UC3845AN STMicroelectronics, UC3845AN Datasheet

IC CURR-MODE PWM CTRLR 8-MINIDIP

UC3845AN

Manufacturer Part Number
UC3845AN
Description
IC CURR-MODE PWM CTRLR 8-MINIDIP
Manufacturer
STMicroelectronics
Datasheet

Specifications of UC3845AN

Pwm Type
Current Mode
Number Of Outputs
1
Frequency - Max
500kHz
Duty Cycle
50%
Voltage - Supply
8.2 V ~ 25 V
Buck
No
Boost
Yes
Flyback
Yes
Inverting
No
Doubler
No
Divider
No
Cuk
No
Isolated
Yes
Operating Temperature
0°C ~ 70°C
Package / Case
8-DIP (0.300", 7.62mm)
Frequency-max
500kHz
Lead Free Status / RoHS Status
Contains lead / RoHS non-compliant
Other names
497-3083-5

Available stocks

Company
Part Number
Manufacturer
Quantity
Price
Part Number:
UC3845AN
Manufacturer:
TI
Quantity:
5 510
Part Number:
UC3845AN
Manufacturer:
ST
0
Part Number:
UC3845AN
Manufacturer:
HTC
Quantity:
20 000
Part Number:
UC3845AN
Manufacturer:
TI
Quantity:
7 383
Part Number:
UC3845AN
Manufacturer:
TI
Quantity:
3 555
Part Number:
UC3845AN
Manufacturer:
ST
Quantity:
8 497
Part Number:
UC3845AN1
Manufacturer:
ST
0
.
.
.
.
.
.
.
.
.
The UC384xA family of control ICs provides the nec-
essary features to implement off-line or DC to DC
fixed frequency current mode control schemes with
a minimal external parts count. Internally imple-
mented circuits include a trimmed oscillator for pre-
cise DUTY CYCLE CONTROL under voltage lock-
out featuring start-up current less than 0.5mA, a pre-
cision reference trimmed for accuracy at the error
amp input, logic to insure latched operation, a PWM
BLOCK DIAGRAM (toggle flip flop used only in UC3844A and UC3845A)
March 1999
HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER
DESCRIPTION
TRIMMED OSCILLATOR DISCHARGE CUR-
RENT
CURRENT MODE OPERATION TO 500kHz
AUTOMATIC FEED FORWARD COMPENSA-
TION
LATCHING PWM FOR CYCLE-BY-CYCLE
CURRENT LIMITING
INTERNALLY TRIMMED REFERENCE WITH
UNDERVOLTAGE LOCKOUT
HIGH CURRENT TOTEM POLE OUTPUT
UNDERVOLTAGE LOCKOUT WITH HYSTER-
ESIS
LOW START-UP CURRENT (< 0.5mA)
DOUBLE PULSE SUPPRESSION
CURRENT
GROUND
SENSE
®
COMP
RT/CT
VFB
Vi
7
5
4
2
1
3
34V
+
-
ERROR AMP.
OSC
2.50V
UVLO
2R
R
S/R
REF
5V
1V
VREF GOOD
LOGIC
comparator which also provides current limit control,
and a totem pole output stage designed to source
or sink high peak current. The output stage, suitable
for driving N-Channel MOSFETs, is low in the off-
state.
Differences between members of this family are the
under-voltage lockout thresholds and maximum duty
cycle ranges. The UC3842A and UC3844A have
UVLO thresholds of 16V (on) and 10V (off), ideally
suited off-line applications The corresponding thresh-
olds for the UC3843A and UC3845A are 8.5 V and
7.9V. The UC3842A and UC3843A can operate to
duty cycles approaching 100%. A range of the zero to
< 50 % is obtained by the UC3844A and UC3845A by
the addition of an internal toggle flip flop which blanks
the output off every other clock cycle.
COMPARATOR
CURRENT
SENSE
UC2842A/3A/4A/5A
UC3842A/3A/4A/5A
S
R
INTERNAL
T
BIAS
Minidip
LATCH
PWM
UC3842A
D95IN331
8
6
5V 50mA
OUTPUT
SO8
VREF
1/15

Related parts for UC3845AN

UC3845AN Summary of contents

Page 1

HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER . TRIMMED OSCILLATOR DISCHARGE CUR- . RENT . CURRENT MODE OPERATION TO 500kHz AUTOMATIC FEED FORWARD COMPENSA- . TION LATCHING PWM FOR CYCLE-BY-CYCLE . CURRENT LIMITING INTERNALLY TRIMMED REFERENCE WITH . UNDERVOLTAGE LOCKOUT ...

