The UC1526A Series are improved-performance pulse-width modulator circuits intended for direct replacement of equivalent non- “A”
versions in all a pplications. Higher frequency ope ration has been
enhanced by several significant improvements including: a more accurate oscillator with less minimum dead time, reduced circuit delays (particularly i n current limiting), and an improved output stage
with negligible cross-condu ction current. Additional improvements
include the incorporation of a precisi on, band-g ap reference generator, reduced overall supply current, and the addition of thermal
shutdown protection.
Along with these improvements, the UC1526A Series retains the
protective features of under-voltage lockou t, soft-start, digital current limiting, double pulse suppression logic, and adjustable
deadtime. For ease of interfacing, all digital control ports are TTL
compatible with active low logic.
Five volt (5V) operation is possible for “logic level” applications by
connecting V
factory for additional information.
IN, VC and VREF to a precision 5V input supply. Consult
Note 3: Range over which the device is functional and
parame te r limit s are guar ant eed .
PACKAGE PIN FUNCTION
FUNCTIONPIN
N/C1
+ERROR2
-ERROR3
COMP.4
SS5
C
RESET6
- CURRENT SENSE7
+ CURRENT SENSE8
SHUTDOWN9
TIMING10
R
T11
C
D12
R
SYNC13
OUTPUT A14
C15
V
N/C16
GROUND17
OUTPUT B18
IN19
+V
REF20
V
2
UC1526A
UC2526A
UC3526A
+V
ELECTRICAL CHARACTERISTICS:
PARAMETERTEST CONDITIONS
Reference Sec tion (Note 4)
Output Volt ageT
Line Regulatio n+V
Load RegulationI
Temperature StabilityOver Operating T
Total Output Voltage
Range
Short Circuit CurrentV
Under-Voltage Lockout
RESET Output VoltageVREF = 3.8V0.20.40.20.4V
Oscillato r Sect io n (Note 6)
Initial AccuracyT
Voltage Stability+V
Temperature StabilityOver Operating T
Minimum FrequencyR
Maximum FrequencyR
Sawtooth Peak Voltage+ V
Sawtooth Valley Voltage+V
SYNC Pulse WidthTJ = 25°C, RL = 2.7kΩ to V
Error Ampl i fier Section (Note 7)
Input Offs et Vo lta geR
Input Bias Cur rent-350-1000-350-2000nA
Input Offs et Cu rr ent3510035200nA
DC Open Loop Gai nR
HIGH Output VoltageV
LOW Output VoltageV
Common Mode Rejec tionR
Supply Voltage Rejection+V
PWM Comparator (Note 6)
Minimum Duty CycleV
Maximum Duty CycleV
Digi tal Ports (
SYNC, SHUTDOWN, and RESET)
HIGH Output VoltageI
LOW Output VoltageI
HIGH Input CurrentV
LOW Input CurrentV
Shutdown DelayFrom Pin 8, T
Current Limit Compar ato r (Note 8)
Sense VoltageR
Input Bias Cur rent-3-10-3-10µA
Shutdown DelayFrom pin 7, 100m V Over driv e, T
Note 4: I
L =
0mA.
Note 5: Guaranteed by design, not 100% tested in product ion.
Note 6: F
OSC
= 40kHz, (RT = 4.12 kΩ ± 1%, CT = 0.01µF± 1%,
D
= 0 Ω).
R
J = +25°C4.955.005.054.905.005.10V
IN = 7 to 35V210215mV
L = 0 to 20mA520520mV
Over Recomme nded Opera ting
Conditio ns
REF = 0V25501002550100mA
VREF = 4.7V2.44.72.44.8V
J = +25°C±3±8±3±8%
IN = 7 to 35V0.510.51%
T = 150kΩ, CT = 20µF (Note 5)11Hz
T = 2kΩ, CT = 470pF5 50650kHz
IH = +2.4V-125-200-125-200µA
IL = +0.4V-225-36 0-225-360µA
S≤ 50Ω9010011080100120mV
IN = 15V, and over operating ambient temper ature, unless ot herwise specified TA = TJ.
UC1526A / UC2526AUC3526A
MINTYPMAXMINTYPMAX
J (Note 5)15501550mV
4.905.005.104.855.005.15V
J (Note 5)2613%
REF
J = 25°C160160ns
J = 25°C260260ns
Note 7: V
Note 8: V
Note 9: V
Note 10 :V
CM
CM
C
IN
1.11.1µs
= 0 to +5.2V
= 0 to +12V.
= +15V .
= +35V , RT = 4.12kΩ.
UNITS
3
UC1526A
UC2526A
UC3526A
ELECTRICAL CHARACTERISTICS:
PARAMETERTEST CONDITIONS
+VIN = 15V, and over operating ambient temperature, unless otherwise specified T A = TJ.
