ipm6220 Intersil Corporation, ipm6220 Datasheet - Page 7

• Manufacturer Part Number: ipm6220
• Description: Advanced Triple Pwm And Dual Linear Power Controller For Portable
• Manufacturer: Intersil Corporation

converters for 5V Main and 3.3V Main buses, two linear
regulators for 3.3V ALWAYS and 5V ALWAYS, and a 12V
boost converter.
The two synchronous converters operate out of phase to
substantially reduce the input-current ripple, minimizing input
filter requirements, minimizing battery heating and
prolonging battery life.
The 12V boost controller uses a 100kHz clock derived from
the main clock. This controller uses leading edge modulation
with the maximum duty cycle limited to 33%.
The chip has three input control lines SDWN1, SDWN2 and
SDWNALL. These are provided for Advanced Configuration
and Power Interface (ACPI) compatibility. They turn on and
off all outputs, as well as provide independent control of the
3.3V Main and +5V Main outputs.
To maximize efficiency for the 5V Main and 3.3V Main outputs,
the current-sense technique is based on the lower MOSFET
r
hysteretic mode of operation which is automatically engaged at
light loads when the inductor current becomes discontinuous.
3.3V Main and 5V Main Architecture
These main outputs are generated from the unregulated
battery input by two independent synchronous buck
converters. The IC integrates all the components required
for output voltage setpoint and feedback compensation,
significantly reducing the number of external components,
saving board space and parts cost.
The buck PWM controllers employ a 300kHz fixed frequency
current-mode control scheme with input voltage feed-
forward ramp programming for better rejection of input
voltage variations.
Figure 4 shows the out-of-phase operation for the 3.3V Main
and 5V Main outputs. The phase node is the junction of the
upper MOSFET, lower MOSFET and the output inductor.
The phase node is high when the upper MOSFET is
conducting and the inductor current rises accordingly. When
the phase node is low, the lower MOSFET is conducting and
the inductor current is ramping down as shown.
Current Sensing and Current Limit Protection
Both PWM converters use the lower MOSFET on-state
resistance, r
technique eliminates the need for a current sense resistor
and the associated power losses. If more accurate current
protection is desired, current sense resistors may be used in
series with the lower MOSFETs’ source.
To set the current limit, place a resistor, RSNS, between the
ISEN inputs and the drain of the lower MOSFET (or optional
current sense resistor). The required value of the RSNS
resistor is determined from the following equation:
DS(ON).
Light-load efficiency is further enhanced by a
DS(ON)
, as the current-sensing element. This
7
IPM6220
where IOCDC is the desired DC overcurrent limit; RCS is
either the r
optional current-sense resistor, Vo is the output voltage and L
is the output inductor. Also, the value of RCS should be
specified for the expected maximum operating
temperature.
The sensed voltage, and the resulting current out of the
ISEN pin through RSNS, is used for current feedback and
current limit protection. This is compared with an internal
current limit threshold. When a sampled value of the output
current is determined to be above the current limit
threshold, the PWM drive is terminated and a counter is
initiated. This limits the inductor current build-up and
essentially switches the converter into current-limit mode. If
an overcurrent is detected between 26Ps to 53Ps later, an
overcurrent shutdown is initiated. If during the 26Ps to 53Ps
period, an overcurrent is not detected, the counter is reset
and sampling continues as normal.
This current limit scheme has proven to be very robust in
applications like portable computers where fast inductor
current build-up is common due to a large difference
between input and output voltages and a low value of the
inductor.
Light-Load (Hysteretic) Operation
In the light-load (hysteretic) mode the output voltage is
regulated by the hysteretic comparator which regulates the
output voltage by maintaining the output voltage ripple as
shown in Figure 5. In Hysteretic mode, the inductor current
flows only when the output voltage reaches the lower limit of
the hysteretic comparator and turns off at the upper limit.
Hysteretic mode saves converter energy at light loads by
supplying energy only at the time when the output voltage
requires it. This mode conserves energy by reducing the
power dissipation associated with continuous switching.
RSNS
0 A, V
0 A, V
5A
5A
=
5V PHASE (10V/DIV.)
----------------- - Iocdc
135PA
DS(ON)
Rcs
V
FIGURE 4. OUT OF PHASE OPERATION
IN
= 10.8V
I
§
©
L5V
of the lower MOSFET, or the value of the
(2A/DIV.)
+
---------------------------------------- -
L
u
2 300kHz
u
1Ps/DIV.
Vo
3.3V PHASE (10V/DIV.)
·
¹
I
–
L3.3V
100
(2A/DIV.)