unless otherwise stated, these specifications apply over specific
temperature range. V
IN
= V
DD
= 15V; R
T
= 71 kΩ; C
T
= 150 pF.
TC18C43
TC28C43
Parameter
Reference Section
Output Voltage
Line Regulation
Load Regulation
Temp Stability
Output Noise Voltage
Long Term Stability
Output Short Circuit
T
A
= 25°C, I
O
= 1mA
9.5V
≤
V
IN
≤
15V, I
O
= 1mA
1mA
≤
l
O
≤
11mA
(Note 1)
10Hz
≤
f
≤
10 kHz,T
A
= 25°C (Note 1)
T
A
= 125°C, 1000 Hrs. (Note 1)
4.9
—
—
—
—
—
-20
90
—
—
2.25
2.45
1
—
—
70
650
80
1.2
3
5.65
0.1
—
—
2.8
0.85
70
—
—
5
±3
±5
±0.25
100
±0.5
-50
100
±0.2
±0.01
2.5
2.65
—
±15
±0.3
90
750
100
1.5
3.4
6
0.7
5
3
2.9
0.95
80
±0.3
140
5.1
±10
±15
±0.5
—
—
-100
110
±0.3
±0.05
2.75
2.85
—
±50
±2
—
—
—
—
—
6.5
1.1
7
5
3.1
1.05
—
±2
160
4.90
—
—
—
—
—
-30
93.8
—
—
2.25
2.45
1
—
—
70
650
80
1.5
3.9
5.65
0.1
—
—
2.8
0.85
70
—
—
5
±3
±3
±0.25
100
±0.5
-50
100
±0.2
±0.01
2.5
2.65
—
±15
±0.3
90
750
100
1.7
4.2
6
0.7
5
3
2.9
0.95
80
±0.3
140
5.10
±10
±10
±0.5
—
—
-100
106.5
±0.3
±0.03
2.75
2.85
—
±50
±2
—
—
—
—
—
6.5
1.1
7
5
3.1
1.05
—
±2
150
V
mV
mV
mV/°C
µV(rms)
%
mA
kHz
%
%/°C
mA
V
MHz
mV
nA
dB
kHz
dB
mA
mA
V
V
µsec
µsec
V/V
V
dB
nA
nsec
TC38C43
Max
Min
Typ
Max
Units
Test Conditions
Min
Typ
Oscillator Section
Initial Accuracy
Voltage Stability
Temp Stability
Clock Ramp Reset
Amplitude
Maximum Freq
T
A
= 25°C (Note 4)
9.5V
≤
V
IN
≤
15V
T
MIN
≤
T
A
≤
T
MAX
(Note 1); Figure 2
R
T
/C
T
Pin at 4V
R
T
/C
T
Pin Peak to Peak
Note 1
V
(CMPTR)
= 2.5V
(Note 1)
2V
≤
V
O
≤
4V
(Note 1)
9.5V
≤
V
IN
≤
15V
V
FB
= 2.7V, V
(CMPTR)
= 1.1V (Note 1)
V
FB
= 2.3V, V
(CMPTR)
= 5V (Note 1)
V
FB
= 2.3V, R
L
= 10k to Ground
V
FB
= 2.7V, R
L
= 10k to V
REF
Note 1
Note 1
Notes 2 & 3
V
(CMPTR)
= 5V (Note 2)
9.5V
≤
V
IN
≤
15V (Notes 1, 2 & 5)
Note 1
V
(
I
SENSE)
= 1V (Note 1); Figure 3
Error Amp Section
Input Offset Voltage
Input Bias Current
A
VOL
Gain Bandwidth Product
PSRR
Output Sink Current
Output Source Current
V
OUT
High
V
OUT
Low
Rise Response
Fall Response
Current Sense Section
Gain Ratio
Maximum Input Signal
PSRR
Input Bias Current
Delay to Output
4-94
TELCOM SEMICONDUCTOR, INC.
BiCMOS CURRENT MODE
PWM CONTROLLERS
TC18C43
TC28C43
TC38C43
1
ELECTRICAL CHARACTERISTICS
(Cont):
unless otherwise stated, these specifications apply over specified
temperature range. V
IN
= V
DD
= 15V; R
T
= 71 kΩ; C
T
= 150 pF.
