2-447

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

DC-DC converter with a 3

µH 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

influence. Figure 3 displays these terms.

Based on some simplifying assumptions, the DeCAPitator

power dissipation can be approximated as follows:

where:

and:

and amplifiers are not active (300

µA typical)

typical)

typical)

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

and varies the step size (as well as the transient frequency).

As mentioned in the previous section, these conditions give

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.

FIGURE 3. IDEALIZED WAVEFORMS OF DeCAPitator

OPERATION

P

DISS

P

BIAS

P

UP

P

DWN

++

=

(EQ. 3)

P

UP

V

CC

V

OUT

–

()

I

STEP

2

----------------

T

R1

T

TRAN

-------------------

•







•

=

(EQ. 4)

P

DWN

V

OUT

()

I

STEP

2

----------------

T

R2

T

TRAN

-------------------

•







•

=

(EQ. 5)

P

BIAS

V

CC

I

BIAS

()

•

=

(EQ. 6)

I

BIAS

I

IDLE

Ibias

UP

t

ACTIVE

•

T

TRAN

---------------------------------------------------

Ibias

DWN

t

ACTIVE

•

T

TRAN

--------------------------------------------------------

++

=

(EQ. 7)

FIGURE 4. ESTIMATED HIP6200, HIP6201 POWER

TRANSIENT FREQUENCY (Hz)

0.1

0.2

0.3

0.4

0.5

0.6

HIP6200, HIP6201