application
INFO
available
UC1825
UC2825
UC3825
High Speed PWM Controller
FEATURES
•Compatible with Voltage or Current Mode Topologies
•Practical Operation Switching Frequencies to 1MHz
•50ns Propagation Delay to Output
•High Current Dual Totem Pole Outputs (1.5A Peak)
•Wide Bandwidth Error Amplifier
•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 (1.1mA)
DESCRIPTION
The UC1825 family of PWM control ICs is optimized for high frequency switched mode power supply applications. Particular care was given to minimizing propagation delays through the comparators and logic circuitry while maximizing bandwidth and slew rate of the error amplifier. This controller is designed for use in either cur- rent-mode or voltage mode 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 section with 800mV of hysteresis assures low start up current. During under-voltage lockout, the outputs are high impedance.
These devices feature totem pole outputs designed to source and sink high peak currents from capacitive loads, such as the gate of a power MOSFET. The on state is designed as a high level.
BLOCK DIAGRAM
UDG-92030-2 |
SLUS235A - MARCH 1997 - REVISED MARCH 2004 |
ABSOLUTE MAXIMUM RATINGS (Note 1)
Supply Voltage (Pins 13, 15) . . . . . . . . . . . . . . . . . . . . . . . . 30V Output Current, Source or Sink (Pins 11, 14)
DC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.5A Pulse (0.5 s) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 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
SOIC-16 (Top View)
DW Package
UC1825
UC2825
UC3825
CONNECTION DIAGRAMS
DIL-16 (Top View)
J or N Package
PLCC-20 & LCC-20 |
PACKAGE PIN FUNCTION |
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FUNCTION |
PIN |
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(Top View) |
N/C |
1 |
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Q & L Packages |
INV |
2 |
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NI |
3 |
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E/A Out |
4 |
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Clock |
5 |
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N/C |
6 |
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RT |
7 |
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CT |
8 |
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Ramp |
9 |
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Soft Start |
10 |
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N/C |
11 |
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ILIM/SD |
12 |
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Gnd |
13 |
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Out A |
14 |
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Pwr Gnd |
15 |
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N/C |
16 |
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VC |
17 |
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Out B |
18 |
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VCC |
19 |
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VREF 5.1V |
20 |
THERMAL RATINGS TABLE
Package |
JA |
JC |
DIL-16J |
80-120 |
28(2) |
DIL-16N |
90(1) |
45 |
PLCC-20 |
43-75(1) |
34 |
LCC-20 |
70-80 |
20(2) |
SOIC-16 |
50-120(1) |
35 |
2
UC1825
UC2825
UC3825
ELECTRICAL CHARACTERISTICS: Unless otherwise stated, these specifications apply for , RT = 3.65k, CT = 1nF, VCC = 15V, -55° C<TA<125° C for the UC1825, –40° C<TA<85° C for the UC2825, and 0° C<TA<70° C for the UC3825, TA=TO.
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UC1825 |
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UC3825 |
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PARAMETERS |
TEST CONDITIONS |
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UC2825 |
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MIN |
TOP |
MAX |
MIN |
TOP |
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MAX |
UNITS |
Reference Section |
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Output Voltage |
TO = 25° C, IO = 1mA |
5.05 |
5.10 |
5.15 |
5.00 |
5.10 |
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5.20 |
V |
Line Regulation |
10V < VCC < 30V |
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2 |
20 |
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2 |
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20 |
mV |
Load Regulation |
1mA < IO < 10mA |
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5 |
20 |
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5 |
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20 |
mV |
Temperature Stability* |
TMIN < TA < TMAX |
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0.2 |
0.4 |
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0.2 |
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0.4 |
mV/° C |
Total Output Variation* |
Line, Load, Temperature |
5.00 |
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5.20 |
4.95 |
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5.25 |
V |
Output Noise Voltage* |
10Hz < f < 10kHz |
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50 |
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50 |
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V |
Long Term Stability* |
TJ = 125° C, 1000hrs. |
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5 |
25 |
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5 |
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25 |
mV |
Short Circuit Current |
VREF = 0V |
-15 |
-50 |
-100 |
-15 |
-50 |
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-100 |
mA |
Oscillator Section |
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Initial Accuracy* |
TJ = 2° C |
360 |
400 |
440 |
360 |
400 |
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440 |
kHz |
Voltage Stability* |
10V < VCC < 30V |
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0.2 |
2 |
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0.2 |
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2 |
% |
Temperature Stability* |
TMIN < TA < TMAX |
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5 |
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5 |
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% |
Total Variation* |
Line, Temperature |
340 |
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460 |
340 |
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460 |
kHz |
Oscillator Section (cont.) |
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Clock Out High |
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3.9 |
4.5 |
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3.9 |
4.5 |
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V |
Clock Out Low |
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2.3 |
2.9 |
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2.3 |
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2.9 |
V |
Ramp Peak* |
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2.6 |
2.8 |
3.0 |
2.6 |
2.8 |
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3.0 |
V |
Ramp Valley* |
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0.7 |
1.0 |
1.25 |
0.7 |
1.0 |
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1.25 |
V |
Ramp Valley to Peak* |
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1.6 |
1.8 |
2.0 |
1.6 |
1.8 |
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2.0 |
V |
Error Amplifier Section |
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Input Offset Voltage |
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10 |
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15 |
mV |
Input Bias Current |
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0.6 |
3 |
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0.6 |
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3 |
A |
Input Offset Current |
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0.1 |
1 |
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0.1 |
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1 |
A |
Open Loop Gain |
1V < VO < 4V |
60 |
95 |
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60 |
95 |
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dB |
CMRR |
1.5V < VCM < 5.5V |
75 |
95 |
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75 |
95 |
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dB |
PSRR |
10V < VCC < 30V |
85 |
110 |
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85 |
110 |
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dB |
Output Sink Current |
VPIN 3 = 1V |
1 |
2.5 |
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1 |
2.5 |
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mA |
Output Source Current |
VPIN 3 = 4V |
-0.5 |
-1.3 |
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-0.5 |
-1.3 |
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mA |
Output High Voltage |
IPIN 3 = -0.5mA |
4.0 |
4.7 |
5.0 |
4.0 |
4.7 |
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5.0 |
V |
Output Low Voltage |
IPIN 3 = 1mA |
0 |
0 .5 |
1.0 |
0 |
0.5 |
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1.0 |
V |
Unity Gain Bandwidth* |
|
3 |
5.5 |
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3 |
5.5 |
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MHz |
Slew Rate* |
|
6 |
12 |
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6 |
12 |
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V/ s |
3
UC1825
UC2825
UC3825
ELECTRICAL CHARACTERISTICS: Unless otherwise stated, these specifications apply for , RT = 3.65k, CT = 1nF, VCC = 15V, -55° C<TA<125° C for the UC1825, –40° C<TA<85° C for the UC2825, and 0° C<TA<70° C for the UC3825, TA=TJ.
