Datasheet CR6853, CR6853S, CR6853T Datasheet (Chip-Rail)

Novel Low Cost Green-Power PWM Controller

Feature

 Low Cost, PWM&PFM&CRM (Cycle

Reset Mode)

 Low Start-up Current (about 1.5µA)
 Low Operating Current (about 1.4mA)
 Current Mode Operation
 Under Voltage Lockout (UVLO)
 Built-in Synchronized Slope

Compensation

 Built-in Low EMI Technique
 Programmable PWM Frequency
 Audio Noise Free Operation
 Leading edge Blanking on Sense input
 Constant output power limiting for

universal AC input Range

 SOT-23-6L 、SOP8 and DIP-8 Pb-Free

Applications

 Switching AC/DC Adaptor
 Battery Charger
 Open Frame Switching Power Supply

General Description

The CR6853 is a highly integrated low cost
current mode PWM controller, which is ideal
for small power current mode of offline
AC-DC fly-back converter applications.
Making use of external resistors, the IC
changes the operating frequency and
automatically enters the PFM/CRM (Cycle
Reset Mode) under light-load/zero-load
conditions. This can minimize standby
power consumption and achieve power­saving functions. With a very low start-up
current, the CR6853 could use a large value
start-up resistor (2MΩ).
Built-in synchronized slope compensation
enhances the stability of the system and
avoids sub-harmonic oscillation. Dynamic
peak current limiting circuit minimizes output
power change caused by delay time of the
system over a universal AC input range.
Leading edge blanking circuit on current

CR6853

With Low EMI Technique

Packaging

 Compatible with SG6848 (6849) /

SG5701/SG5848/LD7535 (7550) /
OB2262 (2263)/OB2278（（（（2279））））

 Complete Protection with
 Soft Clamped GATE output voltage

18.0V

 VDD over voltage protect 34.0V
 Cycle-by-cycle current limiting
 Sense Fault Protection
 OTP (Over Temperature Protection)
 Output SCP (Short circuit Protection)
 Output OLP (Over Load Protection)
 Latch mode After OLP&SCP
 High-Voltage CMOS Process with ESD

 Standby Power Supplies
 Set-Top Box Power Supplies
 384X Replacement

sense input could remove the signal glitch
due to snubber circuit diode reverse
recovery and thus greatly reduces the
external component count and system cost
in the design. Cycle-by-Cycle current
limiting ensures safe operation even during
short-circuit.
Excellent EMI performance is achieved
built-in soft driver and low EMI technique.
The CR6853 offers perfect protection like
OVP(Over Voltage Protection)、OLP(Over

Load Protection) 、 SCP(Short circuit
protection)、OTP、Sense Fault Protection

and OCP(Over current protection). The
CR6853’s output driver is soft clamped to
maximum 18.0V to protect the power
MOSFET. CR6853 is offered in SOT-23-6L,
SOT-8 and DIP-8 packages.

Dec, 2007 V1.1 1/11

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CR6853

Pin Assignment

Pin Descriptions

Name Description

GND GND Pin

Voltage feedback pin. Output current of this pin could controls the PWM

FB

duty cycle、OLP and SCP.

RI

SEN

VDD

GATE

This pin is to program the switching frequency. By connecting a resistor
to ground to set the switching frequency.
Current sense pin, a resistor connects to sense the MOSFET current.
Supply voltage pin.
Totem output to drive the external power MOSFET.

