Document Outline
- Return to Contents
- List of Figures
- 1. R1 and R2 Set Maximum Peak Output Current
- 2. Resistive Sensing
- 3. Transformer Isolated Current Sense
- 4. Master/Slave Parallel Operation
- 5. External Clock Synchronization
- 6 . Oscillator Circuit
- 7. Oscillator Frequency vs Oscillator Resistance
- Features
- Ordering Information
- Functional Block Diagram
- General Description
- Absolute Maximum Ratings*
- Electrical Characteristics: VIN = 16V, RO = 24kW, CO = 1 nF, TA = 25C, unless otherwise indicated.
- Pin Description
- Pin Configurations
- Peak Current Limit Setup
- Output Shutdown
- Soft Restart From Shutdown
- Soft-Start Power-Up
- Current-Sense Amplifier
- Undervoltage Lockout
- Circuit Synchronization
- Oscillator Frequency and Output Dead Time
- Typical Characteristics
4-119
TELCOM SEMICONDUCTOR, INC.
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TC170
CMOS CURRENT MODE PWM CONTROLLER
FEATURES
s
Low Supply Current With
CMOS Technology ................................. 3.8mA Max
s
Internal Reference ............................................. 5.1V
s
Fast Rise/Fall Times (C
L
= 1000pF) ............. 50nsec
s
Dual Push-Pull Outputs
s
Direct-Power MOSFET Drive
s
High Totem-Pole Output Drive .................... 300mA
s
Differential Current-Sense Amplifier
s
Programmable Current Limit
s
Soft-Start Operation
s
Double-Pulse Suppression
s
Undervoltage Lockout
s
Wide Supply Voltage Operation ............... 8V to16V
s
High Frequency Operation .......................... 200kHz
s
Available with Low OFF State Outputs
s
Low Power, Pin-Compatible Replacement for UC3846
ORDERING INFORMATION
Temperature
Part No.
Package
Range
TC170COE
16-Pin SOIC (Wide)
0
C to +70
C
TC170CPE
16-Pin Plastic DIP (Narrow) 0
C to +70
C
GENERAL DESCRIPTION
The TC170 brings low-power CMOS technology to the
current-mode-switching power supply controller market.
Maximum supply current is 3.8 mA. Bipolar current-mode
control integrated circuits require five times more operating
current.
The dual totem-pole CMOS outputs drive power
MOSFETs or bipolar transistors. The 50nsec typical output
rise and fall times (1000pF capacitive loads) minimize
MOSFET power dissipation. Output peak current is 300mA.
The TC170 contains a full array of system-protection
circuits (see features).
Current-mode control lets users parallel power supply
modules. Two or more TC170 controllers can be slaved
together for parallel operation. Circuits can operate from a
master TC170 internal oscillator or an external system
oscillator.
The TC170 operates from an 8V to 16V power supply.
An internal 2%, 5.1V reference minimizes external compo-
nent count. The TC170 is pin compatible with the Unitrode
UC1846/2846/3846 bipolar controller.
Other advantages inherent in current-mode control in-
clude superior line and load regulation and automatic sym-
metry correction in push-pull converters.
+
5.1-VOLT
REFERENCE
OSCILLATOR
3.15 CURRENT
AMPLIFIER
PWM
COMPARATOR
POSITIVE
FEEDBACK
15
9
10
3
4
7
5
8
6
VIN
SYNC
() CURRENT
SENSE INPUT
(+) CURRENT
SENSE INPUT
COMP
(+) ERROR
AMP INPUT
() ERROR
AMP INPUT
ERROR
AMPLIFIER
100A
0.75V
LIMIT BUFFER
AMPLIFIER
Q4
350mV
LOCK-UP
AMPLIFIER
Q3
Q1
Q2
3.5k
SHUTDOWN
COMPARATOR
350
mV
6k
SHUTDOWN
CURRENT LIMIT/
SOFT-START ADJUST
NOTE: Outputs low in
OFF state.
16
1
S
S
R
Q
C
D Q
Q
GROUND
VDD
OUTPUT
A ( )
12
14
11
13
PWM LATCH
TC170
VREF
2
+
RO
CO
VDD
+
+
+
+
+
UNDERVOLTAGE
LOCKOUT
OUTPUT
B ( )
TC170-5 10/1/96
FUNCTIONAL BLOCK DIAGRAM
4-120
TELCOM SEMICONDUCTOR, INC.
