MB39C313 FUJITSU [Fujitsu Component Limited.], MB39C313 Datasheet - Page 28

• Manufacturer Part Number: MB39C313
• Description: 4ch System Power Management IC for LCD Panel
• Manufacturer: FUJITSU [Fujitsu Component Limited.]

MB39C313
(6) Soft Start Capacitor Selection
3. Positive Charge Pump Design
(1) Positive Charge Pump Block Diagram
(2) Output Voltage Selection
28
R7
R8
D
A soft start function is to slow the rate of rising output voltage and minimize the large inrush current at startup.
The soft start time is adjustable by connecting external capacitor to SS pin. Soft start capacitor can be
estimated by defining the soft start time thought equation below:
Where:
I
t
V
In general, startup time for power supply is larger than 10 us. The startup time of Boost converter of
MB39C313 is defined as 1.5 ms.
Theoretically, the maximum output voltage is the sum of input voltage and pumping clock voltage of a charge
pump. In MB39C313, the maximum output voltage is V
which is 17.7 V + 17.7 V + 2(0.4 V) = 34.6 V with typical setting. Due to the regulated voltage control, the
output voltage can be configured by equation below:
Typically, multiple 2 (x2) function for Positive Charge Pump. Its output voltage will be limited by V
≤ V
adding pumping stage by using SW pin. With multiple 3 (x3) function of Positive Charge Pump, the output
voltage should be limited by 2V
ss
ss
C =
C =
V
FB
= soft start charging current;
= soft start time;
GH
GH
= voltage at FB pin.
FBP
= V
≤ V
14
I
I
ss
ss
REF
V
V
s
× t
× t
FB
FB
+ V
enb4
×
ss
ss
(
SUP
,
1 +
=
− 2 V
15 μA × 1.5 ms
R7
R8
L priority
1.146 V
diode
1.213 V
)
. For other application that requires higher output voltage, MB39C313 allows
−
+
+
= 1.213 ×
V
Amp4
Error
TH
±
S
2.1%
+ V
diode(Vs)
= 19.6 nF, therefore, 22 nF soft start capacitor is selected.
OSC
(
1 +
− 2V
R7
R8
Current
<< CH4(Positive Charge Pump) >>
Control
Logic
diode
)
≤ V
GH
DRV
S
≤ 2V
(Boost converter output voltage) + V
S
+ V
diode(Vs)
+ V
SUP
10
8
SUP
DRP
− 4V
Vs (17.7 V)
diode
.
DS04–27267–1E
D
(32 V / 50 mA Max)
SUP
S
− 2V
VGH
− 2V
diode
diode