Fairchild Semiconductor KA3511 Datasheet

November 2,1999

AN4003 PC POWER SUPPLY DESIGN WITH KA3511

Sang-Tae Im

1. GENERAL DESCRIPTION

The KA3511 is a fixed-frequency improved-performance pulse-width modulation control circuit with complete housekeep ing circuitry for use in the s econdary side of SMPS (Swit ched mode power supply). It cont ains variou s functions, which are p recision vol tage referenc e, over vol tage protection, under voltage protection, remote on/off control, power good signal generator and etc.

OVP (Over voltage protection) section

It has OVP functio ns for +3.3V,+5V,+12V and PT outputs. The circu it is made u p of a com parator with four detecting inpu ts a nd wi thou t hysteresis voltage. Especi al ly, PT (Pin16) is prepared for an extra OVP input or another protection signal.

UVP (Under voltage protection) section

It also has UVP functions for +3.3V , +5V, +12V outputs. The block is made up of a comparator with three detecting inputs and without hysteresis voltage.

Remote on/off section

Remote on/off section is used to control SMPS externally. If a high signal is supplied to the remote on/off input, PWM signal becomes a high state and all secondary outputs are grounded. The remote on/off signal is transferred with some on- delay and off-delay time of 8ms, 24ms respectively.

Precision reference section

The reference voltage trimmed to ±2% (4.9V<Vref<5.1V)

PG (Power good signal generator) section

Power good signal generator is to monitor the voltage level of power supply for safe operation of a microprocessor.

KA3511 requires few external components to accomplish a complete housekeeping circuits for SMPS. The KA3511 is available in a 22-pin dual in-line package.

Rev C, November 1999

ORDERING INFORMATION

Device Package Operating Temperature

KA3511 22 DIP -25°C ~ 85°C

FEATURES

• Complete PWM control and hou se ke epi ng circ uitr y

• Few external components

• Precision voltage reference trimmed to 2%

• Dual output for push-pull opera tio n

• Each output TR for 200mA sink current

• Variable duty cycle by dead time control

• Soft start capability by using dead time control

• Double pulse suppression logic

• Over voltage protection for 3.3V / 5V / 12V

• Under voltage protection for 3.3V / 5V / 12V

• One more external input for various protection (PT)

• Remote on/off control function (PS-ON)

• Latch function controlled by remote and protection input

• Power good signal generator with hysteresis

• 22-Pin dual in-line package

2. BLOCK DIAGRAM

22-DIP-400

V5 V12

E/A(-)

E/A(+)

DEAD TIME

CONTROL

COMP

12 VREF

VREF

DET

OSCILLATOR

Start Up

1.25V

INTERNAL

BIAS

1.25V

0.1V

COMP1

COMP2

PWM

CONTROL

DEAD TIME

CONTROLLER

Ichag

VREF

2.2uF

GENERATOR

COMP3

1.8V 0.6V

CONTROLLER

UVP

2.2uF

DELAY

VREF

17 1810

OVP

COMP

UVP

COMP

REMOTE ON/OFF

1.4V

1.25V

GND

REM

(PS-ON)

REM

V12

V3.3

Rev C, November 1999

3. PIN DESCRIPTION

Vref

#12

#22

V3.3

V5V12PTTUVPGNDDTCC2EC1

KA3511

#1 #11

COMP E/A(-) EA(+) TREM REM RT CT DET TPG PG

Pin No. Name I/O Function

1 V

I Supply voltage 12 Vref O Precision reference VTG

2 COMP O E/A output 13 V3.3 I OVP, UVP input for 3.3V 3 E/A(-) I E/A (-) input 14 V5 I OVP, UVP input for 5V 4 E/A(+) I E/A (+) input 15 V12 I OVP, UVP input for 12V 5 TREM – Remote on/off delay 16 PT I Extra protection input 6 REM I Remote on/off input 17 T 7 RT – Oscillation freq. setting R 18 GND – Signal ground 8 CT – Oscillation freq. setting C 19 DTC I Deadtime control input 9 DET I Detect input 20 C2 O Output 2

10 T

– PG delay 21 E – Power ground

11 PG O Power good signal output 22 C1 O Output 1

Pin No. Name I/O Function

– UVP delay

UVP

Rev C, November 1999

Pin No. Name Function

1 V

Supply voltage. Operating range is 14V~30V. VCC =20V, Ta=25°C at test.

