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ZXSC410 ZXSC420
VOLTAGE MODE BOOST CONVERTER
DESCRIPTION
The ZXSC410 is voltage mode boost converter in SOT23-6 package. Its excellent load and line regulation means that for the full supply range from lithium Ion cells, the output voltage will typically change by less than 1%. Using high efficiency Zetex switching transistors allow output voltages of tens of volts depending on the selected transistor. The ZXSC420 includes a battery low indicator. This operates by indicating when the converter is no longer able to maintain the regulated output voltage rather than setting a preset threshold, thereby making it suitable for various battery options and load currents.
FEATURES
* 1.65V to 8V supply range * Typical output regulation of 1% * Over 85% typical efficiency * Output currents up to 300mA * 4.5 A typical shutdown current ZXSC410 * End of regulation output ZXSC420
SOT23-6
ORDERING INFORMATION
DEVICE ZXSC410E6TA ZXSC420E6TA REEL SIZE 7"
7"
TAPE WIDTH 8mm 8mm
QUANTITY PER REEL 3000 units 3000 units
APPLICATIONS
* System power for battery portable products * LCD bias * Local voltage conversion
TYPICAL APPLICATIONS DIAGRAM
L1 VIN
ZHCS1000
D1 VOUT
C1 Q1 U1
VCC DRIVE STDN SENSE GND VFB
FMMT617
R2 C2
ZXSC410
R1
R3
DEVICE MARKING
* C410 ZXSC410 * C420 ZXSC420
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SEMICONDUCTORS
ZXSC410 ZXSC420
ABSOLUTE MAXIMUM RATINGS
VCC DRIVE EOR STDN VFB, SENSE Operating Temp. Storage Temp. Power Dissipation -0.3V to -0.3V to -0.3V to -0.3V to -0.3V to -40C to -55C to 450mW +10V VCC + 0.3V VCC + 0.3V The lower of (+5.0V) or (VCC + 0.3V) The lower of (+5.0V) or (VCC + 0.3V) +85C +125C * (ZXSC420 only) * (ZXSC410 only)
ELECTRICAL CHARACTERISTICS
Test Conditions VCC= 3V, T= -40C to 85C unless otherwise stated.
Symbol Parameter Conditions Min Supply parameters V CC Iq 1 I STDN Eff 2 Acc REF TCO REF T DRV F OSC V SENSE I SENSE V FB I FB 2 V IH V IL dV LN I OUT 3 I DRIVE V DRIVE C DRIVE VOH EOR VOL EOR T EOR dI LD
Note
1 2 Excluding gate/base drive current. 3 IFB is typically half of these values at
Limits Typ Max
Units
V CC Range Quiescent Current Shutdown Current V CC = 8V
1.8
8 220 4.5
V A A
Efficiency Reference tolerance Reference Temp Co Discharge pulse width Operating Frequency
50mA > I OUT > 300mA 1.8V < V CC < 8V 1.8V < V CC < 8V -3.0
85 3.0 0.005 1.7 200
% % %/ C s kHz
Input parameters sense voltage sense input current Feedback voltage Feedback input current Shutdown high voltage Shutdown low voltage Line voltage regulation V FB =0V;V SENSE =0V T A = 25C V FB =0V;V SENSE =0V 22 -1 291 -1.2 1.5 0 0.5 1 28 -7 300 34 -15 309 -4.5 V CC 0.55 V V %/V mV A mV A
Output parameters 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 I EOR = -300nA I EOR = 1mA T A = 25C 2.5 0 70 195 V IN > 2V, V OUT = V IN V DRIVE = 0.7V 1.8V < V CC < 8V 300 2 0 300 V CC 1.15 250 0.01 3.4 5 V CC -0.4 mA mA V pF V V s %mA
3V System not device spec, including recommended transistors.
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ZXSC410 ZXSC420
TYPICAL CHARACTERISTICS
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SEMICONDUCTORS
ZXSC410 ZXSC420
DEVICE DESCRIPTION
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.
STDN Shutdown VCC
Block Diagrams
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 ISENSE. Once the current sense voltage across the sensing resistor exceeds 20mV, comparator Comp2 through gate U1 triggers a re-triggerable monostable and turns off the output drive stage for 2s. The inductor discharges to the load of the application. After 2s 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 The EOR circuit is a retriggerable 120s 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 120s are ignored. If the output voltage falls below the nominal value for more than 120s, 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.
R3 R1
Bandgap Reference
Bias Generator
+ Comp 1 _
R2
+ Comp 2 _
U1
Monostable 2s
Dynamic Drive
DRIVE
GND VFB
SENSE
Fig. 1 ZXSC410
Fig. 1 ZXSC420
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ZXSC410 ZXSC420
PIN DESCRIPTIONS
Pin No. 1 2 3 4 5 6 Name V CC GND STDN/EOR SENSE V FB DRIVE Description Supply voltage, 1.8V to 8V. Ground Shutdown ZXSC410 / End of regulation ZXSC420 Inductor current sense input. Internal threshold voltage set to 28mV. Connect external sense resistor. 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.
APPLICATIONS INFORMATION
Switching transistor selection The choice of switching transistor has a major impact on the converter efficiency. For optimum performance, a bipolar transistor with low VCE(SAT) and high gain is required. The VCEO of the switching transistor is also an important parameter as this sees the full output voltage when the transistor is switched off. Zetex SuperSOTTM transistors are an ideal choice for this application. 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 Zetex ZHCS Series meet these needs. Combination devices To minimise the external component count Zetex recommends the ZX3CDBS1M832 combination of NPN transistor and Schottky diode in a 3mm x 2mm MLP package. This device is recommended for use in space critical applications. The IC is also capable of driving MOSFETs. Zetex recommends the ZXMNS3BM832 combination of low threshold voltage N-Channel MOSFET and Schottky diode in a 3mm x 2mm MLP package. This device is recommended for use in space critical applications. 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. A list of recommended inductors is listed in the table below:
Part No. Manufacture L I PK R DC (A) ( )
CMD4D11-100MC Sumida CMD4D11-220MC Sumida LPO2506OB-103 ST2006103 Coilcraft Standex Electronics Inc
10H 0.5 0.457 22H 0.4 0.676 10H 1.0 0.24 10H 0.6 0.1
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 temperature extremes. Once IPK is decided the value of RSENSE can be determined by: RSENSE = VSENSE IPK
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SEMICONDUCTORS
ZXSC410 ZXSC420
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, VSENSE. Below is a table of recommended sense resistors:
Manufacture Cyntec IRC Series RL1220 LR1206 R DC ( ) Range 0.022 - 10 0.010 - 1.0 Size 0805 1206 Tolerance 5% 5% URL http://www.cyntec.com http://www.ictt.com
Output power calculation By making the above assumptions for inductance and peak current the output power can be determined by: POUT = IAV x VIN x where IAV = and TON = and IPK x L TDIS = VOUT - VIN and TOFF 1.7s (internally set by ZXSC410) and = efficiency i.e. 100% = 1 Operating frequency can be derived by: F= 1 TON + TOFF IPK x L VIN IPK (TON + T DIS) X 2 (TON + T OFF ) = (Watts)
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, IRIPPLE and ESR. The capacitance value is selected to meet the load transient requirements. The capacitors IRIPPLE rating must meet or exceed the current ripple of the 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. Input capacitors The input capacitor is chosen for its voltage and RMS current rating. The use of low ESR electrolitic 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 capcitor is effectively in series with the input and hence contributes to efficiency losses in the order of IRMS2 . ESR.
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ZXSC410 ZXSC420
Output voltage adjustment The ZXSC410/420 are adjustable output converters allowing the end user the maximum flexibilty. For adjustable operation a potential divider network is connected as follows: Layout issues Layout is critical for the circuit to function in the most efficient manner in terms of electrical efficiency, thermal considerations and noise. For `step-up converters' there are four main current loops, the input loop, power-switch loop, rectifier loop and output loop. The supply charging the input capacitor forms the input loop. The power-switch loop is defined when Q1 is `on', current flows from the input through the inductor, Q1, RSENSE and to ground. When Q1 is `off', the energy stored in the inductor is transferred to the output capacitor and load via D1, forming the rectifier loop. The output loop is formed by the output capacitor supplying the load when Q1 is switched back off. To optimise for best performance each of these loops kept separate from each other and interconnected with short, thick traces thus minimising parasitic inductance, capacitance and resistance. Also the RSENSE resistor should be connected, with minimum trace length, between emitter lead of Q1 and ground, again minimising stray parasitics.
