HIP6201 INTERSIL [Intersil Corporation], HIP6201 Datasheet - Page 7

• Manufacturer Part Number: HIP6201
• Manufacturer: INTERSIL [Intersil Corporation]

L
I
The value of the capacitor at the CAP pin should be sized so
that the HIP6200 can be active in response to a transient for
longer than the greater of T
DC-DC converter with a 3 H inductor and a 8A maximum
response. Though the HIP6200 will be active for longer than
necessary in response to the low-to-high load transient, the
amount of power wasted will be minimal. The upper amplifier
will be active, drawing about 15mA, but the power npn
darlington will pinch off after the inductor current slews up.
The following section details power dissipation further.
Thermal Considerations
HIP6200 Power Dissipation
The power dissipated by the DeCAPitator is a function of
many variables. The load transient step size (I
frequency of the transient events (1/T
converter response time (T
influence. Figure 3 displays these terms.
Based on some simplifying assumptions, the DeCAPitator
power dissipation can be approximated as follows:
P
where:
transient step size, T
CAP capacitor should be chosen for the worst-case T
P
P
P
STEP
OUT
DISS
UP
DWN
BIAS
FIGURE 3. IDEALIZED WAVEFORMS OF DeCAPitator
=
= output inductor value
I
I
= transient current step amplitude
OUT
CPU
=
=
=
V
P
V
CC
V
T
BIAS
CC
T
R1
OUT
R2
–
OPERATION
V
+
OUT
I
BIAS
P
T
UP
TRAN
I
----------------
STEP
R1
+
2
P
I
----------------
= 2.3 s and T
STEP
DWN
2-447
2
------------------ -
T
R1
R1
TRAN
T
, T
R2
and T
------------------ -
T
R2
TRAN
T
R1
) have the largest
R2
TRAN
R2
. For a 12V to 1.7V
= 14.1 s. Thus, the
), and the
STEP
), the
I
HIP6200, HIP6201
STEP
R2
(EQ. 3)
(EQ. 4)
(EQ. 5)
(EQ. 6)
and:
I
and amplifiers are not active (300 A typical)
Ibias
typical)
Ibias
typical)
t
capacitor and should be at least as long as T
The bias power is a very small percentage of the total chip
power dissipation, but is included for completeness.
Based on these equations, the two figures below show how
the power dissipation varies with the transient frequency
(1/T
response time (T
and V
and varies the step size (as well as the transient frequency).
As mentioned in the previous section, these conditions give
T
holds I
The converter response time often differs from the ideal
(Equations 1 and 2) substantially and therefore should be
verified experimentally.
Figures 4 and 5 show the relationships between the
DeCAPitator power dissipation and the load transient
frequency, load transient step size and the converter
response time. The power dissipation is linear with the
transient frequency but is shown on the log scale to
emphasize the fact that the HIP6200/1 power is minimal at
frequencies below a few hundred Hertz.
I
IDLE
ACTIVE
BIAS
R1
0.6
0.5
0.4
0.3
0.2
0.1
FIGURE 4. ESTIMATED HIP6200, HIP6201 POWER
TRAN
= 2.3 s and T
UP
DWN
= nominal supply current when HIP6200 is powered
OUT
=
STEP
= upper amplifier bias current when active (15mA
I
= time amplifiers are active. This time is set by CAP
IDLE
), step load change (I
= lower amplifier bias current when active (30mA
= 1.7V. Figure 4 assumes a 3 H output inductor
constant at 8A and varies the response time.
DISSIPATION vs I
+
Ibias
-------------------------------------------------- -
R1
10
R2
, T
2
TRANSIENT FREQUENCY (Hz)
UP
T
= 14.1 s for I
TRAN
R2
I
t
). Both figures assume V
STEP
ACTIVE
I
STEP
= 6A
STEP
STEP
10
= 8A
3
+
Ibias
------------------------------------------------------- -
STEP
), and converter
DWN
= 8A. Figure 5
T
TRAN
10
R2
t
4
ACTIVE
I
.
STEP
IN
= 12V
= 4A
(EQ. 7)
10
5