Diodes ZXSC410E6TA, ZXSC420E6TA, ZXSC440X8TA Schematic [ru]

ZXSC410/ZXSC420/ZXSC440

Document number: DS33618 Rev. 6 - 2

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ZXSC410/ZXSC420/ZXSC440

Description

The ZXSC410/420/440 are DC-DC boost controllers. Their wide input voltage range makes them suitable for operation for a number of battery configurations including single Li-Ion cell and 2~3 alkaline/NiCd/NiMH cells. Using high gain Diodes Zetex-brand switching npn-transistors allows high-voltage boost ratios and/or high output current depending on the transistor. The ZXSC410/440 has a shutdown feature that can also be used for some dimming functionality. ZXSC420/440 includes an End of Regulation flag that can be used to indicate when the regulator is no longer able to maintain the regulated output voltage/current or has reached the required current/voltage. The ZXSC440 combines the features of the ZXSC410 and ZXSC420 into one device.

Features

 1.65V to 8V Supply Range  Typical Output Regulation of ±1%  Over 85% Typical Efficiency  Output Currents Up to 300mA  4.5µA Typical Shutdown Current ZXSC410/440  End of Regulation Output ZXSC420/440  Available in SOT26 and MSOP-8  Totally Lead-Free & Fully RoHS Compliant (Notes 1 & 2)  Halogen and Antimony Free. “Green” Device (Note 3)

Pin Assignments

ZXSC410 (SOT26)

DRIVE

VFB SENSE

GND

STDN

1 2

8 7

ZXSC420 (SOT26)

DRIVE

VFB

SENSE

GND EOR

1 2 3

8 7 6

ZXSC440 (MSOP-8)

DRIVE

VFB

SENSE

N/C

GND

EOR STDN

3 4

6 5

Applications

 System Power for Battery Portable Products  LCD Bias  Local Voltage Conversion  High-Brightness LED Driving

ZXSC410

ZXTN25012EFH

ZHCS2000

22µH

18mΩ 820mΩ

22µF

100µF

DC-DC BOOST SWITCHING CONTROLLERS

Notes: 1. No purposely added lead. Fully EU Directive 2002/95/EC (RoHS) & 2011/65/EU (RoHS 2) compliant.

2. See http://www.diodes.com/quality/lead_free.html for more information about Diodes Incorporated’s definitions of Halogen- and Antimony-free, "Green" and Lead-free.

3. Halogen- and Antimony-free "Green” products are defined as those which contain <900ppm bromine, <900ppm chlorine (<1500ppm total Br + Cl) and <1000ppm antimony compounds.

Typical Applications Circuit

ZXSC410/ZXSC420/ZXSC440

Document number: DS33618 Rev. 6 - 2

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ZXSC410/ZXSC420/ZXSC440

Pin Name

Pin Number

Function

ZXSC410

ZXSC420

ZXSC440

VCC

1 1 8

Supply Voltage

GND 2 2

Ground

STDN 3 —

Shutdown (ZXSC410 and ZXSC440)

EOR — 3

End of regulation (ZXSC420 and ZXSC440)

Sense 4 4

Inductor current sense input. Internal threshold voltage set to 28mV. Connect external sense resistor.

VFB

5 5 2

Reference voltage. Internal threshold set to 300mV. Connect external resistor network to set output voltage.

Drive 6 6

Drive output for external switching transistor. Connect to base or gate of external switching transistor.

NC — —

No connection

Pin Descriptions

Functional Block Diagram

ZXSC410/ZXSC420/ZXSC440

Document number: DS33618 Rev. 6 - 2

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ZXSC410/ZXSC420/ZXSC440

Parameter

Rating

Unit

VCC

-0.3 to +10

Drive

-0.3 to VCC +0.3

EOR

-0.3 to VCC +0.3

STDN

-0.3 to The lower of (+5.0) or (VCC +0.3)

VFB, Sense

-0.3 to The lower of (+5.0) or (VCC +0.3)

Operating Temperature

-40 to +85

°C

Storage Temperature

-55 to +120

°C

Power Dissipation @ +25°C

450

Symbol

Parameter

Min

Max

Unit

VCC

VCC Range

1.8 8 V

Ambient Temperature Range

-40

+85

°C

VIH

Shutdown Threshold

1.5

VCC V VIL

Shutdown Threshold

0.55

Symbol

Parameter

Conditions

Min

Typ

Max

Unit

IQ (Note 4)

Quiescent Current

VCC = 8V

- - 220

µA

STDN

Shutdown Current

4.5 - µA

EFF (Note 5)

Efficiency

50mA > I

OUT

> 300mA

85 - %

ACC

REF

Reference Tolerance

1.8V < VCC < 8V

-3.0 - +3.0

TCO

REF

Reference Temp Co.

