HIP6201 datasheet(7/9 Pages) INTERSIL

7 / 9 page

2-447

LOUT = output inductor value

ISTEP = transient current step amplitude

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 TR1 and TR2. For a 12V to 1.7V

DC-DC converter with a 3

µH inductor and a 8A maximum

transient step size, TR1 = 2.3µs and TR2 = 14.1µs. Thus, the

CAP capacitor should be chosen for the worst-case TR2

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 (ISTEP), the

frequency of the transient events (1/TTRAN), and the

converter response time (TR1, TR2) have the largest

inﬂuence. Figure 3 displays these terms.

Based on some simplifying assumptions, the DeCAPitator

power dissipation can be approximated as follows:

where:

and:

IIDLE = nominal supply current when HIP6200 is powered

and ampliﬁers are not active (300

µA typical)

IbiasUP = upper ampliﬁer bias current when active (15mA

typical)

IbiasDWN = lower ampliﬁer bias current when active (30mA

typical)

tACTIVE = time ampliﬁers are active. This time is set by CAP

capacitor and should be at least as long as TR2.

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/TTRAN), step load change (ISTEP), and converter

response time (TR1, TR2). Both ﬁgures assume VIN = 12V

and VOUT = 1.7V. Figure 4 assumes a 3µH output inductor

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

As mentioned in the previous section, these conditions give

TR1 = 2.3µs and TR2 = 14.1µs for ISTEP = 8A. Figure 5

holds ISTEP constant at 8A and varies the response time.

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

IOUT

TR1

TR2

ICPU

TTRAN

ISTEP

DISS

BIAS

DWN

(EQ. 3)

OUT

–

()

STEP

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

TRAN

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

•







•

(EQ. 4)

DWN

OUT

()

STEP

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

TRAN

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

•







•

(EQ. 5)

BIAS

()

•

(EQ. 6)

BIAS

IDLE

Ibias

ACTIVE

•

TRAN

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

Ibias

DWN

ACTIVE

•

TRAN

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

(EQ. 7)

FIGURE 4. ESTIMATED HIP6200, HIP6201 POWER

DISSIPATION vs ISTEP

TRANSIENT FREQUENCY (Hz)

102

103

104

105

0.1

0.2

0.3

0.4

0.5

0.6

ISTEP = 8A

ISTEP = 4A

ISTEP = 6A

HIP6200, HIP6201

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