MAX1515ETG+T Maxim Integrated Products, MAX1515ETG+T Datasheet - Page 14

• Manufacturer Part Number: MAX1515ETG+T
• Description: IC REG DDR LV 24-TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX1515ETG+T

• Applications: Converter, DDR
• Voltage - Input: 1.3 ~ 3.6 V
• Number Of Outputs: 2
• Voltage - Output: 0.5 ~ 2.7 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-TQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Low-Voltage, Internal Switch,
Step-Down/DDR Regulator
The MAX1515 requires a 3.3V bias supply for its inter-
nal circuitry. Typically, this 3.3V bias supply is the note-
book’s 95%-efficient, 3.3V system supply. The 3.3V
bias supply must provide V
V
maximum current drawn is:
where I
cy, and Q
FET total gate charge of approximately 1nC.
The input supply (V
V
fixed 3.0V to 3.6V supply. If the 3.3V bias supply pow-
ers up prior to the input supply, the enable signal
(SHDN going from low to high) must be delayed until
the input voltage is present to ensure startup.
The MAX1515 provides peak current limiting to protect
the MOSFETs during source/sink overload and short
circuit. During source mode the controller switches the
high-side MOSFET off when the inductor current
exceeds 4.2A. Use the following equation to calculate
the maximum source current:
where I
I
and t
ditions and component selection, this results in a maxi-
mum source current of 3.7A.
In sink mode, the MAX1515 does not issue an off-time
until the inductor current is above -3.2A. Use the follow-
ing equation to calculate the maximum sink current:
where I
is the sink inductor current limit (-3.0A typ), t
current-limit propagation delay of approximately 500ns,
and t
ditions and component selection, this results in a maxi-
mum sink current of -2.5A.
14
I
LIMIT_P
SINK MAX
DD
DD
I
BIAS
) can be connected together if the input source is a
______________________________________________________________________________________
OFF
OFF
(gate-drive and reference buffer power), so the
I
_
SOURCE MAX
CC
SINK_MAX
= I
SOURCE_MAX
is the source inductor current limit (4.2A typ),
is the fixed off-time. For typical operating con-
is the fixed off-time. For typical operating con-
G(LOW)
CC
is 450µA (typ), f
=
+3.3V Bias Supply (V
I
+ I
LIMIT N
_
REFOUT
is the maximum sink current, I
and Q
_
IN
=
) and 3.3V bias inputs (V
is the maximum source current,
+
I
LIMIT P
V
+ f
G(HIGH)
OUT OFF
SW
SW
_
t
CC
is the switching frequen-
(Q
−
(PWM controller) and
G(LOW)
are the internal MOS-
−
V
2
OUT
(
V
2
Current Limit
IN
L
2
CC
−
+ Q
×
×
V
L
OUT
and V
t
G(HIGH)
OFF
DLY
)
CC
LIMIT_N
t
is the
DLY
DD
and
)
)
Soft-start allows a gradual increase of the internal cur-
rent limit to reduce input surge currents at startup and at
exit from shutdown. A timing capacitor, C
from SS to GND sets the rate at which the internal cur-
rent limit is changed. Upon power-up, when the device
comes out of undervoltage lockout (2.6V typ) or after the
SHDN pin is pulled high, a 5µA (typ) constant-current
source charges the soft-start capacitor and the voltage
on SS increases. When the voltage on SS is less than
approximately 0.7V, the current limit is set to zero. As
the voltage increases from 0.7V to approximately 1.8V,
the current limit is adjusted from 0 to the current-limit
threshold (see the Electrical Characteristics). The volt-
age across the soft-start capacitor changes with time
according to the equation:
where I
Electrical Characteristics.
The time when full current limit is available is given by:
The soft-start current limit varies with the voltage on the
soft-start pin, SS, according to the equation:
where I
Electrical Characteristics. The constant-current source
stops charging once the voltage across the soft-start
capacitor reaches 1.8V (Figure 3).
The MAX1515 has internal current-limit circuitry that
limits the maximum current through the NMOS to 4.2A.
For applications that require a lower current limit, the
maximum current limit can be reduced by placing a
resistor (R
the soft-start current limit is R
where I
I
Characteristics.
LIMIT_P
R
LIMIT_P
SS(SRC)
LIMIT
SS
and I
SSI
SS
=
LIMIT
) from SS to GND. The time constant for
is the desired reduced current limit, and
⎛
⎜
⎝
is the positive current threshold from the
V
SS(SRC)
is the soft-start source current from the
REF
I
V
LIMIT P
=
t
SS
Adjustable Positive Current Limit
=
×
V
SS
C
=
_
I
I
V
SS
SS SRC
LIMIT
are taken from the Electrical
I
SS SRC
REF
−
(
× 1 8 .
0 7 .
(
C
SS
SS
+
Soft-Start Current Limit
V
)
)
V
x C
0 7
×
.
×
t
SS
V
⎞
⎟
⎠
I
LIMIT P
.
/
I
SS SRC
_
(
SS
, placed
)