SGS Thomson Microelectronics L4960 Datasheet



2.5APOWER SWITCHING REGULATOR

2.5AOUTPUTCURRENT

5.1V TO40V OPUTPUTVOLTAGERANGE
PRECISE(±2%) ON-CHIPREFERENCE
HIGH SWITCHING FREQUENCY
VERYHIGH EFFICIENCY (UP TO 90%)
VERYFEW EXTERNALCOMPONENTS
SOFT START
INTERNALLIMITINGCURRENT
THERMALSHUTDOWN

L4960

HEPTAWATT

ORDERING NUMBERS: L4960(Vertical)

L4960H(Horizontal)

DESCRIPTION

TheL4960 is a monolithicpower switching regula­tor delivering2.5Aat a voltage variable from 5V to
40V in step down configuration.
Featuresofthe device includecurrentlimiting,soft
start,thermal protectionand 0 to 100% dutycycle
for continuousoperationmode.

BLOCKDIAGRAM

TheL4960is mountedina Heptawattplastic power
package and requires very few external compo­nents.
Efficient operation at switching frequencies up to
150KHzallows a reductionin the size and cost of
externalfiltercomponents.

June 2000

1/16

L4960

PIN CONNECTION

(Top view)

ABSOLUTE MAXIMUM RATINGS

Symbol Parameter Value Unit

V

V

1-V7

V

V

3,V6

V

P

T

,T

j

Input voltage 50 V

1

Input to output voltage difference 50 V
Negative output DC voltage -1 V

7

Negative output peak voltage at t = 0.1µs; f= 100KHz -5 V
Voltageat pin 3and 6 5.5 V
Voltageat pin 2 7V

2

Pin 3 sink current 1 mA

I

3

I

Pin 5 source current 20 mA

5

Power dissipation at T

tot

Junction and storage temperature -40 to150 °C

stg

case

C15W

≤90°

PIN FUNCTIONS

N° NAME

1 SUPPLYVOLTAGE Unregulated voltage input. An internal regulator powers the

internal logic.

2 FEEDBACK INPUT The feedback terminal of the regulation loop. The output is

connected directly to this terminal for 5.1V operation; it is
connected viaa divider for higher voltages.

3 FREQUENCY

COMPENSATION

A series RC network connected between this terminal and
ground determines the regulation loop gain characteristics.

4 GROUND Common ground terminal.

5 OSCILLATOR AparallelRC network connected tothis terminal determines the

switching frequency.

6 SOFT START Soft start time constant. A capacitor is connected between this

terminal and ground to define the soft start time constant. This
capacitor also determines the average short circuit output
current.

7 OUTPUT Regulator output.

FUNCTION

2/16

THERMALDATA

Symbol Parameter Value Unit

R

th j-case

R

th j-amb

Thermal resistance junction-case max 4
Thermal resistance junction-ambient max 50

L4960

C/W

°

C/W

°

ELECTRICAL CHARACTERISTICS

(Refer to the test circuit, T

=25°C, Vi= 35V, unless otherwise

j

specified)

Symbol Parameter Test Conditions Min. Typ. Max. Unit

DYNAMICCHARACTERISTICS

V

∆ V
∆

V

∆

∆

V

I

I

Output voltage range Vi= 46V Io=1A V

o

V

Input voltage range Vo=V

i

Line regulation Vi= 10V to 40V Vo=V

o

V

Load regulation Vo=V

o

Internal reference voltage

ref

ref

ref

Vi= 9V to46V Io= 1A 5 5.1 5.2 V

to 36V Io= 2.5A 9 46 V

=1A 15 50 mV

refIo

Io= 0.5A to 2A 10 30 mV

ref

(pin 2)

V

Average temperature

ref

coefficient of refervoltage

T

Dropout voltage Io= 2A 1.4 3 V

d

Maximum operatingload

om

current
Current limiting threshold

7L

(pin 7)

