MB3785A_03 Datasheet, PDF (16/30 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
5V
VO [ V ] 10
200 ns
0
IO [ mA ] 40
20
0
−20
10 mV
−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
VO
8k.₉2
2k.₉7
7 pin
16