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E-UC3845BD1013TR

P1-P3P4-P6P7-P9P10-P12P13-P15
UC2842B/3B/4B/5B
UC3842B/3B/4B/5B
March 1999
HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER
.
TRIMMED OSCILLATOR FOR PRECISE FRE-
QUENCY CONTROL
.
OSCILLATOR FREQUENCY GUARANTEED
AT 250kHz
.
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 AND OPERATING CURRENT
DESCRIPTION
The UC384xB 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
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 UC3842B and UC3844B have
UVLO thresholds of 16V (on) and 10V (off), ideally
suited off-line applications The corresponding thresh-
olds for the UC3843B and UC3845B are 8.5 V and 7.9
V. The UC3842B and UC3843B can operate to duty
cycles approaching 100%. A range of the zero to <
50 % is obtained by the UC3844B and UC3845B by
the addition of an internal toggle flip flop which blanks
the output off every other clock cycle.
BLOCK DIAGRAM (toggle flip flop used only in UC3844B and UC3845B)
UVLO
S/R
5V
REF
34V
INTERNAL
BIAS
VREF GOOD
LOGIC
2.50V
T
S
R
OSC
R1V
CURRENT
SENSE
COMPARATOR
2R
+
-
PWM
LATCH
7
5
4
2
1
3
8
6
ERROR AMP.
Vi
GROUND
RT/CT
VFB
COMP
CURRENT
SENSE
VREF
5V 50mA
OUTPUT
D95IN331
Minidip
®
SO8
UC3842B
1/15
*
All voltages are with respect to pin 5, all currents are positive into the specified terminal.
PIN CONNECTION (top view)
COMP
V
FB
I
SENSE
R
T
/C
T
GROUND
OUTPUT
Vi
V
REF
1
3
2
4
6
5
7
8
D95IN332
Minidip/SO8
ORDERING NUMBERS
SO8 Minidip
UC2842BD1; UC3842BD1
UC2843BD1; UC3843BD1
UC2844BD1; UC3844BD1
UC2845BD1; UC3845BD1
UC2842BN; UC3842BN
UC2843BN; UC3843BN
UC2844BN; UC3844BN
UC2845BN; UC3845BN
ABSOLUTE MAXIMUM RATINGS
Symbol Parameter Value Unit
V
i
Supply Voltage (low impedance source) 30 V
V
i
Supply Voltage (Ii < 30mA) Self Limiting
I
O
Output Current
±
1
A
E
O
Output Energy (capacitive load) 5
µ
J
Analog Inputs (pins 2, 3) – 0.3 to 5.5 V
Error Amplifier Output Sink Current 10 mA
P
tot
Power Dissipation at T
amb
≤
25
°
C (Minidip)
1.25 W
P
tot
Power Dissipation at Tamb
≤
25
°
C (SO8)
800 mW
T
stg
Storage Temperature Range – 65 to 150
°
C
T
J
Junction Operating Temperature – 40 to 150 °C
T
L
Lead Temperature (soldering 10s) 300
°
C
PIN FUNCTIONS
No Function Description
1 COMP This pin is the Error Amplifier output and is made available for loop compensation.
2V
FB
This is the inverting input of the Error Amplifier. It is normally connected to the switching
power supply output through a resistor divider.
3I
SENSE
A voltage proportional to inductor current is connected to this input. The PWM uses this
information to terminate the output switch conduction.
4R
T
/C
T
The oscillator frequency and maximum Output duty cycle are programmed by connecting
resistor R
T
to Vref and cpacitor C
T
to ground. Operation to 500kHz is possible.
5 GROUND This pin is the combined control circuitry and power ground.