T

=0°C to125°C

j

=1A

I

o

Vi= 9V to46V
V

o=Vref

to 36V

Vi= 9V to46V

o=Vref

to 36V

V

2.5 A

0.4 mV/°C

3 4.5 A

40 V

I

SVR Supply voltage ripple

Input average current Vi= 46V; outputshort-circuit 30 60 mA

SH

Efficiency f = 100KHz V

η

=2A Vo= 12V 85 %

I

o

V

=2V

∆

rejection

fripple

V

o=Vref

i

= 100Hz

rms

o=Vref

50 56 dB

Io = 1A

75 %

f Switching frequency 85 100 115 KHz

∆ f

∆

∆

∆

f

max

Voltagestability of
switching frequency

V

i

f

Temperature stability of
switching frequency

T

j

Maximum operating

Vi= 9V to46V 0.5 %

Tj=0°C to125°C1%

Vo=V

ref

Io= 2A 120 150 KHz

switching frequency

T

Thermal shutdown

sd

junction temperature

150

C

°

3/16

L4960

ELECTRICAL CHARACTERISTICS

(continued)

Symbol Parameter Test Conditions Min. Typ. Max. Unit

DC CHARACTERISTICS

I

Quiescent draincurrent 100% dutycycle

1Q

pins 5and 7 open

V

= 46V

i

0% duty cycle 15 20 mA

-I

Output leakagecurrent 0% duty cycle 1 mA

7L

30 40 mA

SOFT START

I

6SO

I

Source current 100 140 180
Sink current 50 70 120

6SI

ERRORAMPLIFIER

V

V
I

High level output voltage V2= 4.7V I3= 100µA 3.5 V

3H

Low level output voltage V2= 5.3V I3= 100µA 0.5 V

3L

Sink output current V2= 5.3V 100 150 µA

3SI

A

µ

A

µ

-I

G

Source outputcurrent V2= 4.7V 100 150

3SO

I

Input bias current V2= 5.2V 2 10 µA

2

DC openloop gain V3=1Vto3V 46 55 dB

v

OSCILLATOR

-I

Oscillator sourcecurrent 5 mA

5

A

µ

4/16

L4960

CIRCUITOPERATION

(refertothe blockdiagram)

TheL4960is amonolithicstepdownswitchingregu­latorprovidingoutputvoltagesfrom5.1Vto40Vand
delivering 2.5A.

The regulationloop consists of a sawtoothoscilla­tor, error amplifier, comparator and the output
stage.An errorsignalisproducedbycomparingthe
output voltage with a precise 5.1V on-chip refer­ence (zener zaptrimmedto±2%).

Thiserrorsignalis thencomparedwiththesawtooth
signal to generate the fixed frequencypulse width
modulated pulseswhich drivethe output stage.

The gain andfrequencystabilityof the loop can be
adjusted by an external RC network connectedto
pin 3. Closing the loop directly gives an output
voltage of 5.1V.Higher voltages are obtained by
insertinga voltagedivider.

Output overcurrentsat switchon are prevented by
the softstart function.The erroramplifieroutput is
initially clamped by the external capacitor C

and

ss

Figure1. Softstart waveforms

allowedtorise,linearly,asthiscapacitoris charged
by aconstantcurrentsource.Outputoverloadpro­tection is provided in the form of a current limiter.
The load current is sensed by an internal metal
resistorconnectedtoa comparator.When the load
currentexceedsapresetthresholdthis comparator
sets a flipflop whichdisables the output stage and
dischargesthe soft start capacitor.Asecondcom­parator resets the flipflopwhen thevoltageacross
the soft start capacitorhas fallento 0.4V.

The output stage is thusre-enabledandthe output
voltagerisesunder controlof the soft start network.
If the overload condition is still present the limiter
will trigger again when the threshold current is
reached.Theaverageshortcircuitcurrentislimited
to a safevalueby the dead timeintroduced by the
soft start network. The thermaloverload circuit dis­ables circuit operation when the junctiontempera­ture reaches about 150°C and has hysteresis to
preventunstable conditions.

Figure2. Currentlimiterwaveforms

5/16