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UC3845 Current Mode PWM Controller: Pinout, Feature, Datasheet

Author: Mia Date: 20 Feb 2021  1209

3845

UC3845 is a high-performance fixed-frequency current-mode controller, designed for offline and DC-to-DC converter applications, providing designers with a cost-effective solution that requires minimal external components.

 

These integrated circuits have a fine-tunable oscillator, precise duty cycle control, temperature compensation reference, high gain error amplifier, current sampling comparator and high current totem pole output. It is an ideal devices for driving power MOSFETs.

Catalog

UC3845 Pinout

UC3845 Functional Block Diagram

UC3845 Features

UC3845 Equivalents

UC3845 Applications

UC3845 Package

UC3845 Manufacturer

Component Datasheet

Ordering & Quantity

 


UC3845 Pinout

Pin Functions:

Pin

Type

Description


 

Name

SOIC, CDIP, PDIP (8)

SOIC, CFP (14)

LCCC (20)

COMP

1

1

2

O

Error amplifier compensation pin. Connect external compensation components to this pin to modify the error amplifier output. The error amplifier is internally current-limited so the user can command zero duty cycle by externally forcing COMP to GROUND.

GROUND

5

9

13

G

Analog ground. For device packages without PWRGND, GROUND functions as both power ground and analog ground.

PWRGND

-

8

12

G

Power ground. For device packages without PWRGND, GROUND functions as both power ground and analog ground

ISENSE

3

5

7

I

Primary-side current sense pin. Connect to current sensing resistor. The PWM uses this signal to terminate the OUTPUT switch conduction. A voltage ramp can be applied to this pin to run the device with a voltage-mode control configuration.

NC

-

2, 4, 6, 13

1, 3, 4, 6, 8, 9, 11, 14, 16, 19

-

Do not connect

OUTPUT

6

10

15

O

OUTPUT is the gate drive for the external MOSFET. OUTPUT is the output of the on-chip driver stage intended to directly drive a MOSFET. Peak currents of up to 1 A are sourced and sunk by this pin. OUTPUT is actively held low when VCC is below the turnon threshold.

RT/CT

4

7

10

I/O

Fixed frequency oscillator set point. Connect timing resistor, RRT, to VREF and timing capacitor, CCT, to GROUND from this pin to set the switching frequency. For best performance, keep the timing capacitor lead to the device GROUND as short and direct as possible. If possible, use separate ground traces for the timing capacitor and all other functions. The frequency of the oscillator can be estimated with the following equations:

fosc=1.72/RRT × CCT                                                          (1)

where fosc is in Hertz, RRT is in Ohms and CCT is in Farads. Never use a timing resistor less than 5 kΩ. The frequency of the OUTPUT gate drive of the UCx842 and UCx843, fSW, is equal to fOSC at up to 100% duty cycle; the frequency of the UCx844 and UCx845 is equal to half of the fOSC frequency at up to 50% duty cycle.

VC

-

11

17

I

Bias supply input for the output gate drive. For PWM controllers that do not have this pin, the gate driver is biased from the VCC pin. VC must have a bypass capacitor at least 10 times greater than the gate capacitance of the main switching FET used in the design.

VCC

7

12

18

I

Analog controller bias input that provides power to the device. Total VCC current is the sum of the quiescent VCC current and the average OUTPUT current. Knowing the switching frequency and the MOSFET gate charge, Qg, the average OUTPUT current can be calculated from:

IOUTPUT = Qg × fSW                                                          (2)

A bypass capacitor, typically 0.1 µF, connected directly to GROUND with minimal trace length, is required on this pin. An additional bypass capacitor at least 10 times greater than the gate capacitance of the main switching FET used in the design is also required on VCC.

VFB

2

3

5

I

Inverting input to the internal error amplifier. VFB is used to control the power converter voltage-feedback loop for stability.

VREF

8

14

20

O

5-V reference voltage. VREF is used to provide charging current to the oscillator timing capacitor through the timing resistor. It is important for reference stability that VREF is bypassed to GROUND with a ceramic capacitor connected as close to the pin as possible. A minimum value of 0.1-µF ceramic is required. Additional VREF bypassing is required for external loads on VREF.


