ISL6217ACVZ-T Intersil, ISL6217ACVZ-T Datasheet - Page 13

• Manufacturer Part Number: ISL6217ACVZ-T
• Description: IC CTRLR PWM INTEL PENT 38-TSSOP
• Manufacturer: Intersil

Specifications of ISL6217ACVZ-T

• Applications: Controller, Intel Pentium® IMVP-IV, IMVP+
• Voltage - Input: 5.5 ~ 25 V
• Number Of Outputs: 1
• Operating Temperature: -10°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 38-TSSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -

Overcurrent Setting - OCSET
The ISL6217A overcurrent protection essentially compares a
user-selectable overcurrent Threshold to the scaled and
sampled output current. An overcurrent condition is defined
when the sampled current is equal to or greater than the
threshold current. A step by step process to design for the
user-desired overcurrent set point is detailed next.
STEP 1: SETTING THE OVERCURRENT THRESHOLD
The overcurrent threshold is represented by the DC current
flowing out of the OCSET pin (See Figure 8). Since the
OCSET pin is held at a constant 1.75V, the user need only
populate a resistor from this pin to ground to set the desired
overcurrent threshold, I
of I
Ohm’s Law to determine the necessary resistor to place from
OCSET to ground:
For example, if the desired overcurrent threshold is 15µA,
the total resistance from OCSET must equal 117k Ω .
STEP 2: SELECTING ISEN RESISTANCE FOR DESIRED
OVERCURRENT LEVEL
After choosing the I
what level of total output current is desired for overcurrent.
Typically, this number is between 150% and 200% of the
maximum operating current of the application. For example,
if the max operating current is 46A, and the user chooses
150% overcurrent, the ISL6217A will shut down if the output
current exceeds 46A*1.5 or 69A. According to the Block
Diagram, the equation below should be used to determine
R
In Equation 3, M represents the number of Low-Side
MOSFETs in one channel, and N represents the number of
channels. Using the examples above (I
I
r
STEP 3: THERMAL COMPENSATION FOR r
DESIRED)
If PTCs are used for thermal compensation, then R ISEN is
found using the room temperature value of r
standard resistors are used for RISEN, then the “HOT” value
of r
MOSFET r
efficiency, and board area. However, if more precise current
feedback is desired, a discrete Precision Current Sense
Resistor, R POWER , may be inserted between the SOURCE
of each channels lower MOSFET and ground. The small
R
R
OCSET
DS(ON)
ISEN
OCSET
ISEN
OCSET
DS(ON)
once the overcurrent level, I
=
= 15µA) and substituting the values M = 2, N = 2,
= 6m Ω , R
=
I (
between 10µA and 25µA. Once this is done, use
DS(ON)
OCSET
should be used for this calculation.
I
I
OC
OCSET
. 1
75
⋅
r
V
(
DSON
ISEN
sensing provides advantages in cost,
+
OCSET
M
=
2
µ
R
OCSET
A
is calculated to be 1.5k Ω .
1
)
)
+
⋅
⋅
. 0
R
N
level, the user must then decide
2
2175
13
−
. The user should pick a value
+
4
R
µ
3
A
OC
−
130
, is chosen.
OC
= 69A,
DS(ON)
DS(ON)
. If
(EQ. 2)
(EQ. 3)
(IF
ISL6217A
R ISEN resistor, as described above, is then replaced with a
standard 1% resistor and connected from the ISEN pin of the
ISL6217A controller to the SOURCE of the lower MOSFET.
June 30, 2005
FN9107.3