MP86885 – INTELLI-PHASE SOLUTION IN 4x6mm TQFN
MP86885 Rev. 1.01 www.MonolithicPower.com 9
7/22/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
OPERATION
The MP86885 is a 40A monolithic half-bridge
driver with MOSFETs ideally suited for multi-
phase buck regulators.
When the EN transitions from low to high and
both V
DD
and V
BST
signals are sufficiently high,
operation begins. It is recommended to use EN
pin to startup and shutdown the Intelli-Phase.
To put SW node in a high impedance state, let
PWM pin float or drive PWM pin to mid-state.
Drive the SYNC pin low to enter diode emulation
mode. In diode emulation mode, the LSFET is
off after inductor current crossed zero current.
When HSFET over current is detected, the part
will latch off. Recycling VIN/VDD or toggling EN
will release the latch and restart the device.
When the LSFET detects -25A current, the part
will turn off the LSFET for that cycle.
Current Sense
The CS pin is a bi-directional current source
proportional to the inductor current. Use the
following equations to select the RIN resistance
to connect between RIN pin and IN pin:
IN L_ RIPPLE
R7.55I 170(k)=− × + Ω
ON IN OUT OUT IN OUT
L_RIPPLE
IN SW
t(VV)V (VV)
I
LVFL
×− ×−
==
××
Where I
L_RIPPLE
is the peak to peak inductor ripple
current. For example, if the ripple current is 10A,
then the calculated R
IN
is 94.5kΩ and 95.3kΩ (the
closest 1% resistor value) should be selected for
R
IN
.
The current sense gain is 10μA/A. In general,
there is a resistor, R
CS
, connected from CS pin
and V
OUT
or an external voltage which is capable
to sink small current to provide enough voltage
shift to meet the operating voltage on CS pin.
The CS voltage range of 1V to 3.5V is required to
keep CS’s output current linearly proportional to
inductor current. Use the following equations to
determine a proper reference voltage and/or R
CS
value:
CS CS REF
1V I R V 3.5 V
×+ <
6
CS L
I I 10 10
−
=× ×
Intelli-Phase’s current sense output can be used
by controller to accurately monitor the output
current. The cycle-by-cycle current information
from CS pin can be used for phase current
balancing, over current protection and active
voltage positioning (output voltage droop).
Intelli-Phase’s accurate current sense can
replace traditional inductor DCR current sensing
scheme. In traditional inductor DCR current
sense:
CS L DCR
VIR
×
With Intelli-Phase’s CS output, V
CS
becomes:
6
CS CS CS L CS
VIRIR1010
=× =× ××
Where the R
DCR
term is replaced
with
6
CS
R1010
×× . Figure 2 shows a circuit
replacing inductor DCR sensing with Intelli-
Phase’s CS output. There are several
advantages with this current sensing method:
1. Since current sensing is done by Intelli-
Phase, user can select low DCR
inductors and still have large current
sense signal by selecting larger R
CS
.
2. Tight DCR variation is not required.
3. CS signal is independent of impedance
matching and inductor temperature.