TC18C4X
TC28C4X
Parameter
Output Section
R
DS
R
DS
2
TC38C4X
Max
15
20
60
60
—
18
8.8
7.9
100
0
300
2
Test Conditions
I
SINK
= 20mA
I
SOURCE
= 20mA
C
L
= 1nF (Note 1)
C
L
= 1nF (Note 1)
In Coulombs (Note 1)
Note 1
x8C43
x8C43
x8C43 (Note 1)
Min
—
—
—
—
—
—
7.9
7.2
95
Typ
7
11
40
30
6.5
—
8.4
7.6
97
Min
—
—
—
—
—
—
7.9
7.2
95
Typ
7
11
35
30
6.5
—
8.4
7.6
97
Max
15
15
60
40
—
18
8.8
7.9
100
0
300
1.5
Units
Ω
Ω
nsec
nsec
nC
V
V
V
%
%
µA
mA
(ON)
(ON)
Rise Time
Fall Time
Cross Conduction
V
DD
Ma
Start Threshold
Undervoltage Threshold
3
Undervoltage Lockout Section
PWM Section
Maximum Duty Cycle
Minimum Duty Cycle
4
Supply Current
Start Up
Operating
T
A
= 25°C, V
IN
< V
UV
; Figure 1
V
FB
= V(I
SENSE
) = 0V; Figure 4
50
170
1
50
170
1
NOTES:
1. These parameters, although guaranteed over the
recommended operating conditions, are not tested in
production.
2. Parameter measured at trip point of latch.
3. Gain ratio is defined as:
∆V
COMP
∆V(I
SENSE
)
where 0
≤
V(I
SENSE
)
≤
0.8V
4. Output frequency equals oscillator frequency for the
x8C43.
5. PSRR of V
REF
, Error Amp and PWM Comparator
combination.
5
TelCom Semiconductor reserves the right to make changes in the circuitry or specifications detailed in this manual at any time without notice. Minimums
and maximums are guaranteed. All other specifications are intended as guidelines only. TelCom Semiconductor assumes no responsibility for the use of
any circuits described herein and makes no representations that they are free from patent infringement.
*Static-sensitive device. Unused devices must be stored in conductive material. Protect devices from static discharge and static fields. Stresses above
those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only and functional operation of
the device at these or any other conditions above those indicated in the operational sections of the specifications is not implied. Exposure to Absolute
Maximum Rating Conditions for extended periods may affect device reliability.
6
PIN DESCRIPTION
Pin No.
8-Pin
Pin No
14-Pin
2
4
1
3
5
7
Pin No
16-Pin
1
2
3
4
5
6
Symbol
NC
NC
CMPTR
V
FB
I
SENSE
R
T
/C
T
Description
No Connection
No Connection
Compensation of the feedback loop response.
Feedback of voltage to error amplifier to regulate voltage.
For sensing pass transistor current and terminate drive when current
limit threshold is reached at this pin.
Capacitor and resistor input to set oscillator frequency of this PWM
controller. The resistor is connected from V
REF
output to R
T
/C
T.
The capacitor is connected from R
T
/C
T
to ANALOG GND.
4-95
7
1
2
3
4
8
TELCOM SEMICONDUCTOR, INC.
TC18C43
TC28C43
TC38C43
PIN DESCRIPTION
(Cont.)
Pin No.
8-Pin
Pin No
14-Pin
6
13
8
9
10
11
12
14
BiCMOS CURRENT MODE
PWM CONTROLLERS
Pin No
16-Pin
7
8
9
10
11
12
13
14
15
16
Symbol
NC
NC
NC
POWER GROUND
ANALOG GND
OUTPUT
V
DD
V
IN
V
REF
NC
Description
No Connection
No Connection
No Connection
Ground return of output driver.
For all the low level analog signal returns.
Output to drive switching transistor gate input.
Supply power input terminal for the output drivers.
Voltage bias supply of all PWM Controller circuit functions.
Reference: 5.0 volt output.
No Connection.
5
6
7
8
REFERENCE SECTION
The reference is a zener-based design with a buffer
amplifier to drive the output. It is unstable with capacitances
between 0.01µF and 3.3µF. In a normal application a 4.7µF
is used. In some lower noise layouts the capacitor can be
eliminated entirely.
