Description
The AXPM60631 is designed to drive AMOLED (Active Matrix Organic Light Emitting Diode) displays
requiring positive and negative supply rails. The device integrates a boost converter for VPOS and an
inverting buck boost converter for VNEG and is suitable for battery-operated products. The digital control
pin (CTRL) allows programming the negative output voltage in digital steps. The AXPM60631 uses a
novel technology enabling excellent line transient performance.
Features
▪ Operating input voltage range from 2.9V to 4.5V
▪ Step-up converter (VPOS)
– 4.6V output voltage
– 200mA output current
– 0.5% accuracy (25°C to 85°C)
▪ Inverting converter (VNEG)
– -1.4V to -4.4V programmable output voltage (-2.2V default)
– 200mA output current
▪ Efficiency >90%
▪ Excellent line and load regulation
▪ Short circuit protection
▪ Thermal shutdown
Applications
▪ AMOLED power supply in portable devices like mobile phones, multi-media players, camcorders,
digital still cameras, and wearables.
1 Block Diagram and Application Circuit
2 Pin Description
2.1 Pin Names
2.2 Pin Functions
3. Electrical Specifications
3.1 Absolute Maximum Ratings
3.2 Thermal Data
3.3 ESD and Latch Up
3.4 Electrical Characteristics
VIN=3.7V, CTRL=3.7V, VPOS=+4.6V, VNEG=-2.2V, typical values are at TA = 25°C (unless
otherwise noted).
4 Functional Description
4.1 Overview
The AXPM60631 consists of a boost converter and an inverting buck boost converter. The
VPOS output is fixed at 4.6V and VNEG output is programmable via a digital interface in the
range of -1.4V ~ -4.4V, the default is -2.2V. The transition time of VNEG output is set to a
default fast timing internally. The device has internal over-temperature protection, under
voltage lockout and soft start which guarantees proper operation during start-up.
4.2 Step-up Converter (VPOS)
Step-up converter uses a fixed-frequency current-mode topology. Its output voltage (VPOS) is
programmed at the factory to 4.6V and cannot be changed by the user.
4.3 Inverting Converter (VNEG)
The inverting converter uses a constant-off-time current-mode topology. The converter's default
output voltage (VNEG) is -2.2V. It can be programmed from -1.4V to -4.4V.
4.3.1 Programming VNEG
The digital interface allows programming of VNEG in discrete steps. If the output voltage setting
function is not required, then the CTRL pin can also be used as a standard enable pin. The
digital output voltage programming of VNEG is implemented using a simple digital interface
(SWIRE) with the timing shown in figure 4.
When CTRL is pulled high, the device starts up with its default voltage of -2.2V. The device
includes a DAC that generates the output voltages shown in table 7. The interface counts the
rising edges applied to the CTRL pin once the device is enabled. According to table 7, VNEG
is programmed to -4.1V since 4 rising edges are detected.
4.3.2 VNEG Transition Time
The transition time (tSET) is the time required to move VNEG from one voltage level to the next.
It has by default a fast transition time, typical 300µs.
4.4 Soft Start and Start-up Sequence
AXPM60631 features a soft-start function to limit inrush current. When CTRL goes high, step-
up converter starts with a reduced switch current limit and 10 ms later the inverting converter
starts with its default value of -2.2V. The typical start-up sequence is shown in Figure 5. The 2
step-up converters operate independently.
4.5 CTRL
The CTRL pin serves two functions: one is to enable and disable the device, and the other is
to program the output voltage (VNEG) of the inverting buck-boost converter (see Programming
VNEG). If the VNEG programming function is not required, the CTRL pin can be used as a
standard enable pin for the device, which will start up with its default value of -2.2V on VNEG.
The device is enabled when CTRL is pulled high and disabled when CTRL is pulled low. Note
that to ensure proper start up CTRL must be pulled low for a minimum of 200μs before being
pulled high again.
4.6 Under-voltage Lockout
The device features an under-voltage lockout function that disables it when the input supply
voltage is too low for proper operation.
4.7 Short Circuit Protection
4.7.1 Short Circuit During Operation
The device is protected against short circuit of VPOS and VNEG to ground and short circuit of
these two outputs to each other. During normal operation, an error condition is detected if
VPOS falls below 4.1V for longer than 3ms or VNEG is pulled above 85% of the programmed
nominal output by 500mV for longer than 3ms. In either case the device goes into shutdown
and the outputs are disconnected from the input. This state is latched, and to resume normal
operation, VIN must cycle below the under-voltage lockout threshold, or CTRL must toggle
LOW and then HIGH.
4.7.2 Short Circuit During Start-up
During start-up, an error condition is detected in the following cases:
• VPOS is not in regulation 10ms after CTRL goes HIGH.
• VNEG is higher than threshold level 10ms after CTRL goes HIGH.
• VNEG is not in regulation 20ms after CTRL goes HIGH.
If any of the above conditions is met the device goes into shutdown and the outputs are
disconnected from the input. This state is latched, and to resume normal operation, VIN has to
cycle below the undervoltage threshold, or CTRL has to toggle LOW and HIGH.
4.8 Output Discharge During Shut Down
The device outputs can be programmed for Discharge or HiZ during shutdown. Figure 6 shows
the shutdown output control. Device is default programmed for Discharge during shutdown.
4.9 Device Functional Modes
4.9.1 Operation with VIN<2.9V
The recommended minimum input supply voltage for full performance is 2.9V. The device
continues to operate with input supply voltages below 2.9V but full performance is not
guaranteed. It does not operate with input supply voltages below the UVLO threshold.
4.9.2 Operation with VI≈VPOS (Diode Mode)
AXPM60631 features a "diode" mode that enables it to regulate its VPOS output even when
the input supply voltage is close to VPOS (that is, too high for normal step-up operation). When
operating in diode mode the VPOS boost converter's high-side switch is disabled and its body
diode used as the rectifier. Note that a minimum load of ≈2mA is required to have proper output
regulation in diode mode.
4.9.3 Operation with CTRL
When a low-level signal is applied to the CTRL pin the device is disabled and switching is
inhibited. When the input supply voltage is above the UVLO threshold and a high-level signal
is applied to the CTRL pin the device is enabled and its start-up sequence begins.