ZL2006_14 Datasheet, PDF (14/45 Pages) Intersil Corporation – Adaptive Digital DC-DC Controller with Drivers and Current Sharing

ZL2006
5. Power Conversion Functional Description
5.1 Internal Bias Regulators and Input Supply
Connections
The ZL2006 employs two internal low dropout (LDO)
regulators to supply bias voltages for internal circuitry,
allowing it to operate from a single input supply. The
internal bias regulators are as follows:
VR: The VR LDO provides a regulated 5 V bias
supply for the MOSFET driver circuits. It is
powered from the VDD pin. A 4.7 µF filter
capacitor is required at the VR pin.
V25: The V25 LDO provides a regulated 2.5 V bias
supply for the main controller circuitry. It is
powered from an internal 5V node. A 10 µF
filter capacitor is required at the V25 pin.
When the input supply (VDD) is higher than 5.5 V, the
VR pin should not be connected to any other pins. It
should only have a filter capacitor attached as shown in
Figure 9. Due to the dropout voltage associated with
the VR bias regulator, the VDD pin must be connected
to the VR pin for designs operating from a supply
below 5.5 V. Figure 9 illustrates the required
connections for both cases.
Figure 9. Input Supply Connections
Note: the internal bias regulators are not designed to be
outputs for powering other circuitry. Do not attach
external loads to any of these pins. The multi-mode
pins may be connected to the V25 pin for logic HIGH
settings.
5.2 High-side Driver Boost Circuit
The gate drive voltage for the high-side MOSFET
driver is generated by a floating bootstrap capacitor,
CB (see Figure 6). When the lower MOSFET (QL) is
turned on, the SW node is pulled to ground and the
capacitor is charged from the internal VR bias
regulator through diode DB. When QL turns off and
the upper MOSFET (QH) turns on, the SW node is
pulled up to V_DD and the voltage on the bootstrap
capacitor is boosted approximately 5 V above V_DD to
provide the necessary voltage to power the high-side
driver. A Schottky diode should be used for DB to help
maximize the high-side drive supply voltage.
5.3 Output Voltage Selection
5.3.1 Standard Mode
The output voltage may be set to any voltage between
0.6 V and 5.0 V provided that the input voltage is
higher than the desired output voltage by an amount
sufficient to prevent the device from exceeding its
maximum duty cycle specification. Using the pin-strap
method, V_OUT can be set to any of nine standard
voltages as shown in Table 6.
Table 6. Pin-strap Output Voltage Settings
V0
LOW
OPEN
LOW
0.6 V
0.8 V
V1 OPEN 1.2 V
1.5 V
HIGH 2.5 V
3.3 V
HIGH
1.0 V
1.8 V
5.0 V
The resistor setting method can be used to set the
output voltage to levels not available in Table 6.
Resistors R0 and R1 are selected to produce a specific
voltage between 0.6 V and 5.0 V in 10 mV steps.
Resistor R1 provides a coarse setting and resistor R0
provides a fine adjustment, thus eliminating the
additional errors associated with using two 1%
resistors (this typically adds approx 1.4% error).
14
FN6850.1
December 15, 2010