HT7465 Step-Down DC to DC Converter Feature General Description • Input voltage range: 4.75V to 24V The HT7465 is a 2A high efficiency step-down DCDC converter which includes a fully integrated MOS power transistor. The device uses a current-mode control operating methodology and can operate over a wide input voltage range of 4.75V to 24V for which it can provide a stable adjustable output voltage. • Variable output voltage range: 0.92V to 20V • 2A output current • Efficiency up to 92% • Fixed 380kHz operating frequency • 20mA shutdown current The device includes over temperature protection, over current protection and under voltage lockout protection, features which combine to prevent device damage due to overload conditions. In its shutdown mode the regulator draws a mere 20uA of supply current. • Internal power MOSFET switch • Stable operation using low ESR ceramic capacitors • Over temperature protection • Cycle-by-cycle over current protection • Under voltage lockout protection The device is available in 8-pin SOP package type and provides a very compact system solution with a minimum of external components. • 8-pin SOP package Applications • Battery chargers • Distributed power systems • LED driver • DSL modems • Linear regulator pre power processing • Set-Top-Boxes, DVD players, LCD displays Application Circuits VIN 4.75~24V 10nF C2 10 F C1 VIN EN BS HT7465 GND COMP L SW VOUT 10/15 H B230A FB R1 R3 C5 Efficiency vs Output Current R R2 VOUT VFB 1 R2 R2 22uF C6 C4 Rev. 1.10 1 April 18, 2014 HT7465 Block Diagram EN NC Under-voltage lockout Regulator VIN Current Sense Amplifier Current Sense 5V + BS - SCP + Control Logic OSC 240/380kHz SW PWM Comparator - Error Amplifier Soft-Start + GND 0.92V FB COMP Pin Assignment BS VIN SW GND 1 2 3 4 8 PAD (GND) 7 6 5 NC EN COMP FB HT7465 8 SOP-A (Exposed Pad) Rev. 1.10 2 April 18, 2014 HT7465 Pin Description Pin No. Pin Name Description 1 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. 2 VIN Power supply input. The input supply pin for the device, VIN, is connected to a supply voltage between 4.75V to 24V. 3 SW Power switching output. The internal power MOS drain is connected to the inductor diode and VIN. 4 GND 5 FB Feedback pin. The feedback pin is connected to an external resistor divider to measure the output voltage. 6 COMP 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 and the COMP pin value is 0.92V. 7 EN Enable Input and dimming control. 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. 8 NC Not used Exposed Pad GND Ground. Device ground voltage reference. Ground. Device ground voltage reference. Absolute Maximum Ratings Maximum Input Supply Voltage.............................26V EN Voltage................................................................6V Switch Node Voltage...............................................26V Comp Voltage............................................................6V Feedback Voltage......................................................6V Maximum Junction Temperature........................ 150°C 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. 1.10 3 April 18, 2014 HT7465 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 0.892 0.920 0.948 V VFB Feedback Voltage VUVLO Under Voltage Lockout Threshold — — 4.1 — V — Under Voltage Lockout Threshold Hysteresis — — 200 — mV IQ Quiescent Current VFB=1.2V, VEN=High — 1.1 1.3 mA ISS Shutdown Supply Current VEN=0V — 20 30 mA FOS Oscillator Frequency — 380 — kHz — Short Circuit Frequency VFB=0V — 240 — kHz DMAX Maximum Duty Cycle VFB=0.6V — 90 — % ISW Switch Leakage VEN=0V, VSW=0V — 0 10 mA RDS Switch On Resistance (note 2) IOUT=2A — 0.18 — W ILIMIT Current Limit — — 3.4 — A — Error Amplifier Voltage Gain (note 2) — — 70 — dB — Error Amplifier Trans-conductance (note 2) — — 800 — mA/V VEN Enable Threshold 0.7 1.0 1.3 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. The test specifications by designer. Rev. 1.10 4 April 18, 2014 HT7465 Functional Description triggered the device stops switching and will require a power on input voltage signal, before resuming switching operation. Setting the Output Voltage The HT7465 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 0.92 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: Application Information Inductor 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: • The inductor value • DCR - copper wire resistance R1+R2 VOUT=x0.92 R2 • The saturation current Inductor choice is especially important as it is important to ensure the inductor does not saturate under its peak current conditions. Also ensure that the inductor has a low DCR to minimise power losses. where R2 is the resistor divider lower resistor and R1 is the upper resistor. Compensation Components Input/Output Capacitor 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. 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 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. Table 1 Compensation Values for Typical Output Voltage/Capacitor Combinations. VOUT L R3 C4 C6 C5 2.5 10/15mH 9.1K 2.2n 22mF Ceramic — 3.3 10/15mH 10K 3.9n 22mF Ceramic — 5.0 10/15mH 18K 1.5n 22mF Ceramic — 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. 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 3.4A, the MOSFET oscillator frequency will be transformed from 380kHz to a short circuit frequency of 240kHz and the output current will remain at its current limit value. 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 greater than the maximum input voltage Over — Temperature Protection • Short recovery time -- use Schottky diode A thermal shutdown function is implemented to prevent damages due to excessive heat and power dissipation. Typically the thermal shutdown threshold temperature is 150°C.When the thermal shutdown is Rev. 1.10 • Diode current rating should be greater than the maximum load current 5 April 18, 2014 HT7465 Layout Considerations A recommended PCB layout with component locations is shown below. 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 closec 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). • A full ground plane is always helpful for better EMI performance. Top Layer Bottom Layer Rev. 1.10 6 April 18, 2014 HT7465 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. 1.10 7 April 18, 2014 HT7465 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. 1.10 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 April 18, 2014 HT7465 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. 1.10 9 April 18, 2014