34701_07 Datasheet, PDF (16/38 Pages) Freescale Semiconductor, Inc – 1.5 A Switch-Mode Power Supply with Linear Regulator

FUNCTIONAL DESCRIPTION
INTRODUCTION
FUNCTIONAL DESCRIPTION
INTRODUCTION
The 34701 power supply integrated circuit provides the
means to efficiently supply the Freescale Power QUICC and
other families of Freescale microprocessors. It incorporates a
high-performance synchronous buck regulator, supplying the
microprocessor’s core, and a low dropout (LDO) linear
regulator providing the microprocessor I/O and bus voltages.
This device incorporates many advanced features; e.g.,
precisely maintained up/down power sequencing, ensuring
the proper operation and protection of the CPU and power
system. At the same time, it provides high flexibility of
configuration, allowing the maximum optimization of the
power supply system.
FUNCTIONAL PIN DESCRIPTION
OSCILLATOR FREQUENCY PIN (FREQ)
This switcher frequency selection pin can be adjusted by
connecting external resistor RF to the FREQ pin. The default
switching frequency (FREQ pin left open or tied to VDDI) is
set to 300 kHz.
INVERTING INPUT PIN (INV)
Buck Controller Error Amplifier inverting input.
OUTPUT VOLTAGE PIN (VOUT)
Output voltage of the buck converter. Input pin of the
switching regulator power sequence control circuit.
INPUT VOLTAGE 2 PINS (VIN2)
Buck regulator power input. Drain of the high-side power
MOSFET.
SWITCH PINS (SW)
Buck regulator switching node. This pin is connected to the
inductor.
GROUND PINS (GND)
Analog ground of the IC, thermal heatsinking.
POWER GROUND PINS (PGND)
Buck regulator power ground.
BOOST DRAIN PIN (VBD)
Drain of the internal boost regulator power MOSFET.
BOOST VOLTAGE PIN (VBST)
Internal boost regulator output voltage. The internal boost
regulator provides a 20 mA output current to supply the drive
circuits for the integrated power MOSFETs and the external
N-channel power MOSFET of the linear regulator. The
voltage at the VBST pin is 7.75V nominal.
BOOTSTRAP PIN (BOOT)
Bootstrap capacitor input.
SERIAL DATA PIN (SDA)
I²C bus pin. Serial data.
SERIAL CLOCK PIN (SCL)
I²C bus pin. Serial clock.
LINEAR COMPENSATION PIN (LCMP)
Linear regulator compensation pin.
LINEAR FEEDBACK PIN (LFB)
Linear regulator feedback pin.
LINEAR REGULATOR PIN (LDO)
Input pin of the linear regulator power sequence control
circuit.
CURRENT SENSE PIN (CS)
Current sense pin of the LDO. Overcurrent protection of
the linear regulator external power MOSFET. The voltage
drop over the LDO current sense resistor RS is sensed
between the CS and LDO pins. The LDO current limit can be
adjusted by selecting the proper value of the current sensing
resistor RS.
LINEAR DRIVE PIN (LDRV)
LDO gate drive of the external pass N-channel MOSFET.
INPUT VOLTAGE 1 PIN (VIN1)
The input supply pin for the integrated circuit. The internal
circuits of the IC are supplied through this pin.
34701
16
Analog Integrated Circuit Device Data
Freescale Semiconductor