CS3865C
CS3865C
High Performance Dual Channel
Current Mode Controller with ENABLE
Description
The CS3865C is a high perfor-
mance, fixed frequency, dual cur-
rent mode controller. It is used in
Off-Line and DC to DC converter
applications and require a mini-
mum number of external compo-
nents. This integrated circuit fea-
tures a unique oscillator for precise
duty cycle limit and frequency con-
trol, a temperature compensated
reference, two high gain error
amplifiers, two current sensing
comparators, and two high current
totem pole outputs ideally suited
for driving power MOSFETs. One
of the outputs V
OUT2
is switchable
via the ENABLE
2
pin.
Also included are protective fea-
tures consisting of input and refer-
ence undervoltage lockouts each
with hysteresis, cycle-by-cycle cur-
rent limiting, and a latch for single
pulse metering of each output.
The CS3865C has a 14V start volt-
age and is pin compatible with the
MC34065H.
Features
s
Oscillator has Precise
Duty Cycle
Limit and Frequency
Control
s
500kHz Current Mode
Operation
s
Automatic Feed Forward
Compensation
s
Separate Latching PWMs
for Cycle-By-Cycle
Current Limiting
s
Internally Trimmed
Reference with
Undervoltage Lockout
s
Switchable Second
Output
s
Two High Current Totem
Pole Outputs
s
Input Undervoltage
Lockout with Hysteresis
s
Low Start-Up and
Operating Current
Block Diagram
V
CC
V
REF
5.0V Ref
V
CC
Undervoltage
Lockout
V
REF
Undervoltage
Lockout
SYNC
C
T
R
T
Latching
PWM 1
Oscillator
V
OUT
1
Package Options
Sense
1
+
V
FB1
16L PDIP & SO Wide
SYNC
1
C
T
2
R
T
3
16
15
14
13
12
11
10
9
-
Error
Amp 1
COMP
1
ENABLE
2
Latching
PWM 2
V
OUT2
V
CC
V
REF
ENABLE
2
V
FB2
COMP
2
Sense
2
V
OUT2
Pwr Gnd
V
FB1
4
V
FB2
+
-
Error
Amp 2
COMP
2
Sense
2
COMP
1
5
Sense
1
6
V
OUT1
7
Gnd
8
Gnd
Pwr Gnd
Cherry Semiconductor Corporation
2000 South County Trail, East Greenwich, RI 02818
Tel: (401)885-3600 Fax: (401)885-5786
Email: info@cherry-semi.com
Web Site: www.cherry-semi.com
Rev. 12/16/96
1
A
®
Company
CS3865C
Absolute Maximum Ratings
Total Power Supply and Zener Current .........................................................................................................................50mA
Output Current, Source or Sink (Note 1)...........................................................................................................................1.0A
Output Energy (capacitive load per cycle) .......................................................................................................................5.0µJ
Current Sense, Enable and Voltage ......................................................................................................................-0.3 to +5.5V
Feedback Inputs
High State (Voltage)..........................................................................................................................................5.5V
Low State (Reverse Current) ......................................................................................................................-5.0mA
Error Amp Output Sink Current......................................................................................................................................10mA
Storage Temperature Range ................................................................................................................................-65 to +150°C
Operating Junction Temperature...................................................................................................................................+150°C
Operating Ambient Temperature.............................................................................................................................0 to +70°C
Lead Temperature Soldering
Wave Solder (through hole styles only) .................................................................................10 sec. max, 260°C peak
Reflow (SMD styles only) ..................................................................................60 sec. max above 183°C, 230°C peak
Electrical Characteristics:
V
CC
= 15V, R
T
= 8.2kΩ, C
T
= 3.3nF, for typical values T
A
=25˚C, for min/max values T
A
is the operating
ambient temperature range that applies [Note 3].
TEST CONDITIONS
MIN
PARAMETER
TYP
MAX
UNIT
s
Reference Section
Reference Output Voltage,
V
REF
Line Regulation
Load Regulation
Total Output Variation over
Line, Load and Temperature
Output Short Circuit Current
s
Oscillator and PWM Sections
Total Frequency Variation
over Line and Temperature
Frequency Change with
Voltage
Duty Cycle at each Output
Sync Input Current
11V≤V
CC
≤15V,
T
low
≤T
A
≤T
high
11V≤V
CC
≤15V
Maximum
High State V
IN
=2.4V
Low State V
IN
=0.8V
46.0
46.5
49.0
0.2
49.5
170
80
51.5
1.0
52.0
250
160
kHz
%
%
µA
I
OUT
=1.0mA, T
J
=25°C
11V≤V
CC
≤15V
1.0mA≤I
OUT
≤10mA
4.85
30
100
4.9
5.0
2.0
3.0
5.1
20.0
25.0
5.15
V
mV
mV
V
mA
s
Error Amplifiers
Voltage Feedback Input
Input Bias Current
Open-Loop Voltage Gain
Unity Gain Bandwidth
Output Current
Output Voltage Swing
V
OUT
=2.5V
V
FB
=5.0V
V
OUT
=2.0 to 4.0V
T
J
=25°C (note 6)
Source V
OUT
=3.0V, V
FB
=2.3V
Sink V
OUT
=1.2V, V
FB
=2.7V
High State, R
L
=15k to ground,
V
FB
=2.3V
Low State, R
L
=15k to V
REF
,
V
FB
= 2.7V
2
65
0.7
60
-0.45
2.00
5.0
2.42
2.50
-0.1
100
1.0
90
-1.00
12.00
6.2
0.8
1.1
2.58
-1.0
V
µA
dB
MHz
dB
mA
mA
V
Power Supply Rejection Ratio V
CC
=11V to 15V
CS3865C
Electrical Characteristics:
V
CC
= 15V, R
T
= 8.2kΩ, C
T
= 3.3nF, for typical values T
A
=25˚C, for min/max values T
A
is the operating
ambient temperature range that applies [Note 3].
