ISL85033IRTZ-T Intersil, ISL85033IRTZ-T Datasheet - Page 17

• Manufacturer Part Number: ISL85033IRTZ-T
• Description: IC REG BUCK ADJ DUAL 28TQFN
• Manufacturer: Intersil
• Type: Step-Down (Buck)r

Specifications of ISL85033IRTZ-T

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: 0.8 ~ 28 V
• Current - Output: 3A
• Frequency - Switching: 300kHz ~ 2MHz
• Voltage - Input: 4.5 ~ 28 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-WFQFN exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

regulation, it will enter overcurrent hiccup mode with a
very short hiccup waiting time. The reason is that
VOUT1 is still in regulation and can pull-up SS2 very
quickly via the resistor added between VOUT1 and
SS2.
Figure 42 illustrates output sequencing. When EN1 is
high and EN2 is floating, OUT1 comes up first and
OUT2 won't start until OUT1 > 90% of its regulation
point. If EN1 is floating and EN2 is high, OUT2 comes
up first and OUT1 won't start until OUT2 > 90% of its
regulation point. If EN1 = EN2 = high, OUT1 and OUT2
come up at the same time. Please refer to Table 1 for
conditions related to Figure 42 (Output Sequencing).
Floating
Floating Floating
EN1
High
High
0.22µF
C2
Floating
0.1µF
EN2
C1
0.1µF
High
High
FIGURE 39. INDEPENDENT START-UP
FIGURE 40. RATIOMETRIC START-UP
C
0.1µF
C
1
2
TABLE 1. OUTPUT SEQUENCING
V
SS1
SS2
SS1
SS2
OUT2
Same time
as V
V
After
First
OUT1
ISL85033
ISL85033
OUT2
> 90%
17
V
V
V
V
OUT1
OUT2
OUT1
OUT2
V
OUT1
Same time
as V
V
After
First
OUT2
OUT1
> 90%
C
C
C
C
3
4
3
4
5.0V
3.3V
5.0V
3.3V
Allowed
NOTE
ISL85033
ISL85033
Not
Protection Features
The ISL85033 limits the current in all on-chip power
devices. Overcurrent protection limits the current on the
two buck regulators and internal LDO for V
Buck Regulator Overcurrent Protection
During the PWM on-time, the current through the
internal switching MOSFET is sampled and scaled
through an internal pilot device. The sampled current is
compared to a nominal 5A overcurrent limit. If the
sampled current exceeds the overcurrent limit reference
level, an internal overcurrent fault counter is set to 1 and
an internal flag is set. The internal power MOSFET is
immediately turned off and will not be turned on again
until the next switching cycle.
The protection circuitry continues to monitor the current
and turns off the internal MOSFET as described. If the
overcurrent condition persists for 17 sequential clock
cycles, the overcurrent fault counter overflows indicating
an overcurrent fault condition exists. The regulator is
shut down and power-good goes low.
The buck controller attempts to recover from the
overcurrent condition after waiting 8 soft-start cycles.
0.1µF
C
2
C
0.1µF
C
0.22µF
1
1
FIGURE 42. OUTPUT SEQUENCING
FIGURE 41. ABSOLUTE START-UP
R
8.06k
2
SS1
SS2
EN1
EN2
SS1
SS2
ISL85033
ISL85033
25.5k
R
1
V
V
V
V
OUT1
OUT2
OUT1
OUT2
C
C
C
C
3
4
3
4
CC
December 8, 2010
.
5.0V
3.3V
5.0V
3.3V
FN6676.2