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Ordering number : ENA0588
Monolithic Linear IC
LA5735M
Overview
Separately-Excited Step-Down
Switching Regulator (Variable Type)
The LA5735M is a separately-excited step-down switching regulator (variable type).
Functions
* Time-base generator (300kHz) incorporated. * Current limiter incorporated. * Thermal shutdown circuit incorporated.
Specifications
Absolute Maximum Ratings at Ta = 25C
Parameter Input voltage Maximum output current SW pin application reverse voltage VOS pin application voltage Allowable power dissipation Operating temperature Storage temperature * Specified circuit board : 114.3x76.1x1.6mm3, Symbol VIN IO max VSW VVOS Pd max Topr Tstg glass epoxy board. Mounted on a circuit board.* Conditions Ratings 34 0.6 -1 -0.2 to 7 0.8 -30 to +125 -40 to +150 Unit V A V V W C C
Recommended Operating Conditions at Ta = 25C
Parameter Input voltage range Symbol VIN Conditions Ratings 4.5 to 32 Unit V
Any and all SANYO Semiconductor products described or contained herein do not have specifications that can handle applications that require extremely high levels of reliability, such as life-support systems, aircraft's control systems, or other applications whose failure can be reasonably expected to result in serious physical and/or material damage. Consult with your SANYO Semiconductor representative nearest you before using any SANYO Semiconductor products described or contained herein in such applications. SANYO Semiconductor assumes no responsibility for equipment failures that result from using products at values that exceed, even momentarily, rated values (such as maximum ratings, operating condition ranges, or other parameters) listed in products specifications of any and all SANYO Semiconductor products described or contained herein.
11707 MS PC 20061030-S00008 No.A0588-1/7
LA5735M
Electrical Characteristics at Ta = 25C, VIN = 15V
Parameter Reference voltage Reference pin bias current Switching frequency Short-circuit protection circuit operating switching frequency Saturation voltage Maximum on duty Minimum on duty Output leakage current Supply current Current limiter operating voltage Thermal shutdown operating temperature Thermal shutdown Hysteresis width * Design target value : Design guarantee values are replaced with electrical measurements, and are not measured by temperature. TSD Designed target value. * 15 C Vsat D max D min Ilk Iin IS TSD Designed target value. * IOUT = 0.3A, VOS = 0V VOS = 0V VOS = 5V VIN = 30V,SWOUT = -0.4V VOS = 2V 0.7 165 5 1 100 0 200 10 1.15 V % % A mA A C Symbol VOS IFB fosc fscp 240 IO = 0.3A Conditions min 1.20 Ratings typ 1.23 1 300 15 max 1.26 2 360 V A kHz kHz Unit
Package Dimensions
unit : mm (typ) 3032D
1
Pd max -- Ta
Designated board : 114.3x76.1x1.6mm3 glass epoxy Mounted on a board
5.0 8 5
Allowable power dissipation, Pd max - W
0.8
0.6
4.4 6.4
0.63
0.4
1 (0.65) 1.27
4 0.35 0.15
0.2
(1.5)
1.7max
0.16
0 --30--20
0
20
40
60
80
100
120
140
Ambient temperature, Ta - C
0.1
SANYO : MFP8(225mil)
No.A0588-2/7
LA5735M
Pin Assignment
NC NC GND NC
VIN
NC SWOUT VOS
Block Diagram
VIN
1 Reg. OCP
3 SWOUT
OSC NC NC NC NC 2 Comp. 5 7 8
Reset Drive
TSD 4 VOS
Amp. VREF 6 GND
Note : Since the NC pins are not connected within the IC package, they can be used as connection points.
Application Circuit Example
L1 68H VIN SWOUT
LA5735M
+ C1 470F /50V VOS GND D1 SBD
C3 1000pF
+ C2 100F
R2 R1
No.A0588-3/7
LA5735M
Choke coil L1 * Note that choke coil heating due to overload or load shorting may be a problem. The inductance value can be determined from the following equation once the input voltage, output voltage, and current ripple conditions are known. IR indicates the ripple current value. Reference example : VIN = 12V, VOUT = 5V, IR = 150mA L= VIN - VOUT - Vsat x Ton IR 12 - 5.0 - 1.0 = x 1.58 x 10-6 0.15 68H T Ton = ((V - V IN OUT - Vsat)/(VOUT + VF)) + 1 Toff = T - Ton t : Switching repetition period***************** 3.33s is assumed for the calculation VF : Schottky diode forward voltage ****** 0.4V is assumed for the calculation * Inductance current : peak value The ripple current peak value must be held within the rated current values for the inductor used. Here, IRP is the peak value of the ripple current. IRP can be determined from the following equation. Reference example : VIN = 12V, VOUT = 5V, IOUT = 0.5A, L = 68H IRP = IOUT + VIN - VOUT - Vsat x Ton 2L 12 - 5.0 - 1.0 = 0.5 + x 1.58 x 10-6 2 x 68 x 10-6
0.57A * Inductance current : ripple current value Here IR is the ripple current. IR can be determined from the following equation. If the load current becomes less than one half the ripple current, the inductor current will become discontinuous. IR = VIN - VOUT - Vsat x Ton L 12 - 5.0 - 1.0 = x 1.58 x 10-6 68 x 10-6
0.15A Diode D1 * A Schottky barrier diode must be used for this diode. If a fast recovery diode is used, it is possible that the IC could be destroyed by the applied reverse voltage due to the recovery and the on-state voltage. * Diode current (peak current) Applications must be designed so that the peak value of the diode current remains within the rated current of the diode. The peak value of the diode current will be the same current as the peak value of the inductor current. * Repetitive peak reverse voltage Applications must be designed so that the repetitive peak reverse voltage remains within the voltage rating of the diode. Here, VRRM is the repetitive peak reverse voltage. VRRM can be determined from the following equation. VRRM VCC Since noise voltage and other terms will be added in actual operation, the voltage handling capacity of the device should be about 1.5 times that given by the above calculation.
