HT7466 3A Step-Down DC to DC Converter Feature General Description • Input voltage range: 4.75V to 24V The HT7466 is a DC-DC buck regulator. The builtin high driver NMOS provides a monolithic solution for high efficiency step-down DC-DC converter. With 3A output current, the wide input voltage range and stable output voltage regulation can widely use in all kinds of application, like communication, power for high power LED, battery charger, etc. The protection function include over current and over temperature protection. The soft start function prevent inrush supply current and output overshoot when initial startup. The under voltage lockout is set to 4.1V. It prevents abnormal situation occurring. • Variable output voltage range: 1.222V to 20V • 3A output current • Efficiency up to 91% • Fixed 380kHz operating frequency • 20mA shutdown current • Internal power MOSFET switch • Stable operation using low ESR ceramic capacitors • Over temperature protection • Cycle-by-cycle over current protection The HT7466 requires a minimum number of standard external components and is available in a 8-pin SOP package for small area PCB application. • Soft-start function • Under voltage lockout protection • 8-pin SOP package Applications • Battery chargers • Distributed power systems • LED power supplies • DSL modems • Linear regulator pre power processing • Set-Top-Boxes, DVD players, LCD displays Application Circuit VIN 4.75~24V Efficiency vs Output Current 10nF C2 10 F C1 VIN EN BS HT7466 SS 10nF C3 SW B330A FB GND R R2 VOUT VFB 1 R2 L VOUT 10 H/15 H COMP R1 R3 C5 R2 22 F C6 C4 Rev. 1.20 1 September 11, 2014 HT7466 Block Diagram Pin Assignment SS BS VIN SW 1 2 3 4 8 PAD (GND) 7 6 5 EN COMP FB GND HT7466 8 SOP-A (Exposed Pad) Rev. 1.20 2 September 11, 2014 HT7466 Pin Description Pin No. Pin Name Description 1 SS Soft-start input. If the soft start function is to be used then an external capacitor should be connected between this pin and ground. If the soft start function is not required the pin should be left open. 2 BS Internal power NMOS gate drive boost input. A 10nF or greater value capacitor should be connected from SW to BS for additional Power NMOS gate driving purposes. 3 VIN Power supply input. The input supply pin for the device, VIN, is connected to a supply voltage between 4.75V to 24V. 4 SW Power switching output. The internal power MOS drain is connected to the inductor, diode and VIN. 5 GND 6 FB 7 COMP 8 EN Exposed Pad GND Ground. Device ground voltage reference. Feedback pin. The feedback pin is connected to an external resistor divider to measure the output voltage. Error amplifier output. Used for compensation of the regulation control loop. Connect a series RC network from COMP to GND to compensate the regulation control loop. The COMP pin value is 1.222V. Enable input. This pin is set high to turn on the regulator and low to turn it off. The pin should be left unconnected if not used. Ground. Device ground voltage reference. Absolute Maximum Ratings Maximum Input Supply Voltage.............................26V Comp Voltage............................................................6V Switch Node Voltage...............................................26V SS Voltage.................................................................6V Feedback Voltage......................................................6V Maximum Junction Temperature........................ 150°C EN Voltage................................................................6V Note: These are stress ratings only. Stresses exceeding the range specified under “Absolute Maximum Ratings” may cause substantial damage to the device. Functional operation of this device at other conditions beyond those listed in the specification is not implied and prolonged exposure to extreme conditions may affect device reliability. Recommended Operating Conditions Ambient Temperature Range................ -40°C ~ +85°C Input Supply Voltage.................................4.75V ~ 24V Rev. 1.20 3 September 11, 2014 HT7466 Electrical Characteristics VIN=12V, Ta=25°C, unless otherwise specified refer to circuit of Figure 1. ( note 1) Symbol Parameter Test Condition Min. Typ. Max. Unit 4.75V ≤ VIN ≤ 24V 1.194 1.222 1.250 V VFB Feedback Voltage VUVLO Under Voltage Lockout Threshold — — 4.1 — V — Under Voltage Lockout Threshold Hysteresis — — 200 — mV IQ Quiescent Current VFB=1.5V, VEN=High — 1.0 1.2 mA ISS Shutdown Supply Current VEN=0V — 20 30 mA FOSC Oscillator Frequency — 380 — kHz — Short Circuit Frequency VFB=0V 20 35 50 kHz DMAX Maximum Duty Cycle VFB=1.0V — 90 — % ISW Upper Switch Leakage VEN=0V, VSW=0V — 0 10 mA RDS Switch On Resistance (note 2) IOUT=3A — 95 — mW ILIMIT Current Limit — — 4.3 — A — Error Amplifier Voltage Gain (note 2) — — 70 — dB — Error Amplifier Trans-conductance (note 2) — — 800 — mA/V VEN Enable Threshold 0.9 1.0 1.5 V TJ Thermal Shutdown — 150 — °C — 4.75V ≤ VIN ≤ 24V — Note: 1. Specifications are production tested at Ta=room temperature. Specifications over the -40°C to 85°C operating temperature range are assured by design, characterization and correlation with Statistical Quality Controls (SQC). 2. Designer test specifications. Rev. 1.20 4 September 11, 2014 HT7466 Functional Description Current Limit Protection The device has a cycle-by-cycle current limit to protect the internal power MOSFET. If the inductor current reaches the current limit threshold of 4.3A, the MOSFET oscillator frequency will be transformed from 380kHz to a short circuit frequency of 35kHz and the output current will remain at its current limit value. Setting the Output Voltage The HT7466 is a step down switching DC/DC converter device. The device switching output, SW, is connected to a standard converter LC filter circuit for buck conversion. The output current is sensed using an external voltage divider network connected to the load output voltage and ground, and the sense voltage feedback to the device on the FB pin. By comparing this sense voltage with an internally generated 1.222 voltage reference, suitable regulation can be implemented to achieve the required output voltage. By selecting suitable values of external voltage divider resistors, the desired output voltage can be adjusted to the required level. The output voltage can be calculated using the following formula: Over Temperature Protection A thermal shutdown is implemented to prevent damage due to excessive heat and power dissipation. Typically the thermal shutdown threshold is 150°C. The thermal shutdown is triggered the device stops switching and when the device thermal falls until the temperature hysteresis windows the device will be starts switching again. Application Information Where R2 is the resistor divider lower resistor and R1 is the upper resistor, and the R1, R2 must be kW level. Inductor Compensation Components The inductor is required to supply a constant current to the output load while being driven by the switched input voltage. The choice of inductor affects steady state operation as well as transient behavior and loop stability. There are three important electrical parameters which need to be considered when choosing an inductor: Care must be taken when selecting external components. The COMP pin is the output of the error amplifier and must be properly connected to an external RC network to ensure regulator loop stability. The values of the compensation components given in Table 1 yield a stable control loop for the output voltage and capacitor given. • The inductor value • DCR - copper wire resistance Table 1 Compensation Values for Typical Output Voltage/Capacitor Combinations. VOUT L R3 C4 R1 R2 C6 C5 2.5V 10mH/ 3.9kW 15mH 5.6nF 10.5kW 10kW 22mF Ceramic — 3.3V 10mH/ 4.7kW 15mH 4.7nF 17.0kW 10kW 22mF Ceramic — 5.0V 10mH/ 7.5kW 15mH 2.7nF 30.9kW 10kW 22mF Ceramic — • The saturation current Inductor choice is especially important as it is important to ensure the inductor does not saturate under its peak current conditions, the general rule of keeping the inductor current peak-to-peak ripple approximately 30% of the nominal output current. Using this value of ripple current is a good compromise between excessive output voltage ripple and excessive component size and cost. Also ensure that the inductor has a low DCR to minimize power losses. Bootstrap Circuit In this device bootstrap capacitor is connected from SW to BS pin, the Step-Down converter is use N-Channel MOSFET, and MOS source pin is floating to ground, this drive circuit of the application is called high-side circuit, and the drive circuit used in this kind of situation is called bootstrap circuit. Large capacitor values can keep internal high-side N-Channel MOSFET gate voltage greater than zero when power MOS is turn on; usually a 10nF capacitor is sufficient for most applications. Rev. 1.20 Input/Output Capacitor Input Capacitor Because the Vin pin is connected to the internal power MOSFET, when the power MOSFET is switching and the input current is discontinuous, therefore an input capacitor C1 (in PCB layout C1 and C8 is parallels input capacitor) is required to supply the AC current to the step-down converter while maintaining the DC input voltage. A low ESR ceramic capacitor is required to keep noise to a minimum. 