The reference is active as soon as the 38C4x has
power supplied. This is different than its bipolar counter-
parts, in that the bipolar reference comes on only after the IC
has come out of its under voltage mode. Thus, on the 38C4x,
the reference pin can not be used as a reset function such
as on a soft start circuit.
f
O
≈
1
(R
T
in Ohms and C
T
in Farads)
R
T
C
T
The value of R
T
affects the discharge current and the
upper and lower comparators each have delays. As R
T
gets
smaller and as the frequency of operation gets higher, the
above equation is no longer valid.
14
VREF (5V)
OSCILLATOR SECTION
The oscillator frequency is set by the combination of a
resistor from the reference to the R
T
/C
T
pin and by a
capacitor from this pin to ground. The oscillator is designed
to have ramp amplitude from 0.15 to 2.5 volts. This is
approximate, as over shoot on the oscillator comparator
causes the ramp amplitude to increase with frequency due
to comparator delay. Minimum values for C
T
and R
T
are
33pF and 1kΩ respectively. Maximum values are depen-
dent on leakage currents in the capacitor, not on the input
currents to the R
T
/C
T
pin.
RT
7
RT/CT
CT
9
GND
PIN NUMBERS FOR 14-PIN DIP
FREQUENCY OF OPERATION
The frequency of oscillation for the TC38C43 is con-
trolled by a resistor to V
REF
(R
T
) and a capacitor to ground
(C
T
). V
REF
supplies current through the resistor and charges
the capacitor until its voltage reaches the threshold of the
upper comparator (≈2.5V). A 2.5mA current is then applied
to the capacitor to discharge it to near ground (≈0.15V). The
discharge current is then shut off and the cycle repeats. An
approximate equation for the frequency of operation is:
4-96
TELCOM SEMICONDUCTOR, INC.
BiCMOS CURRENT MODE
PWM CONTROLLERS
TC18C43
TC28C43
TC38C43
Current is sensed through voltage drop across resistor
RS. A small RC filter may be required to suppress switching
transient. This voltage enters PWM Controller at I
SENSE
,
pin 5. A voltage of 0.4 V is added before this is fed into PWM
Comparator (+) input. The PWM Comparator (–) input
senses the voltage feedback error amp output with a limit
buffer that limits this voltage to 1.4V maximum. This limit
buffer limits the peak current across RS to a maximum of
0.95V. In normal operation, the error amplifier controls the
current limit threshold.
SHUTDOWN METHODS
1
Dead Time
The value of R
T
has an effect on the discharge rate but
the primary consideration is the value of C
T
. The time
required to discharge the capacitor is approximately 1000
C
T
.
UNDERVOLTAGE LOCKOUT RANGE
VIN
2
3
IS
TCx8C43
VON = 8.4V
VOFF = 7.6V
1mA
TCx8C43
14
TCx38C43
TCx38C43
1
VREF
CMPTR
170µA
8.4 V
7.6V
VDD
5k
4
SHUTDOWN
9
ISENSE
ANALOG
GND
5
TO CURRENT
SENSE RESISTOR
Undervoltage Lockout Range
The TCx8C43 PWM Controller is used where wide
ranges of input voltage is not required. The range from
starting V
in
voltage threshold to under voltage threshold is
approximately 9.5% of the starting voltage. The typical start-
up voltage is 8.4V and dropout voltage is 7.6V. This range
is used most in DC-to-DC converter applications.
5.1k
SHUTDOWN
5
Duty Cycle Limit
The TCx8C43 PWM Controller has a duty cycle limit
maximum of 99%. The oscillator is running at the same
frequency as the output.
CURRENT SENSE CIRCUIT
ISENSE
R
5
0.4V
PWM
COMPARATOR
Shutdown can be accomplished by either pulling I
SENSE
above 1 volt or pulling CMPTR, pin 1 to GND. This will set the
PWM latch so that the output will remain low until the next
clock pulse after the shutdown condition is removed.
BENCH TEST OPERATIONAL SIMULATION
The timing ramp (R
T
/C
T
) is buffered by the emitter
fullpower and fed back to the I
SENSE
input. This ramp
simulates the dI/dT current ramp which would flow through
the primary of the transformer. The output voltage of the
power supply is simulated by feeding some of the reference
voltage into V
FB
. The combination of the two levels deter-
mined the operating characteristics of the current mode
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