TYPICAL APPLICATION

Dec, 2007 V1.1 2/11

Chengdu Chip-Rail Tech. Co., Ltd. http://www.chiprail.com

8 (10S)

CR6853

Block Diagram

Simplified Internal Circuit Architecture

Absolute Maximum Ratings

Symbol Parameter Rating Unit

V

DD

I

OVP

V

FB

V

SEN

P

D

T

L

T

STG

Supply voltage Pin Voltage 40 V
VDD OVP maximal enter current 20 mA
Input Voltage to FB Pin -0.3 to 6V V
Input Voltage to SEN Pin -0.3 to 6V V
Power Dissipation 300 mW
ESD Capability, HBM Model 2500 V
ESD Capability, Machine Model 250 V

Lead Temperature
(Soldering)

Storage Temperature Range -55 to + 150

SOT-23-6L (20S)
DIP­SOP-8 (10S)

220
260
230

℃
℃
℃
℃

RECOMMENDED OPERATION CONDITION

Symbol Parameter Min ~ Max Unit

VDD VDD Supply Voltage 10~30 V
RI RI PIN Resistor Value 100 K ohm
TOA Operation Ambient Temperature -20~85

P

Maximal Output Power 0~80 W

OMAX

F

PWM

Frequency of PWM 30~150 kHz

℃

Dec, 2007 V1.1 3/11

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CR6853

Electrical Characteristics

Symbol

Supply Voltage (VDD Pin)

VDD
VDD
VDD

I

ST

I

SS

ON

OFF

CLAMP

Startup Current 3.0 20.0

Operating Current

Turn-on Threshold Voltage 13.0 14.0 15.0 V

Turn-off Threshold Voltage 7.8 8.8 9.8 V

VDD Clamp Voltage I
Anti Intermission Surge

VDD

AIS

VDD Voltage

T

OFF

T

RESTART

Over temperature Protection 130
Temperature restart 100

Parameter Conditions Min. Typ. Max. Unit

(Ta=25°C unless otherwise noted, VDD = 15V)

VFB=0V 3.0
VFB=3V 1.4
VFB=Open 1.0

=10mA 34.0

VDD

12.7

µA
mA
mA
mA

V

V

℃
℃

Voltage Feedback (FB Pin)

IFB Short Circuit Current VFB=0V 1.2

VFB Open Loop Voltage VFB=Open 4.8

I

Zero Duty Cycle FB current 1.47

FB_0D

I

PFM

I

CRM

V

PFM

V

CRM

I

OLP&SCP

V

OLP&SCP

T

OLP&SCP

Enter PFM FB current 1.37
Enter CRM FB current 1.45

Enter PFM Threshold V

FB

0.51

Enter CRM Threshold VFB 0.30

Enter OLP&SCP FB current 152
Enter OLP&SCP FB voltage 3.7
OLP&SCP min. delay Time RI=100K 33 35 50 mS

Current Sensing (SEN Pin)

SEN Minimum Voltage Level RI=100K,

V

TH_L

0.70

FB=3.3V

mA
V
mA
mA
mA
V
V
uA
V

V

V

TH_H

0.80

V

FB=3.3V

TPD Delay to Output FB=3.3V 75 ns

SEN Maximum Voltage Level RI=100K,

RCS Input Impedance

V

SCP

Dec, 2007 V1.1 4/11

Sense short protect voltage 177

40 KΩ

mV

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CR6853

T

LEB

( LEB )

Oscillator (RI Pin)

Leading edge blanking time

F

Normal Frequency RI=100Kohm 60 65 70 KHz

OSC

F

PFM Frequency RI=100Kohm 22 KHZ

PFM

DC
DC

ΔF

T

F

MAX_W

MAX_F

TEMP

BLANK

JITTER

Maximum Duty Cycle PWM RI=100Kohm 77 %
Maximum Duty Cycle PFM RI=100Kohm 14 %

Frequency Temp. Stability

Leading-Edge Blanking Time 300

Frequency jitter RI=100Kohm -4 4 %

GATE Drive Output (GATE Pin)

Output Low Level VDD=16V,

V

OL

Output High Level VDD=16V,

V

OH

RI=100K 300

-30-100℃

5 %

0.8 V

IO=20mA

10 V

IO=20mA

nS

nS

VG

T

R1

T

F1

T

R2

T

F2

T

R3

T

F3

T

R4

T

F4

CLAMP

Rising Time
Falling Time CL=500pF 71 ns
Rising Time
Falling Time CL=1000pF 116
Rising Time
Falling Time CL=1500pF 153
Rising Time
Falling Time CL=2000pF 209
Output Clamp Voltage VDD=20V 18.0

