AAT2138 Datasheet, PDF (12/18 Pages) Skyworks Solutions Inc. – High Current Step-Down Converter with High-Precision Programmable Current Limited Load Switch

DATA SHEET
AAT2138
High Current Step-Down Converter
with High-Precision Programmable Current Limited Load Switch
active with soft start. When the REGIN voltage is above
UVLO and reaches 95% of V_SYSIN voltage, the reference
voltage is charged from 0 to 0.6V slowly by an internal
current source to avoid a large input inrush current.
During the soft start, the output voltage increases with
the reference voltage. The soft start time is about 1ms
with a 100μF output capacitor.
REGIN Discharge
The voltage on the capacitor between REGIN and GND is
discharged quickly when the power on SYSIN is removed
quickly (unplugged adaptor). When ENSYS is pulled low
and SYSIN is below 3.0V, AAT2138 automatically turns
on the discharge MOSFET to discharge the REGIN
capacitor storage. Discharge resistance is typical 8ohm
and the specific discharge time depends on the capaci-
tance between REGIN and GND.
Input Under-Voltage Lockout
Under-voltage lockout (UVLO) guarantees sufficient
V_REGIN bias and proper operation of all internal circuitry
prior to activation.
MODE Function
When the MODE pin is pulled high, the part runs in
forced PWM mode operation using the internal oscillator.
When the MODE pin is pulled low, a light-load mode
operation (PFM/PWM) is designed to reduce the domi-
nant switching losses at low output voltage and light-
load condition.
The Step-Down converter can also be synchronized to an
external clock signal fed into the MODE pin. In this case,
the internal oscillator is bypassed. The frequency of the
external clock must be in the range from 1MHz to 3MHz.
Protection Circuitry
The AAT2138 includes protection for overload and over-
temperature conditions. The overload protection turns
off the high-side switch when the inductor current
exceeds the current-limit threshold (3A minimum).
The AAT2138 includes thermal protection that disables
the regulator and the load switch when the die tempera-
ture reaches 150°C. The REGIN pin is maintained in a
high-impendance state. It automatically restarts when
the temperature drops by 15°C or more.
Application Information
Load Switch
Current Limit Setting
The AAT2138's load switch current limit can be pro-
grammed by an external resistor R_SET from RSET to GND.
In most applications, the variation in I_LIM must be taken
into account when determining R_SET. The I_LIM variation is
due to processing variations from part to part, as well as
variations in the voltages at SYSIN and REGIN, plus the
operating temperature. Together, these three factors add
up to a ±5% tolerance (see load switch I_LIM specification
in Electrical Characteristics section). Table 1 gives 1%
standard metal film resistor example values for PMOS
current limit programming.
I_LIM (A)
0.4
0.482
0.51
0.553
0.613
0.798
0.908
1.01
1.078
1.245
1.538
2.07
2.48
2.64
2.9
3
R_SET (kΩ)
13.3
10
9.53
8.88
8.06
6.34
5.6
5.1
4.75
4.02
3.16
2.2
1.74
1.6
1.4
1.3
Table 1: Examples of 1% Standard Resistor Value
of R_SET.
3.3
3.0
2.7
2.4
2.1
1.8
1.5
1.2
0.9
0.6
0.3
0.0
1 2 3 4 5 6 7 8 9 10 11 12 13 14
R_SET (kΩ)
Figure 1: Load Switch Current Limit vs R_SET.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
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202006C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013