TEST CONDITIONS
MIN
PARAMETER
TYP
MAX
UNIT
s
Current Sense Section
Current Sense Input
Voltage Gain
Maximum Current Sense
Input Threshold
Input Bias Current
Propagation Delay
s
Output 2 Enable Pin
Enable Pin Voltage
High State
Low State
Low State Input Current
s
Drive Outputs
Output Voltage
Low State
High State
Output Voltage with
UVLO Activated
Output Voltage Rise Time
Output Voltage Fall Time
I
SINK
=20mA
I
SINK
=200mA
I
SOURCE
=20mA
I
SOURCE
=200mA
V
CC
=6.0V, I
SINK
=1.0mA
C
L
=1.0nF (Note 6)
C
L
=1.0nF (Note 6)
0.1
1.6
13.5
13.4
0.1
28
25
0.4
2.5
V
V
V
V
V
ns
ns
Output 2 enabled
Output 2 disabled
V
IL
= 0V
3.5
0.0
100
250
V
REF
1.5
400
V
V
µA
Current Sense Input to Output (Note 6)
(Notes 4 and 5)
(Note 4)
2.75
430
3.00
480
-2.0
150
3.25
530
-10.0
300
V/V
mV
µA
ns
13.0
12.0
1.1
150
150
s
Undervoltage Lockout Section
Start-Up Threshold
Minimum Operating Voltage
After Turn-On
Hysteresis
s
Total Device
Start-Up Current
Operating Current
V
CC
=12V
(Note 7)
15.5
0.6
20
17.0
1.0
25
19.0
mA
mA
V
CS3865C
13
9.0
14
10.0
4
15
11.0
V
V
V
Power Supply Zener Voltage I
CC
=30mA
Note 1: Maximum package power dissipation limits must be observed.
Note 3: Adjust V
CC
above the Start-Up threshold before setting to 15V.
Note 4: This parameter is measured at latch trip point with V
FB
=0V.
Note 5: Comparator gain is defined as:
∆V
Compensation
AV =
∆V
Current Sense
Note 6: These parameters are guaranteed by design but not 100% tested
in production.
Note 7: Low duty cycle pulse techniques are used during test to main-
tain junction temperature as close to ambient as possible: T
low
=0°C ;
T
high
=+70°C
3
CS3865C
Package Pin Description
PACKAGE PIN #
PIN SYMBOL
FUNCTION
16 L PDIP & SO Wide
1
SYNC
A positive going pulse applied to this input will synchronize the
oscillator. A DC voltage within the range of 2.4V to 5.5V will inhibit
the oscillator.
Timing capacitor C
T
connects pin to ground setting oscillator fre-
quency.
Resistor R
T
connects to ground setting the charge current for C
T
. Its
value must be between 4.0k and 16k.
The inverting input of error amplifier 1. Normally it is connected to
the switching power supply output.
The output of error amplifier 1, for loop compensation.
Output 1 pulse by pulse current limit.
Drives the power switch at output 1.
Logic ground
Power ground. Power device return is connected to this pin.
Drives the power switch at output 2.
Output 2 pulse by pulse current limit.
Output of error amplifier 2, for loop compensation.
Inverting input of error amplifier 2. Normally it is connected to the
switching power supply output.
Output 2 disable. A logic low at this pin disables V
OUT2
.
5.0V reference output. It can source current in excess of 30mA.
The positive supply of the IC.