Low EMI technique

f

EMI

Low EMI frequency RI=100Kohm 64 Hz
Frequency modulation range

∆f_osc

/Base frequency

CL=500pF 123

CL=1000pF 248 ns

ns

ns

CL=1500pF 343 ns

ns

CL=2000pF 508 ns

ns
V

RI=100Kohm -3 3 %

Dec, 2007 V1.1 5/11

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CR6853

OPERATION DESCRIPTION
Current Mode

Compared to voltage mode control,
current mode control has a current feedback
loop. When the voltage of the Sense resistor
peak current of the primary winding reaches
the internal setting value VTH, the register
resets and the power MOSFET cuts off. So,
to detect and modulate the peak current
cycle-by-cycle could control the output of the
power supply. The current feedback has a
good linear modulation rate and a fast input
and output dynamic impact, and avoid the
pole that the output filter inductance brings
and the two-class system descends to the
one-class. So it widens the frequency range
and optimizes overload protection and short
circuit protection.

Startup Current and Under Voltage
Lockout

The startup current of CR6853 is set to
be very low so that a large value startup
resistor can be used to minimize the power
loss. For AC to DC adaptor with universal
input range design, a 2 MΩ, 1/8 W startup
resistor and a 10uF/25V VDD hold capacitor
could be used.

The turn-on and turn-off threshold of the
CR6853 is designed to 12.8V/7.8V. During
startup, the hold-up capacitor must be
charge to 13.0V through the startup resistor.
The hysteresis is implemented to prevent
the shutdown from the voltage dip during
startup.

Internal Bias and OSC Operation

A resistor connected between RI pin
and GND pin sets the internal constant
current source to charge or discharge the
internal fixed capacitor. The charge time and
discharge time determines the internal clock
speed and the switching frequency.
Increasing the resistance will reduce the
value of the input current and reduce the
switching frequency. The relationship
between RI and PWM switching frequency
follows the below equation within the RI
allowed range.

F

OSC

For example, a 100kΩ resistor RI could

6500

=

)(

KRI

Ω

kHz

)(

generate a 13uA constant current and a
65kHz PWM switching frequency. The
suggested operating frequency range of
CR6853 is within 30KHz to 150KHz.

Green Power Operation

The power dissipation of switching
mode power supply is very important in zero
load or light load condition. The major
dissipation results from conduction loss、
switching loss and consume of the control
circuit. However, all of them relates to the
switching frequency. There are many
difference topologies has been implemented
in different chip. The basic operation theory
of all these approaches intends to reduce
the switching frequency under light-load or
no-load condition.

The CR6853`s green power function
adapts PWM、PFM and CRM combining
modulation. When RI resistor is 100kΩ, the
PWM frequency is 65kHz in medium or
heavy load operation. Through modifying
the pulse width, The CR6853 could control
output voltage. The current of FB pin
increases when the load is in light condition
and the internal mode controller enters
PFM&PWM when the feedback current is
over 1.0mA. The operation frequency of
oscillator is to descend gradually. When the
feedback current is over 1.40mA, the
frequency of oscillator is invariable, namely
22kHz.

CR6853 Green-Power Function

To decrease the standby consumption
of the power supply, Chip-Rail introduces
the Cycle Reset Mode technology (CRM). If
the feedback current is over 1.45mA, mode
controller of the CR6853 would reset
internal register all the time and cut off the
GATE pin. While the output voltage is lower
than the set value, the register would be set,

Dec, 2007 V1.1 6/11

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2

CR6853

the GATE pin operate again. So the
frequency of the internal OSC is invariable,
the register would reset some pulses so that
the practical frequency is decreased at the
GATE pin.