UC3845 Functional Block Diagram

UCx844 and UCx845 Block Diagram, Toggle

UCx844 and UCx845 Block Diagram, Toggle


UC3845 Features

  • Optimized for off-line and DC-to-DC converters

  • Low start-up current (< 1 mA)

  • Automatic feedforward compensation

  • Pulse-by-pulse current limiting

  • Enhanced load-response characteristics

  • Undervoltage lockout with hysteresis

  • Double-pulse suppression

  • High-current totem-pole output

  • Internally trimmed bandgap reference

  • Up to 500-kHz operation

  • Error amplifier with low output resistance


UC3845 Equivalents

UC3845 equivalents


UC3845 Applications

  • Switching regulators of any polarity

  • Transformer-coupled DC-DC converters


UC3845 Package

UC3845 Manufacturer

Texas Instruments Incorporated designs and manufactures analog technologies, digital signal processing (DSP) and microcontroller (MCU) semiconductors. TI is a leader in semiconductor solutions for analog and digital embedded and applications processing. A global semiconductor company, TI innovates through design, sales and manufacturing operations in more than 30 countries.


Component Datasheet

UC3845 Datasheet

Ordering & Quality

Photo Mfr. Part # Company Description Package PDF Qty Pricing
(USD)
UC3845ADM-TR UC3845ADM-TR Company:Microchip Technology Remark:IC REG CTRLR BUCK/BOOST 8SOIC Package:8-SOIC (0.154", 3.90mm Width)
DataSheet
In Stock:On Order
Inquiry
Price:
1+: $7.40000
10+: $6.68700
25+: $6.37560
Inquiry
UC3845ADTR UC3845ADTR Company:Texas Instruments Remark:Boost, Buck, Flyback, Forward Regulator Positive, Isolation Capable Output Step-Up, Step-Down, Step-Up/Step-Down DC-DC Controller IC 14-SOIC Package:14-SOIC (0.154"", 3.90mm Width)
DataSheet
In Stock:On Order
Inquiry
Price:
1+: $1.17000
10+: $1.05000
25+: $0.99680
100+: $0.76540
250+: $0.67640
500+: $0.64080
1000+: $0.49840
2500+: $0.47348
5000+: $0.45568
10000+: $0.44144
25000+: $0.42720
Inquiry
UC3845BD1 UC3845BD1 Company:STMicroelectronics Remark:Boost, Flyback Regulator Positive, Isolation Capable Output Step-Up, Step-Up/Step-Down DC-DC Controller IC 8-SO Package:8-SOIC (0.154"", 3.90mm Width)
DataSheet
In Stock:On Order
Inquiry
Price:
1+: $0.92000
10+: $0.82600
25+: $0.78400
100+: $0.60200
250+: $0.53200
500+: $0.50400
1000+: $0.39200
2500+: $0.37240
5000+: $0.35840
Inquiry
UC3845BD1013TR UC3845BD1013TR Company:STMicroelectronics Remark:IC REG CTRLR BOOST/FLYBACK 8SOIC Package:8-SOIC (0.154", 3.90mm Width)
DataSheet
In Stock:On Order
Inquiry
Price:
2500+: $0.31185
5000+: $0.30030
12500+: $0.28875
25000+: $0.28413
62500+: $0.27720
Inquiry
UC3845BD1R2G UC3845BD1R2G Company:ON Semiconductor Remark:IC REG CTRLR BOOST/FLYBACK 8SOIC Package:8-SOIC (0.154", 3.90mm Width)
DataSheet
In Stock:On Order
Inquiry
Price:
2500+: $0.20010
5000+: $0.18630
Inquiry
UC3845BN UC3845BN Company:STMicroelectronics Remark:IC REG CTRLR BOOST/FLYBACK 8DIP Package:8-DIP (0.300", 7.62mm)
DataSheet
In Stock:1109
Inquiry
Price:
1+: $0.87000
10+: $0.76200
25+: $0.71600
100+: $0.54290
250+: $0.46200
500+: $0.43890
1000+: $0.33495
2500+: $0.31185
5000+: $0.30030
Inquiry
UC3845N UC3845N Company:Texas Instruments Remark:IC REG CTRLR MULT TOPOLOGY 8DIP Package:8-DIP (0.300", 7.62mm)
DataSheet
In Stock:553
Inquiry
Price:
1+: $1.57000
10+: $1.40100
25+: $1.33000
100+: $1.02130
250+: $0.90252
500+: $0.85500
1000+: $0.66500
2500+: $0.63175
5000+: $0.60800
Inquiry

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