MB3828 Fujitsu Microelectronics, Inc., MB3828 Datasheet - Page 16

• Manufacturer Part Number: MB3828
• Description: Pentium DC/DC Converter ic
• Manufacturer: Fujitsu Microelectronics, Inc.

16
MB3828
At startup of the MB3828, the capacitor (C
start, by providing output voltage from Error Amp. that is proportional to the CS pin voltage regardless of the
DC/DC converter load current.
TIME SETTING BY SHORT DETECTION
When load conditions change rapidly with the reduced output voltage, as when a load fault occurs, the Capacitor
Cscp connected to the CSCP pin (pin 22) is charged to threshold voltage (V
external FET is turned off (inactive interval 100%).
Short detection time
t
OSCILLATOR FREQUENCY SETTING
The oscillator frequency can be set by connecting resistance to the RT pin (pin 1).
Oscillator frequency
f
METHOD OF SETTING THE DISCHARGE TIME
• An “L” level CTL signal while the ENB pin is set to “H” level causes the resistance (R
• As long as the ENB pin is set to “L” level, the discharge control function is switched OFF.
D/A BLOCK VD4 to VD0 SWITCHING
• Switching of the VD4 to VD0 pin signal during the MB3828 operation may cause transient fluctuation in output
• When all VD4 to VD0 pin signals are set to “H” level, the DC/DC converter output is switched OFF.
METHOD OF SETTING THE SOFT START TIME
PE
OSC
pin to discharge electrical charge the capacitor (C
fall gradually regardless of the DC/DC converter load current.
voltage from the DC/DC converter. The resulting voltage instability may cause an “L” level from the PWRGOOD
block, activating the OVP protection and shutting off the output from the DC/DC converter.
To switch VD4 to VD0 pin settings, first input an “L” level control signal to the CTL pin to place the MB3828
in standby status.
Soft start time (time to output setting voltage VD)
t
(sec)
Discharge time (time to 0.05 V output voltage)
toff (msec)
S
(kHz)
(sec)
~
~
0.68
~
26250 / RT (k )
2 ( A)
~
VD
R
C
S
SCP
(k )
( F) / 2 ( A)
C
S
C
( F)
S
( F)
ln (
V
TH (CS COMP)
S
) connected to the CS pin begins charging. This produces a soft
VD
S
) connected to the CS pin, causing the output voltage to
)
TH
:=0.68V) and sets a latch, the
S
) connected to the RS