0.005

%/°C

DRV

Discharge Pulse Width

1.8V < VCC < 8V

1.7 - µs

OSC

Operating Frequency

- - 200

kHz

Input Parameters

SENSE

Sense Voltage (Note 5)

SENSE

Sense Input Current

VFB = 0V; V

SENSE

= 0V

-1

-7

-15

µA

VFB

Feedback Voltage

TA = +25°C

291

300

309

IFB (Note 6)

Feedback Input Current

VFB = 0V; V

SENSE

= 0V

-1.2 - -4.5

µA

dVLN

Line Voltage Regulation

0.5 - %/V

Output Parameters

OUT

(Note 7)

Output Current

VIN > 2V, V

OUT

= VIN

300 - -

DRIVE

Transistor Drive Current

DRIVE

= 0.7V

3.4 5 mA

DRIVE

Transistor Voltage Drive

1.8V < VCC < 8V

-0.4 V C

DRIVE

MOSFET Gate Drive cpbty

300 - pF

OHEOR

EOR Flag Output High

EOR

= -300nA

2.5

VCC V V

OLEOR

EOR Flag Output Low

EOR

= 1mA

0 - 1.15

EOR

EOR Delay Time

TA = +25°C

195

250

µs

dILD

Load Current Regulation

- - 0.01

%/mA

Absolute Maximum Ratings (@T

Caution: Stresses greater than the 'Absolute Maximum Ratings' specified above, may cause permanent damage to the device. These are stress ratings only; functional operation of the device at these or any other conditions exceeding those indicated in this specification is not implied. Device reliability may be affected by exposure to absolute maximum rating conditions for extended periods of time. Semiconductor devices are ESD sensitive and may be damaged by exposure to ESD events. Suitable ESD precautions should be taken when handling and transporting these devices.

Recommended Operating Conditions (@T

= +25°C, unless otherwise specified.)

Electrical Characteristics (V

= 3V, @TA = +40°C to +85°C, unless otherwise specified.)

Notes: 4. Excluding gate/base drive current.

5. Effective sense voltage observed when switching at approximately 100kHz. The internal comparator propagation delay of approximately 1µs causes an increase in the effective sense voltage over a DC measurement of the sense voltage.

6. IFB is typically half of these values at 3V.

7. System not device specification, including recommended transistors.

ZXSC410/ZXSC420/ZXSC440

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ZXSC410/ZXSC420/ZXSC440

1 82 3 4 5 6 7

29.0

27.0

28.5

28.0

27.5

INPUT VOLTAGE (V)

Input Voltage vs. Sense Voltage

SENSE VOLTAGE (mV)

T = -40°C

T = 25°C

T = 85°C

1 82 3 4 5 6 7

INPUT VOLTAGE (V)

Input Voltage vs. Shutdown Voltage

SHUTDOWN CURRENT (µA)

T = -40°C

T = 25°C

T = 85°C

I = 0V

STDN

1 82 3 4 5 6 7

3.5

3.2

3.4

3.3

3.6

INPUT VOLTAGE (V)

Input Voltage vs. Drive Current

DRIVE CURRENT (mA)

T = -40°C

T = 25°C

T = 85°C

INPUT VOLTAGE (V)

Input Voltage vs. Feedback Voltage

1 82 3 4 5 6 7

310

290

300

FEEDBACK VOLTAGE (mV)

T = -40°C

T = 25°C

T = 85°C

Typical Characteristics

ZXSC410/ZXSC420/ZXSC440

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ZXSC410/ZXSC420/ZXSC440

Application Information

Functional Blocks

Bandgap Reference

All threshold voltages and internal currents are derived from a temperature compensated bandgap reference circuit with a reference voltage of

1.22V nominal.

Dynamic Drive Output

Depending on the input signal, the output is either “LOW” or “HIGH”. In the high state a 2.5mA current source, (max drive voltage = VCC -0.4V) drives the base or gate of the external transistor. In order to operate the external switching transistor at optimum efficiency, both output states are initiated with a short transient current in order to quickly discharge the base or the gate of the switching transistor.

Switching Circuit

The switching circuit consists of two comparators, Comp1 and Comp2, a gate U1, a monostable and the drive output. Normally the DRIVE output is “HIGH”; the external switching transistor is turned on. Current ramps up in the inductor, the switching transistor and external current sensing resistor. This voltage is sensed by comparator, Comp2, at input I 20mV, comparator Comp2 through gate U1 triggers a re-triggerable monostable and turns off the output drive stage for 2μs. The inductor discharges to the load of the application. After 2μs a new charge cycle begins, thus ramping the output voltage. When the output voltage reaches the nominal value and VFB gets an input voltage of more than 300mV, the monostable is forced “on” from Comp1 through gate U1, until the feedback voltage falls below 300mV. The above action continues to maintain regulation.