VOUT RA VFB RB
GND
The output voltage is determined by the equation: RA VOUT = VFB 1+ RB where VFB=300mV The resistor values, RA and RB, should be maximised to improve efficiency and decrease battery drain. Optimisation can be achieved by providing a minimum current of IFB(MAX)=200nA to the VFB pin. Output is adjustable from VFB to the (BR)VCEO of the switching transistor, Q1. Note: For the reference designs, RA is assigned the label R2 and RB the label R3.
CONNECTION DIAGRAMS ZXSC410
SOT23-6
ZXSC420
SOT23-6
VCC GND STDN
DRIVE VFB SENSE
VCC GND EOR
DRIVE VFB SENSE
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SEMICONDUCTORS
ZXSC410 ZXSC420
REFERENCE DESIGNS
ZXSC410 DC-DC Controller VIN=2.5V to 4.2V VOUT=5V; ILOAD=100mA
Bill of Materials
Ref U1 U2 L1 R1 R2 R3 C1 C2 C3 22H 100m 16k 1k 22F/6V3 22F/6V3 1nF Value Part Number ZXSC410E6 ZX3CDBS1M832 CMD4D11-220 LR1206 / RL1220 Generic Generic GRM Series GRM Series Generic Manufacture Zetex Zetex Sumida IRC / Cyntec Generic Generic Murata Murata Generic Comments DC-DC converter IC Low sat NPN + 1A Schottky 1mm height profile 1206 / 0805 size 0603 size 0603 size 1206 size 1206 size 0603 size
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ZXSC410 ZXSC420
Performance Graphs
V=1V/DIV; T=10S/DIV
V=50mV/DIV; T=10S/DIV
Switching Waveform
Output Ripple
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SEMICONDUCTORS
ZXSC410 ZXSC420
ZXSC410 as Triple Output TFT Bias AVDD=9V/180mA VON=18V/10mA VOFF=9V/10mA
ZXSC410 as Triple Output TFT Bias AVDD=9V/180mA VON=27V/10mA VOFF=9V/10mA
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ZXSC410 ZXSC420
Sequencing AVDD and VON
By adding the circuit below to the LCD bias output (VON) of the converter a 10ms delay can be achieved between AVDD power up and VON power up. The circuit operates by a delay in turning the PMOS transistor on, which transfers to a 10ms delay between input and output of the circuit.
The delay is set by the RC time constant of R1 and C1. The diode, D1, discharges the gate of the PMOS when the main system supply is turned off, guaranteeing a delay every turn on cycle.
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SEMICONDUCTORS
ZXSC410 ZXSC420
PACKAGE OUTLINE PAD LAYOUT DETAILS
b
e L2
E
E1
e1 D
a
DATUM A
C
A
A2
A1
CONTROLLING DIMENSIONS IN MILLIMETRES APPROX CONVERSIONS INCHES.
PACKAGE DIMENSIONS
Millimetres DIM Min A A1 A2 b C D 0.90 0.00 0.90 0.35 0.09 2.80 Max 1.45 0.15 1.30 0.50 0.20 3.00 Min 0.35 0 0.035 0.014 0.0035 0.110 Max 0.057 0.006 0.051 0.019 0.008 0.118 E E1 L e e1 L Inches DIM Min 2.60 1.50 0.10 Max 3.00 1.75 0.60 Min 0.102 0.059 0.004 Max 0.118 0.069 0.002 Millimetres Inches
0.95 REF 1.90 REF 0 10
0.037 REF 0.074 REF 0 10
(c) Zetex plc 2003
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These offices are supported by agents and distributors in major countries world-wide. This publication is issued to provide outline information only which (unless agreed by the Company in writing) may not be used, applied or reproduced for any purpose or form part of any order or contract or be regarded as a representation relating to the products or services concerned. The Company reserves the right to alter without notice the specification, design, price or conditions of supply of any product or service. For the latest product information, log on to
www.zetex.com ISSUE 2 - May 2003
SEMICONDUCTORS
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