MB3870 Datasheet, PDF (18/25 Pages) Fujitsu Component Limited. – Pentium II DC/DC Converter IC

MB3870
s CTL LOGIC CIRCUIT OPERATION TIMING CHART
CTL signal
ENB signal
VREF output voltage
CS pin voltage
DC/DC
output voltage
0.05 V
ts
toff
s DC/DC CONVERTER INPUT VOLTAGE (Vin) AND VB VOLTAGE SETTING
The voltage at the CB pin is bootstrapped from the VS pin voltage by an amount equivalent to the VB pin voltage,
as a result of the bootstrap capacitance (CB) between the CB pin and VS pin. Therefore, either the Vin voltage
or VB pin voltage should be adjusted so that the sum of the DC/DC converter block input voltage Vin plus the
VB pin voltage does not exceed the recommended operating conditions for the CB pin boot voltage (VCB).
Drive
1
Drive
2
VB
13
*¹
DC/DC converter block
CB
10
OUT1
8
VS
9
*²
CB
OUT2
*²
11
PGND
12
Vin
VB
VO
*1: To connect the external low VF diode (Schottky barrier diode) makes VB pin voltage drop reduced
and then can perform the higher efficiency.
*2: The switching noise can be reduced (0Ω to 5Ω) by connecting the resistance when the external
MOSFET gate input capacitance (Ciss) is large, caused by the external MOSFET gate drive
current limiting resistance.
18