Typical Performance Characteristics
Timing Resistor vs. Oscillator Frequency
16
MAXIMUM DUTY CYCLE (%)
R
T
TIMING RESISTOR (KΩ)
100p
1.0n
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
C
T
R
T
V
FB1
COMP
1
Sense
1
V
OUT1
Gnd
Pwr Gnd
V
OUT2
Sense
2
COMP
2
V
FB2
ENABLE
2
V
REF
V
CC
Max. Output Duty Cycle vs. Oscillator Frequency
50
48
46
44
42
40
38
10k
V
CC
= 15V
R
T
= 4.0kΩ to 16kΩ
C
L
= 15pF
T
A
= 25°C
30k
50k
100k
300k
500k
1.0M
OUT 1
OUT 2
14
2.2n
p
220
330
F
F
500
F
3.3
pF
12
C
T
=
10n
F
pF
F
5.0
nF
nF
10
8.0
V
CC
=
6.0 15V
T
A
=25°C
4.0
10k
30k
50k
100k
300k
500k
1.0M
f
OSC
OSCILLATOR FREQUENCY (Hz)
f
OSC
OSCILLATOR FREQUENCY (Hz)
Error Amp Open-Loop Gain & Phase vs. Frequency
A
VOL
, OPEN-LOOP VOLTAGE GAIN (dB)
100
80
60
40
20
0
-20
10k
GAIN
V
CC
= 15V
V
O
= 1.5V TO 2.5V
R
L
= 100kΩ
T
A
= 25°C
PHASE
0
30
60
90
120
150
180
10M
Phase Margin (DEGREES)
Vth, CURRENT SENSE
INPUT THRESHHOLD (V)
0.6
Current Sense Input Threshold
vs. Error Amp Output Voltage
V
CC
= 15V
0.5
0.4
0.3
0.2
0.1
0
0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
ERROR AMP OUTPUT VOLTAGE (V)
T
A
= 125°C
T
A
= 25°C
T
A
= -55°C
100k
1.0k
10k
100k
1.0M
f, FREQUENCY (Hz)
4
CS3865C
Typical Performance Characteristics: continued
Reference Voltage Change vs. Source Current
0
V
CC
= 15V
∆
V
REF
, REFERENCE
Voltage (mV)
-4.0
-8.0
-12
-16
-20
-24
0
20
40
60
80
100
I
ref
, REFERENCE SOURCE CURRENT (mA)
120
T
A
= 125°C
T
A
=
25°C
Reference Short Circuit Current vs. Temperature
I
SC
, REFERENCE
SHORT CIRCUIT CURRENT (mA)
120
T
A
= –55°C
100
80
60
-55
-25
0
25
50
75
100
125
T
A
, AMBIENT TEMPERATURE (°C)
Output Saturation Voltage vs. Load Current
0
V
CC
SOURCE SATURATION
(LOAD TO GROUND)
V
CC
=15V
80µS PULSED LOAD
120Hz RATE
T
A
=25°C
Supply Current vs. Supply Voltage CS3865C
32
I
CC,
SUPPLY CURRENT (mA)
R
T
=8.2kΩ
C
T
=3.3nF
V
FB
1.2=0V
CURRENT SENSE 1.2=0V
T
A
=25°C
V
sat
, OUTPUT
SATURATION VOLTAGE (V)
-1.0
-2.0
24
T
A
= –55°C
16
2.0
1.0
0
0
T
A
= –55°C
T
A
=25°C
GND
8.0
SINK
SATURATION
(LOAD TO V
CC
)
0
800
0
4.0
8.0
12
16
20
V
CC,
SUPPLY VOLTAGE (V)
200
400
600
OUTPUT LOAD CURRENT (mA)
Operating Description
The CS3865C is a high performance, fixed frequency, dual
channel current mode PWM controller specifically
designed for off-line and DC to DC converter applications.
It offers the designer a cost effective solution with minimal
external components where independent regulation of two
power converters is required. Each channel contains a high
gain error amplifier, current sensing comparator, pulse
width modulator latch, and totem pole output driver. The
oscillator, reference, and undervoltage lockout circuits are
common to both channels.
Oscillator
The oscillator uses precise frequency and duty cycle con-
trol. The frequency is programmed by the values R
T
and
C
T
. Capacitor, C
T
, is charged and discharged by an equal
magnitude internal current source and sink, generating a
symmetrical 50 percent duty cycle waveform at C
T
. The
oscillator peak and valley thresholds are 3.5V and 1.6V
respectively. The source/sink current magnitude is con-
trolled by resistor R
T
. For proper operation over tempera-
ture range, its value should be between 4.0kΩ and 16kΩ.
As C
T
charges and discharges, an internal blanking pulse
is generated that alternately drives the inputs of the upper
and lower NOR gates high. This, in conjunction with a
precise amount of delay time introduced into each chan-
nel, produces well defined non-overlapping output duty
cycles. The second output, V
OUT2
is enabled while C
T
is
5
charging, and the primary is enabled during the discharge.
Even at 500kHz, each output is capable of approximately
44% duty cycle, making this controller suitable for high
frequency power conversion applications.
In many noise sensitive applications, it may be necessary
to synchronize the converter with an external system
clock. This can be accomplished by applying an external
clock signal. For reliable synchronization, the oscillator fre-
quency should be set about 10% slower than the clock fre-
quency. The rising edge of the clock signal applied to
SYNC, terminates C
T
‘s charging and V
OUT2
‘s conduction.
By tailoring the clock waveform symmetry, accurate duty
cycle clamping of either output can be achieved.
Error Amplifier
Each channel contains a fully-compensated error amplifi-
er. The output and inverting input nodes are accessible.
The amplifier features a typical dc voltage gain of 100 dB,
and a unity gain bandwidth of 1.0 MHz with 71 degrees of
phase margin. The non-inverting input is internally biased
at 2.5V. The converter output voltage is typically divided
down and monitored by the inverting input through a
resistor divider. The maximum input bias current is -1.0µA
which will cause an output voltage error that is equal to
the product of the input bias current and the equivalent
input divider resistance.
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