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.
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.
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
PARAMETERSTEST CONDITIONSUC2824
J.
UC1824
UC3824
MINTYPMAXMINTYPMAX UNITS
Reference Section
Output VoltageT
Line Regulation10V < V
Load Regulation 1mA < I
Temperature Stability*T
= 25°C, IO = 1mA5.055.105.155.005.1 0 5.20V
J
< 30V220220mV
CC
< 10mA520520mV
O
< TA < T
MIN
MAX
0.20.40.20.4mV/°C
Total Output Variat io n*Li ne , Lo ad , Te mp era tu r e5.005.20 4.955.25V
Output Noise Volt ag e*10Hz < f < 10kHz5050
= 125°C, 1000hrs.525525mV
Long Term Stability*T
Short Circuit CurrentV
J
= 0V-15-50-100-15-50-100 mA
REF
Oscillator Section
Initial Accuracy *TJ = 25°C360400440360400440k Hz
< 30V0.220.22%
MIN
CC
< TA < T
MAX
55%
Voltage Stability*10V < V
Temperature Stability*T
Total Variation*Line, Temperature340460340460kHz
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
PARAMETERSTEST CONDITIONSUC2824
MINTYPMAXMINTYPMAX UNITS
Oscillator Section (cont. )
Clock Out High3.94.53.94.5V
Clock Out Low2.32.92.32.9V
Ramp Peak*2.62.83.02.62.83.0V
Ramp Valley*0.71.01.250.71.01.25V
Ramp Valley to Peak*1.61.82.01.61.82.0V
Error Amplifier Section
Input Offset Voltage1015mV
Input Bias Current0.630.63
Input Offset Current0.110.11
Open Loop Gain1V < V
CMRR1.5V < V
PSRR10V < V
Output Sink CurrentV
Output Source CurrentV
Output High VoltageI
Output Low Voltag eI
PIN 3
PIN 3
< 4V60956095dB
O
< 5.5V75957595dB
CM
< 30V8511085110dB
CC
= 1V12.512.5mA
PIN 3
= 4V-0.5-1.3-0.5-1.3mA
PIN 3
= -0.5mA4.04.75.04.04.75.0 V
= 1mA00 .51.000.51.0V
Unity Gain Bandwidth*35.535.5MHz
Slew Rate*612612V/
PWM Comparator Section
Pin 7 Bias CurrentV
= 0V-1-5-1-5
PIN 7
Duty Cycle Range080085%
Pin 3 Zero DC ThresholdV
= 0V1.11.251.11.25V
PIN 7
Delay to Output*50805080ns
Soft-Start Section
= 0.5V39203920
Charge CurrentV
Discharge CurrentV
PIN 8
= 1V11mA
PIN 8
Current Limit / Shutdown Section
Pin 9 Bias Current0 < V
< 4V1510
PIN 9
Current Limit Threshold0.91.01.10.91.01.1V
Shutdown Threshold1.251.401.551.251.401.55V
Delay to Output50805080ns
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 ProximityGeneralized 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
-75-50-250255075100125
T(ns)
Primary Output Deadtime vs Frequency
160
140
120
D
T (ns)
100
TC()
°
80
10k100k
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 SchematicRise/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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In order to minimize risks associated with the customer’s applications, adequate design and operating
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Copyright 1999, Texas Instruments Incorporated
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