EOR, End of Regulation Detector (ZXSC420/440)

The EOR circuit is a retriggerable 120μs monostable, which is re-triggered by every down regulating action of comparator Comp1. As long as regulation takes place, output EOR is “HIGH” (high impedance, 100K to VCC). Short dips of the output voltage of less than 120μs are ignored. If the output voltage falls below the nominal value for more than 120μs, output EOR goes ”LOW”. The reason for this to happen is usually a slowly

progressing drop of input voltage from the discharging battery. Therefore, the output voltage will also start to drop slowly. With the EOR detector, batteries can be used to the ultimate end of discharge, with enough time left for a safe shutdown. It can also be used in high-voltage photoflash with the ZXSC440 to show when the capacitor is fully charged.

Shutdown Control

The ZXSC410/440 offers a shutdown mode that consumes a standby current of less than 5µA. The ZXSC410/440 is enabled, and is in normal operation, when the voltage at the STDN pin is between 1V and 8V (and also open circuit). The ZXSC410/440 is shutdown with the driver disabled when the voltage at the STDN pin is 0.7V or lower. The STDN input is a high impedance current source of 1µA typ. The driving device can be an open-collector or -drain or a logic output with a “High” voltage of 5V max. The device shutdown current depends on the supply voltage, (see typical characteristics graph).The ZXSC440 with its STDN pin and EOR pins can be used as a camera flash driver.

The STDN pin is used to initiate the high-voltage capacitor charge cycle. The EOR pin is used as flag to show when the capacitor has been charged to the appropriate level.

A transformer is used to boost the voltage. If designing a transformer, bear in mind that the primary current may be over an amp and, if this flows through 10 turns, the primary flux will be 10 Amp. Small number of turns and small cores will need an air gap to cope with this value without saturation. Secondary winding capacitance should not be too high as this is working at 300V and could soon cause excessive losses.

. Once the current sense voltage across the sensing resistor exceeds

SENSE

ZXSC410/ZXSC420/ZXSC440

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ZXSC410/ZXSC420/ZXSC440

SENSE



Application Information (continued)

External Component Selection

Switching Transistor Selection

The choice of switching transistor has a major impact on the converter efficiency. For optimum performance, a bipolar transistor with low V and high gain is required. The V transistor is switched off. Diodes SOT26 transistors are an ideal choice for this application.

of the switching transistor is also an important parameter as this sees the full output voltage when the

CEO

Schottky Diode Selection

As with the switching transistor, the Schottky rectifier diode has a major impact on the converter efficiency. A Schottky diode with a low forward voltage and fast recovery time should be used for this application.

The diode should be selected so that the maximum forward current rating is greater or equal to the maximum peak current in the inductor, and the maximum reverse voltage is greater or equal to the output voltage. The Diodes ZHCS Series meets these needs.

Inductor Selection

The inductor value must be chosen to satisfy performance, cost and size requirements of the overall solution. Inductor selection has a significant impact on the converter performance. For applications where efficiency is critical, an inductor with a series resistance of 500mΩ or less should be used.

Output Capacitors

Output capacitors are a critical choice in the overall performance of the solution. They are required to filter the output and supply load transient currents. There are three parameters which are paramount in the selection of the output capacitors, capacitance, I capacitance value is selected to meet the load transient requirements. The capacitors I solution.

The ESR of the output capacitor can also affect loop stability and transient performance. The capacitors selected for the solutions and indicated in the reference designs are optimized to provide the best overall performance.

rating must meet or exceed the current ripple of the

RIPPLE

and ESR. The

RIPPLE

Input Capacitors

The input capacitor is chosen for its voltage and RMS current rating. The use of low ESR electrolytic or tantalum capacitors is recommended. Capacitor values for optimum performance are suggested in the reference design section. Also note that the ESR of the input capacitor is effectively in series with the input and hence contributes to efficiency losses in the order of I ESR.

Peak Current Definition

In general, the IPK value must be chosen to ensure that the switching transistor, Q1, is in full saturation with maximum output power conditions, assuming worse case input voltage and transistor gain under all operating temperatureextremes.Once IPK is decided, the value of R determined by:

SENSE

CE(SAT)

RMS

can be

Sense Resistor

A low-value sense resistor is required to set the peak current. Power in this resistor is negligible due to the low sense voltage threshold, V

SENSE

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