Datasheet CS52843ED8, CS52843ED14, CS52843EDR8, CS52843EDR14 Datasheet (Cherry Semiconductor)

The CS52843 provides all the nec­essary features to implement off­line fixed frequency current-mode
control with a minimum number
of external components.

The CS52843 incorporates a new
precision temperature-controlled
oscillator to minimize variations in
frequency. An undervoltage lock­out ensures that V

REF

is stabilized

before the output stage is enabled.
In the CS52843 turn on is at 8.4V
and turn off at 7.6V.

Other features include low start-up
current, pulse-by-pulse current lim­iting, and a high-current totem pole
output for driving capacitive loads,
such as gate of a power MOSFET.
The output is low in the off state,
consistent with N-channel devices.

1

Features

■

Optimized for Off-line
Control

■ Internally

Temperature

Compensated Oscillator

■ V

REF

Stabilized before

Output Stage is Enabled

■ Very Low Start-up Current

300 µA (typ)

■ Pulse-by-pulse Current

Limiting

■ Improved Undervoltage

Lockout

■ Double Pulse Suppression

■ 2% 5 Volt Reference

■ High Current Totem Pole

Output

Package Options

CS52843

Current Mode PWM

Control Circuit

CS52843

Description

Block Diagram

Absolute Maximum Ratings

Supply Voltage (I

CC

<30mA) ..........................................................Self Limiting

Supply Voltage (Low Impedance Source)...................................................30V

Output Current ...............................................................................................±1A

Output Energy (Capacitive Load) .................................................................5µJ

Analog Inputs (V

FB

, V

SENSE

)...........................................................-0.3V to 5.5V

Error Amp Output Sink Current...............................................................10mA

Lead Temperature Soldering

Reflow (SMD styles only)...........60 sec. max above 183°C, 230°C peak

7

8

2

3

4

5

6

COMP

V

FB

Sense

OSC

V

REF

V

CC

V

OUT

Gnd

8L SO Narrow

A Company

®

10

7

14

13

12

8

1

2

3

4

5

6

11

9

COMP

NC

V

FB

NC

Sense

NC

OSC

V

REF

NC
V

CC

VCC Pwr
V

OUT

Pwr Gnd
Gnd

14L SO Narrow

Rev. 12/23/97

Cherry Semiconductor Corporation

2000 South County Trail, East Greenwich, RI 02818

Tel: [phone] Fax: [phone]

Email: [e-mail]

Web Site: www.cherry-semi.com

V

CC

34V

Gnd

V

FB

COMP

OSC

Sense

Undervoltage Lock-out

V

CC

8.4V/7.6V

Error

Amplifier

2 R

Oscillator

R

­+

R

2.50V

1V

Current

Sensing

Comparator

5.0 Volt

Set/

Reference

Reset

OUTPUT
ENABLE

R

NOR

S

R
PWM

Latch

Internal

Bias

V

Pwr

CC

V

REF

V

OUT

Pwr Gnd

1

2

Electrical Characteristics: -40 ≤ TA ≤ 85˚C; V

CC

= 15V (Note 1); RT = 680Ω; CT = .022µF for triangle mode,

R

T

= 10kΩ; CT = 3.3nF sawtooth mode unless otherwise stated.