ELECTRICAL CHARACTERISTICS:
V
IN
= 16V, R
O
= 24k
, C
O
= 1 nF, T
A
= 25
C, unless otherwise indicated.
Symbol
Parameter
Test Conditions
Min
Typ
Max
Unit
Reference Voltage
V
REF
Output Voltage
I
OUT
= 1mA
5
5.1
5.3
V
Line Regulation
V
IN
= 8V to 16V
5
15
mV
Load Regulation
I
OUT
= 1mA to 10mA
13
20
mV
V
RTC
Temperature Coefficient
Over Operating Temperature Range
0.4
0.5
mV/
C
Oscillator
Oscillator Frequency
35
42
46
kHz
Voltage Stability
V
IN
= 8V to 16V
1.1
1.5
%/V
Temperature Stability
Over Operating Temperature Range
5
10
%
Error Amplifier
V
OS
Input Offset Voltage
30
mV
I
B
Input Bias Current
1
nA
V
CMRR
Common-Mode Input Voltage
V
IN
= 8V to 16V
0
V
DD
2V
V
A
VOL
Open-Loop Voltage Gain
V
OUT
= 1V to 6V
70
dB
BW
Unity Gain Bandwidth
1.2
MHz
CMRR
Common-Mode Rejection Ratio
V
CMV
0V to 14V
60
dB
PSRR
Power Supply Rejection Ratio
V
IN
= 8V to 16V
60
dB
Current Sense Amplifier
Amplifier Gain
Pin 3 = 0V to 1.1V
3
3.15
3.3
V/V
Maximum Differential Input Signal
V
PIN4
V
PIN3
1.1
V
Common-Mode Input Voltage
0
V
DD
3V
V
Current Limit Adjust
Current Limit Offset Voltage
0.5
1
V
I
B
Input Bias Current
1
nA
Shutdown Terminal
V
TB
Threshold Voltage
0.3
0.35
0.4
V
V
IN
Input Voltage Range
0
V
DD
V
Minimum Latching Current at Pin 1
125
A
Maximum Nonlatching Current at Pin 1
50
A
Output Stage
V
DD
Output Voltage
Pin 13
V
IN
0. 5
V
IN
V
IN
+ 0.5
V
V
OL
Output Low Level
I
SINK
= 20mA
0.4
V
V
OL
Output Low Level
I
SINK
= 100mA
2
V
ABSOLUTE MAXIMUM RATINGS*
Supply Voltage ............................................................ 18V
Output Voltage ................................................ V
DD
or 18V
Analog Inputs ..................................... 0.3V to V
S
+ 0.3V
Storage Temperature Range ................ 65
C to +150
C
Lead Temperature (Soldering, 10 sec) ................. +300
C
Maximum Chip Temperature ................................... 150
C
Plastic Package Thermal Resistance:
JA
(Junction to Ambient) ............................. 140
C/W
JC
(Junction to Case) ................................... 70
C/W
CMOS CURRENT MODE
PWM CONTROLLER
TC170
Operating Temperature Range
Commercial ........................................... 0
C to +70
C
*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 perma-
nent 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.
4-121
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ELECTRICAL CHARACTERISTICS (Cont.):
V
IN
= 16V, R
O
= 24k
, C
O
= 1nF, T
A
= 25
C, unless otherwise indicated.
Symbol
Parameter
Test Conditions
Min
Typ
Max
Unit
Output Stage (Cont.)
V
OH
Output High Level
I
SOURCE
= 20mA
V
DD
1V
V
V
OL
Output High Level
I
SOURCE
= 100mA
V
DD
4V
V
t
R
Output Rise Time
C
L
= 1000pF
50
150
nsec
t
F
Output Fall Time
C
L
= 1000pF
50
150
nsec
Undervoltage Lockout
Start-Up
Threshold
7.15
7.7
8.25
V
Threshold Hysteresis
0.5
0.75
1
V
Supply
I
S
Standby Supply Current
2.7
3.8
mA
Pin No.
