HT7627 PFM Step-up DC/DC Converter & Voltage Detector Features · High output voltage accuracy: ±5% · Low current consumption: 14mA with 1.5V input (typ.) · Low ripple and low noise · Fixed output voltage: 2.7V · Low start-up voltage · Built-in 2.1V (typ.) voltage detector (when the output current is 1mA): 0.95V · 8-pin SOP package Applications · Pager · RF Mouse/Keyboard General Description The HT7627 DC/DC converter with built in voltage detector is a high performance CMOS IC, suitable for use in battery-powered system application with low noise and low supply current. The HT7627 consists of two major parts, one is DC/DC converter and the other is voltage detector. The DC/DC converter part consists of reference voltage source, error amplifier, control transis- tor, oscillation circuit and output voltage setting resistor. The voltage detector part consists of a high-precision and low power consumption standard voltage source, a comparator, hysteresis circuit and an output driver. As external parts, a coil, a diode, and a capacitor are available for obtaining a constant output (2.7V) higher than the input voltage for the DC/DC converter part. Block Diagram T E S T V O U T L X R W 1 R R W 2 R R W 3 B u ffe r R O s c illa to r E rro r A m p B ia s V L B ia s V r e fe r e n c e V D E T V S S V H P W D E T C P Pin Assignment N C 1 8 V O U T L X 2 7 N C N C 3 6 V D E T V S S 4 5 C P H T 7 6 2 7 8 S O P -A Rev. 1.00 1 January 18, 2002 HT7627 Pin Description Pin No. Pin Name I/O Description 1, 3, 7 NC ¾ No connection 2 LX I Switching pin 4 VSS 5 CP I External capacitor for adjusting VDET output delay time. 6 VDET O Voltage detector open drain output (needs a pull-high resistor) 8 VOUT O DC/DC converter voltage output ¾ Negative power supply, ground Absolute Maximum Ratings Supply Voltage ............................ VSS-0.3V to VSS+6V Storage Temperature .......................... -40°C to 125°C Switching pin Voltage .................. VSS-0.3V to VSS+6V Operating Temperature ......................... -25°C to 70°C Power Consumption ........................................ 150mW Note: These are stress ratings only. Stresses exceeding the range specified under ²Absolute Maximum Ratings² 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. Electrical Characteristics Symbol Parameter Ta=25°C, VOUT=2.7V Test Conditions Min. Typ. Max. Unit VOUT Output Voltage ¾ 2.56 2.7 2.75 V VIN Input Voltage ¾ ¾ ¾ 5 V Vstart Starting Voltage ¾ 0.95 1.1 V Vhold Voltage Hold 0.9 ¾ ¾ V Iin Current Consumption Measure at no load ¾ 14 20 mA ILX LX Switching Current VIN=1.5V 60 ¾ ¾ mA ILEAK LX Leakage Current ¾ ¾ 1 mA fOSC Oscillator Frequency ¾ 139 ¾ kHz L=330mH, IL=1mA ¾ ¾ VIN=1.5V H®L Detectable Voltage ¾ 2.0 2.1 2.2 V L®H Detectable Voltage ¾ 2.2 2.3 2.4 V VHYS Hysteresis Width ¾ ¾ 0.2 ¾ V IDETOL VDET Output Sink Current 0.5 ¾ ¾ mA VDET VOUT=2.2V, VDET=0.2V Functional Description Off, voltage VL is generated at the edges of L because of the energy accumulated during the ton period. Therefore, the peak value of the voltage generated at that time is VIN+VL, and it is stored in the output capacitor CL via SD. This generates the step-up output voltage VOUT that is larger than VIN. Operation of step-up DC/DC converter The following figures show the basic circuit configuration of the step-up operation of the IC. In the configuration, when the transistor tr is entirely Off, the output voltage is the value of the input voltage VIN minus the voltage reduced by inductor L and Schottky diode SD. When tr has been On for time ton and is suddenly turned Rev. 1.00 