MB3785A Datasheet, PDF (16/29 Pages) Fujitsu Component Limited. – Switching Regulator Controller (4 Channels plus High-Precision, High-Frequency Capabilities)

MB3785A
s METHOD OF SETTING THE OUTPUT CURRENT
The output circuit is comprised of a totem-pole configuration. Its output current waveform is such that the ON-current
value is set by constant current and the OFF-current value is set by a time constant as shown in Figure 2. These
output currents are set using the equations below.
• ON-current = 2.5/RE [A]
(Voltage on output current-setting pin VE = 2.5 V)
• OFF-current time constant = proportional to the value of CB
Figure 1. CH1 to CH4 Output Circuit
Drive transistor
CB
OFF-current
setting block
OFF-current
ON-current
Figure 2. Output Current Waveform
ON-current
0
OFF-current
RE
VE
t
Figure 3. Voltage and Current Waveforms
on Output Pin (CH1)
VCC = 10 V
10
0
40
20
0
–20
–40
0
0.4
0.8
1.2
1.6
2.0
t (µS)
Figure 4. Measuring Circuit Diagram
1000 pF
1
48
VCC
45
MB3785A
IO
46
570 pF
47
82 Ω
8 pin
22 µH
(5 V)
10 µF ^8.2
VO
k
2.7
k
7 pin
16