5 September 11, 2014 HT7466 A recommended PCB layout with component locations is shown below. Output Capacitor The output capacitor is required to maintain the DC output voltage. Ceramic or low ESR electrolytic capacitors is the rule to choice of external load capacitor is also critical and low ESR value capacitors must be used to ensure stability. This capacitor must be connected very close to the inductor, with short traces for good noise performance. Schottky Diode The output diode conducts when the internal power MOSFET is switched off. There are three important electrical parameters to consider when choosing the diode: • The diode maximum reverse voltage value must be greater than the maximum input voltage. • Short recovery time and low forward voltage -- use a schottky diode type. Top Layer • Diode current rating should be greater than the maximum load current. Layout Considerations Circuit board layout is a very important consideration for switching regulators if they are to function properly. Poor circuit layout may result in related noise problems. In order to minimise EMI and switching noise, follow the guidelines below: • All tracks should be as wide as possible. • The input and output capacitors, C1 (C8) and C6 (C7), should be placed close to the VIN, VOUT and GND pins (C1 and C8 is parallel; C6 and C7 is parallel). • The Schottky diode D and inductor L must be placed close to the SW pin. • Feedback resistor, R1 (R1-1) and R2, must be placed close to the FB and GND pins (R1 and R1-1 is series). Bottom Layer • A full ground plane is always helpful for better EMI performance. Rev. 1.20 6 September 11, 2014 HT7466 Package Information Note that the package information provided here is for consultation purposes only. As this information may be updated at regular intervals users are reminded to consult the Holtek website for the latest version of the package information. Additional supplementary information with regard to packaging is listed below. Click on the relevant section to be transferred to the relevant website page. • Further Package Information (include Outline Dimensions, Product Tape and Reel Specifications) • Packing Meterials Information • Carton information Rev. 1.20 7 September 11, 2014 HT7466 8-pin SOP_EP (150mil) Outline Dimensions for Thermally Enhanced Variations Only (Exposed Pad) Symbol Dimensions in inch Min. Nom. Max. A ― 0.236 BSC ― B ― 0.154 BSC ― C 0.012 ― 0.020 C' ― 0.193 BSC ― D ― ― 0.069 D1 0.059 ― ― E ― 0.050 BSC ― E2 0.039 ― ― F 0.004 ― 0.010 G 0.016 ― 0.050 H 0.004 ― 0.010 α 0° ― 8° Symbol Rev. 1.20 Dimensions in mm Min. Nom. Max. A ― 6.00 BSC ― B ― 3.90 BSC ― C 0.31 ― 0.51 C' ― 4.90 BSC ― D ― ― 1.75 D1 1.50 ― ― E ― 1.27 BSC ― E2 1.00 ― ― F 0.10 ― 0.25 G 0.40 ― 1.27 H 0.10 ― 0.25 α 0° ― 8° 8 September 11, 2014 HT7466 Copyright© 2014 by HOLTEK SEMICONDUCTOR INC. The information appearing in this Data Sheet is believed to be accurate at the time of publication. However, Holtek assumes no responsibility arising from the use of the specifications described. The applications mentioned herein are used solely for the purpose of illustration and Holtek makes no warranty or representation that such applications will be suitable without further modification, nor recommends the use of its products for application that may present a risk to human life due to malfunction or otherwise. Holtek's products are not authorized for use as critical components in life support devices or systems. Holtek reserves the right to alter its products without prior notification. For the most up-to-date information, please visit our web site at http://www.holtek.com. Rev. 1.20 9 September 11, 2014