2 January 18, 2002 HT7627 The operation will be explained with reference to the following diagrams: i2 L V IO S D V IN i1 C tr U T O U T L IL IL IL m a x to p e n m in t to t ff n t= 1 /fO S C Step1: tr is turned ON and current IL (=i1) flows, so that energy is charged in L. At this moment, IL (=i1) is increased from ILmin to reach ILmax in proportion to the on-time period (ton) of tr. Step2: When tr is turned OFF, Schottky diode (SD) is turned ON in order that L maintains IL at ILmax, so that current IL (=i2) is released. Step3: IL (=i2) is gradually decreased, IL reaches ILmin after a time period of topen, so that SD is turned OFF. tr will be turned ON in the next cycle. In the case of PWM control system, the output voltage is maintained constant by controlling the on-time period (ton), with the oscillator frequency (fOSC) being maintained constant. Voltage detector operation The HT7627 built-in voltage detector is equipped with a high stability voltage reference which is connected to the negative of a comparator ¾ denoted as Vref in the following figure for NMOS output voltage detector. When the voltage drop to the positive input of the comparator (i.e. VB) is higher than Vref, VOUT goes high, and VB is expressed as VBH=VDD ´ (RB+RC) / (RA+RB+RC). If VDD is decreased so that VB falls to a value less than Vref, the comparator output inverts from high to low, VOUT goes low, VC is high, RC is bypassed, and VB becomes: VBL=VDD ´ RB/(RA+RB), which is less than VBH. By so doing, the comparator output will remain low to prevent the circuit from oscillating when VB»Vref. If VDD falls below the minimum operating voltage, the output becomes undefined. When VDD goes from low to VDD ´ RB / (RA+RB) > Vref, the comparator output and VOUT goes high. The detectable voltage is defined as: VDETECT (-)= RA + RB + RC ´ Vref RB + RC The release voltage is defined as: VDETECT (+)= Rev. 1.00 RA + RB + RC ´ Vref RB 3 January 18, 2002 HT7627 The hysteresis width is VHYS= VDETECT(+) - VDETECT (-) V R A C o m p a r a to r w ith h y s te r e s is V V R (V O U T ) D E T M N B R V re f V C D D B C The following figure shows the hysteresis effect according to the previous figure. V D E T V V D E T E C T (- ) V Rev. 1.00 V D E T E C T O U T (+ ) H Y S 4 January 18, 2002 HT7627 Application Circuits V C C (1 .5 V ) 3 3 0 m H + + V 2 2 m F S c h o ttk y D io d e 1 2 3 4 N C V O U T L X N C N C V D E T V S S 8 7 H T 7 6 2 7 T + 6 5 C P C D D 2 2 m F 2 7 0 k W V E X T E x te r n a l C a p a c ito r fo r D E L A Y ( O p tio n a l) D D R E S E T M C U V Rev. 1.00 5 S S January 18, 2002 HT7627 Holtek Semiconductor Inc. (Headquarters) No.3, Creation Rd. II, Science-based Industrial Park, Hsinchu, Taiwan Tel: 886-3-563-1999 Fax: 886-3-563-1189 http://www.holtek.com.tw Holtek Semiconductor Inc. (Sales Office) 11F, No.576, Sec.7 Chung Hsiao E. Rd., Taipei, Taiwan Tel: 886-2-2782-9635 Fax: 886-2-2782-9636 Fax: 886-2-2782-7128 (International sales hotline) Holtek Semiconductor (Hong Kong) Ltd. RM.711, Tower 2, Cheung Sha Wan Plaza, 833 Cheung Sha Wan Rd., Kowloon, Hong Kong Tel: 852-2-745-8288 Fax: 852-2-742-8657 Holtek Semiconductor (Shanghai) Inc. 7th Floor, Building 2, No.889, Yi Shan Rd., Shanghai, China Tel: 021-6485-5560 Fax: 021-6485-0313 http://www.holtek.com.cn Holmate Technology Corp. 48531 Warm Springs Boulevard, Suite 413, Fremont, CA 94539 Tel: 510-252-9880 Fax: 510-252-9885 http://www.holmate.com Copyright Ó 2002 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 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.tw. Rev. 1.00 6 January 18, 2002