Rev. 1.20

4

March 12, 2013

HT7L4091

Functional Description

TheHT7L4091isauniversalAC/DCconstantcurrent

LEDdriverdesignedforpeakcurrentmodecontrol.

ThedeviceprovidesbothLEDLinearandPWM

dimmingcurrentfunctions.Thehighinputvoltage

fromarectified85Vto260VACpowerisclamped

tounder25Vbyanexternalcircuitandaninternal

Zenerdiode.ThedevicealsocontainsaninputUnder-

Voltage-Lockout(UVLO)circuit.Whenthevoltage

suppliedontheVINpinexceedstheUVLOhigh

threshold,thegatedriverisenabled.Iftheinput

voltagefallsbelowtheUVLOlowthreshold,thegate

driveristurnedoff.

LED Current Control

The HT7L4091 device is a constant off-time

peak current mode controller.With reference to

theApplicationCircuit,theLEDpeakcurrentis

connectedbetweentheCSandthegroundpins.The

CSpinisconnectedtoanon-invertingterminalof

aninternalcomparatorofwhichaninternal250mV

referenceistiedtotheinvertingterminal.TheLED

avoltagewhichisappliedonthecomparatornon-

invertingterminalandcomparewiththeinternal

250mVreferencevoltage.IfthevoltageontheCSpin

islessthantheinternalreferencevoltage250mV,the

LEDgatedrivingcircuitrywillbeturnedon.While

thevoltageontheCSpinislargerthantheinternal

referencevoltage,theLEDgatedrivingcircuitry

ifthevoltageontheCSpinislessthantheinternal

referencevoltage.Goodlineregulationisafeature

ofconstantoff-timeoperationandtheLEDcurrentis

independentoftheinputvoltage.Sincetheinductor

currentrippleisdependentontheLEDstringvoltage,

theLEDstringvoltagevariationwillresultinLED

currentvariation.Thisistypicallynotaproblemsince

theLEDvoltagevariationforagivenloadisfairly

small.

LED

peak

CS

I

Ripple)

/

(

.

I

.

R

⋅

×

+

=

=

2

1

1

25

0

25

0

WhereIpeakistheMaximumLEDCurrent,Ripple

AverageLEDCurrent.Ripplecanbecontrolledby

theinductor.0

L

V

T

I

Ripple

I

out

off

Ripple

LED

×

=

=

×

Refer to “Inductor Design” for the inductor

calculation.Referto“ProgrammableOffTime”for

Symbol

Description

Test Condition

Min.

Typ.

Max.

Unit

Delay from CS trip to GDR

—

110

—

ns

Linear Dimming pin voltage range

—

0

—

V

Blanking interval

—

200

300

400

ns

Off time

14.7

16.4

18.1

μs

GATE Output Low Level

—

—

0.3

V

GATE Output High Level

12

—

—

V

Gate output rise time

—

120

—

ns

Gate output fall time

—

50

—

ns

Thermal shutdown temperature

—

—

140

—

—

Thermal shutdown temperature hysteresis

—

—

25

—

—

Switch frequency jitter ratio

—

—

±4

—

%

Jitter Period

—

4

—

ms

Short circuit protection Voltage

—

0.45

0.5

0.55

V

Note 3: Specifications are production tested at TA=room temperature. Specifications over the -40°C to 85°C

operating temperature range are assured by design, characterization and correlation with Statistical Quality

Controls (SQC).