ISL976787IBZ-T 데이터 시트보기 (PDF) - Intersil

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ISL976787IBZ-T

4-Channel LED Driver with Phase Shift Control and 10-Bit Dimming Resolution

Intersil 

ISL97687

Typical Performance Curves (Continued)

I_INDUCTOR

V_STV

I_INDUCTOR

V_STV

I_CH1

V_CH2

FIGURE 16. VSYNC ENABLED DIMMING WITHOUT PHASE SHIFT

(VIN: 19V, ICH: 120mA, LEDs: 4P18S, 180Hz OUTPUT

PHASE AND FREQUENCY LOCKED TO 60Hz STV)

I_CH1

V_CH2

FIGURE 17. VSYNC ENABLED WITH PHASE SHIFT (VIN: 19V,

ICH: 120mA, LEDs: 4P18S, 180Hz OUTPUT PHASE

AND FREQUENCY LOCKED TO 60Hz STV)

V_CH

V_PWM

I_INDUCTOR

I_CH

I_CH

FIGURE 18. PWM SWITCHING AND TRANSIENT RESPONSE OF

INDUCTOR CURRENT

Theory of Operation

PWM Boost Converter

The current mode PWM boost converter produces the minimal

voltage needed to enable the LED string with the highest forward

voltage drop to run at the programmed current. The ISL97687

employs current mode control boost architecture that has a fast

current sense loop and a slow voltage feedback loop. The

number of LEDs that can be driven by ISL97687 depends on the

type of LED chosen in the application. The ISL97687 is capable

of boosting up to greater than 70V and driving 4 Channels of

LEDs at a maximum of 160mA per channel.

OVP and VOUT

The Overvoltage Protection (OVP) pin has a function of setting the

overvoltage trip level as well as limiting the VOUT regulation

range.

FIGURE 19. MINIMUM DIMMING DUTY CYCLE (0.05%, fDIM: 500Hz,

ICH = 120mA, DIRECT PWM MODE)

The ISL97687 OVP threshold is set by RUPPER and RLOWER as

shown in Equation 1:

VOUT

=

1----.-2----1----(--R-----U---P----P---E---R-----+-----R----L---O----W-----E---R----)

RLOWER

(EQ. 1)

and VOUT can only regulate between 30% and 100% of the

VOUT_OVP such that:

Allowable VOUT = 30% to 100% of VOUT_OVP

For example, a 1MΩ RUPPER and 19kΩ RLOWER sets OVP to

65.4V. The boost can regulate down to 30% of OVP, so it can go

as low as 19.6V. If VOUT needs to be lower than this, the OVP level

must be reduced. Otherwise, VOUT will regulate to 19.6V, and the

ISL97687 may overheat. However, it’s recommended that the

OVP be set to no more than 20% above the nominal operating

voltage. This prevents the need for output capacitor voltage

ratings and the inductor current rating to be set significantly

higher than needed under normal conditions, allowing a smaller

10

FN7714.0

September 15, 2011

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