Zetex (Now Diodes) ZXLD1101 Schematic [ru]

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ZXLD1101

ADJUSTABLE LED DRIVER WITH INTERNAL SWITCH IN TSOT23-5

DESCRIPTION

The ZXLD1101 is a PFM inductive boost converter designed for driving 2, 3 or 4 series connected white

LEDs from a Li-Ion cell and up to 8 LEDs from a 5V supply. The device operates from an input supply of between 2.5V and 5.5V and provides an adjustable output current of up to 50mA.

The ZXLD1101 includes the output switch and peak current sense resistor, and can operate with a maximum output voltage of 28V.

Quiescent current is typically 60 A and a shutdown function is provided to reduce this current to less than 500nA in the 'off' state.

Output current can be adjusted by applying a PWM control signal to the 'Enable' pin. Depending upon the control frequency, this will provide either a continuous or a 'chopped' output current. The PWM filter components are contained within the chip.

The device is assembled in the TSOT23-5 pin package with 1mm maximum height profile.

ADVANCED FEATURES

True Analog Dimming via PWM

FEATURES

1mm height profile TSOT23-5 pin package

Internal PWM filter for flicker free output

High efficiency (80% typ)

Wide input voltage range: 2.5V to 5.5V

Up to 50mA output current

Low quiescent current: (60 A typ)

500nA maximum shutdown current

Up to 1MHz switching frequency

Low external component count

Inherently matched LED currents

APPLICATIONS

Mobile phones

Digital cameras

PDAs

LCD modules

Portable internet appliances

Palmtop computers

TYPICAL APPLICATION CIRCUIT

PIN CONNECTIONS

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SEMICONDUCTORS

ZXLD1101

ORDERING INFORMATION

DEVICE

DEVICE DESCRIPTION

TEMPERATURE RANGE

PART MARK

TAPING

 

 

 

 

OPTIONS

 

 

 

 

 

ZXLD1101ET5

Boost converter in TSOT23-5

-40°C to +85°C

1101

TA, TC

 

 

 

 

 

ZXLD1101ET5TA for 7” reel of 3,000 devices

ZXLD1101ET5TA for 13” reel of 10,000 devices

ABSOLUTE MAXIMUM RATINGS (Voltages to GND unless otherwise stated)

PARAMETER

SYMBOL

LIMIT

UNIT

 

 

 

 

Input voltage

(VIN)

7

V

LX output voltage

(VLX)

30

V

Switch output current

(ILX)

500

mA

Power dissipation

(PD)

300

mW

 

 

 

 

Operating temperature

(TOP)

-40 to 85

°C

Storage temperature

(TST)

-55 to 150

°C

Junction temperature

(Tj MAX)

125

°C

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ZXLD1101

ELECTRICAL CHARACTERISTICS (at VIN = 3V, Tamb = 25°C unless otherwise stated(1))

SYMBOL

PARAMETER

CONDITIONS

MIN.

TYP.

MAX.

UNIT

 

 

 

 

 

 

 

VIN

Input voltage

 

2.5

 

5.5

V

IIN

Supply current

 

 

 

 

 

 

Quiescent

VEN = VIN, ILX = 0,

 

60

100

A

 

 

Output not switching

 

 

 

 

 

Shutdown

VEN = 0V

 

 

500

nA

VFB

FB pin control voltage

 

90.5

 

109.5

mV

IFB

FB pin input current

 

 

 

100

nA

fLX

Operating frequency

L=10 H, VOUT =10V,

 

0.35

1

MHz

 

 

IOUT=20mA

 

 

 

 

TOFF

LX output 'OFF' time

 

350

500

 

ns

TON

LX output 'ON' time (2)

 

 

 

5

µs

ILXpk

Switch peak current limit

L=10 H, VOUT =10V,

 

320

 

mA

 

 

IOUT=20mA

 

 

 

 

RLX

Switch 'On' resistance

 

 

1.5

 

 

ILX(leak)

Switch leakage current

VLX =20V

 

 

1

µA

VOUT

Controller output voltage

Normal operation

 

 

28

V

VENH

EN pin High level Input voltage

Device active

1.5

 

VIN

V

VENL

EN pin Low level Input voltage

Device in shutdown

 

 

0.4

V

IENL

EN pin Low level input current

VEN =0V

 

 

-100

nA

IENH

EN pin High level input current

VEN =VIN

 

 

1

A

TEN(hold)

EN pin turn off delay (3)

VEN switched from high

 

120

 

µs

 

 

to low

 

 

 

 

T/T

PWM duty cycle range at ‘EN’ input for

10kHz < f < 100kHz,

20

 

100

%

 

filtered PWM control (4)

VENH =VIN

 

 

 

 

fLPF

Internal PWM low pass filter cut-off

 

 

4

 

kHz

 

frequency

 

 

 

 

 

ALPF

Filter attenuation

f=30kHz

 

52.5

 

dB

T/T

PWM duty cycle range at ‘EN’ input for

f < 1kHz, VENH =VIN

0

 

100

%

 

‘gated’ output current control (5)

 

 

 

 

 

NOTES:

(1)Production testing of the device is performed at 25°C. Functional operation of the device over a -40°C to +85°C temperature range is guaranteed by design, characterisation and process control.

