support) where a failure of the TI product would reasonably be expected to cause severe personal injury or death, unless officers of the parties have executed an agreement specifically governing such use. Buyers represent that they have all necessary expertise in the safety and regulatory ramifications of their applications, and acknowledge and agree that they are solely responsible for all legal, regulatory and safety-related requirements concerning their products and any use of TI products in such safety-critical applications, notwithstanding any applications-related information or support that may be provided by TI. Further, Buyers must fully indemnify TI and its representatives against any damages arising out of the use of TI products in such safety-critical applications.

TI products are neither designed nor intended for use in military/aerospace applications or environments unless the TI products are specifically designated by TI as military-grade or "enhanced plastic." Only products designated by TI as military-grade meet military specifications. Buyers acknowledge and agree that any such use of TI products which TI has not designated as military-grade is solely at the Buyer's risk, and that they are solely responsible for compliance with all legal and regulatory requirements in connection with such use.

TI products are neither designed nor intended for use in automotive applications or environments unless the specific TI products are designated by TI as compliant with ISO/TS 16949 requirements. Buyers acknowledge and agree that, if they use any non-designated products in automotive applications, TI will not be responsible for any failure to meet such requirements.

Following are URLs where you can obtain information on other Texas Instruments products and application solutions:

Products Applications

Amplifiers amplifier.ti.com Audio www.ti.com/audio Data Converters dataconverter.ti.com Automotive www.ti.com/automotive DSP dsp.ti.com Broadband www.ti.com/broadband Clocks and Timers www.ti.com/clocks Digital Control www.ti.com/digitalcontrol Interface interface.ti.com Medical www.ti.com/medical Logic logic.ti.com Military www.ti.com/military Power Mgmt power.ti.com Optical Networking www.ti.com/opticalnetwork Microcontrollers microcontroller.ti.com Security www.ti.com/security RFID www.ti-rfid.com Telephony www.ti.com/telephony RF/IF and ZigBee® Solutions www.ti.com/lprf Video & Imaging www.ti.com/video

Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265

Wireless www.ti.com/wireless