6 OUTPUT This output directly drives the gate of a power MOSFET. Peak currents up to 1A are sourced
and sunk by this pin.
7V
CC
This pin is the positive supply of the control IC.
8V
ref
This is the reference output. It provides charging current for capacitor C
T
through resistor R
T
.
UC2842B/3B/4B/5B - UC3842B/3B/4B/5B
2/15
ELECTRICAL CHARACTERISTICS ( [note 1] Unless otherwise stated, these specifications apply for
-25
< T
amb
< 85°C for UC284XB; 0 < T
amb
< 70°C for UC384XB; V
i
= 15V (note 5); R
T
= 10K; C
T
= 3.3nF)
Symbol Parameter Test Conditions
UC284XB UC384XB
Unit
Min. Typ. Max. Min. Typ. Max.
REFERENCE SECTION
V
REF
Output Voltage
T
j
= 25
°
C I
o
= 1mA
4.95 5.00 5.05 4.90 5.00 5.10 V
∆
V
REF
Line Regulation
12V
≤
V
i
≤
25V
220 220mV
∆
V
REF
Load Regulation
1
≤
I
o
≤
20mA
325 325mV
∆
V
REF
/
∆
T
Temperature Stability (Note 2) 0.2 0.2
mV/
°
C
Total Output Variation Line, Load, Temperature 4.9 5.1 4.82 5.18 V
e
N
Output Noise Voltage
10Hz
≤
f
≤
10KHz T
j
= 25
°
C
(note 2)
50 50
µ
V
Long Term Stability
T
amb
= 125
°
C, 1000Hrs
(note 2)
525 525mV
I
SC
Output Short Circuit -30 -100 -180 -30 -100 -180 mA
OSCILLATOR SECTION
f
OSC
Frequency
T
j
= 25
°
C
T
A
= T
low
to T
high
T
J
= 25°C (R
T
= 6.2k, C
T
= 1nF)
49
48
225
52
–
250
55
56
275
49
48
225
52
–
250
55
56
275
KHz
KHz
KHz
∆
f
OSC
/
∆
V
Frequency Change with Volt. V
CC
= 12V to 25V – 0.2 1 – 0.2 1 %
∆
f
OSC
/
∆
T
Frequency Change with Temp. T
A
= T
low
to T
high
–1––0.5–%
V
OSC
Oscillator Voltage Swing (peak to peak) – 1.6 – – 1.6 – V
I
dischg
Discharge Current (V
OSC
=2V) T
J
= 25°C
T
A
= T
low
to T
high
7.8
7.5
8.3
–
8.8
8.8
7.8
7.6
8.3
–
8.8
8.8
mA
mA
ERROR AMP SECTION
V
2
Input Voltage V
PIN1
= 2.5V 2.45 2.50 2.55 2.42 2.50 2.58 V
I
b
Input Bias Current V
FB
= 5V -0.1 -1 -0.1 -2
µ
A
A
VOL
2V
≤
V
o
≤
4V
65 90 65 90 dB
BW Unity Gain Bandwidth T
J
= 25°C 0.7 1 0.7 1 MHz
PSRR Power Supply Rejec. Ratio
12V
≤
V
i
≤
25V
60 70 60 70 dB
I
o
Output Sink Current V
PIN2
= 2.7V V
PIN1
= 1.1V 2 12 2 12 mA
I
o
Output Source Current V
PIN2
= 2.3V V
PIN1
= 5V -0.5 -1 -0.5 -1 mA
V
OUT
High V
PIN2
= 2.3V;
R
L
= 15K
Ω
to Ground
5 6.2 5 6.2 V
V
OUT
Low V
PIN2
= 2.7V;
R
L
= 15K
Ω
to Pin 8
0.8 1.1 0.8 1.1 V
CURRENT SENSE SECTION
G
V
Gain (note 3 & 4) 2.85 3 3.15 2.85 3 3.15 V/V
V
3
Maximum Input Signal V
PIN1
= 5V (note 3) 0.9 1 1.1 0.9 1 1.1 V
SVR Supply Voltage Rejection
12
≤
V
i
≤
25V (note 3)
70 70 dB
I
b
Input Bias Current -2 -10 -2 -10
µ
A
Delay to Output 150 300 150 300 ns
THERMAL DATA
Symbol Description Minidip SO8 Unit
R
th j-amb
Thermal Resistance Junction-ambient. max. 100 150
°
C/W
UC2842B/3B/4B/5B - UC3842B/3B/4B/5B
3/15
P1-P3P4-P6P7-P9P10-P12P13-P15

E-UC3845BD1013TR

Mfr. #:
Buy E-UC3845BD1013TR
Manufacturer:
STMicroelectronics
Description:
Switching Controllers 0.5mA Current Mode
Lifecycle:
New from this manufacturer.
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