UNITRODE UC1824, UC2824, UC3824 Technical data

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High Speed PWM Controller
FEATURES DESCRIPTION
Complementary Outputs
Practical Operation Switching Frequencies
to 1MHz
50ns Propagation Delay to Output
High Current Dual Totem Pole Outputs
(1.5A Peak)
Fully Latched Logic with Double Pulse
Suppression
Pulse-by-Pulse Current Limiting
Soft Start / Max. Duty Cycle Control
Under-Voltage Lockout with Hysteresis
Low Start Up Current (1.1 mA)
The UC1824 family of PWM control ICs is optimized for high fre­quency switched mode power supply applications. Particular care was given to min imi zin g pr opagati on delays through the comparators and logic c ircuitry while maximizing bandwidth and slew rate of the error amplifier. This controller is designed for use in either current­mode or voltage mod e systems with the capability for input voltage feed-forward.
Protection circuitry includes a current limit comparator with a 1V threshold, a TTL compatible shutdown port, and a soft start pin which will double as a maximum duty cycle clamp. The logic is fully latched to provide jitter free operation and prohibit multiple pulses at an out­put. An under-voltage lockout s ection with 800mV of hysteresis as­sures low start up current. Dur ing under-voltage lockout, the outputs are high impedance.
These devices feature totem pole outputs designed to source and sink high peak currents from capacitive l oads, such as the gate of a power MOSFET. The on state is designed as a high level.
UC1824 UC2824 UC3824
Trimmed Bandgap Reference (5.1V ± 1%)
BLOCK DIAGRAM
3/97
UDG-92034-1
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Supply Voltage (Pins 13, 15) . . . . . . . . . . . . . . . . . . . . . . . . 30V
Output Current, Source or Sink (Pins 11, 14)
DC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.5A
Pulse (0.5µs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.0A
Analog Inputs
(Pins 1, 2, 7) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 7V
(Pin 8, 9). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 6V
Clock Output Current (Pin 4) . . . . . . . . . . . . . . . . . . . . . . . -5mA
Error Amplifier Output Current (Pin 3) . . . . . . . . . . . . . . . . 5mA
Soft Start Sink Current (Pin 8) . . . . . . . . . . . . . . . . . . . . . 20mA
Oscillator Charging Current (Pin 5) . . . . . . . . . . . . . . . . . . -5mA
Power Dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1W
Storage Temperature Range . . . . . . . . . . . . . . -65°C to +150°C
Lead Temperature (Soldering, 10 seconds) . . . . . . . . . . 300°C
Note 1: All voltages are with respect to GND (Pin 10); all cur­rents are positive into, negative out of part; pin numbers refer to DIL-16 package. Note 3: Consult Unitrode Integrated Circuit Databook for ther­mal limitations and considerations of package.
SOIC-16 (Top View) DW Package
CONNECTION DIAGRAMS
DIL-16 (Top View) J Or N Package
PLCC-20 & LCC-20 (Top View) Q & L Packages
UC1824 UC2824 UC3824
PACKAGE PIN FUNCTION
FUNCTION N/C 1 INV 2 NI 3 E/A Out 4 Clock 5 N/C 6 R
T
C
T
Ramp 9 Soft Start 10 N/C 11 ILIM/SD 12 Gnd 13 Out 14 Pwr Gnd 15 N/C 16 V
C
INV
OUT
V
CC
V
5.1V 20
REF
PIN
7 8
17 18 19
ELECTRICAL CHARACTERISTICS:
Unless otherwise stated,these spe ci fi ca tions apply for , RT = 3.65k, CT = 1nF, V = 15V, -55°C<TA<125°C for the UC1824, –40°C<TA<85°C for the UC2824, and 0°C<TA<70°C for the UC3824, TA=T
PARAMETERS TEST CONDITIONS UC2824
J.
UC1824
UC3824
MIN TYP MAX MIN TYP MAX UNITS
Reference Section
Output Voltage T Line Regulation 10V < V Load Regulation 1mA < I Temperature Stability* T
= 25°C, IO = 1mA 5.05 5.10 5.15 5.00 5.1 0 5.20 V
J
< 30V 2 20 2 20 mV
CC
< 10mA 5 20 5 20 mV
O
< TA < T
MIN
MAX
0.2 0.4 0.2 0.4 mV/°C Total Output Variat io n* Li ne , Lo ad , Te mp era tu r e 5.00 5.20 4.95 5.25 V Output Noise Volt ag e* 10Hz < f < 10kHz 50 50
= 125°C, 1000hrs. 5 25 5 25 mV
Long Term Stability* T Short Circuit Current V
J
= 0V -15 -50 -100 -15 -50 -100 mA
REF
Oscillator Section
Initial Accuracy * TJ = 25°C 360 400 440 360 400 440 k Hz
< 30V 0.2 2 0.2 2 %
MIN
CC
< TA < T
MAX
55%
Voltage Stability* 10V < V Temperature Stability* T Total Variation* Line, Temperature 340 460 340 460 kHz
2
CC
µ
V
UC1824 UC2824 UC3824
ELECTRICAL CHARACTERISTICS (cont.)
Unless otherwise stated,these spe ci fi ca tions apply for , R = 1nF, VCC = 15V, -55°C<TA<125°C for the UC1824, –40°C<TA<85°C for the UC2824, and 0°C<TA<70°C for the UC3824, TA=T
J.
