LM3687 Datasheet, PDF (14/35 Pages) National Semiconductor (TI) – Step-Down DC-DC Converter with Integrated Low Dropout Regulator and Startup Mode

LM3687
SNVS473A – DECEMBER 2007 – REVISED JULY 2008
Electrical Characteristics^{(1) (2)} External Components, Recommended Specification ⁽³⁾
Symbol
Parameter
Conditions
Value
Limit
Min
Max
C_{VOUT_LIN}
Output Capacitance for
linear regulator
2.2
1.5
10
C_{VIN_LIN}
Input Capacitance for
linear regulator
V_{IN_LIN} is biased separately, not by
V_{OUT_DCDC} (no C_{VIN_LIN} needed for
post regulation application)
1.0
0.47
C_VBATT
Input Capacitance for DC-
DC converter
4.7
C_{VOUT_DCDC}
DC-DC converter output
filter capacitor
10
C_ESR
ESR of all capacitors
Inductance
0.003
0.300
2.2
L
I_SAT
DCR
1.6
200
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Units
µF
µF
µF
µF
Ω
µH
A
mΩ
(1) All voltages are with respect to the potential at the SGND pin.
(2) Min and Max limits are guaranteed by design, test, or statistical analysis. Typical numbers are not guaranteed, but do represent the
most likely norm. Unless otherwise specified, conditions for typ. specifications are: V_BATT = 3.6V and T_A = 25°C.
(3) The capacitor tolerance should be 30% or better over temperature. The full operating conditions for the application should be considered
when selecting a suitable capacitor to ensure that the minimum value of capacitance is always met. Recommended capacitor type is
X7R. However, dependent on application, X5R, Y5V, and Z5U can also be used. The shown minimum limit represents real minimum
capacitance, including all tolerances and must be maintained over temperature and dc bias voltage (See capacitor section in
Applications Hints)
Block Diagram
EN_DCDC
DC-DC
Converter
V_BATT
FB
SW
EN_LIN
Startup LDO
Linear
Regulator
Mode Switch
V_{IN_LIN} > V_REF +
200 mV
SGND
Figure 5. Simplified Block Diagram
PGND
V_{IN_LIN}
V_{OUT_LIN}
14
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