DS1227 Datasheet, PDF (10/20 Pages) Dallas Semiconductor – KickStarter Chip

DS1227
1) the correct inductance value must be selected.
2) the inductor must be able to handle the required peak
currents.
3) the inductor must have acceptable series resistance
and must not saturate.
When the internal N-channel MOSFET turns on, the
current through the inductor rises linearly since:
di
dt
+
V
L
where L is the inductance value
At the end of the on-time, t_ON, the peak current, I_PK is:
I_PK
+
V
t_ON
L
where : t_ON
+
1
2f_O
The energy in the inductor is:
E_L
+
L
I_PK ²
2
At maximum load this cycle is repeated f₀ (typically 40
KHz) times per second, and the power transferred
through the coil is P_L = f₀ x E_L. Since the coil only sup-
plies the voltage above the input voltage:
I_OUT
+
P_L
V_OUT * V_IN
DC-DC CONVERTER Figure 7
VDCO
BOOST
VDCI
EXTERNAL
PINS
OSCEXT
DC TO DC CONVERTER
ERROR
COMPARATOR
–
+
DQ
Q
CLR
8 CLK DELAY
40 KHZ
OSCILLATOR
CATCH
DIODE
VDCI
DRIVER
LOAD
COMPARATOR
+
–
M
U
X
BANDGAP
REFERENCE
VCCO
HIENUF
INTERNAL
SIGNALS
PWRON*
(INTERNAL
SIGNAL)
022698 10/20