UC1824
PARAMETERS TEST CONDITIONS UC2824
MIN TYP MAX MIN TYP MAX UNITS
Oscillator Section (cont. )
Clock Out High 3.9 4.5 3.9 4.5 V Clock Out Low 2.3 2.9 2.3 2.9 V Ramp Peak* 2.6 2.8 3.0 2.6 2.8 3.0 V Ramp Valley* 0.7 1.0 1.25 0.7 1.0 1.25 V Ramp Valley to Peak* 1.6 1.8 2.0 1.6 1.8 2.0 V
Error Amplifier Section
Input Offset Voltage 10 15 mV Input Bias Current 0.6 3 0.6 3 Input Offset Current 0.1 1 0.1 1 Open Loop Gain 1V < V CMRR 1.5V < V PSRR 10V < V Output Sink Current V Output Source Current V Output High Voltage I Output Low Voltag e I
PIN 3 PIN 3
< 4V 60 95 60 95 dB
O
< 5.5V 75 95 75 95 dB
CM
< 30V 85 110 85 110 dB
CC
= 1V 12.5 12.5 mA
PIN 3
= 4V -0.5 -1.3 -0.5 -1.3 mA
PIN 3
= -0.5mA 4.0 4.7 5.0 4.0 4.7 5.0 V
= 1mA 0 0 .5 1.0 0 0.5 1.0 V Unity Gain Bandwidth* 35.5 35.5 MHz Slew Rate* 612 612 V/
PWM Comparator Section
Pin 7 Bias Current V
= 0V -1 -5 -1 -5
PIN 7
Duty Cycle Range 0 80 0 85 % Pin 3 Zero DC Threshold V
= 0V 1.1 1.25 1.1 1.25 V
PIN 7
Delay to Output* 50 80 50 80 ns
Soft-Start Section
= 0.5V 3 9 20 3 9 20
Charge Current V Discharge Current V
PIN 8
= 1V 1 1 mA
PIN 8
Current Limit / Shutdown Section
Pin 9 Bias Current 0 < V
< 4V 15 10
PIN 9
Current Limit Threshold 0.9 1.0 1.1 0.9 1.0 1.1 V Shutdown Threshold 1.25 1.40 1.55 1.25 1.40 1.55 V Delay to Output 50 80 50 80 ns
Output Section
= 20mA 0.25 0.40 0.25 0.40 V
Output Low Level I
Output High Level I
Collector Leakage V
OUT
I
= 200mA 1.2 2.2 1.2 2.2 V
OUT
= -20mA 13.0 13.5 13.0 13.5 V
OUT
I
= -200mA 12.0 13.0 12.0 13.0 V
OUT
= 30V 100 500 10 500
C
Rise/Fall Time* CL = 1nF 3060 3060ns
Under-Voltage Lockout Section
Start Threshold 8.8 9.2 9.6 8.8 9.2 9.6 V UVLO Hysteresis 0.4 0.8 1.2 0.4 0.8 1.2 V
Supply Current Section
Start Up Current VCC = 8V 1.1 2.5 1.1 2.5 mA ICC V
PIN 1
, V
PIN 7
, V
PIN 9
= 0V; V
= 1V 22 33 22 33 mA
PIN 2
* This parameter not 100% tested in production but guaranteed by design.
= 3.65k, C
T
UC3824
T
µ µ
µ
µ
µ
µ
A A
µ
s
A
A
A
A
3
UC1824 Printed Circuit Board Layout Consider ations
High speed circuits demand careful attention to layout and component placement. To assure proper performance of the UC1824 fol low these rules: 1) Use a ground plane.
2) Damp or clamp parasitic inductive kick energy from the gate of driv en MOSFETs. Do not allow the output pins to ring below ground. A series ga te resist or or a shunt 1 Am p Schottky diode at the outp ut pin will se rve this p urp os e. 3 )
Error Amplifier Circuit
Simplified Schematic
UC1824 UC2824 UC3824
CC
Bypass V capacitors with low equivalent series inductance. Allow less than 1 cm o f total le ad length for each capaci tor be­tween the bypassed pin and the ground plane. 4) Treat the timing capacitor, C
, VC, and V
REF
. Use 0.1µF monolithic ceramic
T
, like a bypass capacitor.
Open Loop Frequency Response Unity Gain Slew Rate
Synchronized Operation
Two Units in Close Proximity Generalized Synchronization
4
Oscillator Circuit
UC1824 UC2824 UC3824
Primary Output Deadtime vs CT (3k ≤ RT ≤ 100k)
µ
Timing Resistance vs Frequency
Typical Non-Overlap Time (TNO) Over Temperature
80 70 60 50
NO
40 30 20
10
0
-75 -50 -25 0 25 50 75 100 125
T (ns)
Primary Output Deadtime vs Frequency
160
140
120
D
T (ns)
100
TC()
°
80
10k 100k
1.0nF
470pF
FREQ (Hz)
1M
Non-Overlap Time (TNO)
5
Forward Technique for Off-Line Voltage Mo de Application
Constant Volt-Second Clamp Circuit
The circuit shown here will achieve a constant volt-sec­ond product clamp over varying input voltages. The
T
ramp generator components, R that the ramp at Pin 9 crosses the 1V threshold at the same time the desired maximum volt-second product is reache d. The delay through the functional nor bloc k must be such that the ramp capacitor can be com­pletely discharged during the minimum deadtime.
and CR are chosen so
UC1824 UC2824 UC3824
Output Section
Simplified Schematic Rise/Fall Time (CL=1nF)
Rise/Fall Time (CL=10nF) Saturation Curves
6
Open Loop Laboratory Test Fixtu re
UC1824 UC2824 UC3824
This test fixture is useful for exercising many of the UC1824’s functions and measuring their specifications.
UDG-92036-2
As with any wideband circuit, careful grounding and by­pass procedures should be followed. The use of a ground plane is highly recommended.
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7
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