HV9608TS 데이터 시트보기 (PDF) - Supertex Inc

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HV9608TS

Active Clamp Current-Mode PWM Controller

Supertex Inc 

SLOPE COMPENSATION

The HV9608 PWM controller uses an internal slope compensation

scheme that is externally programmable by appropriately selecting

two resistors RSC1 and RCS2. The slope compensation ramp

generated at the CS pin can be calculated as:

[ ] [ ] mSC

V / µs

= 5.7 ⋅10−6 ⋅ FOSC

Hz

⋅ RSC2

R SC1

RSC1 must be selected greater than 5 kΩ.

When a current sense RC filter is needed at the SC pin, the value

of RCS2 will be dictated by the filter capacitor and the corner

frequency of the filter. The filter capacitor externally connected to

the CS pin is discharged prior to each switching cycle. It is not

recommended to use a capacitor larger than 220pF for this reason.

GATE DRIVE OUTPUTS

The HV9608 provides two gate-drive outputs that are configured

for driving a low-side clamp DC-DC converter, having a main

switching N-channel MOSFET (Q1) and an auxiliary active clamp

P-channel MOSFET (Q2). The GATE output is designed to drive

the main N-channel MOSFET Q1, while the AGATE output drives

Q2 via a negative output charge pump circuit C4, D1, R5. Delays

between the leading and the trailing edges of the gate drive

outputs can be programmed using external resistors RDT1 and RDT2

connected to the DT1 and DT2 pins, respectively. The values of

RDT1 and RDT2 can be calculated according to the following

equations:

[ ] R DT1 = 8 ×1011 ⋅ d1 s ,

[ ] R DT2 = 8×1011 ⋅ d2 s ,

HV9608

where d1 is the leading edge delay, d2 is the trailing edge delay.

(Refer to Fig. 2.)

GATE

AGATE

d1

d2

Figure 2. Gate Drive Output timing diagram.

VOLT-SECOND CLAMP

The duty cycle of the active DC-DC converter may become very

large during load transients. This condition may cause saturation of

the power transformer or excessive voltage stress at the clamp

capacitor C3, potentially damaging for all switching devices. In

order to prevent this condition, the HV9608 includes a volt-second

clamp circuit that can be programmed to limit the maximum duty

cycle of the PWM controller, which is inversely proportional to the

input voltage of the DC-DC converter. The maximum duty cycle

DMAX is set by merely connecting a single resistor RVS between the

positive input terminal of the converter and the VS pin. RVS can be

calculated with the following equation.

( ) RVS

= 1.72×109 ⋅

VIN [V ] − 0.7

⋅

⎛

⎜⎜⎝

DMAX

[ FOSC Hz

]

+

d1

[

s]

+

2

×10−8

⎞

⎟⎟⎠

Doc. #: DSFP-HV9608

6

A122104

A122104

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