Page 2

... D95IN332 Description to Vref and cpacitor C to ground. Operation to 500kHz is possible. T Value 30 Self Limiting 1 5 – 0.3 to 5.5 10 1.25 800 – 150 – 150 300 V REF Vi OUTPUT GROUND through resistor R T Minidip UC2842AN; UC3842AN UC2843AN; UC3843AN UC2844AN; UC3844AN UC2845AN; UC3845AN Unit ° ...

Page 3

THERMAL DATA Symbol R Thermal Resistance Junction-ambient. th j-amb ELECTRICAL CHARACTERISTICS ( [note 1] Unless otherwise stated, these specifications apply for -25 < T < for UC284XA; 0 < T amb Symbol Parameter REFERENCE SECTION V Output Voltage ...

Page 4

UC2842A/3A/4A/5A - UC3842A/3A/4A/5A ELECTRICAL CHARACTERISTICS (continued) Symbol Parameter OUTPUT SECTION V Output Low Level OL V Output High Level OH V UVLO Saturation OLS t Rise Time r t Fall Time f UNDER-VOLTAGE LOCKOUT SECTION Start Threshold Min Operating Voltage ...

Page 5

Figure 1: Open Loop Test Circuit. 4.7K 2N2222 100K ERROR AMP. ADJUST 1K I 4.7K SENSE ADJUST 5K D95IN343 High peak currents associated with capacitive loads necessitate careful grounding techniques. Timing and bypass capacitors should be connected close Figure 2: ...

Page 6

UC2842A/3A/4A/5A - UC3842A/3A/4A/5A Figure 4: Oscillator Discharge Current vs. Tem- perature. I dischg (mA) 8.5 8.0 7.5 7.0 -55 - Figure 6: Current Sense Input Threshold vs. Er- ror Amp Output Voltage (V) V =15V ...

Page 7

Figure 9: Output Saturation Voltage vs. Load Current. V sat (V) Source Saturation V i (Load to Ground =25˚ =15V Pulsed Load 120Hz Rate 3 T =-40˚ Sink Saturation ...

Page 8

UC2842A/3A/4A/5A - UC3842A/3A/4A/5A Figure 14 : Error Amp Configuration Figure 15 : Under Voltage Lockout. 7 ON/OFF COMMAND OFF Figure 16 : Current Sense Circuit . CURRENT ...

Page 9

Figure 17 : Slope Compensation Techniques. V REG SLOPE SENSE R S Figure 18 : Isolated MOSFET Drive and Current Transformer Sensing ...

Page 10

UC2842A/3A/4A/5A - UC3842A/3A/4A/5A Figure 19 : Latched Shutdown. 2N 3905 SCR must be selected for a holding current of less than 0.5mA at T The simple two transistor circuit can be used in place of the SCR as shown. All ...

Page 11

Figure 21: External Clock Synchronization. EXTERNAL SYNC INPUT 0.01 F The diode clamp is required if the Sync amplitude is large enough to cause the bottom side Figure 22: External Duty Cycle Clamp and Multi Unit Synchronization. ...

Page 12

UC2842A/3A/4A/5A - UC3842A/3A/4A/5A Figure 23: Soft-Start Circuit Figure 24: Soft-Start and Error Amplifier Output Duty Cycle Clamp BC109 V CLAMP 12/15 R BIAS R ...

Page 13

DIM. MIN. TYP. MAX. MIN. A 1.75 a1 0.1 0.25 0.004 a2 1.65 a3 0.65 0.85 0.026 b 0.35 0.48 0.014 b1 0.19 0.25 0.007 C 0.25 0.5 0.010 c1 45 (typ.) D (1) 4.8 5.0 0.189 E 5.8 ...

Page 14

UC2842A/3A/4A/5A - UC3842A/3A/4A/5A mm DIM. MIN. TYP. MAX. A 3.32 a1 0.51 0.020 B 1.15 1.65 0.045 b 0.356 0.55 0.014 b1 0.204 0.304 0.008 D 10.92 E 7.95 9.75 0.313 e 2.54 e3 7.62 e4 7.62 F 6.6 I ...

Page 15

... No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specification mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. STMi- croelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics ...

Related keywords