Low Ripple Design Guide. Learn by case study of DC/DC Converters XC9235/XC9236/XC9237 Series. (1/5)

Power configuration linear regulator or DC/DC converter?

When considering the power configuration for a device, do you ever have difficulty deciding whether to use a linear regulator or a DC/DC converter? If the LSI operating voltage drops to 1.8 V or 1.2 V, using a linear regulator for the drive from a 5 V line or lithium battery will result in a large thermal loss and power cannot be used efficiently. In this type of situation, it is well known that using a step-down DC/DC converter permits highly efficient voltage conversion. However, using a DC/DC converter raises many concerns, such as the generation of an excessive amount of noise, increased cost due to additional external components, and the complexity of setting various constants.

This edition of Application Notes will help you understand the basic features and operation of DC/DC converters through an explanation of the operation of the Torex XC9235/XC9236/XC9237 Series of DC/DC converters. The XC9235/XC9236/XC9237 are all-in-one DC/DC converters that require few external components and no adjustment of constants. The dual achievement of low noise and high conversion efficiency makes these ICs a popular choice for wireless device applications.

Features of XC9235/XC9236/XC9237 Step-Down DC/DC Converter ICs

Recent step-down DC/DC converters require few external components, and many products have been released that feature easy operation by simply adding a coil and capacitors. Such DC/DC converters provide a highly efficient power source, while only requiring one additional small coil compared with LDO regulators.

XC9235/XC9236/XC9237 Series

Torex XC9235/XC9236/XC9237 Series of step-down synchronous rectification-type DC/DC converters integrate two MOSFETs (one N-channel and one P-channel) to supply the output current. Circuit constants required for stable operation are set within the IC, and the only external components needed by these all-in-one DC/DC converters are the input and output capacitors and a coil indicated in the datasheet. An output current of up to 600 mA can be supplied. (See Fig. 1)

Fig.1: XC9235/XC9236/XC9237 Series Standard Circuit

The control method of this IC varies by model number. The XC9235 uses PWM control, the XC9236 operates in PWM/PFM auto switching control, and the XC9237 permits to select manually between PWM/PFM auto switching control and PWM control. You can select between two switching frequencies, 1.2MHz for applications where higher efficiency is desired, and 3MHz which permits the use of a smaller coil, thus providing a smaller overall solution. A wide variety of functions and optional of features are available to meet the needs of your application.
The high-speed soft-start and CL discharge features enable respectively quick starting and stopping at on/off, which is convenient when building the power sequence of the set.

Table 1: XC9235/XC9236/XC9237 Options
Output Voltage Type Operationg Voltage Range Description
Fixed output voltage
(Vout product)
A 2V to 6V No CL high-speed discharge
B CL high-speed discharge, high-speed soft start
C CL high-speed discharge
E 1.8V to 6V CL high-speed discharge
G CL high-speed discharge, high-speed soft start
External output voltage
setting(FB product)
D CL high-speed discharge
F CL high-speed discharge, high-speed soft start

Packages are SOT-25, USP-6C (2.0 mm×1.8 mm, t = 0.6 mm MAX) and USP-6EL (2.0 mm×1.8 mm, t = 0.4 mm MAX), WLP-5-03(1.26mm×1.06mm, t=0.4mm).

Photo 1: Package Photo

SOT-25

WLP-5-03

USP-6EL

USP-6C

Photo 2: Mounting Board Photo

Fig. 2:Internal Block Diagram of the XC9235/XC9236/XC9237

The internal circuitry includes the reference voltage, error amplifier, oscillator, ramp waveform, PWM comparator, UVLO, and current limit circuit. In the fixed output voltage type, the internal resistance ratio R1/R2 is adjusted by laser trimming. The operating voltage range is 1.8 V to 6 V. The amplifier phase correction, transmission frequency, and soft-start time are adjusted internally, allowing the product to be used without any adjustments.

Torex Products in this article

XC9235

Driver Tr. Built-In, Synchronous PWM Control, Step-Down DC/DC Controller, Maximum Output Current 600mA

Driver Tr. Built-In, Synchronous PWM Control, Step-Down DC/DC Controller, Maximum Output Current 600mA

XC9236

Driver Tr. Built-In, Synchronous Step-Down DC/DC Converters , PWM/PFM auto switching, Maximum Output Current 600mA

Driver Tr. Built-In, Synchronous Step-Down DC/DC Converters , PWM/PFM auto switching, Maximum Output Current 600mA

XC9237

Driver Tr. Built-In, Synchronous Step-Down DC/DC Converters , PWM/PFM manual switching, Maximum Output Current 600mA

Driver Tr. Built-In, Synchronous Step-Down DC/DC Converters , PWM/PFM manual switching, Maximum Output Current 600mA

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