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HT7627
PFM Step-up DC/DC Converter & Voltage Detector
Features
* High output voltage accuracy: 5% * Low ripple and low noise * Low start-up voltage * Low current consumption: 14mA with 1.5V input (typ.) * Fixed output voltage: 2.7V * Built-in 2.1V (typ.) voltage detector * 8-pin SOP package
(when the output current is 1mA): 0.95V
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 transistor, 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
TEST LX B u ffe r R O s c illa to r B ia s E rro r A m p B ia s V r e fe r e n c e V
L
VOUT R
RW 1
RW 2
R
RW 3
VDET VSS V
H
PW DET CP
Pin Assignment
NC 1 LX 2 NC 3 VSS 4
8 7 6 5
VOUT NC VDET CP
H T7627 8 S O P -A
Rev. 1.00 1 January 18, 2002
HT7627
Pin Description
Pin No. 1, 3, 7 2 4 5 6 8 Pin Name NC LX VSS CP VDET VOUT I/O 3/4 I 3/4 I O O No connection Switching pin Negative power supply, ground External capacitor for adjusting VDET output delay time. Voltage detector open drain output (needs a pull-high resistor) DC/DC converter voltage output Description
Absolute Maximum Ratings
Supply Voltage ............................ VSS-0.3V to VSS+6V Switching pin Voltage .................. VSS-0.3V to VSS+6V Power Consumption ........................................ 150mW 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. Storage Temperature .......................... -40C to 125C Operating Temperature ......................... -25C to 70C
Electrical Characteristics
Symbol VOUT VIN Vstart Vhold Iin ILX ILEAK fOSC VDET VHYS IDETOL Parameter Output Voltage Input Voltage Starting Voltage Voltage Hold Current Consumption LX Switching Current LX Leakage Current Oscillator Frequency H(R)L Detectable Voltage L(R)H Detectable Voltage Hysteresis Width VDET Output Sink Current VIN=1.5V 3/4 3/4 3/4 VOUT=2.2V, VDET=0.2V Test Conditions 3/4 3/4 L=330mH, IL=1mA 3/4 Measure at no load VIN=1.5V 3/4 Min. 2.56 3/4 3/4 0.9 3/4 60 3/4 3/4 2.0 2.2 3/4 0.5 Typ. 2.7 3/4 0.95 3/4 14 3/4 3/4 139 2.1 2.3 0.2 3/4
Ta=25C, VOUT=2.7V Max. 2.75 5 1.1 3/4 20 3/4 1 3/4 2.2 2.4 3/4 3/4 Unit V V V V mA mA mA kHz V V V mA
Functional Description
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 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.
Rev. 1.00
2
January 18, 2002
HT7627
The operation will be explained with reference to the following diagrams:
i2
L V
IN i1
SD V tr C
L OUT
IO
UT
IL
IL IL
m in
m ax
to
pen
t to
n
t ff
t= 1 /fO
SC
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 3/4 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 VBVref. 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 RA + RB + RC Vref RB
The release voltage is defined as: VDETECT (+)=
Rev. 1.00
3
January 18, 2002
HT7627
The hysteresis width is VHYS= VDETECT(+) - VDETECT (-)
V R
A DD
(V
OUT
)
C o m p a r a to r w ith h y s te r e s is V
C
DET
V V
B
MN
V re f R
R
B
C
The following figure shows the hysteresis effect according to the previous figure.
V
DET
V V
DETECT
OUT
(- ) V V
HYS
DETECT
(+ )
Rev. 1.00
4
January 18, 2002
HT7627
Application Circuits
V
CC
(1 .5 V ) 330mH S c h o ttk y D io d e 1 2 3 4 NC LX NC VSS VOUT NC VDET CP 5 270kW
EXT
V
DD
+ + -
22m.
8 7 6 + 22m.
H T7627
C
V RESET
DD
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)
MCU
V
SS
Rev. 1.00
5
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 O 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

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