MC34710 Datasheet, PDF (9/18 Pages) Motorola, Inc – Adjustable Dual Output Switching Power Supply

FUNCTIONAL DESCRIPTION
INTRODUCTION
FUNCTIONAL DESCRIPTION
INTRODUCTION
V_I/O Switching Regulator
The V_I/O switching regulator output voltage is determined
by the Mode digital input pins. The 34710’s Mode pins select
the output voltage. For example, if Mode2, Mode1, and
Mode0 are set to 0, 0, 0 (respectively) then V_I/O will be set
to 5.0V; if Mode2, Mode1, and Mode0 are all left floating (i.e.,
Open, Open, and Open), then the voltage for V_I/O will be set
to 3.3V. Table 5 provides the truth table for setting the various
combination of regulator outputs via the Mode pins.
The topology of the regulator is a hysteretic buck regulator
operating from the internal ~200kHz oscillator.
V_CORE Linear Regulator
The V_CORE linear LDO (low drop-out) regulator can
produce either a +3.3V, 2.5V, 1.8V, or 1.5V output voltage at
currents up to 500mA. The input to the VCORE regulator is a
pin that may be connected to the V_I/O regulator output or to
an external power supply. Note, the minimum input voltage
level must be equal to or greater than the selected V_CORE
voltage + 0.8V. (I.e., 0.8V is the LDO regulator drop out
voltage.)
The Mode pins select the output voltage as depicted in
Table 5.
Mode2
0
Table 5. V_I/O and V_CORE Regulator
Output Voltage Selection
Mode1 Mode0
V_{I /O} (V)
V_CORE (V)
0
0
5.0
3.3
0
0
Open
3.3
2.5
0
Open
0
5.0
1.8
0
Open
Open
3.3
1.8
Open
0
0
5.0
2.5
Open
0
Open
3.3
2.5
Open
Open
0
5.0
1.5
Open
Open
Open
3.3
1.5
Open indicates pin is not connected externally (i.e. floating).
FUNCTIONAL PIN DESCRIPTION
POWER SUPPLY INPUT (B+)
Main supply voltage for the V_I/O Switching Regulator and
general chip bias circuitry.
CORE VOLTAGE REGULATOR INPUT (LIN B+)
Supply voltage for the V_CORE Regulator. May be provided
by the V_I/O regulator output or from an independent supply.
MODE CONTROL (MODE 0,1,2)
Mode select pins to select the V_I/O and V_CORE output
voltages per table 2. Pull to ground for low state, float for high
state.
SWITCHING CAPACITORS 1 AND 2 (CP1/CP2)
Pins for the Charge Pump capacitor.
BOOST VOLTAGE (VB)
The Boost Voltage is an output pin used for the charge
pump boost voltage and is a connection point for the Charge
Pump bulk capacitor.It provides a gate drive for the V_I/O
Switch FET.
RESET (RST)
Reset is an output pin for supervisory functions. This pin is
in high state during normal operation and low state during
fault conditions. This pin has no input function and requires
an external pull-up resistor.
The RST pin is an open drain output driver to prevent
oscillations during the transition. It is recommended to
connect a 0.1uF capacitor between the CT pin and RST pin.
Note: error conditions must be present for a minimum time,
t_FILTER, before the 34710 responds to them. Once all error
conditions have been cleared, RST is held low for an
additional time of t_DELAY.
RESET DELAY CAPACITOR (CT)
This pin is the external delay. It is used with a capacitor to
ground to delay RST turn-on time and to RST to prevent RST
oscillations during chip power-on.
VI/O SWITCHING REGULATOR FEEDBACK (VFB)
This pin is the feedback input for the V_I/O Switching
Regulator and the output of the regulator application.
VI/O SWITCHING REGULATOR OUTPUT
(VSWITCH)
This pin is the Switching output for the V_I/O Buck
Regulator. It has internal high side FET.
Analog Integrated Circuit Device Data
Freescale Semiconductor
34710
9