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參數(shù)資料
| 型號(hào)： | G5111 |
| 廠商： | Electronic Theatre Controls, Inc. |
| 英文描述： | Micro-power Step-Up DC/DC Converters in SOT23-5 |
| 中文描述： | 微功率升壓型DC / DC轉(zhuǎn)換器采用SOT23 - 5 |
| 文件頁數(shù)： | 3/5頁 |
| 文件大小： | 89K |
| 代理商： | G5111 |
Ver 0.2 Preliminary
Jan 09, 2002
TEL: 886-3-5788833
http://www.gmt.com.tw
3
G5111
Global Mixed-mode Technology Inc.
Pin Description
PIN
NAME
1
SW
Switch Pin. The collector of the internal NPN power switch. Connect this pin to inductor.
2
GND
Ground.
Feedback Pin. Set the output voltage by selecting values for R1 and R2 (see Block Diagram):
V
OUT
-1
FUNCTION
3
FB
R1 = R2
2
4
SHDN
Active-Low Shutdown Pin. Tie this pin to logic-high to enable the device or tied it to logic-low to turn this
device off.
Input Supply Pin. Bypass this pin with a capacitor as close to the device as possible.
5
VCC
Function Description
The G5111 is a boost converter with a NPN switch
embedded (refer to Block Diagram). The boost cy-
cle is getting started when FB pin voltage drop be-
low 1.2V as the NPN switch turns on. During the
switch on period, the inductor current ramps up until
350mA current limit is reached. Then turns the
switch off, while the inductor current flows through
external schottky diode, and ramps down to zero.
During the switch off period, the inductor current
charges output capacitor and the output voltage is
boosted up. This pumping mechanism continues
cycle by cycle until the FB pin voltage exceed 1.2V
and entering the none switching mode. In this mode,
the G5111 consumes as low as 20uA typically to
save battery power.
Applications Information
Choosing an Inductor
There are several recommended inductors that work
well with the G5111 in Table 1. Use the equations and
recommendations in the next few sections to find the
proper inductance value for your design.
Table 1. Recommended Inductors
PART
LQH3C4R7
LQH3C100
LQH3C220
CD43-4R7
CD43-100
CDRH4D18-4R7
CDRH4D18-100
DO1608-472
DO1608-103
DO1608-223
VALUE
(
μH) MAX DCR
(
)
4.7
10
22
4.7
10
4.7
10
4.7
10
22
VENDOR
0.26
0.30
0.92
0.11
0.18
0.16
0.20
0.09
0.16
0.37
Murata
www.murata.com
Sumida
www.sumida.com
Coilcraft
www.coilcraft.com
Inductor Selection—Boost Regulator
The appropriate inductance value for the boost regu-
lator application may be calculated from the following
equation. Select a standard inductor close to this
value.
V
OUT
-V
IN(MIN)
+V
D
I
LIM
L =
x t
OFF
Where V
D
= 0.4V (Schottky diode voltage), I
LIM
=
350mA and t
OFF
= 500ns. A larger value can be used
to lightly increase the available output current, but limit
it to about twice the calculating value. When too large
of an inductor will increase the output voltage ripple
without providing much additional output current. In
varying V
IN
condition such as battery power applica-
tions, use the minimum V
IN
value in the above equa-
tion. A smaller value can be used to give smaller
physical size, but the inductor current overshoot will
be occurs (see Current Limit Overshoot section).
Inductor Selection—SEPIC Regulator
For a SEPIC regulator using the G5111, the approxi-
mate inductance value can be calculated by below
formula. As for the boost inductor selection, a larger or
smaller value can be used.
V
OUT
+ V
D
I
LIM
L = 2
x t
OFF
Current Limit Overshoot
The G5111 use a constant off-time control scheme,
the power switch is turned off after the 350mA current
limit is reached. When the current limit is reached and
when the switch actually turns off, there is a 100ns
delay time. During this time, the inductor current ex-
ceeds the current limit by a small amount. The formula
below can calculate the peak inductor current.
V
IN(MAX)
- V
SAT
L
I
PEAK
= I
LIM
+
x 100ns
Where V
SAT
= 0.25V (switch saturation voltage). When
the systems with high input voltages and uses smaller
inductance value, the current overshoot will be most
apparent. This overshoot can be useful as it helps
increase the amount of available output current. To
use small inductance value for systems design, the
current limit overshoot can be quite high. Even if it is
internally current limited to 350mA, the power switch of
the G5111 can operate larger currents without any
problem, but the total efficiency will suffer. The I
PEAK
is
keep below 500mA for the G5111 will be obtained
best performance.
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