Diodes ZXSC410, ZXSC420, ZXSC440 User Manual

ZXSC410/ZXSC420/ZXSC440

DC-DC BOOST SWITCHING CONTROLLERS

Description

The ZXSC410/420/440 are DC-DC boost controllers. Their wide input

voltage range make suitable for operation from 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

allow high voltage boost ratios and/or high output current depending

on 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)

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 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.

Pin Assignments

ZXSC410 (SOT26)

V

1

CC

GND

STDN

2
3

ZXSC420 (SOT26)

1

V

CC

GND
EOR

2
3

ZXSC440 (MSOP-8)

DRIVE

SENSE

VFB

N/C

1

2
3
4

Applications

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

8
7
6

DRIVE

8

VFB

7

SENSE

6

8

7
6
5

DRIVE
VFB
SENSE

V

CC

GND
EOR
STDN

Typical Applications Circuit

ZXSC410/ZXSC420/ZXSC440

Document number: DS33618 Rev. 5 - 2

22µF

ZXSC410

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22µH

ZXTN25012EFH

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100µF

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Pin Descriptions

ZXSC410/ZXSC420/ZXSC440

Pin Name

VCC

GND 2 2 7 Ground

STDN 3 — 5 Shutdown (ZXSC410 and ZXSC440)

EOR — 3 6 End of regulation (ZXSC420 and ZXSC440)

Sense 4 4 3

VFB

Drive 6 6 1

NC — — 4 No connection

ZXSC410 ZXSC420 ZXSC440

Pin Number

1 1 8 Supply Voltage

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

5 5 2

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

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

Functional Block Diagram

Function

ZXSC410/ZXSC420/ZXSC440

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ZXSC410/ZXSC420/ZXSC440

Absolute Maximum Ratings (@T

Parameter Rating Unit

VCC

Drive

EOR

STDN

-0.3 to +10 V

-0.3 to V

-0.3 to V

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

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 mW

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

Symbol Parameter Min Max Unit

VCC VCC Range

TA

VIH

VIL

Ambient Temperature Range

Shutdown Threshold

Shutdown Threshold

Electrical Characteristics (V

Symbol Parameter Conditions Min Typ Max Unit

IQ (Note 4)

I

STDN

EFF (Note 5)

ACC

REF

TCO

REF

T

DRV

F

OSC

Input Parameters

V

SENSE

I

SENSE

VFB

IFB (Note 6)

dVLN

Output Parameters

I

(Note 7)

OUT

I

DRIVE

V

DRIVE

C

DRIVE

V

OHEOR

V

OLEOR

T

EOR

dILD

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. I

7. System not device specification, including recommended transistors.

Quiescent Current

Shutdown Current

Efficiency

Reference Tolerance

Reference Temp Co.

Discharge Pulse Width

Operating Frequency

Sense Voltage (Note 5)

Sense Input Current

Feedback Voltage

Feedback Input Current

Line Voltage Regulation

Output Current

Transistor Drive Current

Transistor Voltage Drive

MOSFET Gate Drive cpbty

EOR Flag Output High

EOR Flag Output Low

EOR Delay Time

Load Current Regulation

is typically half of these values at 3V.

FB

= +25°C, unless otherwise specified.)

A

CC

CC

+0.3

+0.3

CC

+0.3)

V

V

V

V

= +25°C, unless otherwise specified.)

A

1.8 8 V

-40 +85 °C

1.5

VCC

V

0 0.55 V

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

CC

VCC = 8V

220 µA

4.5 µA

50mA > I

> 300mA

OUT

1.8V < VCC < 8V

85 %

-3.0 +3.0 %

0.005 %/°C

1.8V < VCC < 8V

1.7 µs

200 kHz

22 28 34 mV

VFB = 0V; V

TA = +25°C

VFB = 0V; V

SENSE

SENSE

= 0V

= 0V

-1 -7 -15 µA

291 300 309 mV

-1.2 -4.5 µA

0.5 %/V

VIN > 2V, V

V

DRIVE

OUT

= 0.7V

1.8V < VCC < 8V

= VIN

300 mA

2 3.4 5 mA

0

V

-0.4

CC

300 pF

I

= -300nA

EOR

I

= 1mA

EOR

TA = +25°C

2.5

VCC

0 1.15 V

70 195 250 µs

0.01 %/mA

V

V

ZXSC410/ZXSC420/ZXSC440

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N

OLTAG

)

R

CUR

REN

T

)

Typical Characteristics

E (mV

SE V

SE

29.0

28.5

28.0

27.5

T = 25°C

A

T = -40°C

A

T = 85°C

A

8

7

6

5

4

SHUTDOWN CURRENT (µA)

3

ZXSC410/ZXSC420/ZXSC440

I = 0V

STDN

T = -40°C

A

T = 25°C

A

T = 85°C

A

27.0
18234567

INPUT VOLTAGE (V)

Input Voltage vs. Sense Voltage

3.6

T = 85°C

A

3.5

T = 25°C

A

2

182345 67

INPUT VOLTAGE (V)

Input Voltage vs. Shutdown Voltage

310

T = 25°C

A

(mA

T = -40°C

A

IVE
D

3.4

3.3

T = -40°C

A

300

T = 85°C

A

FEEDBACK VOLTAGE (mV)

3.2
18234567

INPUT VOLTAGE (V)

Input Voltage vs. Drive Current

290

18234567

INPUT VOLTAGE (V)

Input Voltage vs. Feedback Voltage

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 2s. The inductor

discharges to the load of the application. After 2s 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 120s 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 V

the output voltage falls below the nominal value for more than 120s, 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.

ZXSC410/ZXSC420/ZXSC440

Document number: DS33618 Rev. 5 - 2

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. Once the current sense voltage across the sensing resistor exceeds

SENSE

). Short dips of the output voltage of less than 120s are ignored. If

CC

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ZXSC410/ZXSC420/ZXSC440

Application Information (cont.)

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 meet 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 500m 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 optimised 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 I

is decided the value of R

can be determined by:

SENSE

R

SENSE

V

SENSE



I

PK

PK

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

CE(SAT)

RMS

SENSE

.

2

ZXSC410/ZXSC420/ZXSC440

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