(16-Pin PDIP)
Symbol
Description
1
SOFT START/I
LIM
Soft Start Adjust / Current Limit. For setting the peak current threshold of sense inputs (pins
3 and 4). Second function of this pin is Soft-Start Adjust.
2
V
REF
OUT
Reference supply output of 5.1 volts. It can supply a minimum of 10mA.
3
I
SENSE
IN
Current Sense Input. Inverting input for sensing peak current of the pass transistor
through series sense current monitor resistor.
4
+ I
SENSE
IN
+ Current Sense Input. Non-inverting input used in conjunction with pin 3. This senses the
positive end of current monitor resistor.
5
+ ERROR AMP IN
+ Error Amp In. Non-inverting input for output voltage regulation.
6
ERROR AMP IN
Error Amp In. Inverting input of the amplifier for the reference voltage.
7
CMPTR
For compensation of the feedback loop response.
8
C
O
Timing capacitor (C
O)
input to set oscillator frequency in conjunction with pin 9, R
O
, resistor
input. Second function is for setting crossover dead time of pin 11and 14 outputs.
9
R
O
Timing resistor (R
O)
input to set oscillator frequency by setting constant current charge rate
to charge capacitor C
O
.
10
SYNC
For PWM controller oscillator synchronization of two or more controllers. or as a clock input
to sync oscillator from external signal.
11
OUTPUT A
A output drive of phase A from push pull transistors.
12
GND
Ground return for all input and output pins.
13
V
DD
Supplies power to operate the output drivers only.
14
OUTPUT B
Output of phase B from push pull transistors.
15
V
IN
Voltage bias supply for all TC170 circuits except the output transistors.
16
SHUTDOWN
Input pin to disable both output drives to 0V OFF.
PIN CONFIGURATIONS (DIP and SOIC)
TC170
CPE
SHDN
VDD
SOFT START/
ILIM
OUTPUT B
VREF
I SENSE IN
+ I SENSE IN
+ ERROR AMP IN
CMPTR
GND
OUTPUT A
SYNC
RO
OUT
ERROR AMP IN
NOTE: Outputs LOW in "OFF" state.
VIN
CO
1
2
3
4
16
15
14
13
5
6
7
12
11
10
9
8
ACOM
1
2
3
4
15
16
14
13
5
6
7
12
11
10
9
8
TC170COE
BUF
VSS
CINT
+
VREF
CREF
CREF
CAZ
CMPTR OUT
A
DIGITAL GND
B
VDD
+
+
VIN
VIN
VREF
CMOS CURRENT MODE
PWM CONTROLLER
TC170
PIN DESCRIPTION
4-122
TELCOM SEMICONDUCTOR, INC.
CMOS CURRENT MODE
PWM CONTROLLER
TC170
Peak Current Limit Setup
Resistors R1 and R2 at the current limit input (pin 1)
set the TC170 peak current limit (Figure 1). The potential at
pin 1 is easily calculated:
V1 = V
REF
R2
R1 + R2
R1 should be selected first. The shutdown circuit fea-
ture is not latched for (V
REF
0.35)/R1 < 50
A and is
latched for currents greater than 125
A.
The error amplifier output voltage is clamped from
going above V1 through the limit buffer amplifier. Peak
current is sensed by RS and amplified by the current
amplifier which has a fixed gain of 3.15.
I
PCL
, the peak current limit, is the current that causes
the PWM comparator noninverting input to exceed V1, the
potential at the inverting input. Once the comparator trip
point is exceeded, both outputs are disabled.
I
PCL
is easily calculated:
I
PCL
=
V1 0.75V
3.15 (RS)
where:
V1 = V
REF
V
REF
= Internal voltage reference = 5.1V
3.15 = Gain of current-sense amplifier
0.75V = Current limit offset
Both driver outputs (pins 11 and 14) are OFF (LOW)
when the peak current limit is exceeded. When the sensed
current goes below I
PCL
, the circuit operates normally.
Output Shutdown
The TC170 outputs can be turned OFF quickly through
the shutdown input (pin 16). A signal greater than 350 mV
at pin 16 forces the shutdown comparator output HIGH.
The PWM latch is held set, disabling the outputs.