CS52843

PARAMETER TEST CONDITIONS MIN TYP MAX UNIT

■ Reference Section

Output Voltage TJ = 25˚C, I

REF

= 1mA 4.90 5.00 5.10 V

Line Regulation 12 ≤ V

CC

≤ 25V 6 20 mV

Load Regulation 1 ≤ I

RE F

≤ 20mA 6 25 mV

Temperature Stability (Note 1) 0.2 0.4 mV/˚C

Total Output Variation Line, Load, Temp. (Note 1) 4.82 5.18 V

Output Noise Voltage 10Hz ≤ f ≤ 10kHz, T

J

= 25˚C (Note 1) 50 µV

Long Term Stability TA = 125˚C, 1000 Hrs. (Note 1) 5 25 mV

Output Short Circuit T

A

= 25˚C -30 -100 -180 mA

■ Oscillator Section

Initial Accuracy Sawtooth Mode, T

J

= 25˚C (Note 1) 47 52 57 kHz

Triangle Mode, T

J

= 25˚C 44 52 60 kHz

Voltage Stability 12 ≤ V

CC

≤ 25V 0.2 1.0 %

Temperature Stability Sawtooth Mode T

MIN

≤ TA ≤ T

MAX

5%

Triangle Mode T

MIN

≤ TA ≤ T

MAX

(Note 1) 8 %

Amplitude V

OSC

(peak to peak) 1.7 V

Discharge Current T

J

= 25˚C 7.3 8.3 9.3 mA

T

MIN

≤ TA ≤ T

MAX

6.8 9.8 mA

■ Error Amp Section

Input Voltage V

COMP

= 2.5V 2.42 2.50 2.58 V

Input Bias Current V

FB

= 0V -0.3 -2.0 µA

A

VOL

2 ≤ V

OUT

≤ 4V 65 90 dB

Unity Gain Bandwidth (Note 1) 0.7 1.0 MHz

PSRR 12 ≤ V

CC

≤ 25V 60 70 dB

Output Sink Current V

FB

= 2.7V, V

COMP

= 1.1V 2 6 mA

Output Source Current V

FB

= 2.3V, V

COMP

= 5V -0.5 -0.8 mA

V

OUT

HIGH V

FB

= 2.3V, RL = 15kΩ to Gnd 5 6 V

V

OUT

LOW V

FB

= 2.7V, RL = 15kΩ to V

REF

0.7 1.1 V

■ Current Sense Section

Gain (Notes 2 & 3) 2.85 3.00 3.15 V/V

Maximum Input Signal V

COMP

= 5V (Note 2) 0.9 1.0 1.1 V

PSRR 12 ≤ V

CC

≤ 25V (Note 2) 70 dB

Input Bias Current V

Sense

=0V -2 -10 µA

Delay to Output TJ=25˚C (Note 1) 150 300 ns

■ Output Section

Output Low Level I

SINK

= 20mA 0.1 0.4 V

I

SINK

= 200mA 1.5 2.2 V

Output High Level I

SOURCE

= 20mA 13.0 13.5 V

I

SOURCE

= 200mA 12.0 13.5 V

3

CS52843

Package Pin Description

PACKAGE PIN # PIN SYMBOL FUNCTION

PARAMETER TEST CONDITIONS MIN TYP MAX UNIT

8L 14L

SO Narrow SO Narrow

1 1 COMP Error amp output, used to compensate error amplifier.

23 V

FB

Error amp inverting input.

3 5 Sense Noninverting input to Current Sense Comparator.

4 7 OSC Oscillator timing network with Capacitor to Ground, resistor to V

REF

.

5 8 Gnd Ground.

5 9 Pwr Gnd Output driver Ground.

610V

OUT

Output drive pin.

711V

CC

Pwr Output driver positive supply.

712V

CC

Positive power supply.

814V

REF

Output of 5V internal reference.

2,4,6,13 NC No Connection.

Electrical Characteristics: -40 ≤ TA ≤ 85˚C; V

CC

= 15V (Note 1); RT = 680Ω; CT = .022µF for triangle mode,

R

T

= 10kΩ; CT = 3.3nF sawtooth mode unless otherwise stated.

Rise Time TJ = 25˚C, CL = 1nF (Note 1) 50 150 ns

Fall Time TJ=25˚C, CL=1nF (Note 1) 50 150 ns

Output Leakage UVLO Active V

OUT

= 0 -.01 -10.0 µA

■ Total Standby Current

Start-Up Current 300 500 µA

Operating Supply Current VFB=V

Sense

=0V RT=10kΩ, CT=3.3nF 11 17 mA

VCCZener Voltage ICC=25mA 34 V

■ Undervoltage Lockout Section

Start Threshold 7.8 8.4 9.0 V

Min. Operating Voltage After Turn On 7.0 7.6 8.2 V

Notes: 1.These parameters, although guaranteed, are not 100% tested in production.

2. Parameter measured at trip point of latch with VFB=0.

3. Gain defined as:
A = ; 0 ≤ V

Sense

≤ 0.8V.

∆V

COMP

∆V

Sense

Figure 1: Startup voltage for the CS52843.

Undervoltage Lockout

During Undervoltage Lockout (Figure 1), the output driv­er is biased to sink minor amounts of current. The output
should be shunted to ground with a resistor to prevent
activating the power switch with extraneous leakage cur­rents.

PWM Waveform

To generate the PWM waveform, the control voltage from
the error amplifier is compared to a current sense signal
which represents the peak output inductor current (Figure

2). An increase in V

CC

causes the inductor current slope to
increase, thus reducing the duty cycle. This is an inherent
feed-forward characteristic of current mode control, since
the control voltage does not have to change during
changes of input supply voltage.