No.A0588-4/7
LA5735M
Diode D1 * Low-impedance, high-frequency components designed for use in switching power supplies must be used for C1 and C2 since large ripple currents flow in these capacitors. Note that if a ceramic capacitor, tantalum capacitor, or other capacitor with an extremely low equivalent series resistance (ESR) is used for C2, abnormal oscillations may occur in the output waveform. Do not use such a capacitor for C2. The following equation gives the stability condition for the C2 capacitor and ESR values. 1 20kHz******************* Equation 5 2 x x C2 x ESR * Repetitive peak reverse voltage The AC ripple currents flowing in the input capacitor will be larger currents than those flowing in the output capacitors. The RMS current is given by the following equation. Note that capacitors must only be used with currents that are within their current ratings. IC1= VOUT VOUT IOUT 2 1- V VIN IN 1 + 12 x IR2 [Arms]
* Output capacitor RMS current Since the ripple current, an AC current, flowing in the output capacitors has a sawtooth waveform, the RMS value is given by the following equation. Select output capacitors whose allowable ripple current rating is not exceeded by this value. VOUT (VIN - VOUT) 1 IC2 = 2 3 x L x fsw x VIN [Arms]
fsw = Switching frequency ******************* 300kHz Resistors R1 and R2 * The resistors R1 and R2 set the output voltage. The error in the VOS pin voltage increases as the values used for these resistors increase. Note also that the output voltage may rise due to leakage current in the switching transistors during light load operation. For these reasons, R1 and R2 should be selected so that the current flowing in them is on the order of 500A. R1= 1.23V 2.4k 500A We recommend values in the range 2.0 to 2.4k
VOUT R2= 1.23V -1 x R1 The following equation gives the output voltage set by R1 and R2. R2 VO= 1+ R1 x 1.23V (typ)
No.A0588-5/7
LA5735M
Protection Circuit Functional Descriptions 1. Overcurrent protection function The overcurrent protection function detects, on a cycle-by-cycle basis, the output transistor current and turns off that output transistor current if it exceeds 0.7A in a cycle-by-cycle manner.
Limit current Inductor current
SWOUT voltage
2. Short circuit protection function This IC prevents the current from increasing when the outputs are shorted by setting the switching frequency to 15kHz if the VOS pin voltage falls below 0.8V. Note : At startup, since the switching frequency will be 15kHz while the VOS pin voltage is 0.8V or lower, the current capacity is reduced. If the load is applied at startup and the applications has trouble starting, increase the value of the inductor to resolve this problem.
Timing Chart
VIN voltage
15kHz
300kHz
SWOUT voltage
1.23V 0.8V VOS voltage 0V
No.A0588-6/7
LA5735M
Specifications of any and all SANYO Semiconductor products described or contained herein stipulate the performance, characteristics, and functions of the described products in the independent state, and are not guarantees of the performance, characteristics, and functions of the described products as mounted in the customer's products or equipment. To verify symptoms and states that cannot be evaluated in an independent device, the customer should always evaluate and test devices mounted in the customer's products or equipment. SANYO Semiconductor Co., Ltd. strives to supply high-quality high-reliability products. However, any and all semiconductor products fail with some probability. It is possible that these probabilistic failures could give rise to accidents or events that could endanger human lives, that could give rise to smoke or fire, or that could cause damage to other property. When designing equipment, adopt safety measures so that these kinds of accidents or events cannot occur. Such measures include but are not limited to protective circuits and error prevention circuits for safe design, redundant design, and structural design. In the event that any or all SANYO Semiconductor products (including technical data,services) described or contained herein are controlled under any of applicable local export control laws and regulations, such products must not be exported without obtaining the export license from the authorities concerned in accordance with the above law. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying and recording, or any information storage or retrieval system, or otherwise, without the prior written permission of SANYO Semiconductor Co., Ltd. Any and all information described or contained herein are subject to change without notice due to product/technology improvement, etc. When designing equipment, refer to the "Delivery Specification" for the SANYO Semiconductor product that you intend to use. Information (including circuit diagrams and circuit parameters) herein is for example only; it is not guaranteed for volume production. SANYO Semiconductor believes information herein is accurate and reliable, but no guarantees are made or implied regarding its use or any infringements of intellectual property rights or other rights of third parties.
This catalog provides information as of January, 2007. Specifications and information herein are subject to change without notice. PS No.A0588-7/7

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