2 COMP Error amplifier output. It is connected to non-inverting input of pulse width

modulator comparator. 3 E/A(-) Error amplifier inverting input. Its reference voltage is always 1.25V. 4 E/A(+) Error amplifier non-inverting input feedback voltage.This pin may be used to

sense power supply output volt age . 5 TREM Remote on/off delay. Ton/Toff=8ms/24ms (Typ.) with C=0.1µF. Its high/low

threshold voltage is 1.8V/0.6V. 6 REM Remote on/off input. It is TTL operation and its threshold voltage is 1.4V. Voltage

at this pin can reach normal 4.6V, with absolutely maximum voltage, 5.25V. If

REM = “Low”, PWM = “Low”. That means the main SMPS is operational. When

REM = “High”, then PWM = “High” and the main SMPS is turned-off. 7 RT Oscillation frequency setting R. (Test Condition R 8 CT Oscillation frequency setting C. (Test Condition C

=10kΩ)

=0.01µF)

9 DET Under-voltage detect pin. Its threshold voltage is 1.25V Typ.

10 T

PG delay. Td=250ms (Typ) with CPG=2.2µF. The high/low threshold voltage are

1.8V/0.6V and the voltage of Pin10 is clamped at 2.9V for noise margin.

11 PG Power good output signal. PG = “High” means that the power is “Good” for

operation and PG = “Low” means “Power fail”.

12 Vref Precision voltage reference trimmed to 2%. (Typical Value = 5.03V) 13 V3.3 Over voltage protection for output 3.3V. (Typical Value = 4.1V) 14 V5 Over voltage protection for output 5V. (Typical Value = 6.2V) 15 V12 Over voltage protection for output 12V. (Typical Value = 14.2V) 16 PT This is prepared for an extra OVP input or another protection signal. (Typical

Value = 1.25V)

17 T

Timing pin for under voltage protection blank-out time. Its threshold voltage is

UVP

1.8V and clamped at 2.9V after full charging. Target of delay time is 250ms and

it is realized through external (C=2.2µF).

18 GND Signal ground. 19 DTC Deadtime control input. The dead-time control comparator has an effective

120mV input offset which limits the minimum output dead time. Dead time may

be imposed on the output by setting the dead time control input to a fixed

voltage, ranging between 0V to 3.3V.

20 C2 Output drive pin for push-pull operation. 21 E Power ground. 22 C1 Output drive pin for push-pull operation.

Rev C, November 1999

4. ABSOLUTE MAXIMUM RATINGS

Characteristic Symbol Value Unit

Supply voltage V Collector output voltage V Collector output current I

C1 C1

, V

, I Power dissipation P Operating temperature T Storage temperature T

OPR STG

TEMPERATURE CHARACTERISTICS

Characteristic Symbol

Temperature coefficient of Vref (-25 °C<

Ta<85°C)∆Vref/∆T – 0.01 – %/°C

40 V 40 V

200 mA

1 W

-25 to 85 °C

-65 to 150 °C

Value

Unit Min. Typ. Max.

Rev C, November 1999

5. ELECTRICAL CHARACTERISTICS

(VCC =20V, TA =25°C)

Value

Characteristic Symbol Test Condition

REFERENCE SECTION

Reference output voltage Vref Iref=1mA 4.9 5 5.1 V Line regulation Load regulation Temperature coefficient of Vref Short-circuit output current I

∆

Vref.

LINE

∆

Vref.

(1)

∆Vref/∆T -25°C<Ta<85°C – 0.01 – %/°C

LOAD

14V<VCC<30V – 2.0 25 mV

1mA<Iref<10mA – 1.0 15 mV

Vref=0 15 35 75 mA

OSCILLATOR SECTION

Oscillation frequency fosc C Frequency change with

temperature

(1)

fosc/T CT=0.01µF, RT=12k – 2 – %

=0.01µF, RT=12k – 10 – kHz

DEAD TIME CONTROL SECTION

Input bias current I Maximum duty voltage DC Input threshold voltage V

TH(DT)

B(DT)

Pin19 (DTC)=0V 45 48 50 %

MAX

Zero Duty Cycle – 3.0 3.3 V

– -2.0 -10 µA

Max. Duty Cycle 0 – –

ERROR AMP SECTION

Inverting reference voltage Vref(EA) 1.20 1.25 1.30 % Input bias current I Open-loop voltage gain Unit-gain bandwidth

(1)

Output sink current I Output source curren t I

B(EA)

GVO 0.5V<V

BW – 650 – kHz

SINK

SOURCE

V V

=2.5V – -0.1 -1.0 µA

COMP

<3.5V 70 95 – dB

COMP

=0.7V 0.3 0.9 – mA

COMP

=3.5V -2.0 -4.0 – mA

COMP

PWM COMPARATOR SECTION

Input threshold voltage V

TH(PWM)

Zero Duty Cycle – 4 4.5 V

OUTPUT SECTION

Output saturation voltag e V

CE(SAT)

Collector off-state current I Rising time T Falling time T

IC=200mA – 1.1 1.3 V

C(off)

VCC=VC=30V, VE=0V – 2 100 µA – 100 200 ns – 50 200 ns

PROTECTION SECTION

Over voltage protection for 3.3V V

OVP1

3.8 4.1 4.3 V

Unit Min. Typ. Max.