4

CS52843

Test Circuit Open Loop Laboratory Test Fixture

V

REF

V

CC

V

OUT

1kΩ
1W

0.1µF

0.1µF

V

REF

V

CC

V

OUT

Gnd

V

FB

Sense

OSC

COMP

5kΩ

100kΩ

4.7kΩ

1kΩ

Error Amp

Adjust

4.7kΩ

Sense
Adjust

R

T

2N2222

C

T

Gnd

A

Typical Performance Characteristics

FREQ. (kHz)

Oscillator Frequency vs C

T

Oscillator Duty Cycle vs R

T

Circuit Description

900
800

700

600

500

400

300

200

100

.0005 .001 .002 .003 .005 .01 .02 .03 .04

RT =1.5kΩ

R

=680Ω

T

RT =10kΩ

CT (µF)

100

90
80

70
60
50
40

DUTY CYCLE (%)

30
20
10

.05

100 200 700 1k 2k 5k 7k 10k

RT (Ω)

4k3k500400300

V

CC

V

ON

V

OFF

I

CC

<15mA

<500µA

ON/OFF Command

to reset of IC

=8.4V

= 7.6V

V

V

ONVOFF

CC

When the power supply sees a sudden large output cur­rent increase, the control voltage will increase allowing the
duty cycle to momentarily increase. Since the duty cycle
tends to exceed the maximum allowed to prevent trans­former saturation in some power supplies, the internal
oscillator waveform provides the maximum duty cycle
clamp as programmed by the selection of oscillator timing
components.

Figure 2: Timing Diagram

Figure 3: Oscillator Timing Network and Parameters

Setting the Oscillator

The times T

c

and Tdcan be determined as follows:

t

c

= RTCTln

t

d

= RTCTln

Substituting in typical values for the parameters in the
above formulas:

V

REF

= 5.0V, V

UPPER

= 2.7V, V

LOWER

= 1.0V, Id= 8.3mA,

then

t

c

≈ 0.5534RTC

T

td= RTCTln

For better accuracy RTshould be ≥10kΩ.

Grounding

High peak currents associated with capacitive loads neces­sitate careful grounding techniques. Timing and bypass
capacitors should be connected close to Gnd in a single
point ground.

The transistor and 5kΩ potentiometer are used to sample
the oscillator waveform and apply an adjustable ramp to
Sense.

)

2.3 - 0.0083 R

T

4.0 - 0.0083 R

T

(

)

V

REF

- IdRT- V

LOWER

V

REF

- IdRT- V

UPPER

(

)

V

REF

- V

LOWER

V

REF

- V

UPPER

(

V

5

CS52843

Circuit Description

Triangular Mode

Sawtooth Mode

OSC

OSC

RESET

Toggle

F/F Output

EA Output

Switch

Current

V

CC

I

O

V

O

V

V

LARGE R

SMALL R

upper

lower

V

REF

OSC

Gnd

(≈10kΩ)

T

(≈700kΩ)

T

t

c

R

T

C

T

t

d

V

OSC

Internal Clock

V

REF

Internal Clock

6

Part Number Description

CS52843ED8 8L SO Narrow
CS52843EDR8 8L SO Narrow (tape & reel)
CS52843ED14 14L SO Narrow
CS52843EDR14 14L SO Narrow (tape & reel)

Rev. 12/23/97

CS52843

D

Lead Count Metric English

Max Min Max Min

8L SO Narrow 5.00 4.80 .197 .189

14L SO Narrow 8.75 8.55 .344 .337

Thermal Data 8L SO Narrow 14L SO Narrow

R

ΘJC

typ 45 30 ˚C/W

R

ΘJA

typ 165 125 ˚C/W

Package Specification

PACKAGE DIMENSIONS IN mm (INCHES)

PACKAGE THERMAL DATA

Ordering Information

© 1999 Cherry Semiconductor Corporation

Cherry Semiconductor Corporation reserves the
right to make changes to the specifications without
notice. Please contact Cherry Semiconductor
Corporation for the latest available information.

Surface Mount Narrow Body (D); 150 mil wide

1.27 (.050) BSC

0.51 (.020)

0.33 (.013)

6.20 (.244)

5.80 (.228)

4.00 (.157)

3.80 (.150)

1.57 (.062)

1.37 (.054)

D

0.25 (0.10)

0.10 (.004)

1.75 (.069) MAX

1.27 (.050)

0.40 (.016)

REF: JEDEC MS-012

0.25 (.010)

0.19 (.008)