NTE1720
Integrated Circuit
Pulse Width Modulator (PWM) Regulator
Description:
The NTE1720 PWM switching regulator control circuit contains all the essential circuitry to implement
singleended or pushpull switching regulators. Included on the circuit are oscillator, voltage refer-
ence, a pulse width modulator, error amplifier, overload protection circuitry and output drivers.
A substance zener reference has been used to provide excellent stability with time and the reference
has been used to provide excellent stability with time and the reference is trimmed at the wafer level
to provide an initial accuracy of 2%. Additionally, the oscillator is trimmed to provide a medium toler-
ance of 6%.
Features:
D
Reference Tolerance:
2%
D
Oscillator Tolerance:
6%
D
Long Term Stability: 10mV/1000 Hrs
D
Operates Above 100kHz
Applications:
D
Switching Power Supplies
D
Motor Speed Control
D
OffLine Power Converters
Absolute Maximum Ratings:
Input Voltage, V
I
40V
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Reference Output Current
50mA
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Output Current (Each Output)
100mA
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Oscillator Charging Current (Pin6 or Pin7)
5mA
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Internal Power Dissipation (Note 1), P
D
1W
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Operating Temperature Range, T
opr
55
C to +125
C
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Storage Temperature Range, T
stg
65
C to +150
C
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Lead Temperature (During soldering, 10 sec), T
L
+300
C
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Note 1. For operating at elevated temperatures, the NTE1720 is derated at 150
C/W to a maximum
junction temperature of 115
C.
Electrical Characteristics: (T
A
= +25
C, V
IN
= 20V, f = 20kHz unless otherwise specified)
Parameter
Test Conditions
Min
Typ
Max
Unit
Reference Section
Output Voltage
4.8
5.8
5.2
V
Line Regulation
V
IN
= 8V to 40V
10
20
mV
Load Regulation
I
L
= 0mA to 20
20
50
mV
Ripple Rejection
t = 120Hz
66
dB
Short Circuit Current Limit
V
REF
= 0
100
mA
Temperature Stability
0.3
1
%
Long Term Stability
20
mV/kHz
Oscillator Section
Maximum Frequency
C
T
= 0.001pF, R
T
= 2k
300
kHz
Initial Accuracy
R
T
and C
T
Constant
6
%
Voltage Stability
V
IN
= 8V to 40V
1
%
Temperature Stability
2
%
Output Amplitude
Pin3
3.5
s
Output Pulse Width
C
T
= 0.01
F, T
A
= 25
C
0.5
s
Error Amplifier Section
Input Offset Voltage
V
CM
= 2.5V
0.5
5
mV
Input Bias Current
V
CM
= 2.5V
2
10
A
Open Loop Voltage Gain
72
80
dB
CommonMode Voltage
1.8
3.4
V
CommonMode Rejection Ratio
70
dB
Small Signal Bandwidth
A
V
= 0dB
3
MHz
Output Voltage
0.5
3.8
V
Comparator Section
Minimum Duty Cycle
0
%
Maximum Duty Cycle
45
40
%
Input Threshold
Zero Duty Cycle
1
V
Input Bias Current
1
A
Current Limiting Section
Sense Voltage
Pin 9 = 2V with Error Amplifier Set for Max Out
180
200
220
mV
Sense Voltage T.C.
0.2
mV/
C
CommonMode Voltage
1
1
V
Output Section (Each Output)
CollectorEmitter Voltage
40
V
Collector Leakage Current
V
CE
= 40V
0.1
50
A
Saturation Voltage
I
C
= 50mA
1
2
V
Emitter Output Voltage
V
IN
= 20V
17
16
V
Rise Time
R
C
= 2k
0.2
s
Fall Time
R
C
= 2k
0.1
s
Total Standby Current
V
IN
= 40V, Note 2
8
10
mA
Note 2. Standby current does not include the oscillator charging current, error and current limit divid-
ers, and the outputs are open circuit.
APPLICATIONS INFORMATION: (Functional Description and Pin Functions)
Voltage Regulator
The Internal 5V regulator (Input Pin15, output Pin16) supplies a regulated 5V to all Internal circuitry,
as well as up to 50mA for external circuitry. For operation below 8V externally applied.
Oscillator
The Internal oscillator circuitry sets the frequency of operation for the switching regulator. The oscilla-
tor waveform is a ramp from about 1V to 3.5V (Pin7). Frequency is set by a timing resistor from Pin6
to ground and a capacitor from Pin7 to GND. The oscillator period is approximately RC for the recom-
mended range of 1.8K to 100K for R and 0.001
F to 0.1
F for C.
The fall time of the ramp sets the blanking or dead time where both outputs are off in pushpull regula-
tors. This is controlled by the value of the capacitor alone.
Output Transistors
The two output transistors have both the emitters (Pin11 and Pin14) and the collectors available
(Pin12 and Pin13). Internal current limiting for both of these transistors is about 100mA. The two
transistors are driven 180
out of phase by the flipflop. For singleended operation they should be
connected in parallel.
Error Amplifier
The differential Input (Pin1 and Pin2) singleended output (Pin9) transconductance amplifier pro-
vides about 80dB of gain, as well as providing a point for loop frequency compensation or electronic
shutdown.
DC gain of the loop can be controlled by resistive loading, while AC compensation is usually accom-
plished with a series RC conncected from Pin9 to GND. The output impedance at Pin9 is about 5M
and current is about 200
A, so external opamps or voltage sources can easily drive the comparator
input. Normally, the 5V reference is divided down to generate a voltage within the common mode
range of the error ampliifier.
Synchronous Operation
When an external clock is desired, a clock pulse of approximately 3V can be applied directly to the
oscillator output, Pin3. The impedance to GND at this point is approximately 2k
. In this configura-
tion, R
T
C
T
must be selected for a clock period slightly greater than that of the external clock.
If two or more NTE1720 regulators are to be operated synchronously, all oscillator output terminals
should be tied together. The oscillator programmed for the minimum clock period will be the master
from which all the other operate. In this application, the C
T
R
T
value of the slaved regulators must
be set for a period approximately 10% longer than that of the master regulator. In addition, C
T
(master)
= 2 C
T
(slave) to ensure that the master output pulse, which occurs first, has a wider pulse width and
will subsequently reset the slave regulators.
Shutdown
A logic high at Pin10 will shut down the regulator and cause both output transistors to turn off.
Current Limit
Current limiting is activated when the voltage between Pin4 and Pin5 exceeds 200mV. The output
of the current limit amplifier Internally sums with error amplifier to shorten the output pulse width. The
gain of the current limit circuitry is relatively low, so current control in limit is typically about 5%. Two
areas of caution should be observed with current limiting. First, the reponse time of the current limit
is set by the loop rolloff on Pin9. Fast current limiting requires external circuitry. Second, the com-
monmode range of the current limit amplifier is limited. Even fast spikes outside this range can dis-
rupt operation.
V
IN
V
ref
I
LIMIT
Sense ()
I
LIMIT
Sense (+)
Pin Connection Diagram
C
T
R
T
1
2
3
4
Inverting Input
NonInverting Input
OSC Output
5
6
7
16
15
14
13
Emitter B
Collector B
12
Collector A
11
Emitter A
10
Shutdown
8
GND
9
Compensation
.700 (17.78)
.100 (2.54)
1
8
16
9
.200
(5.08)
Max
.870 (22.0) Max
.260 (6.6)
Max
.099 (2.5) Min
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