33730_12 Datasheet, PDF (19/28 Pages) Freescale Semiconductor, Inc – Switch Mode Power Supply with Multiple Linear Regulators

FUNCTIONAL DEVICE OPERATION
OPERATION DESCRIPTION
REGON
The REGON feature permits the microcontroller to select
a delayed shutdown of the 33730. It holds off the activation of
the reset signals to the microcontroller after the V_IGN signal
has transitioned. This allows the microcontroller to control the
power up and power down of the main regulator outputs
except for the standby supplies. The REGON pin input
threshold voltages allow control by the standard 2.5 V (up to
5.0 V) logic ICs.
HARDWARE RESETS (RSTL, RST3, RSTH, and
RSTKAM)
The Hardware Resets are open drain, active low outputs
capable of sinking 5.0 mA current and able to withstand
+7.0 V.
The RSTL control circuit monitors the V_DDL output. If the
V_DDL output is out of regulation (low), the device will assert
the RSTL signal low.
The RST3 control circuit monitors the V_DD3 output. If the
V_DD3 output is out of regulation (low), the device will assert
the RST3 signal low.
The RSTH control circuit monitors the V_DDH output. If the
V_DDH output is out of regulation (low or high), the device will
assert the RSTH signal low.
The RSTKAM control circuit monitors the V_KAM output. If
the V_KAM output is out of regulation (low), the device will
assert the RSTH signal low.
All Reset monitoring circuits have a 20 μs delay filter to
avoid unintended resets caused by noise glitches on the
regulator output lines.
HR TIMER
The HR (Hardware Reset) Timer provides the delay
between the time when the particular regulator output voltage
is in regulation and the release of the Reset signal. This delay
can be programmed by a single external resistor. This
solution provides better accuracy than the commonly used
external RC timer. The HR Timer delay can be programmed
in eight 8ms steps from 0 to 56 ms (see Table 8)
.
Table 8. HR Timer Delay Programming
Programming Resistor
Value R_HRT [ohms]
Delay (typ.) [ms]
68 k
0
33 k
10
16 k
19
8.2 k
29
3.9 k
39
2.0 k
48
1.0 k
58
470
68
B att ery
Vo ltage
4.5V
VKAM = 1.0V
VDDH = 5.0 V
VDDL = VDD3 = 3.3V
RS TKA M
RST L, RST 3
POR Delay
POR Delay
RSTH
POR Delay
Figure 6. Battery Voltage Ramp Up
Analog Integrated Circuit Device Data
Freescale Semiconductor
33730
19