MB39C313 Datasheet, PDF (29/52 Pages) Fujitsu Component Limited. – 4ch System Power Management IC for LCD Panel

MB39C313
(3) Pumping Capacitor and Output Capacitor Selection
Ceramic capacitor is recommended for its non-polarized, more stable over temperature, low leakage and
small ESR. Choosing a pumping capacitor should consider the required voltage rating and output current
loading. For 32 V output voltage setting, the pumping clock voltage is calculated below.
ΔVDRP = VGH − VS + 2(Vdiode) = 32 V − 17.7 V + 2(0.4 V) = 15.1 V
The minimum pumping capacitor is determined by following equation.
Iout
C≥
,
f × ΔVDRP
Where:
Iout = the output current
f = switching frequency (500 kHz or 750 kHz)
ΔVDRP = pumping clock voltage
The charge stored on pumping capacitor is transferred to output capacitor cycle-by-cycle. Output capacitor
determines output ripple voltage of charge pump. The ripple voltage is estimated by:
Vripple =
Iout
2f × Cout
+ Iout × ESRCout
Where:
Cout = output filtering capacitance
ESRCout = equivalent series resistance of output filtering capacitor
4. Negative Charge Pump Design
(1) Negative Charge Pump Block Diagram
C
R5
FBN
13
R6
REF
(1.213 V)
VTH
0 V ± 36 mV
Error
− Amp3
+
enb3
OSC
<< CH3(Negative Charge Pump) >> AVIN
Current
Control
Logic
DRV
DRN
11
C
VGL
(−5 V/50 mA)
(2) Output Voltage Selection
Recall from functional description, the maximum negative output voltage is − VDRN + Vdiode ideally, which is
−12 V + 0.4 V = −11.6 V. Similar to Positive Charge Pump, the regulated output voltage can be set by equation
below:
R5
R5
VGL = −VREF ×
= −1.213 ×
R6
R6
DS04–27267–1E
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