Global Mixed-mode Technology Inc.
Pin Description
PIN
1
2
3
4
5
G5104
NAME
SW
GND
FB
SHDN
FUNCTION
Switch Pin. The drain of the internal NMOS power switch. Connect this pin to inductor.
Ground.
Feedback Pin. Set the output voltage by selecting values for R1 and R2 (see Block Diagram):
R1 = R2
V
OUT
-1
1.2
VCC
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.
Function Description
The G5104 is a boost converter with a NMOS
switch embedded (refer to Block Diagram). The
boost cycle is getting started when FB pin voltage
drop below 1.2V as the NMOS switch turns on.
During the switch on period, the inductor current
ramps up until 500mA 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 cur-
rent charges output capacitor and the output volt-
age is boosted up. This pumping mechanism con-
tinues cycle by cycle until the FB pin voltage ex-
ceed 1.2V and entering the none switching mode.
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.
I
PEAK
= I
LIM
+
V
IN(MAX )
−
V
SAT
x 100ns
L
Applications Information
Choosing an Inductor
There are several recommended inductors that work
well with the G5104 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
972AS-4R7M
972AS-100M
A914BYW-4R7
M
A914BYW-100M
Where V
SAT
= 0.2V (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 in-
crease 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 500mA, the power switch of the
G5104 can operate larger currents without any prob-
lem, but the total efficiency will suffer. The I
PEAK
is keep
below 700mA for the G5104 will be obtained best per-
formance.
Capacitor Selection
Low ESR (Equivalent Series Resistance) capacitors
should be used at the output to minimize the output
ripple voltage and the peak-to-peak transient voltage.
Multilayer ceramic capacitors (MLCC) are the best
choice, as they have a very low ESR and are available
in very small packages. Their small size makes them a
good match with the G5104’s SOT-23 package. If solid
tantalum capacitors (like the AVX TPS, Sprague 593D
families) or OS-CON capacitors are used, they will
occupy more volume than a ceramic ones and the
higher ESR increases the output ripple voltage. Notice
that use a capacitor with a sufficient voltage rating.
A low ESR surface-mount ceramic capacitors also
make a good selection for the input bypass capacitor,
which should be placed as close as possible to the
G5104. A 47µF input capacitor is sufficient for most
applications.
VALUE(µH) MAX DCR
(Ω)
4.7
10
22
4.7
10
4.7
10
0.26
0.30
0.92
0.22
0.48
0.072
0.125
VENDOR
Murata
www.murata.com
TOKO
www.toko.co.jp
Current Limit Overshoot
The G5104 use a constant off-time control scheme,
the power switch is turned off after the 500mA current
limit is reached. When the current limit is reached and
when the switch actually turns off, there is a 100ns
Ver: 1.2
Mar 01, 2005
TEL: 886-3-5788833
http://www.gmt.com.tw
5
GMT [ GLOBAL MIXED-MODE TECHNOLOGY INC ]