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UC1825 |
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UC3825 |
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PARAMETERS |
TEST CONDITIONS |
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UC2825 |
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MIN |
TOP |
MAX |
MIN |
TOP |
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MAX |
UNITS |
PWM Comparator Section |
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Pin 7 Bias Current |
VPIN 7 = 0V |
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-1 |
-5 |
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-1 |
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-5 |
A |
Duty Cycle Range |
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0 |
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80 |
0 |
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85 |
% |
Pin 3 Zero DC Threshold |
VPIN 7 = 0V |
1.1 |
1.25 |
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1.1 |
1.25 |
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V |
Delay to Output* |
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50 |
80 |
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50 |
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80 |
ns |
Soft-Start Section |
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Charge Current |
VPIN 8 = 0.5V |
3 |
9 |
20 |
3 |
9 |
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20 |
A |
Discharge Current |
VPIN 8 = 1V |
1 |
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1 |
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mA |
Current Limit / Shutdown Section |
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Pin 9 Bias Current |
0 < VPIN 9 < 4V |
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15 |
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10 |
A |
Current Limit Threshold |
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0.9 |
1.0 |
1.1 |
0.9 |
1.0 |
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1.1 |
V |
Shutdown Threshold |
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1.25 |
1.40 |
1.55 |
1.25 |
1.40 |
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1.55 |
V |
Delay to Output |
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50 |
80 |
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50 |
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80 |
ns |
Output Section |
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Output Low Level |
IOUT = 20mA |
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0.25 |
0.40 |
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0.25 |
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0.40 |
V |
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IOUT = 200mA |
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1.2 |
2.2 |
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1.2 |
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2.2 |
V |
Output High Level |
IOUT = -20mA |
13.0 |
13.5 |
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13.0 |
13.5 |
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V |
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IOUT = -200mA |
12.0 |
13.0 |
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12.0 |
13.0 |
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V |
Collector Leakage |
VC = 30V |
|
100 |
500 |
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10 |
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500 |
A |
Rise/Fall Time* |
CL = 1nF |
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30 |
60 |
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30 |
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60 |
ns |
Under-Voltage Lockout Section |
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Start Threshold |
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8.8 |
9.2 |
9.6 |
8.8 |
9.2 |
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9.6 |
V |
UVLO Hysteresis |
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0.4 |
0.8 |
1.2 |
0.4 |
0.8 |
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1.2 |
V |
Supply Current Section |
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Start Up Current |
VCC = 8V |
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1.1 |
2.5 |
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1.1 |
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2.5 |
mA |
ICC |
VPIN 1, VPIN 7, VPIN 9 = 0V; VPIN 2 = 1V |
|
22 |
33 |
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22 |
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33 |
mA |
4
Printed Circuit Board Layout Considerations
High speed circuits demand careful attention to layout and component placement. To assure proper performance of the UC1825 follow these rules: 1) Use a ground plane. 2) Damp or clamp parasitic inductive kick energy from the gate of driven MOSFETs. Do not allow the output pins to ring below ground. A series gate resistor or a shunt 1 Amp Schottky diode at the output pin will serve
UC1825
UC2825
UC3825 this purpose. 3) Bypass VCC, VC, and VREF. Use 0.1 F monolithic ceramic capacitors with low equivalent series inductance. Allow less than 1 cm of total lead length for each capacitor between the bypassed pin and the ground plane. 4) Treat the timing capacitor, CT, like a bypass capacitor.
Error Amplifier Circuit
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Simplified Schematic |
Open Loop Frequency Response |
Unity Gain Slew Rate |
PWM Applications
Current-Mode
Conventional (Voltage Mode)
5
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UC1825 |
Oscillator Circuit |
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UC2825 |
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UC3825 |
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Deadtime vs CT (3k RT |
100k) |
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Timing Resistance vs Frequency |
Deadtime vs Frequency |
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160 |
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140 |
1.0nF |
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120 |
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T(ns)D |
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100 |
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470pF |
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80 |
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10k |
100k |
1M |
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FREQ (Hz) |
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Synchronized Operation
Two Units in Close Proximity |
Generalized Synchronization |
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6 |