Pin Description
Pin No.
Pin Name
I/O
Description
1, 3, 7
NC
No connection
2
LX
I
Switching pin
4
VSS
Negative power supply, ground
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
Absolute Maximum Ratings
Supply Voltage ............................ V
SS
0.3V to V
SS
+6V
Storage Temperature .......................... 40 C to 125 C
Switching pin Voltage .................. V
SS
0.3V to V
SS
+6V
Operating Temperature ......................... 25 C to 70 C
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 reliabil-
ity.
Electrical Characteristics
Ta=25 C, V
OUT
=2.7V
Symbol
Parameter
Test Conditions
Min.
Typ.
Max.
Unit
V
OUT
Output Voltage
2.56
2.7
2.75
V
V
IN
Input Voltage
5
V
Vstart
Starting Voltage
L=330 H, I
L
=1mA
0.95
1.1
V
Vhold
Voltage Hold
0.9
V
Iin
Current Consumption
Measure at no load
14
20
A
I
LX
LX Switching Current
V
IN
=1.5V
60
mA
I
LEAK
LX Leakage Current
1
A
f
OSC
Oscillator Frequency
V
IN
=1.5V
139
kHz
V
DET
H
L Detectable Voltage
2.0
2.1
2.2
V
L
H Detectable Voltage
2.2
2.3
2.4
V
V
HYS
Hysteresis Width
0.2
V
I
DETOL
V
DET
Output Sink Current
V
OUT
=2.2V, V
DET
=0.2V
0.5
mA
HT7627
Rev. 1.00
2
January 18, 2002
Functional Description
Operation of step-up DC/DC converter
The following figures show the basic circuit configura-
tion of the step-up operation of the IC. In the configura-
tion, when the transistor tr is entirely Off, the output
voltage is the value of the input voltage V
IN
minus the
voltage reduced by inductor L and Schottky diode SD.
When tr has been On for time ton and is suddenly turned
Off,voltageV
L
isgeneratedattheedgesofLbecauseof
the energy accumulated during the ton period. There-
fore,thepeakvalueofthevoltagegeneratedatthattime
is V
IN
+V
L
, and it is stored in the output capacitor C
L
via
SD. This generates the step-up output voltage V
OUT
that
is larger than V
IN
.