3/97
BLOCK DIAGRAM
• 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)
• Trimmed Bandgap Reference (5.1V ±1%)
The UC1825 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 opagation delay s 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 secti on 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.
UC1825
UC2825
UC3825
High Speed PWM Controller
FEATURES DESCRIPTION
UDG-92030-2
CONNECTION DIAGRAMS
DIL-16 (Top View)
J Or N Package
SOIC-16 (Top View)
DW Package
UC1825
UC2825
UC3825
ELECTRICAL CHARACTERISTICS:
Unless otherwise st ated,these spe ci fi ca ti ons apply for , RT = 3.65k, CT = 1nF, V
CC
= 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=T
J.
UC1825
UC3825
PARAMETERS TEST CONDITIONS UC2825
MIN TYP MAX MIN TYP MAX UNITS
Reference Section
Output Voltage T
J
= 25°C, IO = 1mA 5.05 5.10 5.15 5.00 5.10 5.20 V
Line Regulation 10V < V
CC
< 30V 2 20 2 20 mV
Load Regulation 1mA < I
O
< 10mA 5 20 5 20 mV
Temperature Stability* T
MIN
< TA < T
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
µ
V
Long Term Stability* T
J
= 125°C, 1000hrs. 5 25 5 25 mV
Short Circuit Current V
REF
= 0V -15 -50 -100 -15 -50 -100 mA
Oscillator Section
Initial Accuracy* TJ = 25°C 360 400 440 360 400 440 k Hz
Voltage Stability* 10V < V
CC
< 30V 0.2 2 0.2 2 %
Temperature Stability* T
MIN
< TA < T
MAX
55%
Total Variation* Line, Temperature 340 460 340 460 kHz
PACKAGE PIN FUNCTION
FUNCTION
PIN
N/C 1
INV 2
NI 3
E/A Out 4
Clock 5
N/C 6
R
T
7
C
T
8
Ramp 9
Soft Start 10
N/C 11
ILIM/SD 12
Gnd 13
Out A 14
Pwr Gnd 15
N/C 16
V
C
17
Out B 18
V
CC
19
V
REF
5.1V 20
PLCC-20 & LCC-20
(Top View)
Q & L Packages
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 Dis sipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 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.
2
UC1825
UC3825
PARAMETERS TEST CONDITIONS UC2825
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
µ
A
Input Offset Current 0.1 1 0.1 1
µ
A
Open Loop Gain 1V < VO < 4V 60 95 60 95 dB
CMRR 1.5V < V
CM
< 5.5V 75 95 75 95 dB
PSRR 10V < V
CC
< 30V 85 110 85 110 dB
Output Sink Current V
PIN 3
= 1V 12.5 12.5 mA
Output Source Current V
PIN 3
= 4V -0.5 -1.3 -0.5 -1.3 mA
Output High Voltage I
PIN 3
= -0.5mA 4.0 4.7 5.0 4.0 4.7 5.0 V
Output Low Voltage I
PIN 3
= 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/
µ
s
PWM Comparator Section
Pin 7 Bias Current V
PIN 7
= 0V -1 -5 -1 -5
µ
A
Duty Cycle Range 0 80 0 85 %
Pin 3 Zero DC Threshold V
PIN 7
= 0V 1.1 1.25 1.1 1.25 V
Delay to Output* 50 80 50 80 ns
Soft-Start Section
Charge Current V
PIN 8
= 0.5V 3 9 20 3 9 20
µ
A
Discharge Current V
PIN 8
= 1V 1 1 mA
Current Limit / Shutdown Section
Pin 9 Bias Current 0 < V
PIN 9
< 4V 15 10
µ
A
Current Limi t 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
Output Low Level I
OUT
= 20mA 0.25 0.40 0.25 0.40 V
I
OUT
= 200mA 1.2 2.2 1.2 2.2 V
Output High Level I
OUT
= -20mA 13.0 13.5 13.0 13.5 V
I
OUT
= -200mA 12.0 13.0 12.0 13.0 V
Collector Leakage V
C
= 30V 100 500 10 500
µ
A
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
PIN 2
= 1V 22 33 22 33 mA
Unless otherwise st ated,these spe ci fi ca ti ons apply for , R
T
= 3.65k, C
T
= 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=T
J.
* This parameter not 100% tested in production but guaranteed by design.
