HIP4080A/81AEVALZ Intersil, HIP4080A/81AEVALZ Datasheet - Page 7

• Manufacturer Part Number: HIP4080A/81AEVALZ
• Description: DEMO BOARD FOR HIP4081A
• Manufacturer: Intersil

Specifications of HIP4080A/81AEVALZ

• Main Purpose: Power Management, H Bridge Driver (Internal FET)
• Utilized Ic / Part: HIP4080A, HIP4081A
• Secondary Attributes: -
• Embedded: -
• Primary Attributes: -
• Other names: HIP4080A/81AEVAL; HIP4080A/81AEVAL; Q2670719

approaches 100%, the available “off-time”, t
zero. Equation 2 shows the relationship between t
and the duty cycle.
As soon as the upper MOSFET is turned off, the voltage on
the phase terminal (the source terminal of the upper
MOSFET) begins its descent toward the negative rail of the
high voltage bus. When the phase terminal voltage becomes
less than the V
bootstrap capacitor begins. As long as the phase voltage is
below V
voltages are equal.
The off-time of the upper MOSFET is dependent on the gate
control input signals, but it can never be shorter than the
dead-time delay setting, which is set by the resistors
connecting HDEL and LDEL to V
capacitor is not fully charged by the time the upper MOSFET
turns on again, incomplete refreshing occurs. The designer
must insure that the dead-time setting be consistent with the
size of the bootstrap capacitor in order to guarantee
complete refreshing. Figure7 illustrates the circuit path for
refreshing the bootstrap capacitor.
The bootstrap charging and discharging paths should be
kept short, minimizing the inductance of these loops as
mentioned in the section, “Lower Bias Supply Design”.
Bootstrap Circuit Design - An Example
Equation 1 describes the relationship between the gate
charge transferred to the MOSFET upon turn-on, the size of
the bootstrap capacitor and the change in voltage across the
HIGH SIDE
LOW SIDE
NOTE:
HIP 4080
t OFF
DRIVE
DRIVE
FIGURE 7. BOOTSTRAP CAPACITOR CHARGING PATH
=
CC
Arrows Show Bootstrap Charging Path.
(
Only “A-side” of H-bridge Is Shown for Simplicity.
1-DC
refreshing continues until the bootstrap and V
CC
AHO
AHB
AHS
ALO
)/f PWM
ALS
V
V
CC
SS
voltage, refreshing (charging) of the
D
BS
SUPPLY
BYPASS
CAPACITOR
LOWER
MOSFET
C
7
BS
SS
. If the bootstrap
HIGH VOLTAGE BUS V
OFF
TO LOAD
OF H-BRIDGE
approaches
TO “B-SIDE”
TO “B-SIDE”
Application Note 9404
H-BRIDGE
OFF
(12VDC)
+V
OF
, f
BIAS
(EQ. 2)
PWM
BUS
CC
bootstrap capacitor which occurs as a result of turn-on
charge transfer.
The effects of reverse leakage current associated with the
bootstrap diode and the bias current associated with the
upper gate drive circuits also affect bootstrap capacitor
sizing. At the instant that the upper MOSFET turns on and its
source voltage begins to rapidly rise, the bootstrap diode
becomes rapidly reverse biased resulting in a reverse
recovery charge which further depletes the charge on the
bootstrap capacitor. To completely model the total charge
transferred during turn-on of the upper MOSFETs, these
effects must be accounted for, as shown in Equation 3.
where:
From a practical standpoint, the bootstrap diode reverse
leakage and the upper supply quiescent current are
negligible, particularly since the HIP4080A’s internal charge
pump continuously sources a minimum of about 30µA. This
current more than offsets the leakage and supply current
components, which are fixed and not a function of the
switching frequency. The higher the switching frequency, the
lower is the charge effect contributed by these components
and their effect on bootstrap capacitor sizing is negligible, as
shown in Equation 3. Supply current due to the bootstrap
diode recovery charge component increases with switching
frequency and generally is not negligible. Hence the need to
use a fast recovery diode. Diode recovery charge
information can usually be found in most vendor data sheets.
For example, if we choose a Intersil IRF520R power
MOSFET, the data book states a gate charge, Q
typical and 18nC maximum, both at V
maximum value of 18nC the maximum charge we should
have to transfer will be less than 18nC.
Suppose a General Instrument UF4002, 100V, fast recovery,
1A, miniature plastic rectifier is used. The data sheet gives a
reverse recovery time of 25ns. Since the recovery current
waveform is approximately triangular, the recovery charge can
be approximated by taking the product of half the peak reverse
current magnitude (1A peak) and the recovery time duration
(25ns). In this case the recovery charge should be 12.5nC.
C BS
I
I
Q
Q
f
V
V
C
QBS
DR
PWM
BS1
BS2
BS
RR
G
= Bootstrap diode reverse leakage current
= Turn-on gate charge transferred
=
= Bootstrap capacitance
= Upper supply quiescent current
= Bootstrap diode reverse recovered charge
= Bootstrap capacitor voltage just after upper turn on
= PWM operating frequency
= Bootstrap capacitor voltage just after refresh
Q G
------------------------------------------------------------------------- -
+
Q RR
V BS1 -V BS2
+
(
------------------------------------ -
I DR
f PWM
+
I QBS
)
DS
= 12V. Using the
December 11, 2007
G
, of 12nC
AN9404.3
(EQ. 3)