33730_10 Datasheet, PDF (15/26 Pages) Freescale Semiconductor, Inc – Switch Mode Power Supply with Multiple Linear Regulators

FUNCTIONAL DEVICE OPERATION
OPERATION DESCRIPTION
FUNCTIONAL DEVICE OPERATION
OPERATION DESCRIPTION
INTRODUCTION
The 33730 has two supply inputs. The KA_VBAT pin is the
supply input for the standby regulators V_KAM (and optionally
V_{DD3_SBY,} see Table 6) and for the internal supply circuits.
The VBAT pin is the power input of the integrated buck
regulator, which steps-down the protected battery voltage
providing directly the 5.0 V system supply V_DDH. V_DDH
provides power for the main linear regulator(s) V_DDL, V_DD3,
and also for the other module circuits requiring 5.0 V supply
voltage (e.g. protected V_REF1,2 outputs).
If the supply voltage ramps from zero volts up to its
nominal level, the 33730 will start at the latest when the
supply (battery) voltage reaches V_STUP at the KA_VBAT pin.
If the supply voltage ramps down, the 33730 will keep
operating (with degradation of the output voltage regulation)
down to V_{UVLO_f} at the KA_VBAT pin. The V_KAM output stays
operational down to V_{UVLO_f} at the KA_VBAT pin.
The 33730 will operate in systems with and without
standby mode. In the Standby (sleep) mode of operation the
IC will draw maximum I_Q quiescent current, assuming only
the VKAM is used as a standby output, and it is unloaded.
When VDD3 is used as an additional standby output the
quiescent current increases by approximately another
100 μA.
POWER UP
The 33730 will safely power up when the power is applied
simultaneously (hot plugged) or in the random sequence to
the KA_VBAT, VBAT and VIGN (or REGON) inputs.
POWER DOWN
The 33730 will safely power down when the power is
disconnected from any of the KA_VBAT, VBAT inputs or
when control signals the VIGN or REGON inputs go low.
UNDERVOLTAGE LOCK-OUT (UVLO)
There is an under-voltage lock-out feature implemented
into the IC. When the battery voltage at the KA_VBAT pin
falls below V_{UVLO_f} the under-voltage comparator initiates the
power down sequence for the whole IC. The under-voltage
lock-out circuit has a V_{UVLO_hys} hysteresis and 5.0 μs glitch
filter in order to prevent spurious tripping its threshold level
and consequent system oscillations between the ON and
OFF states.
SWITCHING REGULATOR
The 33730 switching regulator is a fixed frequency
(externally adjustable) PWM voltage mode controller with
integrated low-R_DS(ON) N-channel power MOSFET. This
architecture is widely flexible and provides a possibility to
optimize its operation over a wide range of input voltages.
The 33730 switching regulator provide the following features:
Adjustable Switching Frequency
The adjustable frequency feature provides the ability to
modify the switcher performance for optimized cost (higher
frequency, smaller, cheaper components), or higher
efficiency and better EMC performance (lower switching
frequency for reduced losses and EMI). The operating
frequency of the switching regulator can be adjusted by
means of an external resistor R_F connected from the FREQ
pin to ground (see Figure 4).
600
500
400
300
200
100
0
0
Frequency vs R_Freq
20
40
60
80
100
R_Freq [kohm ]
F_SW ≅ 18.48 + (5098.7/R_FREQ)
F_{SW i}s the switch frequency in kHz
R_FREQ is the resistor value in kOhms
Figure 4. Switching Regulator Frequency vs. R_Freq Value
Adjustable Slew-rate
The adjustable slew-rate option allows, with selection of
the right switching frequency, optimization of the system for
EMC performance.
Over-voltage Lock-Out (Shutdown)
The over-voltage lock-out (shutdown) feature turns the
switching regulator off when the input voltage exceeds the
V_{SHDN_r} limit. This extends the 33730 capability to survive
the severe load dump conditions up to max V_BAT.
Operation at 100% Duty Cycle
The internal charge pump is used to enhance the power
MOSFET gate when the switching regulator reaches 100%
duty cycle during the low battery conditions.
The switching regulator output voltage V_DDH is regulated
to provide 5.0 V @ 2.0 A with ±2% accuracy and it is intended
to directly power the digital and analog circuits of the
Electronic Control Module (ECM). The switching regulator
Analog Integrated Circuit Device Data
Freescale Semiconductor
33730
15