ISL6236AIRZ-T View Datasheet(PDF) - Intersil

Part Name

Description

Manufacturer

ISL6236AIRZ-T

High-Efficiency, Quad-Output, Main Power Supply Controllers for Notebook Computers

Intersil 

ISL6236A

40μs (MAX)

INDUCTOR

CURRENT

0A

FB<ReFgB.P<oRiEntG.POINT

ZeErRoO-C-CroRsOsSinSgING

DeDteEcTtiEoCnTION

ON-TIME (tON)O) N)

FIGURE 73. ULTRASONIC CURRENT WAVEFORMS

Reference and Linear Regulators (VREF3,

REF, LDO and 14V Charge Pump)

The 3.3V reference (VREF3) is accurate to ±1.5% over-

temperature, making VREF3 useful as a precision system

reference. VREF3 can supply up to 5mA for external loads.

Bypass VREF3 to GND with a 0.01µF capacitor. Leave it

open if there is no load.

The 2V reference (REF) is accurate to ±1% over-

temperature, also making REF useful as a precision system

reference. Bypass REF to GND with a 0.1µF (min) capacitor.

REF can supply up to 50µA for external loads.

An internal regulator produces a fixed 5V

(LDOREFIN < 0.2V) or 3.3V (LDOREFIN > VCC - 1V). In an

adjustable mode, the LDO output can be set from 0.7V to

4.5V. The LDO output voltage is equal to two times the

LDOREFIN voltage. The LDO regulator can supply up to

100mA for external loads. Bypass LDO with a minimum

4.7µF ceramic capacitor. When the LDOREFIN < 0.2V and

BYP voltage is 5V, the LDO bootstrap-switchover to an

internal 0.7Ω P-Channel MOSFET switch connects BYP to

LDO pin while simultaneously shutting down the internal

linear regulator. These actions bootstrap the device,

powering the loads from the BYP input voltages, rather than

through internal linear regulators from the battery. Similarly,

when the BYP = 3.3V and LDOREFIN = VCC, the LDO

bootstrap-switchover to an internal 1.5Ω P-Channel

MOSFET switch connects BYP to LDO pin while

simultaneously shutting down the internal linear regulator.

No switchover action in adjustable mode.

In Figure 69, the external 14V charge pump is driven by

LGATE1. When LGATE1 is low, D1a charged C8 sourced

from OUT1. C8 voltage is equal to OUT1 minus a diode

drop. When LGATE1 transitions to high, the charges from C8

will transfer to C12 through D1b and charge it to VLGATE1

plus VC8. As LGATE1 transitions low on the next cycle, C12

will charge C14 to its voltage minus a diode drop through

D2a. Finally, C14 charges C15 thru D2b when LGATE1

switched to high. CP output voltage is:

CP = VOUT1 + 2 ⋅ VLGATE1 – 4 ⋅ VD

(EQ. 4)

where:

• VLGATE1 is the peak voltage of the LGATE1 driver

• VD is the forward diode dropped across the Schottkys

SECFB is used to monitor the charge pump through resistive

divider. In an event when SECFB dropped below 2V, the

detection circuit force the highside MOSFET (SMPS1) off

and the lowside MOSFET (SMPS1) on for 300ns to allow CP

to recharge and SECFB rise above 2V. In the event of an

overload on CP where SECFB can not reach more than 2V,

the monitor will be deactivated. Special care should be taken

to ensure enough normal voltage ripple on each cycle as to

prevent CP shut-down. The SECFB pin has ~17mV of

hysteresis, so the ripple should be enough to bring the

SECFB voltage above the threshold by ~3x the hystersis, or

(2V + 3*17mV) = 2.051V. Reducing the CP decoupling

capacitor and placing a small ceramic capacitor (10pF to

47pF) in parallel with the upper leg of the SECFB resistor

feedback network (R1 of Figure 69), will also increase the

robustness of the charge pump.

Current-Limit Circuit (ILIM ) with rDS(ON)

Temperature Compensation

The current-limit circuit employs a "valley" current-sensing

algorithm. The ISL6236A uses the on-resistance of the

synchronous rectifier as a current-sensing element. If the

magnitude of the current-sense signal at PHASE is above

the current-limit threshold, the PWM is not allowed to initiate

a new cycle. The actual peak current is greater than the

current-limit threshold by an amount equal to the inductor

ripple current. Therefore, the exact current-limit

characteristic and maximum load capability are a function of

the current-limit threshold, inductor value and input and

output voltage.

I PEAK

I LOAD

ΔI

I LOAD(MAX)

ILIM (VAL) = ILOAD -

ΔI

2

I LIMIT

TIME

FIGURE 74. “VALLEY” CURRENT LIMIT THRESHOLD POINT

28

FN6453.0

March 14, 2007

Share Link: