Datasheet CS2841BEN8, CS2841BEDR14, CS2841BED14 Datasheet (Cherry Semiconductor)

1

■ Optimized for

Off-line

Control

■ Internally Trimmed

Temperature
Compensated Oscillator

■ Maximum Duty-cycle

Clamp

■ V

REF

Stabilized before

Output Stage Enabled

■ Low Start-up Current

■ Pulse-by-pulse Current

Limiting

■ Improved Undervoltage

Lockout

■ Double Pulse Suppression

■ 1% Trimmed Bandgap

Reference

■ High Current Totem Pole

Output

Package Options

8 Lead PDIP

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

V

CC

Pwr

V

OUT

Pwr Gnd
Gnd

14 Lead SO Narrow

CS2841B

Automotive Current Mode PWM

Control Circuit

CS2841B

Description

The CS2841B provides all the nec­essary features to implement off­line fixed frequency current-mode
control with a minimum number of
external components.

The CS2841B (a variation of the
CS-2843A) is designed specifically
for use in automotive operation.
The low start threshold voltage of

8.0V (typ), and the ability to sur­vive 40V automotive load dump
transients are important for auto­motive subsystem designs. The
CS-2841 series has a history of

quality and reliability in automo­tive applications.

The CS2841B incorporates a preci­sion temperature-controlled oscil­lator with an internally trimmed
discharge current to minimize vari­ations in frequency. Duty-cycles
greater than 50% are also possible.
On board logic ensures that V

REF

is
stabilized before the output stage
is enabled. Ion implant resistors
provide tighter control of under­voltage lockout.

Block Diagram

Absolute Maximum Ratings

Supply Voltage (Low Impedance Source)...................................................40V

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

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

Analog Inputs (V

FB

, Sense) ............................................................-0.3V to 5.5V

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

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

Features

Rev. 6/23/99

Cherry Semiconductor Corporation

2000 South County Trail, East Greenwich, RI 02818

Tel: [phone] Fax: [phone]

Email: [e-mail]

Web Site: www.cherry-semi.com

A Company

®

V

Gnd

OSC

V

COMP

Sense

CC

8.0V/7.4V

+

FB

–

Amplifier

2.50V

Oscillator

Error

Undervoltage

Lock-out Circuit

V

C

2 R

R

Set/

Reset

Reference

Output
Enable

1 V

5V

Current

Sensing

Comparator

Internal

Bias

NOR

S

PWM

R

Latch

VCC Pwr

V

REF

V

OUT

Pwr Gnd

1

COMP

2

V

FB

3

Sense

4

OSC

8

V

7

V

6

V

5

Gnd

REF

CC

OUT

2

Electrical Characteristics: d -40≤TA≤85˚C RT=680kΩ, CT=0.022µF for triangular mode, VCC=15V (Note 1),

R

T

=10kΩ, CT=3.3nF for sawtooth mode (See Fig. 3), unless otherwise stated.

PARAMETER TEST CONDITIONS MIN TYP MAX UNIT

CS2841B

Notes: 1. Adjust Vccabove the start threshold before setting at 15V. 3. Parameter measured at trip point of latch with VFB=0.

2.These parameters, although guaranteed, are not 100% tested in production. 4. Gain defined as:

A = ; 0 ≤ V

Sense

≤ 0.8V.

∆V

COMP

∆V

Sense

■ Reference Section

Output Voltage TJ=25˚C, I

OUT

=1mA 4.90 5.00 5.10 V
Line Regulation 8.4≤VCC≤16V 6 20 mV
Load Regulation 1≤I

OUT

≤20mA 6 25 mV
Temperature Stability (Note 2) 0.2 0.4 mV/˚C
Total Output Variation Line, Load, Temp. (Note 2) 4.82 5.18 V
Output Noise Voltage 10Hz≤f≤10kHz, TJ=25˚C (Note 2) 50 µV
Long Term Stability TA=125˚C, 1000 Hrs. (Note 2) 5 25 mV
Output Short Circuit TA=25˚C -30 -100 -180 mA

■ Oscillator Section

Initial Accuracy Sawtooth Mode: (See Fig. 3)TJ=25˚C 47 52 57 kHz

Sawtooth Mode: -40˚C≤TA≤+85˚ 44 52 60 kHz

Triangular Mode (See Fig. 3) TJ=25˚C 44 52 60 kHz
Voltage Stability 8.4V≤Vcc≤16V 0.2 1.0 %
Temperature Stability Sawtooth Mode T

MIN≤TA≤TMAX

5%

Triangular Mode T

MIN≤TA≤TMAX

8%

(Note 2)
Amplitude V

OSC

(peak to peak) 1.7 V

Discharge current TJ=25˚C 7.4 8.3 9.2 mA

T

MIN≤TA≤TMAX

7.2 9.4 mA

■ Error Amp Section

Input Voltage V

COMP

=2.5V 2.42 2.50 2.58 V
Input Bias Current VFB=0V -0.3 -2.0 µA
A

VOL

2≤V

OUT

≤4V 65 90 dB
Unity Gain Bandwidth (Note 2) 0.7 1.0 MHz
PSRR 8.4V≤VCC≤16V 60 70 dB
Output Sink Current VFB=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 VFB=2.3V, RL=15kΩ to ground 5 6 V