UC1526A
UC3526A
UC2526A
MINTYPMAXMINTYPMAX
Soft-Start Sec tion
Error Clamp Voltage
C
S Charging CurrentRESET = +2.4V5010015050100150µA
RESET = +0.4V0.10.40.10 .4V
Output Drivers (Each Output) (Note 9)
HIGH Output VoltageI
LOW Output VoltageI
Collector LeakageV
Rise TimeC
Fall TimeC
Cross-Conductio n Charge Per cycle, T
SOURCE = 20mA12.513.512.513.5V
SOURCE = 100m A12131213V
I
SINK = 20mA0.20.30.20.3V
I
SINK = 100mA1.22.01.22.0V
C = 40V5015050150µA
L = 1000pF (Note 5)0.30.60.30.6µs
L = 1000pF (Note 5)0.10.20.10.2µs
J = 25°C88nC
Power Consumption(Note 10)
Standby Current
Note 4: I
L =
0mA.
SHUTDOWN = +0.4V14201420mA
Note 5: Guaranteed by design, not 100% tested in product ion.
Note 6: F
Note 7: V
Note 8: V
Note 9: V
Note 10 :V
OSC
= 40kHz, (RT = 4.12 kΩ ± 1%, CT = 0.01µF± 1%,
D
= 0 Ω).
R
CM
= 0 to +5.2V
CM
= 0 to +12V.
C
= +15V .
IN
= +35V , RT = 4.12kΩ.
UNITS
Open Loop Test Circ uit UC15 26A
4
APPLICATIONS INFORMATION
Volt age Reference
The reference regulator of the UC1526A is based on a
precision band-gap reference, internally trimmed to ±1%
accuracy. The circui try is fully active at supply voltages
above +7V, and provides up to 20mA of load current to
external circuitry a t +5.0V. In systems where additional
current is required, an externa l PNP transistor can be
used to boost the available current. A rugged low frequency audio-type transistor should be used, and lead
lengths between the PWM and transistor should be as
short as possible to minimize the risk of oscillations.
Even so, some types of transistors may require collector-base capacitance for stability. Up to 1 amp of load
current can be obtai ned with excelle nt regulation if the
device selected maintains high current ga in.
Figure 1. Extending Reference O ut put Curr ent
Under-V olta ge Loc kout
The under-voltage locko ut circuit protects the UC1526A
and the power devices it controls from inadequate supply voltage , If +V
output drivers and holds the
vents spurious output pulses while the control circuitry is
stabilizing, and holds the soft-start timing capaci tor in a
discharged state.
IN is too low, the circuit disables the
RESET pin LOW. This pre-
UC1526A
UC2526A
UC3526A
Figure 2. Under-Voltage Loc kout Schemat ic
Soft-Start Circuit
The soft-start circuit protects the power transistors and
rectifier diodes from high curren t surges during power
supply turn-on. When supply voltage is first applied to
the UC1526A, the under-voltage lockout circuit holds
RESET LOW with Q3. Q1 is turned on, which holds the
soft-start capacitor voltage at zero. The second collector
of Q
1 clamps the outpu t of the error amplifier to ground,
guaranteeing zero duty cycle at the driver outputs.
When the supply voltage reaches normal operating
range,
internal 100µA current source to charge C
the error amplifier output to 1V
C
cycle of the PWM l inearly increases to whatever value
the voltage regulation loop requires for an error null.
RESET will go HIGH. Q1 turns off, allowing the
S. Q2 clamps
BE above the voltage on
S. As the soft-start voltage ramps up to +5V, the duty
The circuit consi sts of a +1.2V bandgap reference and
comparator circuit which is active when the reference
voltage has risen t o 3V
BE or +1.8V at 25°C. When the
reference voltage rises to approximately +4.4V, the circuit enables the output drivers and rele ases the
RESET
pin, allowing a normal soft-start. The comparator has
350mV of hysteresis to minimize oscillation at the trip
point. When +V
ence drops to +4.2V, the under-voltage circuit pulls
IN to the PWM is removed and the refer-
RESET LOW again. The soft-start capacitor is immediately
discharged, and the PWM is re ady for another soft-start
cycle.
The UC1526A can operate from a +5V supply by connecting the V
REF pin to the +VIN pin and maintaining the
supply between +4.8 and +5.2V.
Figure 3. Soft-Start Circuit Schematic
Digital Control Ports
The three digital control ports of the UC1526A are bi-directional. Each pin can drive TTL and 5V CMOS logic directly, up to a fan-out of 10 low-power Schottky gates.
Each pin can also be directly driven by open-collector
TTL, open-drain CMOS, and open-collector voltage
comparators; fan-in is equivalent to 1 low-power Schottky gate. Each port i s normally HIGH; the pi n is pulled
LOW to activate the particular function. Driving
LOW initiates a discha rge cycle in the osci llator. Pulling
SHUTDOWN LOW immediately inhibits all PWM output
pulses. Holding
RESET LOW discharges the soft-start
5
SYNC
APPLICATIONS INFORMATION (cont.)
capacitor. The logic threshol d is +1.1V at +25°C. Noise
immunity can be gained at the expense of fan-out with an
external 2k pull-up resistor to +5V.