Internal Synchronized Slop
Compensation

Although there are more advantages of
the current mode control than conventional
voltage mode control, there are still several
drawbacks of peak-sensing current-mode
converter, especially the open loop
instability when it operates in higher than
50% of the duty-cycle. To solve this problem,
the CR6853 is introduced an internal slope
compensation adding voltage ramp to the
current sense input voltage for PWM
generation. It improves the close loop
stability greatly at CCM, prevents the
sub-harmonic oscillation and thus reduces
the output ripple voltage.

V

SLOP

DUTY

DUTY

MAX

DUTY

×=×= 4389.033.0

V

value (

IN

I ×=∆

T

) due to the system

L

D

P

delay time that is from detecting the current
through the Sense pin to power MOSFET off
in the CR6853 (Among these, V

is the

IN

primary winding voltage of the transformer
and LP is the primary wind inductance). V

IN

ranges from 85VAC to 264VAC. To
guarantee the output power is a constant for
universal input AC voltage, there is a
dynamic peak limit circuit to compensate the
system delay T that the system delay brings
on.

IPEAK

IPEAK

MAX

MAX

R

R

V

SENSE

85.0

SENSE

==

IN

V

==

IN

)264(

VV

)85(

VV

65.0

Low EMI technique

The frequency low EMI technique is
introduced in the CR6853. As following
figure, the internal oscillation frequency is
modulated by itself. A whole surge cycle
includes 8 pulses and the jittering ranges
from -4% to +4%. Thus, the function could
minimize the electromagnetic interferer from
the power supply module.

Slop Compensation

Current Sensing & Dynamic peak
limiting

MOSFET comes into being a voltage V
on the Sense pin cycle-by-cycle, which
compares to the internal reference voltage,
and controls the reverse of the internal
register, limits the peak current IMAX of the
primary of the transformer. The transformer

energy is
the R

power of the power supple. The current
flowing by the power MOSFET has an extra

Dec, 2007 V1.1 7/11

The current flowing by the power

SENSE

1

can set the maximal output

SENSE

2

. So adjusting

ILE ××=

MAX

OLP&SCP

To protect the circuit from being
damaged under the over load or short circuit
condition, a smart OLP&SCP function is
implemented in the CR6853. When short
circuit or over load occurs in the output end,
the feedback cycle would enhance the
voltage of FB pin, while the voltage is over

4.2V or the current from FB is below 152uA,
the internal detective circuit would send a
signal to shut down the GATE and pull down
the VDD voltage, then the circuit is restart.
To avoid the wrong operation when circuit
starts, the delay time is set. When the RI

Frequency low EMI

Chengdu Chip-Rail Tech. Co., Ltd. http://www.chiprail.com

10

6

10

6

×

×

×

×

CR6853

resistance is 100Kohm, the delay time
T

OLP&SCP

relationship between RI and T
follows the below equation.

is between 33mS and 50mS. The

RI

2

)(

TmS

3

&

RI

<<

SCPOLP

OLP&SCP

3

3

mS

)(

Over Temperature Protection

The CR6853 has a built-in temperature
sensing circuit to shut down PWM output
once the junction temperature exceeds
130°C. While PWM output is shut down,
VDD voltage will gradually drop to the UVLO
voltage, and VDD voltage will gradually
increase again. If the junction temperature is
still higher than 130°C, the PWM controller
will be shut down again. This situation will
continue until the temperature drops below
100°C. The PWM output will then be turned
back. The temperature hysteresis window
for the OTP circuit is 30°C.

Sense Fault Detect

Changing the resistance of Sense pin
could limit the maximal peak current of
power MOSFET. If the Sense pin is short
circuit to the ground and the CR6853 is
overload, the power MOSFET and
transformer is easy to be shattered. So, the
short circuit protection is built in the CR6853.
Every time to start up, the circuit would
detect the voltage of the Sense pin when the
start signal is send. If the voltage keeps
lower than 177mV, the circuit would be cut
off and restart in 1.2mS. But, when the
switch power is cut off, there could always
be a big noise on the ground, so to achieve
this function, it is strongly suggested that the
board on the ground of the sense pin must
be attention.