(2)Nominal 'on' time (TONnom) is defined by the input voltage (VIN), coil inductance (L) and peak current (ILXpkdc) according to the expression: TONnom = {ILX(pkdc) x L/VIN} +200ns.

(3)This is the time for which the device remains active after the EN pin has been asserted low. This delay is necessary to allow the output to be maintained during dc PWM mode operation.

(4)The minimum PWM signal frequency during this mode of operation is to ensure that the device remains active during PWM control. This provides a continuous dc output current. For lower frequencies, the device will be gated 'on' and 'off' during PWM control.

(5)The maximum PWM signal frequency during this mode of operation should be kept as low as possible to minimise errors due to the turn-off delay of the device (see Enable pin turn-off delay).

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SEMICONDUCTORS

ZXLD1101

PIN DESCRIPTION

PIN NO.

NAME

DESCRIPTION

 

 

 

1

FB

Feedback pin for current control loop (connect resistor R1

 

 

from this pin to GND for output current I=100mV/ R1)

 

 

 

2

GND

Ground (0V)

 

 

 

3

LX

Output of NDMOS switch

 

 

 

4

VIN

Input voltage (2.5V to 5.5V). Decouple with capacitor close

 

 

to device

5

EN

Enable input (active high to turn on device)

 

 

Also used to adjust output current by PWM signal

 

 

Connect to Vin for permanent operation

 

 

 

BLOCK DIAGRAM

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ZXLD1101

DEVICE DESCRIPTION

The device is a PFM flyback dc-dc boost converter, working in discontinuous mode.

With reference to the chip block diagram and typical application circuit, the operation of the device is as follows:

Control loop

When 'EN' is high, the control circuits become active and the low side of the coil (L1) is switched to ground via NDMOS transistor (MN). The current in L1 is allowed to build up to an internally defined level (nominally 320mA) before MN is turned off. The energy stored in L1 is then transferred to the output capacitor (C2) via schottky diode (D1). When the voltage on C2 has risen above the threshold voltage of the series connected LEDs, current will flow through external sense resistor R1. The voltage developed across R1 is sensed at pin 'FB' and compared to a 100mV reference voltage (VREF). A comparator senses when the feedback voltage is above VREF and its output is used to control the 'off' time of the output switch. The control loop is self-oscillating, producing pulses of up to 5 s maximum duration (switch 'on'), at a frequency that varies in proportion to the LED current. The feedback

loop maintains a voltage of VREF at the FB pin and therefore defines a maximum LED current equal to VREF

divided by R1. The minimum 'off' time of the output switch is fixed at 0.5 s nominal, to allow time for the coil's energy to be dissipated before the switch is turned on again. This maintains stable and efficient operation in discontinuous mode.

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Filtered PWM operation

The input of an internal low pass filter is switched to

VREF when the EN pin is high and switched to ground when the EN pin is low. The output of this filter drives

the comparator within the control loop. A continuous high state on EN therefore provides a filtered voltage of value VREF to the comparator. However, by varying the duty cycle of the EN signal at a suitably high frequency

(f>10kHz), the control loop will see a voltage, that has an average value equal to the duty cycle multiplied by VREF. This provides a means of adjusting the output current to a lower value. It also allows the device to be both turned on and adjusted with a single signal at the 'EN' pin. The output during this mode of operation will be a dc current equal to (VREF /R1) x duty cycle

Gated PWM operation

The internal circuitry of the ZXLD1101 is turned off when no signal is present on the 'EN' pin for more than 120 s (nominal). A low frequency signal applied to the EN pin will therefore gate the device 'on' and 'off' at the gating frequency and the duty cycle of this signal can be varied to provide a 'chopped' output current equal to (VREF /R1) x duty cycle. For best accuracy, the gating frequency should be made as low as possible (e.g. below 1kHz), such that the turn off delay of the chip is only a small proportion of the gating period

Further details of setting output current are given in the applications section under brightness control.

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SEMICONDUCTORS

ZXLD1101

TYPICAL CHARACTERISTICS

(For typical application circuit at VIN=3V and TA=25°C unless otherwise stated)

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