UC1526A
UC2526A
UC3526A
the SYNC pin will then lock the oscillator to the external
frequency.
Multiple devices can be synchronized together by programming one master unit for the desired frequency, and
then sharing its sawtooth and clock waveforms with the
slave units. All C
of the master and all
nected to the
nals are left open or connected to V
terminal may be either left open or grounded.
T terminals are connected to the CT pin
SYNC terminals are likewise con-
SYNC pin of the master. Slave RT termi-
REF. Slave RD
Figure 4.
Digital Co ntr ol Port Schematic
Oscillators
The oscillator is programmed for frequency and dead
time with three components: R
forms are generated : a sawtooth waveform at pin 10 for
pulse width modulation, and a logic clock at pin 12. The
following procedure is recommended for choosing timing
values:
1. With R
RT and CT from the graph on page 4 to give the de-
for
D= 0Ω(pi n 11 shorted to ground) select values
sired oscilla tor period. Remember that the frequency at
each driver output is half the oscillator frequency, and the
frequency at the +V
C terminal is the same as the oscilla-
tor frequency.
2. If more dead time is required, select a larger value of
D. At 40kHz dead time increases by 400ns/ Ω.
R
3. Increasing the dead time will cause the oscillator frequency to decrease slig htly. Go back and decrease the
value of R
T slightly to bring the frequency back to the
nominal design value.
The UC1526A can be synchronized to an external logic
clock by programming the oscillator to free-run at a frequency 10% slower than the
T, CT and RD. Two wave-
SYNC frequency.
Figure 6. Error Amplifier C onnections
Error Amplifie r
The error amplifier is a transconductance design, with an
output impedance of 2MΩ. Since all vo ltage gain takes
place at the output pin, the open-loop gain/frequency
characteristics can be controlled with shunt reactance to
ground. When compensated for unity-gain stability with
100pF, the amplifier has an open-loop pole at 800Hz.
The input connections to the error amplifier are determined by the pola rity of the swi tchin g supp ly output voltage. For positive supplies, the common-mode voltage is
+5.0V and the feedback connections in Figure 6A are
used. With negative supplies, the common-mode voltage
is ground and the feedback divider is connected between
the negative output an d the +5.0V reference voltage, as
shown in Figure 6B.
A period ic LOW logic pulse appro ximately 0.5µs wide at
Figure 5. Oscillator Connections and Waveforms
Figure 7. Push-Pull Configuration
6
OUTPUT BLANKING
APPLICATIONS INFORMATION (cont.)
Output Drivers
The totem pole output drivers of the UC1526A are designed to source and sink 100mA continuously and
200mA peak. Loads can be driven either from the output
pins 13 and 16, or from the +V
Since the bottom transistor of the totem-pole is allowed to
saturate, there is a momentary condu ction path from the
C, as required.
UC1526A
UC2526A
UC3526A
+V
C terminal to ground during switching; however, im-
proved design has limited this cross-conduction period to
less than 50ns. Capacitor decoupling at V
mended and careful g rounding of Pin 15 is needed to insure that high peak sink currents from a capacitive load
do not cause ground transients.
C is recom-
Figure 8. Single-Ended Conf i gur ation
TYPICAL CHARACTERIS TICS
OSCILLATOR PERIOD vs RT and CT
Figure 9. Driving N-Channel Power MOSFETs
7
TYPICAL CHARACTERIS TICS (Co nt.)
Output Driver Deadtime vs. RD ValueUnder Voltage Lockout Characteristic
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in
a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
Lead/Ball Finish MSL Peak Temp
CU NIPDAULevel-2-260C-1 YEAR
CU NIPDAULevel-2-260C-1 YEAR
CU NIPDAULevel-2-260C-1 YEAR
CU NIPDAULevel-NC-NC-NC
CU NIPDAULevel-NC-NC-NC
CU SNLevel-2-260C-1 YEAR
CU NIPDAULevel-2-260C-1 YEAR
CU NIPDAULevel-2-260C-1 YEAR
CU NIPDAULevel-2-260C-1 YEAR
CU NIPDAULevel-2-260C-1 YEAR
CU NIPDAULevel-NC-NC-NC
CU NIPDAULevel-NC-NC-NC
CU SNLevel-2-260C-1 YEAR
(3)
(2)
Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS) or Green (RoHS & no Sb/Br) - please check
http://www.ti.com/productcontent for the latest availability information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements
for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered
at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame
retardants (Br or Sb do not exceed 0.1% by weight in homogeneous material)
Addendum-Page 1
PACKAGE OPTION ADDENDUM
www.ti.com
(3)
MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder
temperature.
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15-Nov-2005
Addendum-Page 2
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