Q2 is also turned ON. If V
REF
/R1 is greater than 125
A,
positive feedback through the lock-up amplifier and Q1
keeps the inverting PWM comparator inverting input below
0.75V. Q3 remains ON even after the shutdown input
signal is removed, because of the positive feedback. The
state can be cleared only through a power-up cycle. Out-
puts will be disabled whenever the potential at pin 1 is
below 0.75V.
The shutdown terminal gives a fast, direct way to dis-
able the TC170 output transistors. System protection and
remote shutdown applications are possible.
R2
R1 + R2
The input pulse to pin 16 should be at least 500 nsec
wide and have an amplitude of at least 1V in order to get the
minimum propagation delay from input to output. If these
parameters are met, the delay should be less than
600nsec at 25
C; however, the delay time will increase as
the device temperature rises.
Soft Restart From Shutdown
A soft restart can be programmed if nonlatched shut-
down operation is used.
A capacitor at pin 1 will cause a gradual increase in
potential toward V1. When the voltage at pin 1 reaches
0.75V, the PWM latch set input is removed and the circuit
establishes a regulated output voltage. The soft-start opera-
tion forces the PWM output drivers to initially operate with
minimum duty cycle and low peak currents.
Even if a soft start is not required, it is necessary to
insert a capacitor between pin 1 and ground if the current I
L
is greater than 125
A. This capacitor will prevent "noise
triggering" of the latch, yet minimize the soft-start effect.
Soft-Start Power-Up
During power-up, a capacitor at R1, R2 initiates a soft-
start cycle. As the input voltage (pin 15) exceeds the
undervoltage lockout potential (7.7V), Q4 is turned OFF,
ending undervoltage lockout. Whenever the PWM com-
parator inverting input is below 0.5V, both outputs are
disabled.
When the undervoltage lockout level is passed, the
capacitor begins to charge. The PWM duty cycle increases
until the operating output voltage is reached. Soft-start
operation forces the PWM output drivers to initially operate
with minimum duty cycle and low peak current.
Current-Sense Amplifier
The current-sense amplifier operates at a fixed gain of
3.15. Maximum differential input voltage (V
PIN4
V
PIN3
) is
1.1V. Common-mode input voltage range is 0V to V
IN
3V.
Resistive-sensing methods are shown in Figure 2. In
Figure 2(A), a simple RC filter limits transient voltage spikes
at pin 4, caused by external output transistor-collector
capacitance. Transformer coupling (Figure 3) offers isola-
tion and better power efficiency, but cost and complexity
increase.
In order to minimize the propagation delay from the input
to the current amplifier to the output terminals, the current
ramp should be in the order of 1
s in width (min). Typical
time delay values are in the 300 to 400nsec region at 25
C.
The delay time increases with device temperature so that at
50
C, the delay times may be increased by as much as
100nsec.
4-123
TELCOM SEMICONDUCTOR, INC.
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CMOS CURRENT MODE
PWM CONTROLLER
TC170
4
3
3.15 CURRENT-
SENSE
AMPLIFIER
C
R*
(A) Ground Reference
*OPTIONAL RC FILTER
I
I
4
3
TC170
VOUT
RS
(B) Above-Ground Resistive Sensing
TC170
RS
3.15 CURRENT-
SENSE AMPLIFIER
+
+
Figure 1. R1 and R2 Set Maximum Peak Output Current
Figure 2. Resistive Sensing
TC170
SWITCH
CURRENT
3.15 CURRENT-SENSE
0.75V
+
4
3
7
5
6
VDD
100 A
V1
ERROR
AMPLIFIER
POSITIVE
FEEDBACK
Q2
350mV
Q3
SHUTDOWN
COMPARATOR
350mV
6k
Q4
FROM
UNDERVOLTAGE
LOCKOUT
10
PWM LATCH
S
S
R
Q
LOCK-UP
AMPLIFIER
I L
3.5k
Q1
PWM COMPARATOR
"A" = 1
OUTPUT
OFF (LOW)
VREF
5.1V
2
V1
R2
16
LIMIT
BUFFER
AMPLIFIER
RS
R1
AMPLIFIER
1
+
+
+
+
+
+
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