zl2006 Intersil Corporation, zl2006 Datasheet - Page 11

• Manufacturer Part Number: zl2006
• Description: Adaptive Digital Dc-dc Controller With Drivers And Current Sharing
• Manufacturer: Intersil Corporation

4.2 Power Conversion Overview
The ZL2006 operates as a voltage-mode, synchronous
buck converter with a selectable constant frequency
pulse width modulator (PWM) control scheme that
uses external MOSFETs, capacitors, and an inductor to
perform power conversion.
Figure 6 illustrates the basic synchronous buck
converter topology showing the primary power train
components. This converter is also called a step-down
converter, as the output voltage must always be lower
than the input voltage. In its most simple configuration,
the ZL2006 requires two external N-channel power
MOSFETs, one for the top control MOSFET (QH) and
one for the bottom synchronous MOSFET (QL). The
amount of time that QH is on as a fraction of the total
switching period is known as the duty cycle D, which
is described by the following equation:
Figure 6. Synchronous Buck Converter
I
I
2
2
C
C
SALRT
SALRT
SDA
SDA
SCL
SCL
SA(0,1)
SA(0,1)
VTRK
VTRK
SYNC
SYNC
DDC
DDC
11
>
>
PG
PG
REFCN
REFCN
EN
EN
SYNC
SYNC
GEN
GEN
Communication
Communication
MGN
MGN
Figure 5. ZL2006 Block Diagram
ILIM(0,1)
ILIM(0,1)
Power Management
Power Management
PLL
PLL
DAC
DAC
Compensator
Compensator
Input Voltage Bus
Input Voltage Bus
Digital
Digital
SS
SS
DLY(0,1)
DLY(0,1)
ADC
ADC
V(0,1)
V(0,1)
ADC
ADC
ADC
ADC
D-PWM
D-PWM
ZL2006
FC(0,1)
FC(0,1)
NLR
NLR
NVM
NVM
MUX
MUX
VDD
VDD
During time D, QH is on and V
across the inductor. The current ramps up as shown in
Figure 7.
When QH turns off (time 1-D), the current flowing in
the inductor must continue to flow from the ground up
through QL, during which the current ramps down.
Since the output capacitor C
impedance at the switching frequency, the AC
component of the inductor current is filtered from the
output voltage so the load sees nearly a DC voltage.
Σ
Σ
+
+
MOSFET
MOSFET
Sensor
Sensor
Drivers
Drivers
VDD
VDD
TEMP
TEMP
-
-
Voltage
Voltage
Sensor
Sensor
VSEN
VSEN
ISENB
ISENB
ISENA
ISENA
VSEN+
VSEN+
XTEMP
XTEMP
VSEN-
VSEN-
SW
SW
SW
SW
VR
VR
BST
BST
D ≈
V
V
OUT
IN
OUT
IN
December 15, 2010
– V
exhibits a low
V
V
OUT
OUT
OUT
FN6850.1
is applied