Anti Intermission Surge

When the power supplies change the
heavy load to light load immediately, there
could be tow phenomena caused by system
delay. They are output voltage overshot and
intermission surge. To avoid it, the anti
intermission surge is built in the CR6853. If it
occurs, the FB current is to increase rapidly,
the GATE would be cut off for a while, VDD

pin voltage descends gradually. When VDD
reaches 12.7V, the GATE pin would operate
again, which the frequency is 22KHz and
the max. Duty cycle is 14%.

Leading-edge Blanking (LEB)

Each time the power MOSFET is
switched on, a turn-on spike will inevitably
occur at the Sense pin, which would disturb
the internal signal from the sampling of the
R
blanking time built in to avoid the effect of
the turn-on spike, and the power MOSFET
cannot be switched off during the moment.
So that the conventional external RC
filtering on sense input is no longer required.

. There is a 300nS leading edge

SENSE

Over Voltage Protection (OVP)

There is a 25.6V over-voltage
protection circuit in the CR6853 to improve
the credibility and extend the life of the chip.
When the VDD voltage is over 25.6V, the
GATE pin is to shutdown immediately and
the VDD voltage is to descend rapidly.

GATE Driver & Soft Clamped

The CR6853’ output designs a totem
pole to drive a periphery power MOSFET.
The dead time is introduced to minimize the
transfixion current during the output
operating. The novel soft clamp technology
is introduced to protect the periphery power
MOSFET from breaking down and current
saturation of the Zener.

Dec, 2007 V1.1 8/11

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CR6853

PACKAGE DEMENSIONS
DIP-8L

Dimensions

Symbol

Min. Typ. Max. Min. Typ. Max.

A
A1 0.381
A2 3.175 3.302 3.429 0.125 0.130 0.135

b
b1

D 9.017 9.271 10.160 0.355 0.365 0.400

E
E1 6.223 6.350 6.477 0.245 0.250 0.255

e

L 2.921 3.302 3.810 0.115 0.130 0.150
eB 8.509 9.017 9.525 0.335 0.355 0.375

θ˚ 0˚ 7˚ 15˚ 0˚ 7˚ 15˚

Dec, 2007 V1.1 9/11

Millimeters

1.524

0.457

7.620

2.540

Chengdu Chip-Rail Tech. Co., Ltd. http://www.chiprail.com

5.334

0.015

Inches

0.060

0.018

0.300

0.100

0.210

CR6853

SOT-23-6L

Symbol

Dimensions In Millimeters

Min Max Min Max

A 0.700 1.000 0.028 0.039

A1 0.000 0.100 0.000 0.004

B 1.397 1.803 0.055 0.071

b 0.300 0.559 0.012 0.022
C 2.591 3.000 0.102 0.118
D 2.692 3.099 0.106 0.122

e 0.838 1.041 0.033 0.041
H 0.080 0.254 0.003 0.010

L 0.300 0.610 0.012 0.024

Dimensions In Inches

Dec, 2007 V1.1 10/11

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CR6853

SOP-8L

Dimensions DISCLAIMERS

Millimeter

0.381X45

Symbol

A 1.346

A1 0.101

b
c

D 4.648

E 3.810
e 1.016 1.270 1.524 0.040 0.050 0.060

F

H 5.791

L 0.406

θ˚

Min. Typ. Max. Min. Typ. Max.

0°

0.406

0.203

°

1.752 0.053

0.254 0.004

4.978 0.183

3.987 0.150

6.197 0.228

1.270 0.016
8° 0°

Inch

0.016

0.008

0.015X45

°

0.069

0.010

0.196

0.157

0.244

0.050
8°

Dec, 2007 V1.1 11/11

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