UC1825
UC2825
UC3825
ELECTRICAL CHARACTERISTICS
(cont.)
3
High speed circuits demand careful attention to layout
and component placement. To assure proper performance
of the UC1825 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 sh unt 1 Am p
Schottky diode at the outp ut pin will se rve this p urp ose . 3 )
Bypass V
CC
, VC, and V
REF
. Use 0.1µF monolithic ceramic
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
T
, like a bypass capacitor.
UC1825
UC2825
UC3825
Open Loop Frequency Response Unity Gain Slew Rate
Simplified Schematic
Error Amplifier Circuit
PWM Applications
Conventional (Voltage Mode)
Current-Mode
Printed Circuit Board Layout Consider ations
4
Oscillator Circuit
UC1825
UC2825
UC3825
µ
Deadtime vs CT (3k ≤ R
T
≤
100k)
Timing Resistance vs Frequency
80
100
120
140
160
10k 100k
470pF
1.0nF
1M
FREQ (Hz)
T (ns)
D
Deadtime vs Frequency
Synchronized Operation
Two Units in Close Proximity
Generalized Synchronization
5
UC1825
UC2825
UC3825
Forward Technique for Off-Line Voltage Mo de Ap plication
Constant Volt-Second Clamp Circuit
The circuit shown here will achieve a constant volt-second product clamp over varying input voltages. The
ramp generator components, R
T
and CR are chosen so
that the ramp at Pin 9 crosses the 1V threshold at the
same time the desired maximum volt-second product
is reached. The delay through the functional nor block
must be such that the ramp capacitor can be completely discharged during the minimum deadtime.
Output Section
Simplified Schematic Rise/Fall Time (CL=1nF)
Rise/Fall Time (CL=10nF) Saturation Curves
6
Open Loop Laboratory Test Fixtu re
UDG-92032-2
This test fixture is useful for exercising many of the
UC1825’s functions and measuring their specifications.
As with any wideband circuit, careful grounding and bypass procedures should be followed. The use of a
ground plane is highly recommended.
Design Example: 50W, 48V to 5V DC to DC Converter - 1.5MHz Clock Frequency
UDG-92033-3
UNITRODE CORPORATI ON
7 CONTINENTAL BLVD. • MERRIMACK, NH 03054
TEL. (603) 424- 24 10 • FAX (603) 424-3460
UC1825
UC2825
UC3825
7
IMPORTANT NOTICE
T exas Instruments and its subsidiaries (TI) reserve the right to make changes to their products or to discontinue
any product or service without notice, and advise customers to obtain the latest version of relevant information
to verify, before placing orders, that information being relied on is current and complete. All products are sold
subject to the terms and conditions of sale supplied at the time of order acknowledgement, including those
pertaining to warranty, patent infringement, and limitation of liability.
TI warrants performance of its semiconductor products to the specifications applicable at the time of sale in
accordance with TI’s standard warranty. Testing and other quality control techniques are utilized to the extent
TI deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily
performed, except those mandated by government requirements.
CERT AIN APPLICATIONS USING SEMICONDUCT OR PRODUCTS MAY INVOLVE POTENTIAL RISKS OF
DEATH, PERSONAL INJURY, OR SEVERE PROPERTY OR ENVIRONMENTAL DAMAGE (“CRITICAL
APPLICATIONS”). TI SEMICONDUCTOR PRODUCTS ARE NOT DESIGNED, AUTHORIZED, OR
WARRANTED TO BE SUITABLE FOR USE IN LIFE-SUPPORT DEVICES OR SYSTEMS OR OTHER
CRITICAL APPLICATIONS. INCLUSION OF TI PRODUCTS IN SUCH APPLICA TIONS IS UNDERSTOOD T O
BE FULLY AT THE CUSTOMER’S RISK.
In order to minimize risks associated with the customer’s applications, adequate design and operating
safeguards must be provided by the customer to minimize inherent or procedural hazards.
TI assumes no liability for applications assistance or customer product design. TI does not warrant or represent
that any license, either express or implied, is granted under any patent right, copyright, mask work right, or other
intellectual property right of TI covering or relating to any combination, machine, or process in which such
semiconductor products or services might be or are used. TI’s publication of information regarding any third
party’s products or services does not constitute TI’s approval, warranty or endorsement thereof.
Copyright 1999, Texas Instruments Incorporated
Loading...