7

FN9072.8

May 1, 2012

A falling transition on PWM indicates the turn-off of the upper

MOSFET and the turn-on of the lower MOSFET. A short

PHASE voltage is monitored and the lower gate is allowed to rise

after PHASE drops below 0.5V. The lower gate then rises

Three-State PWM Input

A unique feature of the HIP660X drivers is the addition of a

shutdown window to the PWM input. If the PWM signal enters

and remains within the shutdown window for a set holdoff time,

the output drivers are disabled and both MOSFET gates are pulled

and held low. The shutdown state is removed when the PWM

signal moves outside the shutdown window. Otherwise, the PWM

rising and falling thresholds outlined in the Electrical

Specifications determine when the lower and upper gates are

enabled.

Adaptive Shoot-Through Protection

Both drivers incorporate adaptive shoot-through protection to

prevent upper and lower MOSFETs from conducting

simultaneously and shorting the input supply. This is accomplished

by ensuring the falling gate has turned off one MOSFET before the

other is allowed to rise.

During turn-off of the lower MOSFET, the LGATE voltage is

monitored until it reaches a 2.2V threshold, at which time the

UGATE is released to rise. Adaptive shoot-through circuitry

monitors the PHASE voltage during UGATE turn-off. Once

PHASE has dropped below a threshold of 0.5V, the LGATE is

allowed to rise. PHASE continues to be monitored during the

lower gate rise time. If PHASE has not dropped below 0.5V within

250ns, LGATE is taken high to keep the bootstrap capacitor

charged. If the PHASE voltage exceeds the 0.5V threshold during

this period and remains high for longer than 2

μs, the LGATE

transitions low. Both upper and lower gates are then held low until

the next rising edge of the PWM signal.

Power-On Reset (POR) Function

During initial start-up, the VCC voltage rise is monitored and gate

drives are held low until a typical VCC rising threshold of 9.95V is

reached. Once the rising VCC threshold is exceeded, the PWM

input signal takes control of the gate drives. If VCC drops below a

typical VCC falling threshold of 7.6V during operation, then both

gate drives are again held low. This condition persists until the

VCC voltage exceeds the VCC rising threshold.

Internal Bootstrap Device

The HIP6601B, HIP6603B, and HIP6604B drivers all feature an

internal bootstrap device. Simply adding an external capacitor

across the BOOT and PHASE pins completes the bootstrap circuit.

The bootstrap capacitor must have a maximum voltage rating

above VCC + 5V. The bootstrap capacitor can be chosen from the

following equation:

charge the gate of the upper MOSFET. The

ΔV

defined as the allowable droop in the rail of the upper drive.

As an example, suppose a HUF76139 is chosen as the upper

for a 10V upper gate drive. We will assume a 200mV droop in

drive voltage over the PWM cycle. We find that a bootstrap

capacitance of at least 0.325

μF is required. The next larger

standard value capacitance is 0.33

μF.

In applications which require down conversion from +12V or

higher and PVCC is connected to a +12V source, a boot resistor in

series with the boot capacitor is required. The increased power

density of these designs tend to lead to increased ringing on the

BOOT and PHASE nodes, due to faster switching of larger

currents across given circuit parasitic elements. The addition of the

boot resistor allows for tuning of the circuit until the peak ringing

on BOOT is below 29V from BOOT to GND and 17V from BOOT

to VCC. A boot resistor value of 5

Ω typically meets this criteria.

In some applications, a well tuned boot resistor reduces the ringing

on the BOOT pin, but the PHASE to GND peak ringing exceeds

17V. A gate resistor placed in the UGATE trace between the

controller and upper MOSFET gate is recommended to reduce the

ringing on the PHASE node by slowing down the upper MOSFET

turn-on. A gate resistor value between 2

Ω to 10Ω typically reduces

the PHASE to GND peak ringing below 17V.

Gate Drive Voltage Versatility

The HIP6601B and HIP6603B provide the user total flexibility in

choosing the gate drive voltage. The HIP6601B lower gate drive is

fixed to VCC [+12V], but the upper drive rail can range from 12V

down to 5V depending on what voltage is applied to PVCC. The

HIP6603B ties the upper and lower drive rails together. Simply

applying a voltage from 5V up to 12V on PVCC will set both

driver rail voltages.

Power Dissipation

Package power dissipation is mainly a function of the switching

frequency and total gate charge of the selected MOSFETs.

Calculating the power dissipation in the driver for a desired

application is critical to ensuring safe operation. Exceeding the

maximum allowable power dissipation level will push the IC

beyond the maximum recommended operating junction

temperature of +125°C. The maximum allowable IC power

dissipation for the SO8 package is approximately 800mW. When

designing the driver into an application, it is recommended that the

following calculation be performed to ensure safe operation at the

C

BOOT

Q

GATE

ΔV

BOOT

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

≥

(EQ. 1)

HIP6601B, HIP6603B, HIP6604B