Rev C, November 1999

ELECTRICAL CHARACTERISTICS

(continued)

Value

Characteristic Symbol Test Condition

Over voltage protection for 5V V Over voltage protection for 12V V Input threshold voltage for PT V Under voltage protection for 3.3V V Under voltage protection for 5V V Under voltage protection for 12V V Charging current for UVP delay I

CHG.UVP

UVP Delay Time T

OVP2 OVP3

– 2.1 2.3 2.5 V

UVP1 UVP2 UVP3

C=2.2µF, VTH =1.8V -10 -15 -23 uA

D.UVP

C=2.2µF 100 260 500 ms

– 5.8 6.2 6.6 V – 13.5 14.2 15.0 V – 1.20 1.25 1.30

– 3.7 4.0 4.3 V – 9.2 10 10.8 V

REMOTE ON/OFF SECTION

REM on input voltage V REM off input voltage V REM off input bias voltage I REM on open voltage V

REM(OPEN)

REMH

REML

= -200µA 2.0 – – V

REM

– – – 0.8 V

=0.4V – – -1.6 mA

REM

– 2.0 – 5.25 V REM on delay time Ton C=0.1µF 4 8 14 ms REM off delay time Toff C=0.1µF 16 24 34 ms

REMOTE ON/OFF SECTION

Detecting input voltage V Detecting V5 voltage V

(2)

IN(DET)

5(DET)

– 1.20 1.25 1.30 V

– 4.1 4.3 4.5 V Hysteresis voltage 1 HY1 COMP1, 2 10 40 80 mV Hysteresis voltage 2 HY2 COMP3 0.6 1.2 – V PG output load resistor R Charging current for PG delay I

CHG.PG

PG delay time T PG output saturation voltage V

SAT(PG) IPG

D.PG

C=2.2µF, VTH =1.8V -10 -15 -23 uA C=2.2µF 100 260 500 ms

– 0.5 1 2 k

=10mA – 0.4 0.2 V

TOTAL DEVICE

Standby supply current I

–– 10 20 mA

Unit Min. Typ. Max.

Ω

Notes:

1. These Parameters, although guaranteed over their recommended operating conditions are not 100% tested in production.

2. REM on delay time (Pin6 REM: “L” → “H”), REM off delay time (Pin6 REM: “H” → “L”)

Rev C, November 1999

6. BLOCK DESCRIPTION & APPLICATION INFORMATIONS

6.1 OSCILLATOR BLOCK

Vref V

Figure 1. Oscillator RT, C

12 1

The KA3511 is a fixed-frequency pulse width modulation control circuit. An internal-linear sawtooth oscillator is fre quency-programmable by two external c omponents, R

and CT. The oscillator fre-

quency is determined by

1.1

fosc

300K

100K

10K

-------------------- -=

TCT

VCC=15V

0.001µF

CT=0.01µF

- OSCILLATOR FREQUENCY

100

2K 5K 10K 20K 50K 100K 200K 500K 1M

0.1µF

1.0µF

. TIMING RESISTANCE( Ω)

Figure 2. Oscillator Frequency vs. Timing Resistance

6.2 PWM CONTROL BLOCK

Output pulse width modu latio n is accompl ished by co mparis on of the pos itive sa wtooth wavefo rm across capacitor C Q1 and Q2, are enabled only when the flip-flop clock-input line is in its low state. This happens only during that portion of time when the sawtooth voltage is greater than the control signals. Therefore, an increase in control-signal amplitude c auses a corresponding linear d ecrease of output pulse width. (Refer to the timing diagram shown in Figure 4)

to either of two control signals . T he NOR gate s, whi ch dr iv e outp ut trans is to rs

Rev C, November 1999

OSCILLATOR

Output

Drive

COMP

1.25V

PWM

CONTROL

0.12V

DEAD TIME

CONTROLLER

Figure 3. PWM Control Block

The control signals are external inputs that can be fed into the dead-time control, the error amplifier inputs, or the feedbac k inp ut. The de ad-ti me contr ol com parator has an effective 120m V inp ut offset which limits the mi nimum output de ad time. Dead time m ay be impose d on the output by s etting the dead time control input to a fixed voltage, ranging between 0V to 3.3V.

The pulse width modulator comparator provides a means for the error amplifier to adjust the output pulse width from the max imum percent on-ti me, established by the dead time control input, dow n to zero, as the voltage at the feedb ack pin varies from 0.5V to 3.5V. The error amplifier may b e used to sense powe r-supply output voltage, and its output is conn ect to noninve rting input of th e pulse width modula tor comparator. With this configuration, the amplifier that demands minimum output on time, dominates control of the loop.

When capacitor C

is discharged, a positive pulse is generated on the output of the dead time

comparator, which clocks the pulse-steering flip-flop and inhibits the output transistors, Q1 and Q2. The pulse-steering flip-flop directs the modulated pulses to each of the two output transistors always for push-pull operation. The output frequency is equal to half that of the oscillator.

The KA3511 has an internal 5.0V refer ence capable of sourcing u p to 10mA of load current for external bias circui ts. The reference has an internal accuracy of ±2% with typical thermal dr ift of less than 50mV over an operating temperature range of -25°C to 85°C

Rev C, November 1999

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