ISL8112IRZ Intersil, ISL8112IRZ Datasheet - Page 17

• Manufacturer Part Number: ISL8112IRZ
• Description: IC MAIN POWER SUPP CTRLR 32-QFN
• Manufacturer: Intersil
• Type: Step-Down (Buck)r

Specifications of ISL8112IRZ

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: 0.7 ~ 5.5 V
• Current - Output: 200mA
• Voltage - Input: 5.5 ~ 25 V
• Operating Temperature: -40°C ~ 100°C
• Mounting Type: Surface Mount
• Package / Case: 32-VQFN Exposed Pad, 32-HVQFN, 32-SQFN, 32-DHVQFN
• Power - Output: 5mW
• Rohs Compliant: YES
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Frequency - Switching: -

Automatic Pulse-Skipping Switch Over
(Idle Mode)
In Idle Mode (MODE = GND), an inherent automatic switch
over to PFM takes place at light loads. This switch over is
affected by a comparator that truncates the low-side switch
on-time at the inductor current's zero crossing. This
mechanism causes the threshold between pulse-skipping
PFM and non-skipping PWM operation to coincide with the
boundary between continuous and discontinuous
inductor-current operation (also known as the critical
conduction point):
where K is the on-time scale factor (see “On-Time One-Shot
(FS)” on page 12). The load-current level at which
PFM/PWM crossover occurs, I
the peak-to-peak ripple current, which is a function of the
inductor value (Figure 22). For example, in the ISL8112
typical application circuit with VOUT1 = 5V, V
L = 7.6µH, and K = 5µs, switch over to pulse-skipping
operation occurs at I
The crossover point occurs at an even lower value if a
swinging (soft-saturation) inductor is used.
I
LOAD SKIP
(
)
=
K V
----------------------- -
⋅
2 L
⋅
OUT
LOAD
PH_
VSEN_
FB_
VIN
VIN
ILIM_
V
------------------------------- -
IN
= 0.96A or about on-fifth full load.
VCC
–
V
17
IN
V
FS
LOAD(SKIP)
OUT
5µA
DECODER
FB
+
+
OUT2REF (SMPS2)
VSEN_
FIGURE 21. PWM CONTROLLER (ONE SIDE ONLY)
VREF
SLOPE COMP
, is equal to half
IN
+
+ +
= 12V,
0.9V
1.1V
0.7V
(EQ. 3)
REF
REF
REF
+
+
+
+
+
+
+
+
+
COMP
Â
S
ISL8112
+
+ +
+
+ +
+
+
+
+
+ +
OV_LATCH_
UV_LATCH_
PGOOD_
MODE
The switching waveforms may appear noisy and
asynchronous when light loading causes pulse-skipping
operation, but this is a normal operating condition that
results in high light-load efficiency. Trade-offs in PFM noise
vs. light-load efficiency are made by varying the inductor
value. Generally, low inductor values produce a broader
efficiency vs. load curve, while higher values result in higher
full-load efficiency (assuming that the coil resistance remains
fixed) and less output voltage ripple. Penalties for using
20ms
BLANKING
Q
ONE SHOT
0
S
S
S
R
R
R
Min. t
DETECT
FIGURE 22. ULTRASONIC CURRENT WAVEFORMS
Q
Q
BOOT
Q
Q
Q
ΔI
UV
t
LATCH
I
I
I
ON-TIME
FAULT
LOGIC
R
R
R
S
S
S
OFF
LATCH
FAULT
TRIG
Q
Q
Q
Q
Q
=
V IN -V OUT
V IN -V
V IN -V
V IN -V
TO UG_DRIVER
L
L
L
L
TO LG_ DRIVER
BOOT_
TIME
I
LOAD
I PEAK
I PEAK
I PEAK
I PEAK
August 10, 2010
=
I
PEAK
FN6396.1
/2