MCP1642B Datasheet, PDF (13/32 Pages) Microchip Technology – 1.8A Input Current Switch, 1 MHz Low-Voltage Start-Up Synchronous Boost Regulator

4.0 DETAILED DESCRIPTION
4.1 Device Option Overview
The MCP1642B/D family of devices is capable of low
start-up voltage and delivers high efficiency over a wide
load range for single-cell, two-cell, three-cell alkaline,
Ultimate Lithium, NiMH, NiCd and single-cell Li-Ion
battery inputs. A high level of integration lowers total
system cost, eases implementation and reduces board
area.
The devices feature low start-up voltage, fixed and
adjustable output voltage, PWM mode operation,
integrated synchronous switch, internal compensation,
low noise anti-ringing control, inrush current limit and
soft start.
There are two shutdown options for the MCP1642B/D
family:
• True Output Disconnect mode (MCP1642B)
• Input-to-Output Bypass mode (MCP1642D)
4.1.1
TRUE OUTPUT DISCONNECT
MODE OPTION
The MCP1642B device incorporates a true output
disconnect feature. With the EN pin pulled low, the
output of the MCP1642B is isolated or disconnected
from the input by turning off the integrated P-Channel
switch and removing the switch bulk diode connection.
This removes the DC path that is typical in boost
converters, which allows the output to be disconnected
from the input. During this mode, less than 1 µA of
current is consumed from the input (battery). True
output disconnect does not discharge the output.
4.1.2
INPUT-TO-OUTPUT BYPASS MODE
OPTION
The MCP1642D device incorporates the
Input-to-Output Bypass shutdown option. With the EN
input pulled low, the output is connected to the input
using the internal P-Channel MOSFET. In this mode,
the current drawn from the input (battery) is less than
1 µA with no load. The Input-to-Output Bypass mode is
used when the input voltage is high enough for the load
to operate (e.g. PIC MCU operating in sleep mode).
When a higher regulated output voltage and load
current are necessary, the EN pin must be pulled high,
enabling the boost converter.
MCP1642B/D
4.1.3
ADJUSTABLE OUTPUT VOLTAGE
OPTION
For the MCP1642B/D ADJ option, the output voltage is
adjustable with a resistor divider over a 1.8V minimum
to 5.5V maximum range. The middle point of the
resistor divider connects to the V_FB pin. High-value
resistors are recommended to minimize quiescent
current to keep efficiency high at light loads. The
reference voltage is V_FB = 1.21V.
4.1.4 FIXED OUTPUT VOLTAGE OPTION
For the fixed output voltage option of the MCP1642B/D
devices, the V_FB pin is not connected. There is an
internal feedback divider which minimizes quiescent
current to keep efficiency high at light loads.
The value of the internal divider is 815 k typical.
The fixed set values are: 1.8V, 3.0V, 3.3V and 5.0V.
TABLE 4-1: PART NUMBER SELECTION
BY SHUTDOWN OPTION
Part Number
True Output Input-to-Output
Disconnect
Bypass
MCP1642B-ADJ
X
—
(or -18; 30; 33; 50)
MCP1642D-ADJ
—
X
(or -18; 30; 33; 50)
 2014 Microchip Technology Inc.
DS20005253A-page 13