V

OUT

Low VFB=2.7V, RL=15kΩ to V

REF

0.7 1.1 V

■ Current Sense Section

Gain (Notes 3 & 4) 2.85 3.00 3.15 V/V
Maximum Input Signal V

COMP

=5V (Note 3) 0.9 1.0 1.1 V
PSRR 12V≤VCC≤25V (Note 3) 70 dB
Input Bias Current V

Sense

=0V -2 -10 µA

Delay to Output T

J

=25˚C (Note 2) 150 300 ns

3

CS2841B

Electrical Characteristics:

continued

PARAMETER TEST CONDITIONS MIN TYP MAX UNIT

■ 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

Rise Time T

J

=25˚C, CL=1nF (Note 2) 50 150 ns

Fall Time T

J

=25˚C, CL=1nF (Note 2) 50 150 ns

Output Leakage Undervoltage Active, V

OUT

=0 -0.01 -10.00 µA

■ Total Standby Current

Start-Up Current 0.5 1.0 mA
Operating Supply Current ICCVFB=V

Sense

=0V, RT=10kΩ, CT=3.3nF 11 17 mA

■ Under-Voltage Lockout Section

Start Threshold 7.6 8.0 8.4 V
Min. Operating Voltage After Turn On 7.0 7.4 7.8 V

Package Pin Description

PACKAGE PIN # PIN SYMBOL FUNCTION

8L PDIP 14L 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

9 Pwr Gnd Output driver Ground

610V

OUT

Output drive pin

11 VCCPwr Output driver positive supply

712V

CC

Positive power supply

814V

REF

Output of 5V internal reference

2,4,6,13 NC No Connection

4

CS2841B

V

REF

V

CC

V

O

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

Test Circuit

Undervoltage Lockout

During Undervoltage Lockout (Figure 1), the output driv­er is biased to a high impedance state. The output should
be shunted to ground with a resistor to prevent output
leakage current from activating the power switch.

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 VCCcauses 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.

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 trans-

Circuit Description

Typical Performance Characteristics:

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

800

900

FREQ. (kHz)

CT (µF)

700

600

500

400

300

200

100

.05

RT =1.5kΩ

RT =680Ω

RT =10kΩ

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

80

90

DUTY CYCLE (%)

RT (Ω)

70
60
50
40

30
20
10

4k3k500400300

100

Oscillator Duty Cycle vs R

T

Oscillator Frequency vs C

T

Figure 1: Typical Undervoltage Characteristics

V

CC

V

= 8.0V

ON

V

= 7.4V

OFF

I

CC

7.4V 8.0V

<15mA

<1mA

ON/OFF Command

to reset of IC

V

CC

5

former saturation in some power supplies, the internal
oscillator waveform provides the maximum duty cycle
clamp as programmed by the selection of OSC compo­nents.

Setting the Oscillator

Oscillator timing capacitor, CT, is charged by V

REF

through

R

T

and discharged by an internal current source. During
the discharge time, the internal clock signal blanks out the
output to the Low state, thus providing a user selected
maximum duty cycle clamp. Charge and discharge times
are determined by the general formulas:

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

tc≈ 0.5534RTC

T

td= RTCTln

The frequency and maximum duty cycle can be deter­mined from the Typical Performance Characteristic
graphs.

Grounding

High peak currents associated with capacitive loads neces­sitate careful grounding techniques. Timing and bypass
capacitors should be connected close to Gnd pin 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

(

CS2841B

Circuit Description: continued

Sawtooth Mode

Triangular Mode

OSC

Figure 2: Timing Diagram for key CS2841B parameters

Figure 3: Oscillator Timing Network and parameters

Timing parameters

OSC

RESET

EA Output

Switch

Current

V

CC

I

O

V

O

V

REF

R

T

OSC

C

T

Gnd

LARGE R

SMALL RT (≈700kΩ)

V

V

upper

lower

(≈10kΩ)

T

t

c

t

d

V

OSC

Internal Clock

V

OSC

D

Lead Count Metric English

Max Min Max Min
8 Lead PDIP 10.16 9.02 .400 .355
14 Lead SO Narrow 8.75 8.55 .344 .337

6

Rev. 6/23/99

CS2841B

Part Number Description

CS2841BEN8 8L PDIP
CS2841BED14 14L SO Narrow
CS2841BEDR14 14L SO Narrow

(tape & reel)

Ordering Information

Thermal Data 8 L 14 L

PDIP SO Narrow

R

ΘJC

typ 52 30 ˚C/W

R

ΘJA

typ 100 125 ˚C/W

Package Specification

PACKAGE DIMENSIONS IN mm (INCHES)

PACKAGE THERMAL DATA

© 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.

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)

Surface Mount Narrow Body (D); 150 mil wide

Plastic DIP (N); 300 mil wide

0.39 (.015)
MIN.

2.54 (.100) BSC

1.77 (.070)

1.14 (.045)

D

Some 8 and 16 lead
packages may have
1/2 lead at the end
of the package.
All specs are the same.

.203 (.008)

.356 (.014)

REF: JEDEC MS-001

3.68 (.145)

2.92 (.115)

8.26 (.325)

7.62 (.300)

7.11 (.280)

6.10 (.240)

.356 (.014)

.558 (.022)